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The Antarctic ice sheet is melting and, yeah, it’s probably our fault.

Filed under: — eric @ 14 August 2019

Glaciers in West Antarctica have thinned and accelerated in the last few decades.  A new paper provides some of the first evidence that this is due to human activities.

by Eric Steig

It’s been some time since I wrote anything for RealClimate. In the interim there’s been a lot of important new work in the area of my primary research interest – Antarctica. Much of it is aimed at addressing the central question in Antarctic glaciology: How much ice is going to be lost from the West Antarctic ice sheet, and how soon? There’s been a nearly continuous stream of evidence supporting the view that the West Antarctic Ice Sheet is in serious trouble – perhaps already undergoing the beginning of “collapse”, which John Mercer presaged more than four decades ago.

Yet showing that the ice sheet has changed doesn’t really address the question about what will happen in the future. To do that, we also need to answer another one: How much of the ice loss that has already happened is a response to anthropogenic climate change? A new paper in Nature Geoscience this week is one of the first to attempt an answer, and that is what has inspired me to get back to RealClimate blogging. Full disclosure: I’m a co-author on the paper.

In this post, I’d like to provide a bit of context for our new paper, and to emphasize some points about our findings that are generally going to be lost in popular accounts of our work.

The key finding is that we now have evidence that the increasing loss of ice from the West Antarctic Ice Sheet is a result of human activities — rising greenhouse gas concentrations in particular. Now, some may be surprised to learn that this wasn’t already known. But the argument that humans are responsible has rested largely on the grounds that there must be a connection. After all, why should melting have increased only in the late 20th century, precisely when the impacts of anthropogenic climate change were becoming more and more apparent? It seems an unlikely coincidence.

As Richard Alley* put it:

It has been hard to imagine that the ice sat around happily for millennia and then decided to retreat naturally just as humans started perturbing the system, but the evidence for forcing by natural variability was strong.

To be sure, there have been studies suggesting a discernible anthropogenic impact on Antarctic surface temperature, particularly on the Antarctic Peninsula.  And it’s known that the depletion of stratospheric ozone and the rise in greenhouse gases has caused the circumpolar winds to increase in strength. But there has been little direct evidence that what’s happening to the ice sheet itself can be attributed to human-induced climate changes. Consequently, there has been no paper published that makes a strong claim about this. Indeed, a formal solicitation of expert views in 2013 showed that opinion was pretty much evenly divided on whether observed changes to the Antarctic ice sheet were simply part of the natural variability of the climate/ice-sheet system.  In stark contrast, agreement among those same experts was (and is) unanimous that Greenland is melting because of anthropogenic global warming. 

Before getting into what is new in our paper, it’s worth starting with a bit of background on West Antarctica, and a review of the evidence for the role of natural variability. Since not everyone will want to read the play-by-play, I’ve put most of that in a separate post, here. I hope you’ll read it.

In short, glacier melt in West Antarctica has increased because more Circumpolar Deep Water (which is relatively warm) is getting from the ocean surrounding Antarctica onto the Antarctic continental shelf and reaching the floating ice shelves of the large outlet glaciers that drain the West Antarctic ice sheet into the ocean. As shown by Thoma et al. (2008) in a seminal modeling study in Geophysical Research Letters**, how much Circumpolar Deep Water (CDW) gets onto the continental shelf is strongly influenced by the strength and direction of the winds at the shelf edge. Essentially, stronger westerlies (or simply weaker easterlies) tend to cause more CDW inflow, and hence, more glacial melt.

Because of the important role played by the winds, many have assumed that there must be a link between the melting glaciers and the ozone hole. But the greatest control on wind variability along the coast of West Antarctica is the state of the tropics. Just as El Niño event causes widespread climate anomalies in the Northern Hemisphere — such as increased rainfall in southern California — it also causes changes in the West Antarctic. Indeed, the Amundsen Sea, where the largest West Antarctic glaciers are, is one of the areas on the planet that is most strongly dependent on the El Niño-Southern Oscillation (ENSO) (e.g. Lachlan-Cope and Connolley, 2006). In 2012, we published a paper showing that changes in the winds in this region in the last few decades, which correspond well with variations in the glaciers, are very well explained by changes in ENSO, and very poorly by changes in ozone. We also noted that because big ENSO events had occurred in the past, it was quite plausible that wind conditions not that different than those of today had also occurred in the past. Indeed, we have very good evidence from ice cores that climate conditions in West Antarctica in the 1940s were not very different than those in the 1990s.

It is clear from this work, and much other recent research, that ENSO plays a dominant role in determining the climate conditions in West Antarctica that are relevant to the ice sheet. And since there is little evidence for a long-term anthropogenic change in ENSO, this implies that natural variability in Amundsen Sea winds (driven by natural variability in ENSO) may be the primary driver of observed ice-sheet change in West Antarctica in the last few decades. This is what Richard Alley is referring when he says that the evidence for forcing by natural variability was strong, and it throws a lot of cold water (no pun intended) on the purported link with human activities. But that’s not very satisfying. It doesn’t answer the question of why glacier retreat is occuring now. This is where our new paper comes in.

The new work is led by Paul Holland of the British Antarctic Survey (BAS), with help from Tom Bracegirdle, Adrian Jenkins (also of BAS), Pierre Dutrieux (now at LDEO) and myself. What we argue, in brief, is that although ENSO does indeed dominate the wind variability in the Amundsen Sea on timescales from interannual to multi-decadal, there is also a longer-term trend in the winds, on which the ENSO-related variability is superimposed.

The graph below (Figure 1) summarizes the key finding. What is shown are the winds in the key sector of the Amundsen Sea, centered on ~71°S and ~108°W, with observations in blue, and model results in black and gray. The model results are from an ensemble of simulations, referred to as the “tropical pacemaker” or “PACE” runs, of the CESM climate model. Details are given in Schneider and Deser (2017). Briefly, what has been done is to adjust an otherwise free-running climate model (forced by greenhouse gas emissions) so that it follows the actual history of sea surface temperature in the tropics, but is otherwise left unconstrained by data. We use these experiments as an estimate of how winds have varied over the last century in the Amundsen Sea, a) given what we know happened in the tropics and b) given what the climate model’s physics dictates about how conditions in the tropics affect the Amundsen Sea. Critically, there is nothing done to make the model match observations outside the tropics. Yet the results are in superb agreement with the observed Amundsen Sea winds. While we can never know exactly what happened prior to the advent of satellite observations in the late 1970s, the PACE ensemble provides a set of histories that is plausible, and compatible with modern data. This is probably the best current estimate of how winds have in fact varied in this region.

