QUOTE: “One point that is also worth making is that although volcanos release some CO2 into the atmosphere, this is completely negligable compared to anthropogenic emissions ”
One thing I regularly see from skeptics is exactly the opposite–that anthropgenic emissions are completely negligable compared to volcanic emissions. I’ve seen them say things like (if not exactly) the Pinatubo eruption released more greenhouse gasses than all human activity in history combined.
Is there any reason for the disconnect here?
[Response: Yep. I know what I'm talking about ;) There are both direct measurements of volcanic outgassing (from which I got the 0.15 Gt/year integrated number) and also isotopic and mass balance arguments that absolutely, 100%, no question about it, mean that the current rise in CO2 is anthropogenic. Ask them why there isn't an obvious spike in the Mauna Loa CO2 record after 1991 if indeed Pinatubo released more CO2 than all human activity in history combined - because that is a big number! - gavin]
Good info.! Some readers may wonder why Mt. St. Helens was excluded from your discussion. In Mt. St. Helens’ May 18, 1980 eruption, the ash had little effect on even short-term temperatures for at least three reasons: 1) the initial lateral blast sent much coarse particulate matter low in the troposphere, rather than to the stratosphere; 2) the vertical tephra column that issued subsequently had comparatively large particle size, limiting its atmospheric residence time; and 3) the eruption was VEI=5 but just barely. In other words, it wasn’t huge or long lasting.
You pointed out that the eruption of Lakigigar in Iceland in 1783-84 had a disproportionate effect on the atmosphere despite its subpolar location. It was a very interesting eruption indeed! Although it was an effusive eruption of large volume (about 12 cubic kilometers of basalt) and had comparatively little ash (i.e., low VEI), the long duration and its “messiness” (it indeed had lots of sulphate aerosols that hung around for months) prompted Benjamin Franklin (American ambassador to France at the time) to comment on the blue haze persisting in France. And effects of the eruption in Iceland itself included widespread famine due to crop failure, which also resulting in a significant loss of lifestock.
A tiny correction is that “volcanos” (sic) is correctly spelled “volcanoes.” :-)
[Response: Thanks. Spelling fixed! - I didn't discuss Mt St. Helens for precisely the reason you mention - the most important being that the explosion went 'sideways' and not up. Thanks for the extra details on Laki. - gavin]
Now that Mauna Loa is mentioned, what has happened? It used to be very up to date at http://cdiac.esd.ornl.gov/trends/trends.htm,
but now there is nothing after year 2004. Is no-one working there anymore?
Comment by Fredrik Lundberg — 16 May 2006 @ 4:17 PM
There is an obvious spike in the rate of CO2 increase at that time — in the other direction!
I’ve been all over the CO2 record from Mauna Loa, and I can tell you that just after the Mt. Pinatubo explosion, the growth rate of atmospheric CO2 decreased. From about 1977 to 1990, atmospheric CO2 was increasing at about 1.5 ppmv/yr, but from 1991-1992 the rate dropped to about 0.9 ppmv/yr. It rebounded quickly, and by 1994 was above 1.5 ppmv/yr.
Gavin? Could the Mt. Pinatubo explosion have caused a decrease in atmospheric CO2 increase rate? Or is the dip due to some other cause?
[Response: A small dip is completely understandable in terms of the carbon cycle response to the cooling. It could be a solubility effect (cooler oceans take up more CO2), but it's more likely a biosphere effect - reduced soil respiration maybe. I'd have to look up the relevant literature to be more precise... - gavin]
[Response: A small dip is completely understandable in terms of the carbon cycle response to the cooling. It could be a solubility effect (cooler oceans take up more CO2), but it's more likely a biosphere effect - reduced soil respiration maybe. I'd have to look up the relevant literature to be more precise... - gavin]
[Response: Actually, an important factor is that plants--somewhat counter-intuitively--respond positively (i.e., increased primary production and carbon update) to increased diffuse light which is actually favoured by increased cloud (see e.g. Gu et al, 1999) as well as the stratospheric sulphate aerosol input associated with explosive volcanic eruptions (see e.g. Krakauer and Randerson,2003 and Robock, 2005). -mike]
I’m not an atmospheric scientist or botanist, but on the basis of just the Mauna Loa data I’d think that it’s the biosphere — because the amplitude of annual variation in the Mauna Loa time series doesn’t decrease at that time, it increases from about 5.7 ppmv pre-Pinatubo to about 6.3 just after. Doesn’t that indicate greater biological activity? Does greater biological activity take CO2 out of the air?
