Some of you might have read about the lawsuit by a number of municipalities (including San Francisco and Oakland) against the major oil companies for damages (related primarily to sea level rise) caused by anthropogenic climate change. The legal details on standing, jurisdiction, etc. are all very interesting (follow @ColumbiaClimate for those details), but somewhat uniquely, the judge (William Alsup) has asked for a tutorial on climate science (2 hours of evidence from the plaintiffs and the defendents). Furthermore, he has posted a list of eight questions that he’d like the teams to answer.
It’s an interesting list. They are quite straightforward (with one or two oddities), but really, pretty much textbook stuff. Andrew Dessler made a quick stab at answering them on Twitter:
Here are answers to questions posed by the Judge Alsup re: climate science (https://t.co/DLFDT70PdL). Turns out answers to those questions are actually pretty well known. 1/
— Andrew Dessler (@AndrewDessler) March 8, 2018
But I think we can do better. So what I propose is that we crowd-source the responses. They should be pithy, to the point, with references (not Wikipedia) and, preferentially, accompanied by a good graphic or two. If we can give a credible uncertainty to any numbers in the answer that’s a bonus. I’ve made a start on each, but further voices are needed. Put your response in the comments and I’ll elevate the best ones (giving credit of course) to the main post. If you have any other comments or edits to suggest, feel free to do so. The best of those will also be incorporated. [Update: I realise I can’t possibly incorporate all the good suggestions while still keeping this short. So be sure to read the comments too for additional material. Also, as I should have said to start with, the best responses to these kinds of questions (though not to these specifically) are to be found in the FAQ of the IPCC report, the Royal Society/National Academies report, and the US. National Climate Assessment science report.]
- What caused the various ice ages (including the “little ice age” and prolonged cool periods) and what caused the ice to melt? When they melted, by how much did sea level rise?
- What is the molecular difference by which CO2 absorbs infrared radiation but oxygen and nitrogen do not?
- What is the mechanism by which infrared radiation trapped by CO2 in the atmosphere is turned into heat and finds its way back to sea level?
- Does CO2 in the atmosphere reflect any sunlight back into space such that the reflected sunlight never penetrates the atmosphere in the first place?
- Apart from CO2, what happens to the collective heat from tail pipe exhausts, engine radiators, and all other heat from combustion of fossil fuels? How, if at all, does this collective heat contribute to warming of the atmosphere?
- In grade school, many of us were taught that humans exhale CO2 but plants absorb CO2 and return oxygen to the air (keeping the carbon for fiber). Is this still valid? If so, why hasn’t plant life turned the higher levels of CO2 back into oxygen? Given the increase in human population on Earth (four billion), is human respiration a contributing factor to the buildup of CO2?
- What are the main sources of CO2 that account for the incremental buildup of CO2 in the atmosphere?
- What are the main sources of heat that account for the incremental rise in temperature on Earth?
Note this is an updating text. Last edit: March 16, 2018
- The “ice ages” are the dominant cycles of change over the last 2.5 million years (Snyder, 2016):
They vary in extent and duration. They generally were larger in the last 800,000 years, and the duration changed from about 40,000 years in the first half to about 100,000 years in the later period. It was discovered in the 1970s that the cycles were highly correlated to changes in the variability of the Earth’s orbit – the so-called Milankovich cycles (Hays, Imbrie and Shackleton, 1976). More recent work has shown that the growth and collapse of the ice sheets is strongly tied to the incoming solar radiation (insolation) at high latitudes (Roe, 2006):
The magnitude of the cycles is strongly modified by various feedbacks, including ice-albedo, dust, vegetation and, of course, the carbon cycle which amplify the direct effects of the orbital changes. Estimates of the drivers of global temperature change in the ice ages show that the changes in greenhouse gases (CO2, methane and nitrous oxide) made up about a third of the effect, amplifying the ice sheet changes by about 50% (Köhler et al, 2010).
The sea level changes over these cycles was large. The difference between the last glacial maximum (20,000 yrs ago) and today is about 120 meters (400 ft), but the high levels during some of the warmest interglacials were 6-9 meters (20 to 30 feet) higher than today. These changes are dominated by the amount of ice volume change.
The so-called “Little Ice Age” was a cooling of the Northern Hemisphere climate (and possibly less markedly in the Southern Hemisphere) in the period of the fourteenth century to the the 1850’s, approximately. It came after a period of a relatively warm climate called the Medieval Warm Period. The cause of this relatively short lived cooling (it was not a true “ice age”) is likely due to an increase in volcanic eruptions and with some role for a slightly reduced solar activity. Over the Holocene (last 11,000 yrs) there is a small but persistent cooling trend due to the orbital cycles mentioned above.
- Greenhouse gases are those that are able to absorb and emit radiation in the infrared, but this is highly dependent on the gases molecular structure. Vibrational modes in molecules with three or more atoms (H2O, CO2, O3, N2O, CH4, CFCs, HFCs…) include bending motions that are easier to excite and so will absorb and emit low energy photons which coincide with the infrared radiation that the Earth emits. Thus it is these molecules that intercept the radiation that the Earth emits, delaying its escape to space. More detailed discussion including the importance of the gases dipole moment can be found here. Diatomic molecules (like N2 or O2) have stretching modes (with the distance between the two molecules expanding and contracting), but these require a lot of energy (so they absorb only at higher energies. Some absorption is possible in the infrared due to collisions but calculations suggest this is a very small part (~0.2%) of the overall greenhouse effect (around 0.3 W/m2, compared to a total effect of 155 W/m2) (Höpfner et al, 2012).
Figure showing the vibrational modes for CO2. Arrows indicate the directions of motion. Vibrations labeled A and B represent the stretching of the chemical bonds, one in a symmetric (A) fashion, in which both C=O bonds lengthen and contract together (in-phase), and the other in an asymmetric (B) fashion, in which one bond shortens while the other lengthens. The asymmetric stretch (B) is infrared active (allowed by quantum mechanics) because there is a change in the molecular dipole moment during this vibration. Infrared radiation at 2349 (4.26 um) excites this particular vibration. The symmetric stretch is not infrared active, and so this vibration is not observed in the infrared spectrum of CO2. The two equal-energy bending vibrations in CO2 (C and D) are identical except that one bending mode is in the plane of the paper, and one is out of the plane. Infrared radiation at 667 (15.00 um) excites these vibrations. (source)
- The Earth’s surface emits infrared radiation. This is absorbed by greenhouse gases, which through collisions with other molecules cause the atmosphere to heat up. Emission from greenhouse gases (in all directions, including downwards) adds to the warming at the surface.
The figure shows the easiest mathematical description of the greenhouse effect. The downward radiation from greenhouse gases can be easily measured at the surface in nights under clear skies and no other heat sources in the atmosphere (e.g. Philipona and Dürr, 2004).
- Yes, but not enough to matter. The latest update to the estimates of radiative forcing of CO2 (Etminan et al., 2016) shows a shortwave effect (i.e. a change in the absorption of downward solar radiation) is about -0.14 W/m2 for CO2 going from 389 to 700 ppm (compared to 3.43W/m2 in longwave forcing) – contributing to about a 4% decrease in the net forcing.
- Direct heat generated by the total use of fossil fuels and other forms of energy adds up to about 18TW [IEA,2017]. Spread over the planet that is 0.04W/m2. Compared to anthropogenic forcings since 1750 of about 2.29±1.1W/m2 [IPCC AR5, Figure SPM 5], it’s about 1/100th the size. Locally however (say in cities or urban environments), this can be more concentrated and have a bigger impact.
- The grade school calculation is still valid. All animals (including humans) breathe in oxygen and exhale CO2. The carbon in the exhaled CO2 comes from the food that the animals have eaten, which comes (ultimately) from carbon that plants have taken from the atmosphere during photosynthesis. So respiration is basically carbon neutral (it releases CO2 to the atmosphere that came from the atmosphere very recently). Plants do take up CO2 as they are growing. With higher CO2 concentrations (and higher temperature), plants in fact increase their CO2 uptake somewhat but not as much as would be needed to absorb all the human-caused emissions. Of these emissions only about a quarter is absorbed by plants, while another 20% is absorbed by the oceans, but about half of the emissions stay in the atmosphere.