Figure 1. Zonal wind speed (positive = westerly, negative = easterly) over the continental shelf edge in the Amundsen Sea, Antarctica, since 1920. Observations (ERA-interim data) are in blue. Model results in black (average) and gray (individual ensemble members) are from the tropical pacemaker (PACE) experiments with the CESM climate model, from Schneider and Deser (2017). The dashed line shows the average trend. From Holland et al., 2019.

What Figure 1 suggests is that the winds in this region have varied between easterly and westerly from decade to decade, throughout the 20th century. This is the natural variability associated with ENSO, and is no surprise. But in addition, there is a long-term trend. When averaged over several decades, the winds can be seen to have shifted from mean easterly in the 1920s through 1980s, to mean westerly thereafter.

The trend in the winds is small, and easily lost within the variability of individual model ensemble members, but it is robust (it occurs in all the ensemble members) and statistically significant. Moreover, we know its cause (at least in the model experiments): radiative forcing. Although these experiments also include radiative forcing changes resulting from the ozone hole, it’s clear that the trend in the winds begins well before ozone depletion begins in 1970s. Thus, the key forcing is greenhouse gases.

These results show that variations in the winds that have occurred at the same time as we have been observing the glaciers retreat (i.e., since the 1970’s) are largely attributable to ENSO, as we had thought. But at the same time, the prevalance of strong westerlies in the Amundsen Sea has gradually increased throughout the 20th century. That is, although anomalous westerlies tend to occur most often during an El Niño, the long-term underlying trend means that the likelihood of strong westerlies in any given year is increasing, regardless of whether there is an El Niño or not. Thus, the radiatively-forced change (the trend) accentuates the effect of the natural variabilty (ENSO). As we wrote in the paper, the recent wind anomalies of the last few decades “…reflect Pacific variability that is not at all unusual…. However, when superimposed on the anthropogenic trend, this variability produces periods of absolute westerly winds that are sufficiently anomalous to account for much of the current ice loss.”

Now, a couple of caveats:

First of all, our finding are “simply” the result of looking at climate model simulations. We don’t know exactly what happened in the Amundsen Sea in the last century. On the other hand, Figure 1 looks very much like the data from ice cores from West Antarctica: variability that can be related to ENSO, superimposed upon a long-term trend. (See e.g. Schneider and Steig, 2008 and Steig et al. 2013 for details.)

Second, we are assuming that the Amundsen Sea shelf-edge winds are indeed the most relevant aspect of the system to consider. Again, this is based on the body of work showing that the inflow of CDW onto the Amundsen Sea continental shelf is strongy controlled by these winds. But the physics linking wind variability and CDW inflow is complex, and not everyone agrees with our view on this. Indeed, it is most certainly an oversimplification. Furthermore, as many authors has emphasized, there are complex feedbacks and internal ice-sheet and glacier dynamics involved, and it’s not as if there is a one-to-one relationship between changing winds and glacier retreat. For an excellent discussion of this, see the paper by Christianson et al. (2018).

Third, even without the first two caveats, we are far from proving that the ongoing ice loss from Antarctica can be attributed to human-induced climate change. The challenge here is that the natural component of the wind variabilty is so large that actually detecting (with direct observations) the trend inferred from the model results is not likely to be possible for some time. As we say in the paper, “Decadal internal variability therefore dominates ice-sheet and ocean variability during the modern observational era (since 1979), and will continue to dominate observations for decades to come.” We are not likely to find the smoking gun any time soon.

That all said, our findings are supported by other experiments. It is not only CESM, which is the main focus of the paper, that shows a long-term trend in the winds. In fact, most climate models (i.e., “CMIP5” — see details in our paper) show the same thing. Also, we find that the better the agreement between a given model and observations, the stronger the trend. (Note that the wind speeds shown in the figure above are not anomalies. These are the actual modeled and observed wind speeds. As it happens, CESM has unusally low bias in comparison with observations.)

Finally, our findings provide an important opportunity to glimpse into the future. We examined additional results with CESM, from the so-called “Large Ensemble” (LENS) and “Medium Ensemble” (MENS) set of experiments. These are identical to those of the PACE set-up but without the constraint to follow the observed tropical sea surface temperature. The results are illustrated in Figure 2, below.

Figure 2. Zonal wind speed (positive = westerly, negative = easterly) over the continental shelf edge in the Amundsen Sea, Antarctica, since 1920, and projecting through to 2100. Results are from the “Large Ensemble” (LENS, in black), using known greenhouse gas and other radiative forcing for the past, and “business as usual” RCP 8.5 radiative forcing scenario in the future. Also shown are results from the “Medium Ensemble (MENS) (in red) which uses lower (RCP 4.5) radiative forcing for the future. Gray shows the individual ensemble members from LENS. From Holland et al., 2019. Error bars show the standard deviation of wind anomalies (solid) and the magnitude of historical and projected trends (dashed).

The ensemble mean trend in the LENS experiments is nearly identical to that of the PACE experiments, which further demonstrates that the trend is not part of the natural variability. Comparison between the LENS experiments, which uses the “business-as-usual”*** RCP 8.5 IPCC scenario for the future, and MENS, which uses RCP 4.5, shows that reducing greenhouse gases reduces the future trends.

This is a big deal! Although we humans have evidently caused a long-term increase in westerly winds along the Amundsen Sea coast (which is bad for the West Antarctic ice sheet), the future is not yet written (which is an opportunity). Lowering greenhouse gases to a more modest rate of increase might be enough to prevent further changes in those winds.

Of course, many glaciologists believe we have already passed the point of no return for West Antarctica. I personally think the jury is still out on that. But that’s a discussion for another time.

*The quote from Richard Alley is from a National Geographic article about our paper.

**Not all the most important papers are published in Nature or Science.

***Some people think calling RCP 8.5 “business as usual” is misleading. Hence the quotes.

88 Responses to “The Antarctic ice sheet is melting and, yeah, it’s probably our fault.”

  1. 1
    Nemesis says:

    ” Of course, many glaciologists believe we have already passed the point of no return for West Antarctica. I personally think the jury is still out on that.”