The amplitude then declines steadily from 1992 to 2001, returning to about 5.7 ppmv, hovers there a year or so, then shoots back up to about 6.3 in 2004.
I know it’s hardly critical — but I sure am curious.
I’ve been looking for this myself for some time. I found this graph through a simple web search: http://www.cmdl.noaa.gov/ccgg/trends/index.php
which has through March or April 2006. They say the last year of data hasn’t been officially released yet, pending calibration and quality control checks. There must be somewhat to get the data, but you can estimate the numbers well enough off the graph if you are interested.
In comparison, your take on Mt. Toba explosion, please. Was this about 71,000 years ago? About 74,000 years ago? Accounts seem to vary and I don’t know enough to find it in ice core records. How long thereafter was the climate perturbed? Again, I don’t see it at all in ice core records, but I may not know for what to look…
Comment by David B. Benson — 16 May 2006 @ 5:48 PM
Re. Responce to 6: Isn’t the decrease in early 90′s CO2 production caused by the collapse of the soviet economy, resulting in reduced emissions?
Re 2: Ask a skeptic where their math comes from, but my guess is that they include mid-ocean ridge volcanism- multiplying the CO2 content of MORB by the annual oceanic crustal production should give you a fairly large number. Thing is, all of this CO2 ends up disolved in seawater, or precipitated in hydrothermal alteration, so it has no direct short term impact on the atmosphere. Also, if they use popping rock CO2 values, they are going to get an overestimate, since that rock has twice the standard MORB concentration. Mantle carbon is isotopically heavier than organic carbon, so it is easy to differentiate the two sources.
(No, they don’t support the idea that increased CO2 is good for farmers, they are talking about the changes in primary productivity here.)
… Between 1982 and 1999, 25 percent of the Earth’s vegetated area experienced increasing plant productivity – a total increase of about 6 percent,” says Ramakrishna Nemani, the study’s lead scientist. “That increase occurred mainly in the tropics, and secondarily in high northern latitudes. What’s interesting about our results is that they show how the increase in each of these regions is due to a different climate factor.”
In the tropics, Nemani and his colleagues discovered that the increase in productivity was caused by lack of clouds and increased Sun exposure, while in the northern latitudes, it was mainly due to increased temperatures and to a lesser extent, water availability….
And the attached link is an appropriate footnote to the following:
“One point that is also worth making is that although volcanoes release some CO2 into the atmosphere, this is completely negligable compared to anthropogenic emissions (about 0.15 Gt/year of carbon, compared to about 7 Gt/year of human related sources). ”
Now, take a good look at some serious axles of evil:
correction: a quick front-of-the-post-it calculation gives me a total CO2 contribution from MORB of about 2.1 GT/yr, assuming 50mm/yr average spreading rate, 7 km oceanic crustal thickness, 40,000 km total ridge length, and 0.5 wt% CO2 content. Those are very approximate numers, so if any enterprising undergrads wanna look the correct numbers up and refine that, go for it. Still have no idea where CO2 release that “dwarfs” human emissions comes from. And this contribution still doesn’t reach the atmosphere.
That’s 2.1 GT CO2- do you guys work in CO2 or C? (2.1 GT CO2 is about 0.6 GT C)
[Response: We work in C rather than CO2, and .6Gt is in the right ballpark. It's interesting to note that if the volcanic CO2 were even comparable to the anthropogenic (let's say 6Gt), let alone dominant, that would put the outgassing at values far in excess of what they were believed to have been any time in the past 3.5 billion years. Using the Walker Hayes and Kasting weathering model with the present solar constant, a 6Gt per year outgassing would equilibrate at an atmospheric CO2 concentration of about 57 times the present, or 17000ppmv. That would lead to temperatures in excess of 14K warmer than pre-industrial values. --raypierre]
Re: 6 and 2. Thanks for the info on tectonic carbon sources, though what’s MORB? Mid-ocean ridge basalt?
I think the variations in atmospheric CO2 (after the annual cycle and trend, of course) are dominated by ENSO. As I understand it, the tropical Pacific is a source for atmospheric carbon due to upwelling of cold, carbon-rich waters from deeper in the ocean along the equator. During ENSO events, that upwelling decreases considerably. The early 1990′s were characterized by a series of El Nino events (though there has been a good deal of debate over how to characterize the early 1990′s). If you look at 1982 and 1997 from the Mauna Loa record (link above) you’ll see similar slowdowns in the rate of CO2 increase.