Note that any net change in biomass (whether trees, or cows or even humans) does affect atmospheric CO2, but the direct impact of human population growth is tiny even though our indirect effects have been huge. For scale, the increase of 3 billion people over the last 40 years, is equivalent to:
0.185 (fraction of carbon by mass) * 80 kg (average mass of a human) * 3 billion (additional humans) * 10-3 (conversion to GtC) / 40 years = 0.001 GtC/yr
which, compared to current fossil fuel and deforestation emissions of ~10 GtC/yr is 4 orders of magnitude too small to be relevant.
- Main sources of human CO2 emissions are fossil fuel burning and (net) deforestation. This figure is from the Global Carbon Project in 2017.
- This is the biggie. What is the attribution for the temperature trends in recent decades? The question doesn’t specify a time-scale, so let’s assume either the last 60 years or so (which corresponds to the period specifically addressed by the IPCC, or the whole difference between now and the ‘pre-industrial’ (say the decades around 1850) (differences as a function of baseline are minimal). For the period since 1950, all credible studies are in accord with the IPCC AR5 statement:
It is extremely likely that more than half of the observed increase in global average surface temperature from 1951 to 2010 was caused by the anthropogenic increase in greenhouse gas concentrations and other anthropogenic forcings together. The best estimate of the human-induced contribution to warming is similar to the observed warming over this period.
The US National Climate Assessment attribution statement is a bit more specific than the one in IPCC:
The likely range of the human contribution to the global mean temperature increase over the period 1951–2010 is 1.1° to 1.4°F (0.6° to 0.8°C), and the central estimate of the observed warming of 1.2°F (0.65°C) lies within this range (high confidence). This translates to a likely human contribution of 93%–123% of the observed 1951–2010 change. It is extremely likely that more than half of the global mean temperature increase since 1951 was caused by human influence on climate (high confidence). The likely contributions of natural forcing and internal variability to global temperature change over that period are minor (high confidence).
This summary graphic is useful:
Basically, all of the warming trend in the last ~60yrs is anthropogenic (a combination of greenhouse gases, aerosols, land use change, ozone etc.). To get a sense of the breakdown of that per contribution for the global mean temperature, and over a longer time-period, the Bloomberg data visualization, using data from GISS simulations is very useful.
The difference in the bottom line for attribution for the last ~160 years is that while there is more uncertainty (since aerosol and solar forcings are increasingly shaky that far back), the big picture isn’t any different. The best estimate of the anthropogenic contribution is close to the entire warming. The potential for a solar contribution is slightly higher (perhaps up to 10% assuming maximum estimates for the forcing and impacts). In all cases, the forcing from anthropogenic greenhouse gases alone is greater than the observed warming.
Figure 10.5 from IPCC. Assessed likely ranges (whiskers) and their mid-points (bars) for attributable warming trends over the 1951–2010 period due to well-mixed greenhouse gases (GHG), other anthropogenic forcings (OA) (mainly aerosols), natural forcings (NAT), combined anthropogenic forcings (ANT), and internal variability.
The role of internal climate variability gets smaller as the time-scale increases, but needs to be accounted for in these assessments. Note too that this can go both ways, internal variability might have wanted to cool overall in one period, and warm in another.
Prior to ~1750, atmospheric CO2 had been stable (within a few ppm) for millenia sustained by a balance between natural sources and sinks. This figure shows the changes seen in ice cores and the instrumental record.
- C.W. Snyder, "Evolution of global temperature over the past two million years", Nature, vol. 538, pp. 226-228, 2016. http://dx.doi.org/10.1038/nature19798
- J.D. Hays, J. Imbrie, and N.J. Shackleton, "Variations in the Earth's Orbit: Pacemaker of the Ice Ages", Science, vol. 194, pp. 1121-1132, 1976. http://dx.doi.org/10.1126/science.194.4270.1121
- G. Roe, "In defense of Milankovitch", Geophysical Research Letters, vol. 33, 2006. http://dx.doi.org/10.1029/2006GL027817
- P. Köhler, R. Bintanja, H. Fischer, F. Joos, R. Knutti, G. Lohmann, and V. Masson-Delmotte, "What caused Earth's temperature variations during the last 800,000 years? Data-based evidence on radiative forcing and constraints on climate sensitivity", Quaternary Science Reviews, vol. 29, pp. 129-145, 2010. http://dx.doi.org/10.1016/j.quascirev.2009.09.026
- M. Höpfner, M. Milz, S. Buehler, J. Orphal, and G. Stiller, "The natural greenhouse effect of atmospheric oxygen (O2) and nitrogen (N2)", Geophysical Research Letters, vol. 39, pp. n/a-n/a, 2012. http://dx.doi.org/10.1029/2012GL051409
- R. Philipona, and B. Dürr, "Greenhouse forcing outweighs decreasing solar radiation driving rapid temperature rise over land", Geophysical Research Letters, vol. 31, 2004. http://dx.doi.org/10.1029/2004GL020937
- M. Etminan, G. Myhre, E.J. Highwood, and K.P. Shine, "Radiative forcing of carbon dioxide, methane, and nitrous oxide: A significant revision of the methane radiative forcing", Geophysical Research Letters, vol. 43, 2016. http://dx.doi.org/10.1002/2016GL071930
247 Responses to "Alsup asks for answers"
Keith Woollard says
Your answer to 6 only addresses the last part of the question and is only true if human population does not actively promote plant growth (read “farm”).
The reason plants do not convert all the excess CO2 to O2 is they can’t keep up. There is clear evidence that they are increasing the conversion process however.
Dan DaSilva says
The provable damage produced by these products is smog, not CO2. If you want to attack oil do so on the bases of smog. At least you can demonstrate harm without resorting to highly speculative and politicalized science.
This is especially true for cities in the California San Joaquin Valley which ironically suffer from smog blown into the Valley from the suing cities. The air pollution in the Valley is some of the worst in the USA. Fresno suing San Franciso and Oakland for smog damage at least makes some sense.
To ferret out the truth, try mustelid on this one:
OTOH, the Red Team is dead– the white House killed it.
Martin Vermeer says
Re the second question: the CO2 molecule bends!
Martin Vermeer says
Re 3: Tyndall
“As a dam built across a river causes a local deepening of the stream, so our atmosphere, thrown as a barrier across the terrestrial [infrared] rays, produces a local heightening of the temperature at the Earth’s surface.”
Stefan Kranich says
I have a PhD in mathematics and am interested in climate science (as an amateur).
Still I find sentences like “It was discovered in the 1970’s that the pacing of the cycles seen in benthic foraminiferal oxygen isotopes was highly correlated to the Milankovitch cycles of orbital variability (Hays, Imbrie and Shackleton, 1976).” a bit hard to understand.
How easy would it be for the judge to understand what you are writing? I guess that you are not preparing your answers for the judge, but for the audience of your blog.
However, I think this might be a great opportunity to spread knowledge about climate change to the general public. To that end, I suggest to use simpler language.
Thank you for your great blog!
Digby Scorgie says
1. Mention amount of sea-level rise. Define insolation?
2. To me the short answer is: because the CO2 molecule has three atoms but O2 and N2 only have two. Or is that a bit cheeky?
3. I think the figure needs some explanation or is the link to the explanation meant to provide this?
4. Not enough to matter. I like that, but would the judge need some help with the technical terms that follow?
5. Direct heat of burning compared to … ? Anthropogenic forcing could be expressed differently perhaps. How about: the heat resulting from all the greenhouse gases humans have pumped into the atmosphere.
6. A picture comes to mind: carbon from the atmosphere to plants to animals and back into the atmosphere as exhaled CO2.
7. Does one need to mention the long lifespan (on average) of CO2 in the atmosphere?
8. I like the final picture, but ANT? OA? NAT?
I don’t know if the following fits anywhere, but from a recent article by, I think, Stefan Rahmstorf, I was interested in one figure (a little out of date) from which one could deduce the following:
sources of carbon:
land 120 Gt
ocean 90 Gt
human 7 Gt
sinks for carbon:
land 122 Gt
ocean 92 Gt
human 0 Gt
3 Gt source
And it’s all human!