    You can only know if you have crossed some point of no return, when you have actually crossed it. That’s the funny side of these points of no return:

    You will realize it in the rear mirror, when it’s too late to avoid that nasty point, screeeech BUMM. It’s like bending a guitar string, you bend and you bend more and even more, when will it break, when will be the point of no return? You will only know it, when it’s utlimately broken, never before. So let’s bend that string a little more as “we still need more data yet”, let’s see, when we will know exactly, if we’ve crossed some point of no return. Until then:

    BAU. And: Faster than expected. Rinse and repeat.

    That’s the name of the game, gimme another shot and more popcorn, see you tomorrow, right around the corner, at the “point of no return”

    [Response: I agree of course. My point was a scientific one, not a suggestion we needn’t be concerned. –eric]

  2. 2
    Nemesis says:

    ” I agree of course. My point was a scientific one, not a suggestion we needn’t be concerned”

    I didn’t want to say, that we need to be concerned (I didn’t point that out at all), as this is more than obvious. I wanted to point out, that we will see the collapse of the WAIS, if it didn’t happen now, because the overall game simply does not change. They will bend the string, until it breaks, if it didn’t break already yet. Scientists are just the observer, but politics is the doer. Simple as that.

    I’m an observer too and I have a lot of fun.

  3. 3
    Russell says:

    It’s a timely post, given that Reason‘s Ron Bailey latest “Rising temperatures are mostly happening in the winter and at night” jag coincides with winter darkness at the South Pole.

    [Response: My post has nothing whatsover to do with the South Pole. Or by “South Pole” did you mean Antarctica (which is not at all the same thing)? In any case, I don’t know who Ron Bailey is, but his little article at “Reason.com” is not relevant (nor very good — I have no idea what his point is supposed to be other than he seems to think winter warming is fine, since he doesn’t like winter, something that makes me have a very very low opinion of him). –eric]

  4. 4
    Bruce Tabor says:

    Trivial editing point. You’ve got Geophysical Research Letters* with one asterisk, which should be two as it refers to the footnote
    **Not all the most important papers are published in Nature or Science.

    [Response: Thanks. Fixed. –Eric]

  5. 5

    Is there any hope of constructing a counterfactual? That is, what would the wind series be without forcing? Sure, you have the climate models, but can a baseline ENSO-coupled series be developed which assumes zero forcing?

    Can then these be compared to what’s observed now?

  6. 6
    Hank Roberts says:

    Russell’s just teasing readers with an oxymoron.

    “Ronald Bailey is an American libertarian science writer. He has written or edited several books on economics, ecology, and biotechnology.”

    == Wikipedia

  7. 7
    Victor says:

    “Although these experiments also include radiative forcing changes resulting from the ozone hole, it’s clear that the trend in the winds begins well before ozone depletion begins in 1970s. Thus, the key forcing is greenhouse gases.”

    What you really mean, of course, is that “the key forcing is an increase in temperatures due to the effects of increased anthropogenic greenhouse gas emissions.”

    [Response: LOL. I love how you can’t even imagine that, possibly, just possibly, your understanding is at fault, rather than people’s words not meaning what they say. – gavin]

    How can that be, however, when, as is well known, CO2 emissions were too low to have a significant effect on the rise in global temperatures from 1910 – ca. 1940, and global temperatures fell or remained steady (for whatever reason) from ca. 1940 to ca. 1980?

    And here’s a graph of Antarctic temperature anomalies from 1945, showing a drop in temperature from that year through 1970: https://static.skepticalscience.com/pics/AntarcticTemperatureChange.png

    [Response: I won’t bother responding to the cluelessness here, but I will note that the linked graph is probably meaningless. Climate reanalysis products (such as the own shown) for the Southern Hemisphere high latitudes prior to 1979 are not at all reliable. –eric]

  8. 8
    nigelj says:

    Victor @7, here’s a hint. The temperature trend you posted is for the entire Antarctic continent, while the article is talking about the edge of the western antarctic West Antarctic ice sheet which has a totally different temperature trend. Click on the Antarctic Peninsula link.

    [Response: Quite right. I fixed your “western antarctic”. It’s the “West Antarctic”. Proper name. –eric]

  9. 9
    Erik Lindeberg says:

    It is an interesting theory that the changes in the conditions in Amundsen Sea can be a result of human activities. The blog is, however stained by a sloppy and unnecessary sentence:

    “Third, even without the first two caveats, we are far from proving that the ongoing ice loss from Antarctica can be attributed to human-induced climate change.”

    Certainly not, because if it could be proved, it is not science. We must allays be consequent on the basic principles of science in our communication. Even the best evidence-supported theories will still have some uncertainty, whether it is Newton’s “laws” of motion, Ohm’s “law”, general relativity or AWG. The best we can do is to present evidence for a theory. That AWG allays will have uncertainty is sometimes used by deniers to diminish the accuracy of our statements. This makes it even more impotent to stick to the principles in science and continuously educate the public, media and decision takers about it.

    [Response: “Proof” is used colloquiually here, obviously. If you want to be pedantic, then you need to replace “theory” with “hypothesis” in your first sentence. –eric]

  10. 10
    Felix Pohl says:

    Once again I realize how often you are convinced you know something you don’t really know. I am a PhD student and would say that I am well informed about climate change. If someone had asked me whether the melting of the West Antarctic was connected to global warming, I would, of course, have answered yes. As I’ve learned now, even though it seems very likely, it’s something else to prove it.

    [Response: Thanks! –eric]

  11. 11
    Astringent says:

    Always fun trying to formally classify errors in Victor’s posts.
    2nd sentence looks like a basic ‘False equivalence’ with a harmonic overtone of ‘ad hominem’.
    3rd sentence is ‘argument from fallacy’ with a side-order of ‘appeal to authority’, albeit ‘as is well known’ Of course it’s also just false!
    4th sentence tries ‘affirming a disjunct’ – the authors’ arguments are about wind not temperature. It’s also geographically naive – Antarctic temperature trends aren’t the same as West Antarctic trends. Extra kudos from pulling a graph that was prepared specifically to rebut a denialist claim that the Antarctic was cooling.

  12. 12
    Mary potter says:

    Victor – heard of aerosols?

    Nemesis – I think I share a lot of your points of view and usually enjoy reading your posts…though I only wish I knew how I could have as much fun as you….is that my shortcoming or your sarcasm? Please help.

  13. 13

    Victor–

    How can that be, however…

    Why ask, when you already know you won’t accept the answer–any answer?