Richard Feely at PMEL has an article in Nature (also online at http://www.pmel.noaa.gov/pubs/outstand/feel1868/text.shtml) that attributes 1/3 of the decrease in CO2 increase (got it?) during the 1991-1994 (autumn to autumn) seasons to ENSO. They estimate a -0.6 Gt C decrease in sea-to-air carbon (not CO2) flux in 1992 due to ENSO. There are also some nice model results by Galen McKinley and collaborators that describe the Pacific influence (GRL, 2004; Glob. Biogeochem. Cycles, 2004; http://www.aos.wisc.edu/%7Egalen/).
Maybe the biggest effect of volcano’s on atmospheric CO2 is not their direct carbon dioxide release, but the effect of the iron/aerosols on primary production in the ocean. Andy Watson has made the argument that atmospheric carbon dioxide decreased following the Pinatubo eruption because the iron in the volcanic aerosols fertilized the equatorial Pacific and led to increased rates of phytoplankton uptake of carbon dioxide (Watson, A.J. “Volcanic iron, CO2, ocean productivity and climate.” Nature, 385, 587-588, 1997).
There is one anthropogenic source [coal-fired power plants] we could fix with well-known technology if we could cure the common person of paranoia concerning things nuclear. The average person has never heard of background radiation. See articles by Alex Gabbard [Oak Ridge National Lab] concerning the uranium, arsenic, thorium, etc in coal. Oak Ridge National Laboratory REVIEW
Volume 26 Numbers Three and Four, 1993 Coal Combustion: Nuclear Resource or Danger? by Alex Gabbard
You can download a version of it at http://www.ornl.gov/ORNLReview/rev26-34/text/coalmain.html
but it may hav been modified by a George Bush political appointee. I was unable to paste a copy of the original here. The paste didn’t work.
Silly and slightly off-topic question.. would it be possible to reproduce the climate-cooling effects of a volcano with one or more thermonuclear airbursts near the equator (preferably in an unihabited area, like the middle of the Pacific)?
I’ve read that there are some cooling spikes in the temperature records from around the same time as the ’62 nuclear tests, presumably because these kicked up a globally signifigant amount of aerosols into the stratosphere. Presumably, we could do even better, if we specifically optimized thermonuclear airbursts for maximum climate-cooling effects (e.g., adjusting the height of the explosion, changing the quantity and quality of dust to be vaporized.) Heaven knows, there is no shortage of bombs available for such tests.
I understand that 1) interfering with a system as critical and poorly understood as climate is A Bad Idea, 2) sulfate aerosols would catalyze a lot of ozone destruction, and 3) a bunch of H-Bomb tests may well have unfavorable political consequences.
But the alternative may well be hundreds of millions of at risk of death , or even a James Lovelock Revenge of Gaia or runaway greenhouse scenario. Might it be at least studying the feasibility of such a contingency plan?
It seems to me objection 1) could be overcome with a series of increasingly large tests, comparing observations to model predictions. Would it be possible to optimize thermonuclear explosions to get some cooling with an acceptable amount of ozone loss?
It’s true there were slight dips in the growth rate of atmospheric CO2 around 1982 and 1998, but they’re nothing like the dip around 1991. Also, wasn’t the 1998 el Nino a very strong one? But the dip in CO2 growth rate wasn’t comparably strong.
I’m guessing (only) that while el Nino affects CO2 growth rate, something else happened around 1991 to make the dip so severe. The collapse of the Soviet economy seems a plausible reason, and the coincidence with Mt. Pinatubo is suggestive.
Yes, you can find documentation of the total fossil fuel burned year by year that confirms CO2 release by the former USSR states dropped dramatically, that correspond to the observed growth rate measured in the atmosphere. No time to look it up for you right now, but it shouldn’t be hard to find.
We’ve noted before that it seems only a matter of time before one desperate scheme after another as long as it doesn’t involve reducing the amount of fossil fuel we burn will be proposed. Eventually, one or more of them will be funded and carried out.