Am I allowed to contribute? :-/
It appears this is a hypothetical topic, in that none of this will make it’s way to the Judge.
Given what the judge has Ordered, the questions are interesting however they cannot be removed from his more important invitation which was to present a Tutorial on two different subjects. It appears to me that the 8 questions were an additional request to be sure those specifics were “included” in the Tutorials. Then there was the additional 9th point he so ordered.
It is unwise, and I suggest counter-productive and illogical, to separate the questions from the two tutorials, even within a hypothetical approach.
The two-part tutorials were to be:
(1) The first part will trace the history of scientific study of
(2) The second part will set forth the best science now available on global warming, glacier melt, sea rise, and coastal flooding.
Furthermore the Tutorials and the answers to questions must be grounded within and upon informing the Judge accurately in the real world / practical context of the specific Legal Case being taken by THE PEOPLE OF THE STATE OF CALIFORNIA.
iow it is critical that they cover all the core fundamental scientific issues and expected Impacts/Consequences already laid out in that specific Case.
This is *dangerous* ground to tread. Is there a Lawyer in the House?
In such matters *empathy* is key. If you cannot walk a mile in that Judges moccasins, I caution against proceeding.
Irrespective of this advice it will still undoubtedly be incredibly interesting (to me at least) what follows. Good Luck. You’ll need a lot of it.
Paul Schopf says
Great job on starting this.
For Question 2:
It is first necessary to understand that molecules are made up of atoms (with mass) are held together by bonds, much like two balls linked by springs, and therefore have ways of vibrating at specific frequencies.
The bonds between two atoms in a molecule are particularly strong, and can only vibrate at very high frequencies (emphasize frequencies over energies) well above the frequency of infrared or the solar radiation spectrum.
However, molecules with 3 or more atoms can vibrate by changing the angles between the three atoms, and they can vibrate at additional (lower) frequencies. Molecules like CO2 and H2O have vibrational frequencies within the infrared range. In these vibrations, the strong bonds between Carbon and Oxygen may still have very high vibrational frequencies, but the two Oxygen atoms can vibrate toward or away from each other at this lower frequency.
Molecules with more than 3 atoms can vibrate in even more ways (which means more and more frequencies). Examples are CH4, CFCs, etc.
When upward radiation close to the right frequency hits a CO2 molecule, it can excite the vibrational mode at that frequency. The outward radiation is reduced by the amount of energy that goes into the vibration. We see the reduced amount of outward radiation in the spectra observed by downward looking satellites.
[The observant student then might ask why the energy that goes into the vibration does not just get sent back out to space by emitting a photon – after all, if the same molecule gets hit over and over with photons won’t the vibrational energy increase and increase? There are two answers: the simple part is that yes, the energy can be re-emitted, but the direction of the emitted photons does not have to have the same upward angle. In fact, the extra energy will as likely go down as up. On average, only half of the incoming energy continues on an upward path, half heads back toward Earth to participate in the answer to question 3.
The second answer comes from equipartion of energy. Temperature is a measure of the kinetic energy of the molecules. This kinetic energy is made up of not only the vibrational energy, but also the rotational energy and the classical kinetic energy of moving molecules.
When one molecule with high vibrational energy bumps into another molecule (even one without a vibrational mode) some of that vibration can go into kicking the other molecule into faster motion or higher rotation. So energy gets lost from the vibrational mode and transferred into the general temperature of the surrounding gas. The CO2 molecule has a unique way to absorb energy at a particular frequency, but that energy gets transferred very quickly to its neighboring molecules, most of which have no way to emit radiation at that frequency.
The SCIENCE is not “politicized”. It is the reaction to the science that is politicized.
Radge Havers says
Yeah, I’m with Stefan Kranich @ ~ 6.
It’s early in the A.M. here. Am I missing something? Only part of question 1 is answered (so far I guess).
Anyway you definitely want to avoid pissing off the judge.
The following is a rewording of the second half of point 2, which I think makes it easier to understand. It should I think be clear what it substitutes – I think you’re right to ignore selection rules/quantum physics
[Response: included. Thanks. – gavin]
I feel like almost all of these answers are start at way too high a level and don’t explain several of the basic underlying facts. You have to remember that lawyers and judges did not necessarily take math and science classes beyond high school (or maybe some undergraduate distribution requirements) and have not had to think about scientific topics in their legal careers, necessarily. So it’s best to keep it simple.
#2) The stretching mode in diatomic molecules is between the two “atoms”.
I suggest a simple explanation of the relationship between absorption and emission in the IR for diatomic and triatomic molecules. Not sure of the Judges science background. I’m sure there exists a good
cartoon that explains vibrational and rotational modes.
Since he’s asked for answers from both sides would it be useful to anticipate what the “climychange deniers” might say and explain the flaws or lack of scientific substantiation?
S.B. Ripman says
My first reaction when reading the proposed answers was tremendous disappointment. The scientists of the world have been given a golden opportunity to educate the world’s legal community and what are they doing? They are considering using scientific jargon that 99% of attorneys and judges will find completely unreadable.
If you really want to assist the plaintiffs in the case, check out the articles on climate communication that have been written by Joe Romm and Katharine Hayhoe. Joe is a student of classical rhetoric and Katharine knows how to connect to what matters with an audience. Take their messages to heart and then rewrite your proposed answers entirely.
One approach that the scientific community might find palatable would be to frame each answer in two parts: the first in understandable (and appealing and persuasive) English and the second in the language of science. I wish you good luck with this. From his questions it seems Judge Alsup has a sincere interest in learning about climate science.
MA Rodger says
It should be noted that there is a part of Question 1 which has not been addressed. The questioner asks for the causes of ‘the various ices ages – including the “little ice age” and prolonged cool periods – and what caused the ice to melt?” Presumably this is asking for the cause of these ice ages and the cause of their ending. But do note the inclusion of the not-so-icy “little ice age”.
It is also worth a laugh or two examining what Judith ‘I-used-to-be-a-proper-climate-scientist’ Curry has to say on the matter. Her blog-post attempts rather poorly to address Question Eight.
Her answer runs-&-runs something like this:-
♠ Apparently “There are many factors that contribute to changes in the Earth’s global average surface temperature,” so many it seems that a whole third of anthropogenic climate forcing is irrelevance. Curry argues that most radiative forcing is from CO2 and FF CO2 emissions which “did not start increasing substantially until after 1950.” So ignore the third of AGW forcing that happened before 1950 – it is far too old to be worthy of consideration.
♥ And of course there was warming before 1950, and a bit of cooling afterwards and don’t forget that slowdown 1998-2014, a period apparently “associated with a particularly steep increase in fossil fuel emissions.” The IPCC AR5 Table AII.1.2 of course dutifully shows the average ΔF of 0.31Wm^-2/decade for the period to 2011, this level of “particularly steep increase” being so different to the preceding 16-year period which averaged 0.53Wm^-2/decade and which is thus presumably too “steep” to be considered ‘particular’ but instead ‘perpendicular’.
♦ Curry then indulges in a protracted bout of IPCC-misrepresentation assisted by poor referencing, a practice in which she is not far short of bare-faced lying (were Curry still a proper climatologist).
♣ Then, following a shoddy argument about clouds being important to climate but in ways that are not quantifiable, Judy’s concluding opinion is then set out with rather little evidential support but lots of hand-waving to compensate. While the IPCC anticipate that 100% of the warming since 1950 is AGW, Curry puts it grudgingly at 50%, a value higher than 50% being “as likely as not.” Curry sets out the reason she & the IPCC hold such contrary views as being because the IPCC don’t adequately address the pre-1950 attribution question (although the IPCC only reviews the science, it doesn’t carry-out the science. Even so, they seem to do more than Curry in that regard.)
♠ And the IPCC use of models fails to model known internal variability and for attribution work they are apparently “arguably not fit for the purpose” as they were tuned using the data they attempt to attribute.
♥ A final IPCC mis-representative quote is then provided (ie missing the first sentence shown here in parenthesis) to sum up Curry’s position:-
So IPCC say the data is not available to enable analysis. Curry uses the lack of data to attribute all the early 20th century warming to internal variability which she then projects willy-nilly onto the late 20th century to provide 50% of the warming since 1950 and perhaps even amplifies it to allow for the continuing warming and/or attribution of more-than-50% of post-1950 warming to internal variability.