  14. 14

    Jan said:

    “Is there any hope of constructing a counterfactual? That is, what would the wind series be without forcing? Sure, you have the climate models, but can a baseline ENSO-coupled series be developed which assumes zero forcing?

    Can then these be compared to what’s observed now?”

    That question has come up before: If the wind is providing the forcing, what is forcing the wind?

    Do you recall the last discussion over at the Azimuth Project forum concerning how all the climate indices, from ENSO to the Southern Annual Mode, can reveal a common-mode forcing?

    So I think this is what you’re hinting at — what would the natural variation look like without the additional forcing of CO2 providing further variability.

    [Response: These are good ideas. One problem is that we can’t do a “pure” experiment along these lines, because what has happened in the tropics may itself me a result of anthropogenic radiative forcing. Indeed, there *is* a very slight trend in the pattern of SSTs, and that trend is consistent in direction with the resulting wind shifts. This is probably why, in the experiments we examined, the trend in winds is slightly greater in the PACE than in the LENS average. However, it is a very small effect. If you run a climate model adjusted to observed tropical SST, but without climate forcing, you’d get that tiny (statistically insignificant) trend back again. In our paper we *assume* that all the tropical variability is natural variability, so we are being conservative in our attribution. –eric]

  15. 15
    Russell says:

    3
    Eric, I used South Pole as a trope, reflecting a common meme in the American Climate Wars.

    Whenever summer headlines about Arctic ice loss, or anomalous warmth at the North Pole appear, the Fox TV denialati point to the opposite pole, and claim that all is well with climate because its cold down there, never mentioning that it’s winter down under.

    It’s time to call their bluff.

    [Response: Apologies, I didn’t catch the /sarc/! — best, Eric]

  16. 16
    Mal Adapted says:

    Gavin, inline to Victor:

    What you really mean, of course, is that “the key forcing is an increase in temperatures due to the effects of increased anthropogenic greenhouse gas emissions.”

    [Response: LOL. I love how you can’t even imagine that, possibly, just possibly, your understanding is at fault, rather than people’s words not meaning what they say. – gavin]

    Gavin’s recent RC post called on us to examine our own and other commenters’ “implicit warrants and values”. Victor presents himself as an exercise. He appears to have sufficient intellectual wattage to grasp the fundamental facts of anthropogenic global warming, namely: CO2 is a ‘greenhouse’ gas; half of the fossil carbon burned by humans has accumulated in the atmosphere; GMST is rising, with ramifying consequences for climate, i.e. average weather. That is, the globe is warming, it’s anthropogenic, and it’s driving weather changes that have human costs. Victor even seems to recognize the competence of this blog’s principal authors. Yet he is clearly determined to deny AGW, and so desperate to persuade his audience that he deploys the same transparently fallacious and/or dishonest arguments over and over, undeterred by scornful responses from recognized experts. What are the origins of his implicit warrants? I of course have limited insight into his cognition, but I suspect he’s a black box to himself as well. That’s characteristic of denial, isn’t it?

    I wish to re-direct any responses to the Forced Responses thread, rather than hijack this one. Y’all can form your own hypotheses about my warrants and values 8^).

  17. 17

    Thanks Eric, that is helpful. The various ENSO indices are very flat over time, but the SAM (Southern Annual Mode or Antarctic Oscillation) index does appear to have a subtle positive trend to it (from the start of 1957). That trend may be a warming signal?

    https://climatedataguide.ucar.edu/climate-data/marshall-southern-annular-mode-sam-index-station-based

  18. 18
    Alastair B. McDonald says:

    Eric,

    I am surprised that you have not mentioned a tipping point that has passed. Until September 2014, the satellite record of Antarctic sea ice had shown a trend of increasing maximum extent. The maximum extent ever was recorded in September 2014. The following year, 2015, one of the lowest extent was recorded and since then the trend has been of a decreasing maximum extent. It seems to me that a tipping point occurred in 2015, an El Nino Year.

    Have the scientific community noticed this tipping point and if so what was its cause?

  19. 19
    zebra says:

    I’ve made this point on a couple of previous “attribution” threads:

    If we accept that there has been a substantial increase in energy in the climate system due to CO2, then it makes no sense to question whether a change in this (or any) particular metric can be “attributed to” CO2, in the common usage of that term.

    The system is not the same system that would exist absent the CO2, ceteris paribus.

    What you are doing is characterizing the mechanism, or causal chain, by which CO2 affects the ice, not answering whether it does or not.

  20. 20
    Nemesis says:

    @Mary potter

    Thanks.

    ” I only wish I knew how I could have as much fun as you….is that my shortcoming or your sarcasm? ”

    First of all, I got nothing to lose, that gives a lot of freedom to have fun. And I observe the climate discussion from the perspective of the concrete jungle I grew up in. The concrete jungle is all about survival, not about science and collecting montains of data and discussions about when, how, where will the beast eat us ect ect, as the beast is always everywhere ready to eat you, there’s no time to observe the beast from any comfortable (excessive) abstract scientific perspective, you will be dead before you even try, haha. But I appreciate science very much as science gave me the scientific proof that the beast is real and it will eat us indeed “faster than expected” resp without science I couldn’t participate in the scientific discussion about the beast. So, in the end, I need science only to participate in the civilized scientific discussion outside the concrete jungle and it’s just fun indeed to watch the infinite scientific discussion while the beast is already at our throats.

    There is a crucial difference between the concrete jungle resp the scientific map and the real concrete jungle territory:

    Science is excessively abstract, it’s a virtual business, but the concrete jungle is real, bloody flesh and bones are real. If we need final proof of that kind of pudding, we need to be eaten, not the (scientific) pudding. And we will be eaten quickly.

    Another thing is the huge gap between (hopefully) honest science and dirty politics. That’s fun too. Politics abuses science to proof that “we still have time”, “we still have a budget”, “we still can do juuuust a little more BAU”, just one more shot on the way to the point of no return. The scientific observers are (hopefully) honest, but the doers, the Power is not. In that sense, our final fate will be truely some sort of tragic-comedian joke. So, after all, my fun is gallows humor in the face of the beast, not sarcasm ;)

    @eric

    I highly appreciate what you did and do for climate science, so no pun intended. Respect for your work, you’re the man, while I’m just some bloody nobody and I know it ;)

  21. 21
    andy says:

    Erik @9

    “…stained by a sloppy and unnecessary sentence…Certainly not, because if it could be proved, it is not science.”