Mt Toba, last two eruptions: Here is what I could find, despite all the mis-information out in webland. Wikipedia says the last occured 71,000 years ago with a 4000 year error bar. Another site states 73,000 with the same error bar. Still another states 74,000 years ago. No matter, the following article claims that the global temperature dip for this massive event was about 1 degree C, not the 2–3 usually claimed:
So my amateur reading of all this is that, outside of South Asia, the last Mt Toba eruption was about like the events of 536–8 AD, only about twice as long. Further, the long term climate record basically ignored this event, instead following orbital forcings. Incidently, one might attempt to read into human gene flow data (Alan Templeton, Yearbook of Physical Anthropology, recent) that Mt Toba erupted about 75,000 years ago, again with substantial error bars…)
Comment by David B. Benson — 17 May 2006 @ 5:04 PM
Yes, MORB is Mid-Ocean Ridge Basalt.
Gavin, I think there is one significant factor that you have neglected to mention with regards to the ability of a volcano produce climate-effecting arosols:
The sulfur content of the magma.
El Chichon and Pinatubo are both unusual in that the lava crystalized anhydrite (CaSO4) in both eruptions, indicating a sulfate-saturated (or near-saturated) magma.
Re #7 and #16: The Volcanic Contributions paper from Nick Riley does not agree with the figures on CO2 emissions from ocean spreading centers given by C. W. Magee. The paper claims 97 Mt/yr CO2 (about 33 Mt/yr C, which seems low especially when they claim 25 Mt/yr CO2 for Mt. Etna alone), compared to 0.6 Gt/yr, which at 10% of human emissions seems too high. Is there that much uncertainty, or does someone have it wrong?
I am interested in the idea that the rate of volcanic emissions determines whether the Earth is a warm period (eg. Cretaceous) or cool period. I have read that even flood basalt eruptions only produce 1 or 2 Gt/yr of carbon, which does not seem a lot. By the way, surely the statement from the paper that
Even during extraordinary times in the geological past, such as the eruption of flood basalts [eg. the Deccan Traps 66 Ma], the estimate CO2 emission is estimated to be only 0.3-2 Mt/yr.
is an error, they must mean gigatonnes. They also point out that the increased area of continental basalt plays an important role (180 Mt/yr CO2) in removing carbon dioxide. This may be less significant for sub-ocean basalt eruptions.
The point is, I am having a hard time understanding how volcanic activity could create a warm period lasting 50 million years. Flood basalt eruptions do not last that long. They also have cooling effects (aerosol emissions and basalt area), and the paleotemperature record does not seem to correspond that closely to these events. Is it possible that ocean spreading was that much more active than during other periods? The numbers just do not add up for me.
Blair, can you post a full ref for that paper? I can’t read literature at home, but I can look it up during my lunch break tomorrow.
Note that the calcs I did were
a. rough. If you are really curious about this, you should look up what the total spreading center crust production actually is- it should be a fairly easy number to find.
b. My calculation only gives the total mass of CO2 that 1 year worth of magma contains. How much of that is actually released requires some knowledge of the mid-ocean ridge structure, tectonics, and fluid flow.
c. If you want to calculate co2 contributions for LIPs, you can do the same sort of calculation- CO2 content * total mass/formation time- only make sure you look up the CO2 content, since I seem to recall (perhaps incorrectly) that “hot spot” magmas are generally higher in H2O and lower in CO2 than MORB.
The Nick Riley paper is here. Chapter five is the most relevant to this discussion, and says the extrusion rate at mid-oceanic ridges is 20 cubic km/year.
To answer my own question about the Cretaceous, I found this paper which says “The Cretaceous was a time of unusually high rates of production of oceanic crust both at spreading centers and through the eruption of Large Igneous Provinces (LIPs)” and “The volume of crust produced by LIPs in the Cretaceous was almost three times greater than in prior and subsequent time periods.” So there is a credible source for a carbon dioxide forcing leading to a warm climate. What part is played by heat transfer from the equator to the poles due to the different arrangement of continents is not clear.
[Response: On the other hand, David Rowley's work over the past few years has made a pretty convincing case against major long term variations in the sea floor spreading rate. If that holds up, some other idea about the driver of long term CO2 changes must take the place of the M.O.R. outgassing variations. Ideas in play include weathering rate changes due to change in continental position or weatherable rock exposure, and changes in the amount of sea floor carbonate that gets recycled through subduction. It's a subject that is very much in flux just now. --raypierre]
Looking at that, Nick Riley says on the same page (5) — citing other authors’ work that I haven’t looked up — that hydrothermal alteration of the newly produced lava is a sink, which takes up effectively all of the CO2 produced along the midocean ridges. (The sink and source both vary in proportion to the changes in activity and fresh lava produced.)