[Response: Judith’s ongoing confusion with the issue of attribution and her inability to provide any quantitative reasoning to support her claims is the subject of previous discussions. Note that (somewhat confusingly) she *assumes* the attribution is 100% in her papers on estimating climate sensitivity. – gavin]
Urs Neu says
I strongly support the notion that the language should be much simpler (without technical expressions if possible). People interested in scientific details can consult the corresponding references.
The same for the figures: They should only contain the basic information and one main message.
Example of first figure of question 1: Skip benthic oxygen isotopes; make two figures: one with global temperature only (probably better skip uncertainty range, this is not important here) and pointing to some examples of ice age cycles (first message: how do ice age cycle look like); and a second with change in Antarctic temperature and carbon dioxide, maybe overlayed (second message: ice age cycles are tightly correlated to CO2).
Example for simpler wording of second paragraph in question 1: ‘They vary in extent and duration. They generally were larger in the last 800,000 years, and the duration changed from about 40,000 years in the first half to about 100,000 years in the later period. It was discovered in the 1970s that the cycles were highly correlated to changes in the variability of the Earth’s orbit (the so-called Milankovich cycles; Hays, Imbrie and Shackelton, 1976).
More recent work has shown that the growth and collapse of the ice sheets is strongly tied to the insolation (Roe, 2006).’
It might be advisable to give more than one reference. Although nobody will read it that demonstrates that climate change science is not based on single studies but more than one that gives a similar result.
I can help simplify the text if desired.
Further specific remarks to questions:
I’d give an example of feedbacks so people understand what we mean. E.g. ‘The magnitude of the cycles is strongly modified by various feedbacks. E.g. if temperature rises ice and snow cover which strongly reflects sunlight melts is gradually replaced by darker soil. Bare soil or vegetation take up more radiation and heat, which further increases temperature (known as ‘ice-albedo feedback’). Further feedbacks are known for dust, vegetation or the carbon exchange between oceans, soil, vegetation and atmosphere (the ‘carbon cycle’). …
An explanation of the ‘little ice age’ (combination of solar and volcanic forcing) and the amount of sea level rise and fall during ice ages is missing.
Explain that infrared is the heat radiation (sensible heat). Text could be simplified.
Question 3: Third sentence: ‘Greenhouse gases re-radiate the absorbed energy in all directions, and thus part of this radiation goes back to the surface leads to warming.’
The figure itself is not clear. The ‘easiest description’ is still too complicated. I’d rather just skip it since it is not needed to answer the question.
Maybe one could add instead: ‘This downward radiation from greenhouse gases (and some fine solid air particles (‘aerosols’) e.g. can be measured at the surface in nights with clear sky and no other radiation sources in the atmosphere (e.g. Philipona and Dürr 2004 doi/10.1029/2004GL020937).
Explain calculation or skip.
Note first that the given notion in fact is still valid.
The answer to the question of why plants are not taking up all the fossil fuel emissions is missing, something like: ‘plants in principal only take up as much CO2 as they use for growing. With higher CO2 concentrations (and higher temperature), plants in fact increase their CO2 uptake somewhat but not as much as would be needed to absorb all excess emissions e.g. by fossil fuel burning. Thus plants only take up a part of human emissions (about a fourth to a fifth?), another part is absorbed by the oceans, but about half of the emissions stay in the atmosphere.’
We might add that there is in principal a balance between natural CO2 emissions and natural CO2 uptake which keeps the CO2 concentration in the atmosphere relatively constant. This balance is on long time-scales changed by natural effects (variations of solar radiation and feedbacks, see question 1). In recent decades, human acitvities are the only sources of excess CO2.
[Response: Thanks. I’ve used some of this. – gavin]
Hank Roberts says
This may be helpful to explain bonds and infrared:
I think Judge Alsup will not be afraid of the math on that cited page. Nor would he be put off by the mention of quantum mechanics.
I do think Judge Alsup will read the sources cited for the brief answers. He’s that kind of lawyer, aware that some claims about citations will prove to be unsupported by the claimed source. Cite checking is part of the routine for good judges, or their staff.
[Response: Thanks! Link added. – gavin]
This is very fine, and I will be able to recommend it for the swedes.
However, I have approached the problem from another side and asked what cools us, instead of what heats us. To my understanding, that eases the problem quite a lot.
I once went from Frankfurt over to …. Baaaaasten, (they say). By Lufthansa, who are the tight- packers in the transatlantic human flesh transport business. We went quite incredibly high, waving between 11.5 and 12 Km. And the outdoor thermometer did wave between-65 Down to -70 Celsius,
On Bright afternoon South of Island near autumnal Equinox.
“This must be given a true, physical explaination!” I said to myself.
Because -70 is lower than Siberia at midnight in mid Winter.
That was the so called Isoterm- layer or tropopause.
Explain the Sharp knick in the lapse-rate there, and the very low and steady temperature in that “isotherm”-layer, which is the cool side of the globe enclosing the very Earth. With a quite enormeous heat sink capacity. Because it is cooled by Big Bang, a relativistic phaenomena measuring 2 pi room angle minus 30 arc minutes as seen from here. Keeping a very low average temperature.
It is the chill of Space at very Bright sunshine. The pole caps would have gone long ago if they alone were to cool us.
The even brighter Venus at 0.7AU measures -40 celsius on top of the clouds. = also to be given a true physical explaination before we can discuss climate..
What heats us is another relativistic phaenomena measuring 30 minutes of Arch seen from Our point of wiew, and keeping 5750 Kelvin on its surface.
That is Our basic premises.
Together it gives an average temperature of -18 celsius, and if we find anything different from that, we must discuss Quantum mechanics, material Sciences, and radiation on discontinous spectra.
But in any case I recommend everyone rather to roll it up the opposite way, from the cool side of the globe, that is a very real and distinct physical phaenomena.
The air pressure up there is only about 1/4 bar, so they must have an extreemly good turbo compressor being able to burn away kerosene at that speed.
Jeffrey Tarvin says
Thank you for starting this discussion. Concerning question 2: CO2 absorbs infrared radiation because C has a slight negative charge in the molecule and O has a slight positive charge. Light waves involve oscillating electric fields that cause the C and O to move relative to each other. To be absorbed, the energy in the light wave must match a natural vibration in the molecule. CO2 has vibrations with the right energy for infrared light and they are excited by light. Since the two atoms that form O2 are identical, neither has an electric charge. Consequently, O2 does not absorb infrared light, even though it has a vibration of the right energy. The story is the same for N2. Like CO2, CO absorbs infrared light. For an analogy, think of two young children, one loves apples (CO2) and the other (O2) dislikes them. If a parent says there are no apples in the house, CO2 may cry; but O2 won’t be upset.
Alsups answers seem quite good to me overall as a non climate scientist just interested in the issue.
However item 6 is hard to understand from “note that any change” onwards.
Item 8 could be confusing in having so many messages: “It is extremely likely that more than half of the observed increase in global average surface temperature from 1951 to 2010 was caused by the anthropogenic increase in greenhouse gas…The best estimate of the human-induced contribution to warming is similar to the observed warming over this period….Basically, all of the warming trend in the last ~60yrs is anthropogenic”
Why not just say its “95% certain that almost all the warming over the last 60 years is anthropogenic.” (or something like that) And explain briefly why other causes have been ruled out (solar, volcanos, cosmic rays etc)
Hank Roberts says
Perhaps worth working in somewhere — the mining and drilling companies, once they understood that CO2 and CH4 are greenhouse gases, should (did they?) take into account the emissions from the removal operations — methane leakage that wasn’t flared off; gas escaping from opened up coal seams. That’s in addition to the greenhouse cost of burning the fossil fuel. And the numbers are large for such emissions.
Zeke Hausfather says
I’d add the more recent US National Climate Assessment attribution statement to #8, as its a bit more specific than the one in the IPCC. They say that:
“The likely range of the human contribution to the global mean temperature increase over the period 1951–2010 is 1.1° to 1.4°F (0.6° to 0.8°C), and the central estimate of the observed warming of 1.2°F (0.65°C) lies within this range (high confidence). This translates to a likely human contribution of 93%–123% of the observed 1951–2010 change. It is extremely likely that more than half of the global mean temperature increase since 1951 was caused by human influence on climate (high confidence). The likely contributions of natural forcing and internal variability to global temperature change over that period are minor (high confidence).”
