Is it the beginning of the end?

There is a recent post on Watts Up With That (WUWT) suggesting that it is the beginning of the end : warmists in retreat on sea-level rise and climate sensitivity. It links to a blog post by someone called Pierre Gosselin who claims that the New York Times is conceding a low sensitivity.

In his post, Pierre Gosselin makes a number of claims and statements that I thought I would discuss here. He starts by saying

1. The New York Times first have to learn that science is not about insisting you are correct, or being obsessed with a popular pet hypothesis. In the article Justin Gillis and scientist James Annan come across as having a very hard time departing from the hypothesis that CO2 climate sensitivity is high.

Yes, I agree that science is not about insisting that you are correct, or being obsessed with a pet hypothesis. I do, however, find it a little rich coming from someone who seems to fall within the camp that typically dismisses any climate science that suggests that we should be concerned about anthropogenic climate change (AGW). Admittedly, this camp doesn’t really have a pet theory. Anything that attempts to reduce or dismiss the significance of AGW is acceptable.

2. CO2 lags temperature, history has proven. Moreover, although CO2 has risen tremendously (in relative terms) over the last 15 years, the global temperature has not. For the last 15 years, sensitivity has been zero. Worse, there’s strong, mounting evidence that there isn’t going to be any warming for another 10 or 20 years at least. (Hint: oceans).

I found this comment interesting for a number of reasons. His comment about the last 15 years is presumably based on temperature anomaly data which I addressed in an earlier post. His comment about the next 10 or 20 years lacks evidence but his hint implies that heat will be going into the oceans. This is the point. That means global warming is happening. Just because the energy isn’t currently heating the surface doesn’t mean that global warming has stopped. It is, however, the start of his comment that I find most interesting.

Has history shown that CO2 lags temperature? Yes, in some sense it has. Is it relevant? No, noone is claiming that all rises in global surface temperatures have to be due to increases in atmospheric CO2 concentrations. If anything it helps to make the case for AGW. The figure below shows the Vostok ice core record that goes back more than 400000 years. It shows both temperature and CO2 concentrations. There are a series of cycles, each lasting about 100000 years, in which the temperature rises by about 10o C and then falls back down again. This is associated with a similar rise and fall in the CO2 concentrations.

Vostok ice core record showing temperature and carbon dioxide concentrations for the last 420000 years.

Vostok ice core record showing temperature and carbon dioxide concentrations for the last 420000 years.

It turns out that the rise is CO2 concentration in the Vostok ice core record lags the temperature rise by between 600 – 800 years. People have used this to claim that this proves that the current rise in CO2 concentrations cannot be driving up global temperatures. The interpretation is incorrect. What we see in the Vostok record is a consequence of what is known as Milankovitch cycles.

The Earth’s orbit around the Sun is not fixed. It varies with a period of about 100000 years. These variations result in changes to the amount of energy the Earth receives from the Sun and where this energy is deposited. At the beginning of a cycle the Earth’s temperature will start to rise. The ability of water to retain CO2 depends on temperature and so this rise in temperature results in a rise in the atmospheric CO2 concentration. This increased CO2 concentration further amplifies the warming which then further increases the atmospheric CO2 concentration. The net result is that the surface temperature increases by about 10oC and the CO2 concentration rises by about 100 ppm. An important point, however, is that the orbital variations alone cannot explain this temperature rise. It requires amplification due to enhanced levels of atmospheric CO2.

Later in the cycle, however, the orbital variation changes the amount of energy the Earth is receiving so that temperatures start to decrease. The cooler oceans are able to absorb more CO2 and atmospheric CO2 levels also start to decrease. This reduces the warming influence of CO2 and the system returns back to where it was at the beginning of the cycle. This process can also repeat. There is essentially a feedback relationship between temperature and CO2 levels.

The problem today, is that the rise in CO2 is not because of a rise in surface temperatures. It’s because of us releasing CO2 into the atmosphere through our use of fossil fuels. Pierre Gosselin goes on to say

3. There’s no correlation between CO2 and temperature. Of the last 130 years, CO2 has risen 100% of the time, but temperature have risen only during 45 of those years (1920-45 and 1978-98). That’s a very lousy correlation.