So his sources say that changes in mid-ocean ridge activity would have little effect on atmospheric CO2.
It appears that I significantly overestimated the co2 content of MORB, since my total magma estimates are in the same ballpark (~70%). The way they get that concentration is a bit convoluted, but seems to make sense.
The point, of course, is that even with an overestimate, volcanic CO2 is << industrial output.
“In 1996 investigators studying ice cores from Greenland and Antarctica found the sulfuric acid peak that followed the supereruption of Toba 74,000 years ago. That eruption ejected 2,800 cubic kilometers of lava and ash and reduced average global temperatures by five to 15 degrees C. The consequences of such a chill were undoubtedly severe but did not last as long as once thought: sulfuric acid in the ice record disappeared after only six years; some reserchers suggest that it vanished even earlier.”
All this is well and good except the astounding 5–15 K cooling.
This doesn’t agree with what I found and reported in #27 above.
Surely a 5–15 K cooling ought to produce quite a spike in the ice core records, even at the scale of the book chapter I found and reported in #27 above.
It appears to me that somebody slipped a decimal point. Then 0.5–1.5 K agrees with what I found and reported previously.
I would greatly appreciate some assistance here, before suggesting this possiblity to SciAm and Dr. Bindeman. I am just an amateur regarding paleoclimate. Advice, please, gavin.
[Response: I agree, 5 to 15K sounds extremely unlikely. I suggest emailing Dr. Bindeman and asking for a clarification or a source. I would point out that a global cooling of 15 K is about 3 times larger than the total ice age cooling at the LGM compared to modern.... - gavin]
Comment by David B. Benson — 22 May 2006 @ 2:43 PM
Oppenheimer, Clive. 2002. Limited global change due to the largest known Quaternary eruption, Toba 74kyr BP? Quaternary Science Reviews 21(14-15): 1593-1609.
“… estimates of the sulphur yield of the erupting magma, central to predictions of its atmospheric and climatic impacts, vary by two orders of magnitude (3.5-330 [units mangled by HTML]). Previous estimates of globally averaged surface cooling of 3-5°C after the eruption are probably too high; a figure closer to 1°C appears more realistic. The volcanological uncertainties need to be appreciated before accepting arguments for catastrophic consequences of the Toba super-eruption.”
Re #31: Ray, surely the subduction rate is tied to the ocean spreading rate, so why would the rate of carbonate removal change?
About changes in continental position, that is one reason given for the reduced temperature gradient between the equator and polar regions (although not sufficient in itself). But does this low temperature gradient itself cause a warming effect? The Stefan-Boltzmann law implies the Earth radiates energy proportional to the fourth power as its temperature. If the temperature gradient increases, am I correct to infer that the warmer areas will radiate more additional energy than the cooler areas will lose, so the Earth must cool to return to equilibrium? Conversely, reducing the gradient will cause to Earth to warm. If this is correct, can you tell me how much difference this effect makes?
I compared a world with a uniform 288 K temperature with one divided into two halves of 273 K and 303 K, and calculated a 2% difference. In the real world the change in distribution will be nowhere near that, so this really is a non-issue. If I am right about it in the first place.
CO2 is removed from the atmosphere by carbonic acid (CO2+ H2O- rain water) reacting the Mg or Ca silicates in the earth’s crust to form Mg,Ca carbonates + quartz (via a few intermediate steps.)
This process requires two main ingedients.
1. Exposed volcanic or basement rocks. Sedimentary rocks have very low Ca,Mg silicate concentrations, so if you are only weathering sedimentary rocks, the reaction won’t occur. Furthermore, you need to be uplifting, or erupting, or otherwise exposing the Mg/Ca silicate rocks, or the exposed rocks will just weather down to the water table, and the reactions will stop (or slow).
2. Warm rain. The more rain you get, the more carbonic acid you have to attack your rocks. The warmer it is, the more efficient the reaction.
Neither of these conditions is directly related to the speed of oceanic crust production or subduction, since most rocks that get uplifted above sea level are continental rocks.
“We discovered some amazing places in 2004, including an erupting volcano (NW Rota-1), liquid CO2 venting (NW Eifuku), the shallowest yet discovered “black smoker” chimneys (East Diamante) and more than 12 new species of chemosynthetic organisms at hydrothermal vent sites. All of us came away from the 2004 expedition with a lingering sense of awe ….”