[Response: Thanks! – gavin]
Bob Loblaw says
My vote on #6 would be to show the monthly graph of Mauna Loa CO2, where you can see the planet breathing. Yes,you can see the additional uptake during the northern hemisphere growing season. Then show the calculations that the biosphere is managing to soak up half the emitted CO2 – only half remains in the atmosphere. The system is trying to turn it all back into O2, but it just can’t keep up because of the rapid emission rate.
Ice Pilot says
I agree with comment #6, by Stefan Kranich, that the language must match the audience better. I also have a doctoral degree in a scientific field (not climate science), and I also cringed (literally) when I read the exact same sentence that Stefan criticized.
The answers must be written at the reading level of a typical teenager. Not that Judge Alsup isn’t an excellent reader, but he is not a climate scientist. Also he must communicate his conclusions to the greater public. We can help him, by using the simplest language possible, that still answers the question.
Susan Anderson says
I’m tempted to say “don’t be such scientists” but what do I know. (seriouly, fool rushing in like usual) But this is powerful. “The Last Time the Globe Warmed”
Packs a lot of information in 10 minutes, and requires neither study nor scientific training.
Susan Anderson says
re the above: I am eternally grateful to Kaitlin Naughton (UNSW CCRC, ClimateSight) for introducing us (her readers) many years ago to the Vlog Brothers, aka SciShow, AKA Hank Green, here doing PBS CuriosityStream. They have produced a great deal of other informative material on many subjects, but have a range of climate presentations and present what looks to me to be clear scientific summaries in a straightforward format with a slight touch of nerd.
There are comparisons carbon emissions in the middle that could blow one’s mind. Technical material is provided but doesn’t get in the way. (Danger in them thar hills.)
Fred Magyar says
I tend to agree with Stefan Kranich’s comment @6.
I also believe the answers need to be tailored to the audience if at all possible.
I just came across this lecture By Dr. Jim White and there is a good discussion on how to present complex science to a lay audience at the end of the talk.
Weather and Climate Summit, Day 3 – Dr. Jim White
Mr. Know It All says
First thing they will have to do is to show that there have actually been damages. That will be a huge hurdle to overcome. If they can’t do that, the case will be thrown out.
Then they’ll have to show some kind of negligence on the part of FF companies. And since there is no law against spewing CO2, the case will be thrown out.
Then, the cities, run by believers, will have to sue themselves for not taking steps to deal with rising sea levels that all believers knew about AT LEAST since Al Gore sounded the alarm around 30 years ago. They’ve had ample time to build sea-walls, etc, and as the believers running Nalens did, they did absolutely nothing.
The answer to #6 reveals a solution to the carbon problem. Carbon can be stored in humans. We need to go hog-wild eating tater chips and chocolate, etc, causing each of us to become grossly obese. Hundreds of pounds of carbon stored in each body – wasn’t there a prize of $10MM for anyone who could come up with a workable storage idea? I thought of it first! Any human weighing less than 500 pounds will be charged a stiff carbon tax. Added benefit: for various reasons, soon there will be fewer of us and as many have stated that’s a good thing, right?
Racetrack Playa says:
5 Feb 2018 at 3:34 PM
To continue with the notion of using discrete, short talking points as the basis of communicating climate science to non-experts, politicians, the general public etc., here’s a brief history of the development of climate science over the past two centuries, based mainly on Spencer Weart’s “The Discovery of Global Warming” with some edits for brevity. Here’s the source:
AIP Climate Science History
Milestones in Climate Science, Spencer Weart
1824 Fourier calculates that the Earth would be far colder if it lacked an atmosphere.
1859 Tyndall discovers that some gases block infrared radiation. He suggests that changes in the concentration of greenhouse gases could bring climate change.
1896 Arrhenius publishes the first calculation of global warming from human emissions of CO2.
1930s A global warming trend since the late nineteenth century is reported. Milankovitch proposes orbital changes as the cause of ice ages.
1938 Callendar argues that CO2 greenhouse global warming is under way, reviving interest in the question.
1945 The U.S. Office of Naval Research begins generous funding of many fields of science, some of which happen to be useful for understanding climate change.
1956 Phillips produces a somewhat realistic computer model of the global atmosphere. Plass calculates that adding CO2 to the atmosphere will have a significant effect on the radiation balance.
1957 Revelle finds that CO2 produced by humans is not readily absorbed by the oceans.
1958 Telescope studies show a greenhouse effect raises the temperature of the atmosphere of Venus far above the boiling point of water.
1960 Keeling accurately measures CO2 in Earth’s atmosphere and detects an annual rise. The level is 315 ppm. The mean global temperature (a five-year average) is 13.9°C.
1963 Calculations suggest that feedback with water vapor could make the climate acutely sensitive to changes in the CO2 level.
1965 At a Boulder, Colo., meeting on the causes of climate change, Lorenz and others point out the chaotic nature of the climate system and the possiblity of sudden shifts.
1966 Emiliani’s analysis of deep-sea cores shows the timing of ice ages was set by small orbital shifts, suggesting that the climate system is sensitive to small changes.
1967 The International Global Atmospheric Research Program is established, mainly to gather data for better short-range weather prediction, but climate research is included.
1968 Studies suggest a possiblity of collapse of Antarctic ice sheets, which would raise sea levels catastrophically.
1969 Budyko and Sellers present models of catastrophic ice-albedo feedbacks. The Nimbus 3 satellite begins to provide comprehensive global atmospheric temperature measurements.
1971 A conference of leading scientists (SMIC) reports a danger of rapid and serious global climate change caused by humans, and calls for an organized research effort.
1972 Ice cores and other evidence shows big climate shifts in the past between relatively stable modes in the space of a thousand years or so.
1974 Serious droughts since 1972 increase concern about climate; cooling from aerosols is suspected to be as likely as warming; journalists talk of a new ice age.
1975 Manabe and his collaborators produce complex but plausible computer models that show a temperature rise of several degrees for doubled CO2.
1976 Studies find that CFCs (1975) and methane and ozone (1976) can make a serious contribution to the greenhouse effect. Deep-sea cores show a dominating influence from 100,000-year Milankovitch orbital changes, which emphasizes the role of feedbacks.
1977 Scientific opinion tends to converge on global warming as the biggest climate risk in the next century.
1979 A U.S. National Academy of Sciences report finds it highly credible that doubling CO2 will bring about global warming of 1.5°C – 4.5°C.
1981 Hansen and others show that sulfate aerosols can significantly cool the climate, a finding that raises confidence in models showing future greenhouse warming.
1982 Greenland ice cores reveal dramatic temperature oscillations in the space of a century in the distant past. Stong global warming since mid-1970s is reported; 1981 was the warmest year on record.
1985 Ramanathan and his collaborators announce that global warming may come twice as fast as expected, from a rise of methane and other trace greenhouse gases.
1988 Ice-core and biology studies confirm that living ecosystems make climate feedback by way of methane, which could accelerate global warming. The International Panel on Climate Change (IPCC) is established.
1989 Fossil-fuel and other U.S. industries form the Global Climate Coalition to tell politicians and the public that climate science is too uncertain to justify action. (*Exxon internal documents later show Exxon knew that global warming projections were robust science in 1978)
1990 The first IPCC report says the world has been warming and future warming seems likely.
1991 Mt. Pinatubo erupts; climate scientists predict a cooling pattern, which will validate (*by 1995) computer models of aerosol effects (*and of the water vapor feedback effect). Studies from 55 million years ago (PETM excursion) show a possiblity that the eruption of methane from the seabed could intensify enormous self-sustained warming.
1992 The study of ancient climates reveals climate sensitivity in the same range as that predicted independently by computer models.
1993 Greenland ice cores suggest that great climate changes (at least on a regional scale) can occur in the space of a single decade.
1995 The second IPCC report detects a ‘signature’ of human-caused greenhouse-effect warming; it declares that serious warming is likely in the coming century. Reports of the breakup of Antarctic ice shelves and other signs of actual current warming in polar regions begin to affect public opinion.