    I think it’s yours that is sloppy. Of course things in science can be proven. Enter mathematics. Once a proof is correct, it can’t really be undone. Science is a progression of building blocks, yes, and “settled” theories can be later invalidated, but some blocks cannot be pulled out.

  22. 22
    Russell says:

    15
    Thanks, Eric-

    While, as I hope its scope suggests, The Climate Wars blog aspires more to the sardonic than the sarcastic,coverage of climate science and policy affords ample cause for both.

  23. 23
    Non-Scientist says:

    Does anyone know if this will cause near future (2030) sea level rise? Do we know how much?

    [Response: From 1979 through 2017, the total contribution to sea-level rise from Antarctica averaged 3.6 ± 0.5 mm per decade (from Rignot et al., 2019: https://www.pnas.org/content/116/4/1095). If that remains steady, then it’s “only” another half centimeter. Of course, in reality things appear to be acclerating. –eric ]

  24. 24
    Erik Lindeberg says:

    Eric Stieg wrote in a response to my post #9: ““Proof” is used colloquiually here, obviously. If you want to be pedantic, then you need to replace “theory” with “hypothesis” in your first sentence.”

    Three things:

    1. Correct use of the basic principles in science is not pedantic and for us who are concerned about climate warming it is particularity impotent because our opponents are sometimes try to diminish our arguments by spreading ignorance about these principles.

    2. Whether you use the term “proof” colloquially or written does not matter. Your incorrect use is obvious contiguous because Felix Pohl, in his humble post #10, have got the impression from you that something can be proved in science.

    3. You try to educate me about the differences between hypothesis and theory. You are however wrong again. In scientific reasoning, a hypothesis is constructed before any research has been done. A theory, on the other hand, is supported by evidence: it’s a principle formed as an attempt to explain things that have already been substantiated by data. All the examples I gave are certainly supported by data and are therefor theories including AGW. In your world the theory on AGW should be a hypotheses! You do not mean that?

    [Response: AGW is certainly a theory. But hypothesis is the correct term here. I appreciate that the distinctions are subtle. Here’s Oxford’s definition: “A supposition or proposed explanation made on the basis of limited evidence as a starting point for further investigation.” — Eric]

  25. 25
    Erik Lindeberg says:

    andy in @21: “Of course things in science can be proven. Enter mathematics. Once a proof is correct, it can’t really be undone.”

    Yes, in the subjects of mathematics (and computer science) the concept of proof belongs. Mathematics is, however, is not science (albeit useful in science). Science is the study of the physical and natural world like physics, biology, geology and chemistry while math is a separate and unique subject. Math and science are different in many ways, but most important here is how ideas are tested and accepted based on evidence. In math, formal proof can be conducted to show that something is true. This is not possible in science.

    Again: if something can be proved, then it is not science.

  26. 26
    MA Rodger says:

    Mal Adapted @16,
    A reply as requested is posted here (although that is where it is off-topic).

  27. 27
    explorerkeenan says:

    Hello Eric.
    Very well presented.
    Suggested corrections:
    uncontrained (should be unconstrained)
    thats show (should be that shows)
    I have a directory filled with huge amounts of research on that part of the world.
    Kind regards.
    Thomas

    [Response: Thanks for the typos corrections! Fixed. I blame by #*($ing terrible Macbook keyboard. –eric]

  28. 28

    Can’t argue with what Erik Lindberg is saying. What makes earth science even more challenging in terms of model validation (i.e. not proof) is that controlled experiments are virtually impossible to perform due to the physical impossibility (size, volume, etc) of lab replication. About the only way around this is to make predictions or to cross-validate against as many measures as possible. That’s why it’s so important to examine the relationships of the Antarctic metrics against that of ENSO and other indices. Cross-validating relationships is one of the few ways to proceed given that we can’t wait for predictions to pan out.

    [Response: Actually, the common notion that because we can’t fit earth in a tradiational laboratory (i.e. in a building) we can’t do controlled experiments is dubious, and has been challenged in the literature (see e.g., Cleland, 2001: https://pdfs.semanticscholar.org/81ca/78baf41581a70ddf0af3115ea8255aace4fb.pdf). Indeed, have been doing a controlled experiment for thousands of years (i.e., not changing the forcing appreciably). Now, we’re starting a grand (also quite well-controlled) experiment, this time with increased greenhouse gases. The first general predictions were made in the 19th century and have proven valid. The specific predictions about wind changes need more work, hence my use of “hypothesis”. –Eric]

  29. 29
    zebra says:

    #25 Erik Lindeberg,

    You are certainly correct that most people do not understand how mathematics differs from science. However, your position with respect to “proof” in science is less than rigorous.

    In science, we have facts. We can “prove” them empirically; for each instance of an experiment, you can’t argue that a result coinciding with the prediction (hypothesis) doesn’t constitute “proof” of the correctness of that prediction.

    So, you are correct to complain that Denialists distort the principles, but here you are actually aligned with them in a sense; they endlessly move the goalposts for “proof”. But we can have levels of certainty equivalent to what we achieve with a mathematical proof as long as we exercise control of parameters and variables in an experiment. It’s still science.

  30. 30
    Victor says:

    Despite my skepticism regarding the role of CO2 emissions as the “key forcing” of climate change, I do recognize the very serious danger posed by the clearly fragile state of the west Antarctic ice sheet, as stressed in Steig’s paper. I was not previously aware of John Mercer’s prophetic paper of 1978 and am grateful to Steig for providing the link (the full text is available here: https://www.riotmaterial.com/1978-paper-predicted-nearing-disaster/). Mercer’s paper is especially convincing as 1. it shows no sign whatsoever of cherry picking evidence or confirmation bias; 2. it’s highly objective and balanced, taking into consideration all the available evidence and all points of view; 3. it is remarkably prophetic, predicting present day conditions with unusual accuracy despite the fact that it was written in 1978, at a time when global temperatures had been declining for roughly 40 years. Especially impressive is Mercer’s willingness to acknowledge this anomaly for what it is, without any superficial attempts to explain it away.

    Less impressive is Mercer’s insistence, regardless of this evidence to the contrary, on the importance of CO2 emissions, as he offers no real evidence, aside from some vague references to “climate models,” that such emissions could be responsible for the warming he (so accurately) predicts. I’m skeptical on that score, but as I see it, the ultimate cause of the warming waters threatening to devour the ice shelf and precipitate as much as five meters of sea level rise is beside the point. Even if the “key forcing” IS due to greenhouse gases, there is, as should be obvious, little to nothing we can do at this late date to forestall a “tipping point” that could happen at any time simply by reducing or even eliminating the burning of fossil fuels. No one, even the most committed “climate change” activist, has ever proposed a solution that could work without imposing draconian measures that would meet with fierce resistance everywhere (consider the birth of the “Yellow Vest” movement), possibly leading to civil war. Nor is there reason to believe such a drastic reduction could have much effect considering the stubborn persistence of CO2 molecules already in the atmosphere.