While volcanic CO2 emissions exceeding all anthropogenic emissions is patently silly, isn’t it hard to claim it insignificant? I calculate that the ongoing CO2 emission from Mt. St. Helens is 10%-20% of the CO2 emissions from motor vehicles in the U.S. based on stated 500-1000 tons/day from Helens and 1.8Mtons (CO2, not C) per year from vehicles. Clearly a minority but insignificant? Or is my math wrong? (I assumed 15MPG average for all motor vehicles, one gallon emits 18lbs CO2, three trillion miles driven (2005).)
Another question I’ve been curious about but seldom see addressed: If CO2 absorbs infrared radiation in specific wavelength bands, and the current absorption is close to 100% (as shown on some graphs, at least in its major band), it would seem that increasing the amount of CO2 in the atmosphere will not linearly increase the infrared absorption; and eventually not increase the absorption (and concurrent global warming) at all. Does this make sense?
With all the discussion about “global warming”, I have yet to see any scientific study on the breakdown between human activity vs. natural phenomenon such as (volcano eruption, solar activities, meteorites, forest fires…) If it turns out to be small (say 2-3% due to human activities) then it seems to be the whole discussion is moot. We can’t do much to affect our climate any more than we can stop a volcano from erupting.
If it is large say 25% or more, then perhaps we can do something to reduce our contribution. Without real data, it is as if we are asked to take this “human induced global warming” theory on blind faith. The impact on our future development is huge if we are to adopt some of the proposals ie. Kyoto treaty. We need more convincing data before we adopt any drastic policies which may or may not help in any case.
Who has the scientific data?
Please inform me.
Yorktown Hts. NY
[Response: Almost all of the warming in the last 30 years is anthropogenic. You can see that in the IPCC TAR (link at the right), or in more recent papers such as http://pubs.giss.nasa.gov/abstracts/submitted/Hansen_etal_1.html
Volcanos and solar together would have lead to a very mild cooling over this period, and no-one has been able to reproduce the current trend without including the greenhouse gases. -gavin]
i am just a curious spectator that lives in Fla and i have an off question. Do you think that the possibility of underwater volcanic
flows could be contributing to the warmer water temperatures that are increasing the hurricane activities in the atlantic and carribean? If there are increased emmisions, could not that be a part of our increased activity. Again i have no scientific schooling, but that thought crossed my mind. Thank you for your feedback.
[Response: No. You would expect in such a case that the temperatures would have warmed most near the bottom of the ocean. In fact it is the other way around - warming is most at the surface and upper layers - pointing to an atmospheric cause. -gavin]
Re #34: Following Gavin’s suggestion, I exchanged a few e-mail messages with Dr. Bindeman. He replied by saying that the editors of Scientific American had changed his 5–8 K to 5–15 K. He stands by 5–8 K, over a period of 3–6 years for YTT, the last supereruption of Mt. Toba. He also mentioned that the editors of Scientific American changed his 30 km high for supereruption plume altitudes to 50 km.
I infer there is still some controversy regarding the global temperature drop due to YTT, for example, the article by Oppenheimer indirectly linked both by me in #10 and Hank Roberts in #35. From that article I learned why the temperature proxy record in ice cores is not sufficiently resolved to record this short, sharp temperature drop.
re my own question, #41, re CO2 emissions from Mt. St. Helens vs motor vehicles. My math was close — only missed by three decimal places! (Never could get those right!) Vehicles in the US put out 1.8 BILLION tons a year, not 1.8M tons. This is 10,000 times the volcano, not ten times, and more in line with everyone’s assertions that I was questioning. Sorry.
[Response: Just by posting a comment, you're already as "logged in" as you need to be. The "login" item on the sidebar is just for use by the moderators, giving us permission to do things like post these blue comments. Unlike some blogs, RC doesn't have a registration procedure that needs to be carried out before comments can be posted. So far, we've found that with a little light moderation of comments to filter out some obvious (and very infrequent) bad behavior, we can manage fine without registration. This., we hope, makes life easier for our readers. --raypierre]
Re: what percent of global warming is due to human activity?
Your comment “Almost all of the warming in the last 30 years is anthropogenic…” can’t be true. I examined the paper you referenced by Hansen… and in Fig. 4, it shows that solar activity (11 years cycle) causes as much variation in temperature as the actual variation recorded.
If this data is reliable, then I must conclude that at most (only 50 percent of what we experience in global warming is due to human activity).