1998 A “Super El Niño” causes weather disasters and the warmest year on record (approximately matched by 2005 and 2007). Borehole data confirm an extraordinary warming trend. Qualms about arbitrariness in computer models diminish as teams model ice-age climate and dispense with special adjustments to reproduce current climate.
2000 The Global Climate Coalition dissolves as many corporations grapple with the threat of warming, but the oil lobby convinces the U.S. administration to deny a problem exists.
2001 Debate effectively ends among all but a few scientists. Warming is observed in ocean basins; the match with computer models gives a clear signature of greenhouse-effect warming.
2003 Numerous observations raise concern that collapse of ice sheets (in West Antarctica and Greenland) can raise sea levels faster than most had believed. A deadly summer heat wave in Europe accelerates the divergence between European and U.S. public opinion.
2007 The level of CO2 in the atmosphere reaches 392 ppm. The mean global temperature a five-year average) is 14.5°C, the warmest in hundreds, perhaps thousands, of years.
2015 and 2016 are the warmest years on record. Atmospheric CO2 is now 410 ppm.
Now, if there’s a single take-away from this summary, it would be that the science on the relationship between fossil fuel combustion, rising atmospheric carbon dioxide, and global warming and climate change was really settled by 1979. If someone challenges that statement, the above summary can be given to them; it’s short and concise enough for any audience.
References: pick n choose – California impacts from agw/cc slr storm surges
[2008 paper – 170 cites] Climate change projections of sea level extremes along the California coast
Gradual sea level rise progressively worsens the impacts of high tides, surge and waves resulting from storms, and also freshwater floods from Sierra and coastal mountain catchments. The occurrence of extreme sea levels is pronounced when these factors coincide. The frequency and magnitude of extreme events, relative to current levels, follows a sharply escalating pattern as the magnitude of future sea level rise increases.
[2002 paper – 621 cites] Climate change impacts on U.S. Coastal and Marine Ecosystems
This paper is a summary of the coastal and marine resources sector review of potential impacts on shorelines, estuaries, coastal wetlands, coral reefs, and ocean margin ecosystems. The assessment considered the impacts of several key drivers of climate change: sea level change; alterations in precipitation patterns and subsequent delivery of freshwater, nutrients, and sediment; increased ocean temperature; alterations in circulation patterns; changes in frequency and intensity of coastal storms; and increased levels of atmospheric CO2. Increasing rates of sea-level rise and intensity and frequency of coastal storms and hurricanes over the next decades will increase threats to shorelines, wetlands, and coastal development.
[2011 paper – 211 cites] Assessing climate change impacts, sea level rise and storm surge risk in port cities: a case study on Copenhagen
This study illustrates a methodology to assess the economic impacts of climate change at a city scale and benefits of adaptation, taking the case of sea level rise and storm surge risk in the city of Copenhagen, capital of Denmark. The approach is a simplified catastrophe risk assessment, to calculate the direct costs of storm surges under scenarios of sea level rise, coupled to an economic input–output (IO) model. The output is a risk assessment of the direct and indirect economic impacts of storm surge under climate change, including, for example, production and job losses and reconstruction duration, and the benefits of investment in upgraded sea defences.
[2011 paper 157 cites] Exploring high-end scenarios for local sea level rise to develop flood protection strategies for a low-lying delta—the Netherlands as an example
Sea level rise, especially combined with possible changes in storm surges and increased river discharge resulting from climate change, poses a major threat in low-lying river deltas. In this study we focus on a specific example of such a delta: the Netherlands. To evaluate whether the country’s flood protection strategy is capable of coping with future climate conditions, an assessment of low-probability/high-impact scenarios is conducted, focusing mainly on sea level rise.
[2011 Paper – Cited by 493 times] Transformational adaptation when incremental adaptations to climate change are insufficient
Two conditions set the stage for transformational adaptation to climate change: large vulnerability in certain regions, populations, or resource systems; and severe climate change that overwhelms even robust human use systems.
“A 1-m rise threatens $100 billion of property in California, and extended and enlarged coastal […] to protect a 60-mile section of the Texas coast from the storm surge hazard would […]
[2012 paper – 225 cites] Modelling sea level rise impacts on storm surges along US coasts
We estimate that, by mid-century, some locations may experience high water levels annually that would qualify today as ‘century’ (i.e., having a chance of occurrence of 1% annually) extremes. Today’s century levels become ‘decade’ (having a chance of 10% annually) or more frequent events at about a third of the study gauges, and the majority of locations see substantially higher frequency of previously rare storm-driven water heights in the future. These results add support to the need for policy approaches that consider the non-stationarity of extreme events when evaluating risks of adverse climate impacts.
[2011 paper – cited 37 times] Potential impacts of increased coastal flooding in California due to sea-level rise
We analyzed the effect of a medium-high greenhouse gas emissions scenario (Special Report on Emissions Scenarios A2 in IPCC 2000) and included updated projections of sea-level rise based on work by Rahmstorf (Science 315(5810): 368, 2007). Under this scenario, sea levels rise by 1.4 m by the year 2100, far exceeding historical observed water level increases. By the end of this century, coastal flooding would, under this scenario, threaten regions that currently are home to approximately 480,000 people and $100 billion worth of property.
MR KIA “Then they’ll have to show some kind of negligence on the part of FF companies. And since there is no law against spewing CO2, the case will be thrown out.”
I doubt that it needs a specific law on CO2. All they have to do is show that damage was caused and the defendents knew there was a risk or should have known. This is basic law of torts material. I see your lack of knowledge of the law is similar to your lack of knowledge of other things!
pick n choose from
10 Mar 2018 at 3:19 AM
1988 prediction by Syukuro Manabe, NASA atmospheric physicist of what we now observe: Human caused warming will proceed most rapidly in the northern polar reaches.
2017 Paper — Assessing temperature pattern projections made in 1989
Ronald J. Stouffer * and Syukuro Manabe 2
Successful projection of the distribution of surface temperature change increases our confidence in climate models. Here we evaluate projections of global warming from almost 30 years ago using the observations made during the past half century.
PAPER URL https://goo.gl/hgsy6o
9 Mar 2018 at 7:53 PM
AGW/CC Impacts Agriculture CA USA
Study indicates that climate change will wreak havoc on California agriculture
That’s the assessment of a recent paper by a University of California team led by Tapan Pathak of UC Merced. But the researchers focused on a different aspect of California agriculture: You can kiss much of it goodbye because of climate change.
The paper, published in the journal Agronomy last month, is the most thorough review of the literature on the regional impact of climate change in recent memory. It makes grim reading.
Climate Change Trends and Impacts on California Agriculture: A Detailed Review by Tapan B. Pathak et al
California is a global leader in the agricultural sector and produces more than 400 types
of commodities. The state produces over a third of the country’s vegetables and two-thirds of its
fruits and nuts. Despite being highly productive, current and future climate change poses many
challenges to the agricultural sector. This paper provides a summary of the current state of knowledge
on historical and future trends in climate and their impacts on California agriculture.
Hank Roberts says
Just as a reminder, the gasoline companies have a lot of practice denying the health problems from their products.
Hank Roberts says
and from the same page:
One thing that always seems to be left out of attempts to give clarity to the subject is the fact that it is CO2 in the atmosphere that makes Earth a habitable planet, well one of the things.
What this does is illustrate how effective and important it is and then we can explain how we should not mess with this important aspect of our unique, wonderful, livable planet.
Oxygen is another somewhat important element allowing life on the planet but we would not think of messing with that. (Actually I believe we might be).
Greg Simpson says
The answer to number 4 uses a cheap debating trick. It should not be “Not enough to matter” but instead be “Yes, but not enough to matter”. Don’t be afraid to answer the question!
[Response: Done! – gavin]
Susan Anderson says
How about xkcd’s “A Timeline of Earth’s Average Temperature since the Last Ice Age Glaciation: When people say “The climate has changed before” these are the kinds of changes they are talking about”
Dan DaSilva says
Response to #10 jgnfld
“The SCIENCE is not “politicized”. ”
If that is true then Scientists are exceptionally virtuous people. However, they are just people like the rest of us. An outlandish statement to make in this forum.