    The only recourse that makes sense to me is to take the trillions of dollars now committed to “fighting climate change” by reducing carbon emissions and invest them in the construction of sea walls and similar barriers around all major coastal cities. Modular barriers that could be extended if necessary could be constructed in such a way as to anticipate almost any level of sea rise in the near or far future. Such measures will eventually be needed in any case, as sea levels are steadily rising already and will need to be dealt with sooner or later.

    [Response: You can be “skeptical” all you want about the physics of radiative transfer that’s been known for more than a century, but that won’t change the facts. Your argument makes no sense. Mercer’s prediction of changes to the WAIS was predicated on the prediction that climate would change because of increasing greenhouse gases in the atmosphere. It makes no sense to make policy suggestions (your sea walls, etc.) based on a prediction whose basis you disbelieve. Sea level rise, which your trillions-of-dollars policy suggestions are predicated on, is still primarily from thermal expansion, because the earth is warming because of greenhouse gases. If you believe what you are saying then your policy suggestion should be “let’s do nothing, because we have no way of knowing what will happen in the future.” Maybe it’s just me (and the vast majority of other people), but that’s stupid and irreponsible because all of the evidence is against that view.

    In any case, the main analysis in paper is an analysis of — gasp — climate models so we know with 100% certainy what the key forcing is. CO2 –Eric]

  31. 31
    Nemesis says:

    @eric -> Victor

    ” Your argument makes no sense. ”

    It’s not about making sense, it’s all about keeping the beautiful, infinite climate debate going no matter what. That’s the game of deniers et al. See, a lively climate debate is good for the oil industry and good for business and politics, a lively climate debate prooves that climate heating is still a matter of debate, a subject of debate. That simple.

    If I were a clever guy from the oil industry or from the military-industrial complex (which is fueled by the oil industry), then I’d set up a number of puppets/bots in forums, tv, youtube, talk shows ect blabla, who deny climate heating and I certainly would as well set up a number of puppets/bots, who don’t deny it and this way I’d heavily influence the whole show and I’d have a lot of fun. But I’m no vampire of the oil industry, I’m just a nobody, I have my fun anyway.

  32. 32
    Nemesis says:

    @Eric Lindenberg, #25

    ” if something can be proved, then it is not science.”

    I agree to that. Only the police and judiciary use the term “proof” or “evidence”. A juristic/forensic proof must not be falsifiable at some point in time (when the decree is in effect), but a scientific theory or hypothesis must always be falsifiable, that’s the difference between a proof and any scienctific process.

    https://explorable.com/falsifiability

  33. 33
    nigelj says:

    Victor @30

    “Less impressive is Mercer’s insistence, regardless of this evidence to the contrary, on the importance of CO2 emissions, as he offers no real evidence, aside from some vague references to “climate models,”

    This is a falsehood. The article by Mercer does offer evidence: he explicitly says “Atmospheric carbon dioxide traps some of the long-wave radiation emitted by the Earth’s surface (principally near 15 µm wavelength), thereby tending to warm the troposphere. ” This is based on laboratory and empirical evidence and research on climate sensitivity, not climate models as such (although they have helped). This Mercer article is not obliged to repeat details on how we know CO2 is altering the climate, which is a complex business requiring many pages. Climate models are a different issue attempting to model how the atmosphere works in detail, and predict future warming with accuracy, and based on our specific circumstances.

    “No one, even the most committed “climate change” activist, has ever proposed a solution that could work without imposing draconian measures that would meet with fierce resistance everywhere (consider the birth of the “Yellow Vest” movement), possibly leading to civil war. ”

    Another falsehood. Numerous solutions for renewable energy have been proposed (eg by Jacobson) and the costs involved are not draconian. Numerous analysis of converting the electricity grid to renewables comes down to 1% of global gdp per annum (eg the Stern report). Claiming this would lead to civil war is empty hand waving and hyperoble: the costs of 1% of gdp are obviously not enough to cause hardship, and many ways exist to fairly distribute costs. Even if costs were 5% of global gdp this is manageable. look how much money is wasted on military spending and all the rest.

    “Modular barriers that could be extended if necessary could be constructed in such a way as to anticipate almost any level of sea rise in the near or far future. ”

    The cost of such things is huge, horrendous, and predicting a suitable height is challenging. I know because I used to work in infrastructure design. It’s inevitable that some will have to be built, but prevention is better than cure: ie reducing the use of fossil fuels. I’m no expert on climate change I’m just a layperson but I do know about infrastructure. I do obviously acknowledge Victors implied point that it’s not going to be easy, but he has huge knowledge gaps even for a lay person, jumps to conclusions too easily, and is not objective.

  34. 34

    Victor, #30–

    …as I see it, the ultimate cause of the warming waters threatening to devour the ice shelf and precipitate as much as five meters of sea level rise is beside the point.

    What a silly statement! Obviously the cause matters, because on diagnosis rests treatment. That’s particularly true since the diagnosis is pretty solid at this point–a reality Victor wishes, for whatever reason, to obfuscate.

    And the following statements are even stupider because transparently false–as previous commenters have already pointed out.

  35. 35
    Victor says:

    # 30 Eric, you failed to address my principal point: that, regardless of the cause it seems highly unlikely that, at this late date, anything we do could reverse the disturbing trend predicted by Mercer and reinforced by your own research. Do you really believe cutting back on the burning of fossil fuels could stabilize the West Antarctic ice sheet?

    Another question: what if we do cut back as drastically as you please, and the ice sheet collapses anyhow, raising sea level by 5 meters as predicted? Wouldn’t it be better to be prepared with sea walls than simply hope this tipping point won’t be reached because we’ve been good and “done the right thing”?

    In other words, which is more important to you? Screwing the fossil fuel industry? Or dealing effectively with a potential crisis? (And no, I have no interest in protecting the fossil fuel industry, in fact I think it should be nationalized.)