This is only based on one factor. You have not explained or account for other natual phenomemnon that has an impact on Earth’s climate. If one event such as the Krakatoa erruptions of 1883 can affect Earth’s temperture over a 5 year period, what else is natural that affect our climate and temperature that is much greater than what we can “pollute”?
It seems to me there are a lot of science to do before we conclude that we are the cause. I am an engineer by training and so far the data is not convincing to me. I need more proof before I will act. As we know with other environmental “pie in the sky” theories, sometimes we can do more harm than good. One prime example is the forest management activities which in the past have resulted in worst forest fires than anything nature can produce. What we do does have some consequences. I just want to be sure that we are doing the “right” thing when it comes to controlling our climate.
[Response: You have misread or misunderstood the paper. The IPCC has simulated the response to solar forcing and volcanoes, as well as anthropogenic forcing (greenhouse gases and sulfate aerosols). If you want a quick summary of the results, take a look at Figure 4 of the IPCC Third Assessment Report Summary for Policymakers: http://www.grida.no/climate/ipcc_tar/wg1/007.htm , which shows clearly that since about 1970 the warming is essentially entirely due to human influences. You can be assured that reducing emissions to control the climate is indeed the right thing to do. --raypierre]
In his Fig. 4, the solar cycle is shown causing temperture variations every 11 years on a scale that is significant. Also, in another chart, the affect of Krakatoa in 1883-1887 caused a .5 degree drop in global temperature equal to the current gain of .5 degrees from the norm (supposedly due to human activities). Do you see what I’m concerned about here? If natural phenomenon can cause the affect of climate and temperature we see, is it obvious that we have no control over that piece of global warming or cooling? It is natural for man to want to control his environment. However, nature has a mind of its own.
Suppose a large meteorite hit earth next year and causes the earth to cool 2 degrees. Will we than be debating global cooling and how we can “fix” it? Just a common sense observation.
[Response: Figure 4 is solar forcing, not temperature. You must mean Figure 6 if you're talking about temperature response. In Fig. 6, what you see is the short term cooling (about two tenths of a degree) due to volcanic eruptions. The solar signal is hardly visible. The trend upward is due to anthropogenic forcings. Except for a different way of doing the averaging and a few additional anthropogenic forcings put in, Hansen's calculation does the same thing as IPCC and the results are completely compatible. The upward trend since 1970 or so is due to human influences. We can control that by controlling greenhouse gas emissions. This is not a case of nature having a mind of its own. This is us. It's just common sense. --raypierre]
Indeed, fig. 4 in Hansen et al. is solar forcing, not temperature. Also, the figure indicates solar irradiation in Watts per square meter. That’s the increase in solar energy intercepted by a square meter which is exposed to sunlight head-on. But earth’s surface area (4 pi r^2) is four times earth’s cross-sectional area (pi r^2), so any indicated change in solar irradiance should be divided by 4 to compute the change in solar forcing on earth.
I’ve specifically looked for any hint of the 11-year solar cycle in the global temperature record, and found none. I’m not aware of any scientific work which claims there is a hint of it.
Take a good look at Hansen et al.’s figure 5(a), to get an idea of the strength of solar forcing compared to that of greenhouse gases.
Can some one put things in perspective for me? How does our fossil fuel usage today compare to the Krakatoa erruption of 1883? Here is an excert of what that one event did to affect global temperature from wikipedia quote:
The eruption produced erratic weather and spectacular sunsets throughout the world for many months afterwards, as a result of sunlight reflected from suspended dust particles ejected by the volcano high into Earth’s atmosphere. The area around Java is now known as Lady Bull because of its fiery nature. This worldwide volcanic dust veil acted as a solar radiation filter, reducing the amount of sunlight reaching the surface of the earth. In the year following the eruption, global temperatures were lowered by as much as 1.2 degrees Celsius on average. Weather patterns continued to be chaotic for years, and temperatures did not return to normal until 1888. British artist William Ashcroft made thousands of color sketches of the red sunsets half-way around the world from Krakatoa in the years after the eruption. In 2004, researchers proposed the idea that the blood-red sky shown in Edvard Munch’s famous 1893 painting The Scream is also an accurate depiction of the sky over Norway after the eruption.
[...] impact. Let me see if I can get a graph with Pinatubo labeled. Here’s a brief general discussion: RealClimate Can’t seem to find a graph handy, sorry. Several sources say the aerosols from Pinatubo were [...]