Radge Havers says
Some interesting background on Alsup. He takes his research seriously:
Perhaps provide somewhere that Skeptical Science is a handy, user-friendly reference for answers to contrarian talking points– keeping in mind that the tutorial, in addition to providing general background, has to have some relevance to the way the opposition is likely to argue (misrepresent).
Mr. Know It All says
32 – nigelj
“I doubt that it needs a specific law on CO2. All they have to do is show that damage was caused and the defendents knew there was a risk or should have known. This is basic law of torts material.”
Nigelj, in the USA when you go to court you are judged according to the law, not what would be “just”, or what feels good. If there is no law against spewing CO2, you cannot be found guilty of spewing CO2 even if it’s wrong. Perhaps in NZ it’s different? AND you missed the first point – there have been no damages. They have no case.
Racetrack Playa says
For question (1)
IPCC 2013 Working Group, The Physical Basis, Chapter 5, Information from Paleoclimate Archives:
Q1: What caused the various ice ages (including the “little ice age” and prolonged cool periods) and what caused the ice to melt? When they melted, by how much did sea level rise?
Breaking this question down, each part can be answered by a quote from the 2013 IPCC report, for example:
(A) What caused the various ice ages? [prolonged cool periods?]
Recent modelling work provides strong support for the important role of variations in the Earth’s orbital parameters in generating long-term climate variability. In particular, new simulations with Global Climate Models (Carlson et al., 2012; Herrington and Poulsen, 2012) support the fundamental premise of the Milankovitch theory that a reduction in NH summer insolation generates sufficient cooling to initiate ice sheet growth. Climate–ice sheet models with varying degrees of complexity and forced by variations in orbital parameters and reconstructed atmospheric CO2 concentrations simulate ice volume variations and other climate characteristics during the last and several previous glacial cycles consistent with paleoclimate records (Abe-Ouchi et al., 2007; Bonelli et al., 2009; Ganopolski et al., 2010) (see Figure 5.3).
There is high confidence that orbital forcing is the primary external driver of glacial cycles (Kawamura et al,. 2007; Cheng et al., 2009; Lisiecki, 2010; Huybers, 2011). However, atmospheric CO2 content plays an important internal feedback role.Orbital-scale variability in CO2 concentrations over the last several hundred thousand years covaries (Figure 5.3) with variability in proxy records including reconstructions of global ice volume (Lisiecki and Raymo, 2005), climatic conditions in central Asia (Prokopenko et al., 2006), tropical (Herbert et al., 2010) and Southern Ocean SST (Pahnke et al., 2003; Lang and Wolff, 2011), Antarctic temperature (Parrenin et al., 2013), deep-ocean temperature (Elder eld et al., 2010), biogeochemical conditions in the Northet al., 2008). Such close linkages between CO2 concentration and climate variability are consistent with modelling results suggesting with high confidence that glacial–interglacial variations of CO2 and other greenhouse gases [CH4, N2O] explain a considerable fraction of glacial–interglacial climate variability in regions not directly affected by the northern hemisphere continental ice sheets (Timmermann et al., 2009; Shakun et al., 2012).
(B) Including the little ice age? [and the medieval warm period]
Many paleoclimate archives document climate changes that happened at rates considerably exceeding the average rate of change for longer-term averaging periods prior and after this change. . . A variety of mechanisms have been suggested to explain the emergence of such abrupt climate changes (see Section 12.5.5). Most of them invoke the existence of nonlinearities or, more specifically, thresholds in the underlying dynamics of one or more Earth-system components. Both internal dynamics and external forcings can generate abrupt changes in the climate state. . .
. . .Continental-scale surface temperature reconstructions show, with high confidence, multi-decadal periods during the Medieval Climate Anomaly (950 to 1250) that were in some regions as warm as in the mid-20th century and in others as warm as in the late 20th century. With high confidence, these regional warm periods were not as synchronous across regions as the warming since the mid-20th century. Based on the comparison between reconstructions and simulations, there is high confidence that not only external orbital, solar and volcanic forcing, but also internal variability, contributed substantially to the spatial pattern and timing of surface temperature changes between the Medieval Climate Anomaly and the Little Ice Age (1450 to 1850).
C) What caused the ice to melt?
There is high confidence that changes in atmospheric CO2 concentration play an important role in glacial–interglacial cycles. Although the primary driver of glacial–interglacial cycles lies in the seasonal and latitudinal distribution of incoming solar energy driven by changes in the geometry of the Earth’s orbit around the Sun (“orbital forcing”), reconstructions and simulations together show that the full magnitude of glacial–interglacial temperature and ice volume changes cannot be explained without accounting for changes in atmospheric CO2 content and the associated climate feedbacks. During the last deglaciation, it is very likely2 that global mean temperature increased by 3°C to 8°C. . .
. . .Polar amplification explains in part why Greenland Ice Sheet and the West Antarctic Ice Sheet appear to be highly sensitive to relatively small increases in CO2 concentration and global mean temperature. . .
. . .Polar amplification occurs if the magnitude of zonally averaged surface temperature change at high latitudes exceeds the globally averaged temperature change, in response to climate forcings and on time scales greater than the annual cycle. Polar amplication is of global concern due to the potential effects of future warming on ice sheet stability and, therefore, global sea level (see Sections 5.6.1, 5.8.1 and Chapter 13) and carbon cycle feedbacks such as those linked with permafrost melting (see Chapter 6). . . .The magnitude of polar amplification depends on the relative strength and duration of different climate feedbacks, which determine the transient and equilibrium response to external forcings.
(D) When they melted, by how much did sea level rise?
The onset of melting of the Last Glaciam Maximum ice sheets occurred at approximately 20,000 years ago and was followed by a Global Mean Sea Level rise of ~130 meters in ~13,000 years (Lambeck et al., 2002b). Coeval with the onset of the Bølling warming in the Northern Hemisphere, a particularly rapid rise of ~ 20 m occurred within ~ 340 years (Meltwater Pulse 1A, MWP-1A), as most recently documented by Deschamps et al. (2012) from a new Tahiti coral record. At this location sea level rose between 14 and 18 m at a rate approaching 5 m per century. . .
[this is useful, the pre-ice age era, ~2.5 – 3.6 million years ago, last time CO2 levels were as high as today]
In response to Pliocene climate, ice sheet models consistently produce near-complete deglaciation of the Greenland ice sheet (+7 m) and West Antarctic ice sheet (+4 m) and retreat of the marine margins of the Eastern Antarctic ice sheet (+3 m) (Lunt et al., 2008; Pollard and DeConto, 2009; Hill et al., 2010), altogether corresponding to a global mean sea level rise of up to 14 m.
Perhaps the IPCC language can be simplified for a more general audience, but that’s a good source. All the chapters are linked here:
Kevin McKinney says
Jef, #36, said “Actually I believe we might be [messing with].”
Right you are, Jef:
Climate warming and nutrient pollution are vastly expanding the area of anoxic waters around the world. (Though it’s worth noting that serious effort has resulted in ameliorating the problem quite considerably in Chesapeake Bay.)
We’re actually decreasing atmospheric oxygen, too, but that effect, while pretty diagnostic of the fact that it’s combustion that is increasing atmospheric CO2, is not going to cause practical problems.
Chris Colose says
I also had a quick twitter thread on this (probably not the most useful for directing it toward a courtroom).
1) What caused the ice ages (including Little Ice Age) and what caused the ice to melt? When they melted, how much did sea level rise?
It seems necessary to actually distinguish between glacials (where, e.g. much more of N. America & Canada had extensive ice cover…the last peak was ~25-,000-20,000 years ago) vs. the little ice age (LIA), which is small potatoes comparatively.
Last Millennium people like the LIA (loosely 1500-1800s depending on who you ask), to the extent such a term is useful (given spatial and temporal structure in such an “event”). Globally, the temp reduction during a glacial is an order of magnitude larger than that of the LIA.
In contrast, the much more expansive ice volume maxima (equivalently, sea level minima) during a glacial maximum is more defined. The last glacial sea level was ~400 feet(!) lower than modern day. That turns out to be a lot of feet.
With small things like the LIA, there’s probably internal variability involved. The big external forcing here is volcanoes. The Sun, greenhouse gases, and orbit don’t matter much during the pre-industrial interval of the last millennium.