    [Response: Yes, I really believe that cutting back on the burning of fossil fuels could stabilize the West Antarctic ice sheet. I may be wrong of course. (Suppose you find that you have cut yourself with a knife while chopping vegetables. First, stop chopping vegetables and put down the knife. Then apply a bandage. Not the other way around. If the cut’s too deep you may still be bleeding, but that doesn’t change the fact that you should stop chopping first.–Eric]

  36. 36
    Al Bundy says:

    andy: things in science can be proven.

    AB: I like to use the usable lifespan of the universe as the definition of “proof”. If something wouldn’t likely happen even once over that time frame then it has been proven impossible. The example I visualize is repeatedly dropping a pencil onto a table. It is unlikely that said pencil will ever fall through said table even if you continue the experiment until the universe ends. Yeah, it “could” happen, but I don’t have that much patience, and think that folks who bring “could” into a practical discussion about life-and-death decisions are, to say the least, unhelpful.

    For the sake of policy discussions “theory” = “proven”. For the sake of science discussions “theory” = “proven to n significant digits”. Science’s goal is to increase n. (Yeah, not everything fits this neatly, so quibble away!)

  37. 37
    Dan says:

    Everyone needs to remember that Victor has shown time and time again that he has no clue about the scientific method, is too insecure to admit to being wrong in the face of facts and laws of thermodynamics, and cowardly avoids the peer-reviewed science since it does not tell him what he wants to believe. He is a classic example of poor scientific education and inability to think critically. Yet he somehow thinks he knows something that literally every single professional climate organization (including the National Academy of Science) in the world do not. Talk about absolute scientific ignorance and arrogance. Yet he flaunts it in desperation for his insecurity and inability or want to learn.

  38. 38

    Victor, #35:

    You may want to re-read Eric’s conclusion, which IMO is ‘presponsive’ to your comment:

    Although we humans have evidently caused a long-term increase in westerly winds along the Amundsen Sea coast (which is bad for the West Antarctic ice sheet), the future is not yet written (which is an opportunity). Lowering greenhouse gases to a more modest rate of increase might be enough to prevent further changes in those winds.

    Of course, many glaciologists believe we have already passed the point of no return for West Antarctica. I personally think the jury is still out on that. But that’s a discussion for another time.

  39. 39
    CCHolley says:

    RE. Victor @35

    In other words, which is more important to you? Screwing the fossil fuel industry? Or dealing effectively with a potential crisis?

    Screw the fossil fuel industry? What a joke. The fossil fuel industry has known for fifty years that the burning of fossil fuels would raise global temperatures, but rather than preparing for the day that continuing to exploit their use would no longer be permissible they instead chose a policy of spreading disinformation and corrupting the political process. Who exactly is screwing who? What industry has the right to exist when their existence is amoral and overall detrimental to not only humankind but the entirety of life? Somehow Victor must think that the fossil fuel industry deserves some special consideration because it powered us into the modern age and thus has rights to continue unabated regardless of the consequences–otherwise they are being screwed? How shallow is that thinking? Especially when there are actually cost effective alternatives, regardless of Victor’s contentions to the contrary (as usual, he is clueless).

    More simple minded Victor. Dealing with the real crisis effectively requires BOTH resilience and mitigation.

    Sea walls may be a partial short term bandaid in limited areas, but they are certainly not a solution.

    Can you imagine trying to protect Bangladesh which is a low-lying densely populated river delta with an irregular sea coast and a maze of river shorelines with sea walls? It is an impossible and absurd possibility. BTW, we’re going to be sending those 160 million to Victor’s neighborhood when the flooding is complete.

    My home is in Florida and unfortunately in Florida sea walls will not keep the water out. The bed rock is porous and the water will just pass underneath any barrier. Because of this, sea level rise is already a problem with salt water contaminating aquifers due to underground intrusion. Complete loss of fresh water sources will be our first calamity. Also, the low-lying community of Miami Beach is already suffering regularly from sunny day flooding at high tides due to higher seas and the only solution is to raise its streets and raise homes. There is a limit to how much of that can be done and it IS expensive.

    Absolutely sea level rise is already a problem in Florida and most seaside communities ARE already planning on how to become more resilient to the rise while understanding that climate action will also be necessary. Every foot of rise matters and we don’t know what tipping points have been already reached. So isn’t it better to take action now rather than allow the possibility of oceans to eventually rise over 200 feet? No, let’s just build sea walls. Moronic.

    Screw the fossil fuel industry.

  40. 40
    Al Bundy says:

    nigelj: The cost of such things is huge, horrendous, and predicting a suitable height is challenging. I know because I used to work in infrastructure design.

    AB: Yeah, blithely stating that all we have to do is build that 10ft seawall with the thickness and foundation required for a 200ft seawall! Consider not just sinking of the seawall but the torque. 200ft of water puts one heck of a lateral force on that wall one heck of a distance from the foundation. Nigel, what would you estimate the relative cost of a typical 10′ seawall built to spec versus a 10′ seawall built to be easily extended to 200′?

    And then there’s the cost of pumping every river up to sea level. Saving a coastal zone from more than trivial rises in sea level is impractical.

  41. 41
    nigelj says:

    This proof issue might come down to the audience whether its scientists or the general public. Strictly speaking proof is not possible with scientific theories and laws, but in terms of communicating science to the general public saying we can’t absolutely prove things like gravity might just confuse people and be generally unhelpful.

  42. 42
    nigelj says:

    Al Bundy @40

    “Nigel, what would you estimate the relative cost of a typical 10′ seawall built to spec versus a 10′ seawall built to be easily extended to 200′?”

    200′ in height is certainly the worst case. This is off the chart stuff, that would require detailed engineering design and might not even be feasible. Given the size of the cantilever footing required I can only guessitmate that it would increase the cost of a typical 10 foot sea wall by a factor of about 50 times at least. Nobody is going to do that, the capital costs will be too high. Even building a wall extendable from 10 feet to 20 feet in height would be costly, and a nightmare especially connecting old and new reinforcing bars and getting a strong enough junction and controlling rust.

    In most cases its just not going to be feasible to protect coastlines with barriers because you need so many, and they have to extend laterally so much and cost so much. You can keep small increases in sea level of a few inches at bay with simple sea walls of a few feet in height, and only extendable in height by token amounts, but even they are expensive. I would say it’s going to mostly be “managed retreat”. Local government are not going to want to deal with sea walls, because it will mean huge increases in rates.

    The exceptions are places like Holland who have no option and very wealthy places, and protecting a few business districts for limited periods of time, but even there the politics of doing it and apportioning costs will obviously be a nightmare.

    Regarding movable barriers, I recall something on the movable Thames Barrier to stop tidal surges which cost about 2 billion dollars american. Italy has also built a system of barriers to stop Venice flooding called the MOSE project, which cost a fortune and is already rusting badly and has been a bit of a disaster. Taste of things to come.

  43. 43
    nigelj says:

    AlBundy @40 just an addendum. The idea of a 200 foot high sea wall is of course an absurdity, but I take the idea at face value and show a few of the practical difficulties. You cant really easily extend the height of retaining walls continuously because the junction is very difficult to design and becomes horrendously impractical and expensive.

  44. 44
    Victor says:

    #40 et al. See https://interestingengineering.com/netherlands-billion-dollar-sea-wall

    The Dutch have been fending off the rising ocean for hundreds of years, despite large portions of the country lying below sea level.

  45. 45
    Marco says:

    Victor simply does not get it isn’t an either-or issue. Regardless of any mitigation, we will have to adapt, but without mitigation, we’re going to have to adapt even more. That 5 meter wall we *might* have to build even with drastic mitigation will be a 10 meter wall we *may* have to build without mitigation.

  46. 46
    eric says:

    Response: All right guys, this is interesting, but it’s 100% off topic. No more comments on the philosophy of scientific “proof”, or and no more comments on sea walls (none here that is — you can always used our monthly Unforced Variations) section.

    I’d delete everything but then I’d get accused of violating your 1st Amendment rights.

    We decided some time ago that off-topic (and/or abusive) comments go in the The Borehole, and you’ll find such comments there if you submit more.

  47. 47
    zebra says:

    “Just The Facts”, ignored:

    I thought that was an excellent post, but then I’ve been saying something similar for a while now.

    And worse, tit-for-tat exchanges of facts, each with differing implied warrants are almost totally pointless since the tacit (and conflicting) contexts are not being addressed.

    If the goal is to generate more light than heat, these warrants need to be explicitly acknowledged and discussed (and that goes beyond mere facts). Conversely, if people are tossing out irrelevant facts, countering with other facts isn’t going to be productive. Either examine the implicit warrants and values, or just move on.

    But there appears to be no inclination to follow this advice, and that may be true for the attribution community as well as the Denialists like Victor.

    My approach to Victor is to ask him to state explicitly whether he agrees that:

    Increasing CO2 has caused the energy in the climate system to increase.

    That should be a precondition for any further interaction. But, there are more than enough people willing to do the exchange-of-factoids dance, as in the quote, which validates and enables Victor’s continued addiction.

    My complaint with the attribution folks is that they seem to be somewhat co-dependent with the Denialist warrant. They communicate the impression that… maybe, CO2 isn’t causing the energy in the system to increase, and we’re doing these studies to demonstrate that it is. But this is exactly the endlessly-moving-goalpost fallacy the Denialists promote.

    [Response: I agree. There is a tendency — including among many scientists who certainly know better — to talk about climate change as if we saw it changing and then came up with CO2 as the answer. Of course, the truth is exactly the opposite: climate change was predicted.

    That all said, see my note above. No more discussion about whether deniers gonna deny. It’s a waste of time.–Eric ]

  48. 48
    Nick Odoni says:

    Great post, Eric, and thank you for all this detail and the associated links.

    Just one point I want to be clear on. You say, towards the end,

    “Lowering greenhouse gases to a more modest rate of increase might be enough to prevent further changes in those winds.”

    Is that correct? Is it really the *rate of increase* that needs to be slowed, in order to prevent further changes?

    Or should it really be *the concentration* that needs to be held steady, or even reduced if possible?

    It seems to me that over time, the latter – to reduce the concentrations – is going to be necessary. How we achieve it and by how much are matters of argument, and probably ones which will occupy many minds for the next 100 years or more.

    [Response: Very good point, and I agree with you. The reason that we refer to the *rate* of increase is simply that we were comparing two model scenarios: RCP 8.5 and RCP 4.5. In both cases, CO2 is still increasing, but the rate is lower in RCP 4.5. And in that scenario, the winds no longer increase much, if at all. So do the “what happens if we hold CO2 constant” experiment. But I am sure you are right that it’s the concentration, not the rate that matters most. –Eric ]

  49. 49
    Mal Adapted says:

    Eric”, inline:

    There is a tendency — including among many scientists who certainly know better — to talk about climate change as if we saw it changing and then came up with CO2 as the answer.

    Thankfully, not all scientists who know better talk that way. I recommend Charles D. Keeling’s 1998 short scientific autobiography, Rewards and Penalties of Monitoring the Earth, to RC readers. Great stuff! It’s full of dogged determination against proliferating obstacles – should be required reading for all Earth Science doctoral candidates.

    Keeling had heard about the CO2 greenhouse effect, but it had yet to show up in the global temperature record by the early 1960s. Nonetheless, as early as 1965, once his measurements showed atmospheric CO2 rising yearly, Keeling along with Revelle made the connection to potentially dangerous global warming:

    In 1969, I spoke on invitation before the American Philosophical Society on the implications of rising atmospheric CO2. This rise was of interest, I said, because if it persisted it was likely to inhibit the escape of heat radiating upward from the Earth’s surface and bring about a warmer climate—the so-called “greenhouse effect,” although I didn’t use that expression.

    The remainder of my talk (34) was inspired by my having helped to write a
    [1965] report for the President’s Science Advisory Council. Roger Revelle, the lead author of the report (57), was struck by the fact that the human race was returning to the air a significant part of the carbon that had been slowly extracted by plants and buried in sediments during a half billion years of Earth history. He thought that measurable, perhaps even marked, changes in climate might occur from an increasing greenhouse effect. He believed that careful measurements should be made to check such predictions.

    Half a century later, here we are 8^(.

  50. 50
    Alastair B. McDonald says:

    In #49 Mal Adapted quoted from Charle Keeling’s short auto biography. With a hat tip to Mal, I would like to add another quote from that article

    Without risk one can comment dispassionately on sociological, political, and religious perspectives of the global warming issue, for example, as an historian might, beginning with the first hints of man-made global change and progressing toward the time, not yet arrived, when there may be convincing proof of global warming. (Perhaps convincing proof will be acknowledged to have arrived when a substantial number of US Congressman are discovered to have secretly purchased real estate in northern Canada.)

    Or perhaps when the president of the USA attempts to purchase Greenland?