For the last glacial maxima, volcanoes and sun don’t matter now and the orbit and GHGs are nearly the entire story. Specifically, changes in the Earth’s tilt/seasonality that pace the glacial process and the carbon cycle feedbacks that change CO2 by ~100 ppm.
Oh, and we’ve increased CO2 by 100 ppm already (it doesn’t quite have the punch of the other 100 ppm because of logarithmic effects, yadda yadda, but the court can be assured we’re going to warm up by about an ice age by 2100).
Unlike the LIA, the last glacial/deglacial process look more like global events (not quite synchronous, but let’s think of it that way). CO2 changes help synchronize the globe and cool the tropics. The orbit changes high latitude summer sunlight by many tens of W/m2.
Such “cycles” are important on Earth (and Mars) but occur on timescales of tens to hundreds of thousands of years, so not meaningful for present day global warming considerations. But it turns out that ice still melts when you make it warmer, regardless of cause.
2) What is the molecular difference by which CO2 absorbs infrared
radiation but oxygen and nitrogen do not?
In Earth’s atmosphere, H2O has a permanent electric dipole moment (a charge separation within the molecule) allowing to interact with electromagnetic radiation. CO2 also has an electric dipole, but must bend/stretch to generate it, due to it being a linear molecule.
N2 and O2, like CO2, are symmetric,but cannot bend or stretch to create a dipole moment. So they are not usually considered greenhouse gases. They could, in principle, be GHGs under the right conditions (and are in the outer solar system) via e.g., collisions in dense atmospheres. Your honor may not want a full quantum physics tutorial, though, so we’ll leave it there.
3) What is the mechanism by which infrared radiation trapped by CO2 in the atmosphere is turned into heat and finds its way back to sea level?
The absorption of radiation is not strongly dependent on the temperature of most things, but the emission is. Greenhouse gases absorb intense emission from the surface and re-emit less intense energy at colder temperatures, resulting in an efficient heat trapping mechanism.
This increased opacity means less energy escapes to space for a given temperature. But you need to have the same amount of energy escaping as what comes in to have a climate that isn’t warming or cooling. This is done through a tug of war between temperature and opacity.
4) Does CO2 in the atmosphere reflect any sunlight back into space such that the reflected sunlight never penetrates the atmosphere in the first place?
At modern day concentrations, CO2 does not matter much for absorbing/reflecting incoming sunlight, though in a very, very dense CO2 atmosphere it would. Venus would still be quite bright even w/o its thick sulfuric acid clouds due to CO2 Rayleigh scattering.
On Earth, most of the reflected energy to space comes from the atmosphere & most of that comes from clouds and N2/O2. But adding CO2 on Earth is an infrared problem,- you’d need more than a tenth of an atmosphere of CO2 before the increased albedo competed w inc greenhouse effect
5) What happens to collective heat from tail pipes, etc…how does it contribute to warming of the atmosphere
This is a forcing because the heat we generate is dissipated in the Earth-atmosphere system. Looking up numbers for world energy consumption is ~5.5e20 joules annually. That is ~0.03 W/m2 for a global forcing, less than the geothermal heat flux.
That is Watts per square matter, your honor. Think of lightbulbs and stuff. Turn out we can currency convert CO2’s warming effect into lightbulb numbers. Pretty cool, eh? Science figures out cool stuff.
CO2 forcing is ~2 W/m2 now since pre-industrial, total is 1-2 W/m2. But bc of our tug of war (increase temp) emission to space is going up, so Earth is still gaining maybe 0.5 W/m2. The direct waste heat small globally, though can matter locally. It’s an impt future regional forcing.
6) …taught that humans exhale CO2 but plants absorb CO2 and return O2 to the air (keeping the carbon for fiber). Is this still valid? If so, why hasn’t plant life turned the higher levels of CO2 back into oxygen?
Your grade school learnings are still valid. Indeed, the atmosphere would have virtually no O2 without photosynthesis. The biosphere is not a huge carbon reservoir though, and would need to at least double to keep up with our fossil fuel emissions.
The biosphere has taken up some of our C. But the most impt part of the future carbon fate will be oceans & inorganic carbon cycle. The ocean removes excess atmos CO2, by dissolving in and reacting with surface waters, acidifying them. This sink is limited chemically, however.
In fact, it will take tens to hundreds of thousands of years for all of the excess carbon to be removed, by pH recovery/ocean neutralization by CaCO3 and by slow processes that react CO2 with silicate rocks.
7) What are the main sources of CO2 that account for the incremental buildup of CO2 in the atmosphere?
Fossil fuel emissions, especially electricity generation, transportation, and some influence from deforestation.
8) What are the main sources of heat that account for the incremental rise in temperature on Earth?
It’s all due to the radiative effect of greenhouse gases, chiefly CO2. And that answer is robust enough to be good enough for government work, or jury duty.
[Response: Thanks, gavin]
I think its important to keep answers fairly concise. The answers above might be a little too brief, but you don’t want to hand this judge hundreds of pages to wade through. However a reasonably concise set of answers could have a couple of supplementary appendix attached, such as a bibliography of references, and the simple historical record at comment 20 is powerful, and could be attached as an appendix.
People talk about the need for simplicity. I agree it needs to be kept reasonably simple and free of too much jargon. If jargon is included, it needs a definition in brackets. I think the answers jotted down in the article are about right in approach, if some things are untangled a bit. Perhaps some of the terminology is a bit over complicated.
But you don’t want it to be overly simplistic at a cartoon sort of level, or primary school level, as it could come across as patronising. Judges are very smart people, and do understand complexity as long as there’s minimal jargon ( or terms are defined in brackets). The ice ages were well explained and some of the jargon was defined, although the term insolation wasn’t.
Some of the suggestions in the comments are getting too wordy, complex and full of jargon, especially on the properties of the CO2 molecule. Its enough to state that 3 atom molecules can wobble where 2 atom molecules cant. This is easy to grasp and getting into far more detail might be frustrating and remember a lot of this material might be new to the judge and people can only absorb so much. Pages of details on the CO2 molecule might be better as an appendix.
Simply play this for the Judge during the Tutorial.
The Science Show
Climate – what’s next?
Saturday 10 March 2018 12:05PM
radio audio w Transcripts
Digby Scorgie says
Yes, carbon dioxide is a goldilocks gas — too little and the planet freezes, too much and the planet swelters!
nigelj @ #32 You write: “I doubt that it needs a specific law on CO2. All they have to do is show that damage was caused and the defendents [sic] knew there was a risk or should have known.”
The relevant legislation (USA) is the Clean Air Act which grants authority to regulate CO2 & other greenhouse gasses. It’s been adjudicated, see Massachusetts v. Environmental Protection Agency, 549 U.S. 497 (2007) https://www.supremecourt.gov/opinions/06pdf/05-1120.pdf
Omega Centauri says
A lot of pretty good responses here. I would like to add that for (1) it is a combination of external forcings (orbital) that aren’t particularly strong, as amplified by feedback effects, which include snow/ice albedo, and vegetation cover changes (including atmospheric dust levels), as well as CO2 which also changes wrt. the state of the global climate. The important point here is that a small external forcing (orbital for ice-ages, or GHG plus aerosols & land use changes in the modern context) can be strongly amplified by the positive feedback mechanism (the strongest and quickest is atmospheric water vapor -a strong GHG, and has already been observed to increase.
Effectively (1) can be used to motivate the discussion of climate sensitivity, and is in fact one important data point in constraining the size of the climate sensitivity.
Of note of course is that there are many independent ways to estimate sensitivity, and they all come up with similar results.
Mike Flynn says
Nobody seems to have even managed to answer question 1.
The answers could take the form of – ” . . . caused the ice ages. . . . caused the ice to melt. The sea levels rose by . . . as a result.”
Judges tend to be aware of rules of evidence as they are involved in the administration of law. Hearsay, evasion, and incomprehensible jargon may not be accepted gladly.
Didn’t Gavin get awards for Science Communicator of the Year, and so on? This should be a snap for him. It might be seen as a bit odd if he is seeking assistance for a simple matter of answering a few questions. Even more so if the judge is aware of this blog.