This, again, is essentially illustrating why people are concerned. Anthropogenic global warming does not imply that temperatures should increase at all times. There are other processes that can lead to changes in surface temperature. Just because there have been periods of cooling, does not mean that global warming is not happening. The important point is that the cooling periods do not result in a corresponding reduction in CO2 concentrations (as they have in the past). Humans are causing CO2 levels to continue to rise even when the surface temperatures are dropping. HotWhopper has an interesting post with diagrams that illustrate exactly this point. At the end of some period of cooling, the surface temperatures do not return to where they were at the beginning of the warming phase. They return to the level determined by the underlying warming trend.

This is why it’s concerning. In the past, what we might call natural variations could control the process and, in some sense, make it self-limiting. Warming would lead to rising CO2 levels that would amplify the warming, but the start of a cooling phase would reduce CO2 levels and consequently reduce surface temperatures. Now that we’ve removed the dependence of CO2 concentrations on surface temperatures we run the risk of a runaway process. It may not happen. Maybe we don’t have enough fossil fuels for this to be a real issue, but there is currently no feedback in the system that can act to prevent runaway global warming (unless we choose to do so ourselves).

Pierre Gosselin finishes by saying

4. It is clear that scientists are now abandoning the high CO2 sensitivity values in droves. Naturally we don’t expect them to abandon the high values and to run right over to the low CO2 climate sensitivity values. The next logical step is that they adopt the middle sensitivity values, and act like those are going to be catastrophic as well.

Really? I appreciate that there have been recent studies suggesting that climate sensitivity might be between 1.5 and 2oC but most predict that it is between 2 and 3oC and there’s no evidence that any significant number of climate scientists are suddenly suggesting that it is probably much lower than previously thought.

This post has got rather long. I’m meant to be preparing a talk for a meeting next week and am clearly in procrastination mode. To summarise though

1. There is no evidence to suggest that global warming stopped 15 years ago. If anything, there is evidence suggesting it has accelerated. It’s time people stopped using temperature anomaly data alone to determine whether or not global warming is happening.

2. Yes, in the past increases in CO2 levels have lagged increases in temperature. This does not prove that what we are currently experiencing cannot by due to the currently observed increases in CO2 concentrations. If anything, this past data illustrates the importance of CO2 in determining surface temperatures.

3. Scientists are not abandoning higher climate sensitivity values. Yes, there are some recent papers suggesting that it might be lower than previously thought, but these are actually consistent with most earlier studies and most studies still support a higher climate sensitivity than these newer studies.

So, I don’t think there is any evidence to suggest those who are called “warmists” are in retreat. I just think there are some who would like this to be true. As many would agree, wishing it to be true does not make it so.

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18 Responses to Is it the beginning of the end?

  1. P Gosselin says:

    I see you’ve skipped over the point I made about the Eemiam. Slipped your mind, did it? 🙂

  2. I did indeed, but I didn’t claim I would comment on everything 🙂 I did try look up what you were saying happened during the Eemian, but didn’t find much – although I did write this just before having to rush out of the office. If I look at the figure that I included, I don’t quite see what you claim to have happened, but you’re welcome to elaborate.

  3. Lars Karlsson says:

    It seems Mr Gosselin has never heard about the Milankovitch cycles.

  4. Lars Karlsson says:

    But I don’t agree with the part about runaway global warming. It makes no difference wether the initial warming is caused by the Milankovitch cycles or CO2 from fossil fuels. The CO2 feedback (with approx 20 ppm for each degree between glacial tand interglacial) does not seem to be strong enough to cause a runaway effect.

  5. Rachel says:

    The “800-year lag” unravelled –

    The Eemian temperature was a result of orbital forcing rather than CO2 –

  6. I tend to agree. I wasn’t really suggesting that the process is likely to runaway (my use of the word “risk” was meant to convey that, but maybe I didn’t make that clear enough). Most of our CO2 is probably tied up in carbonate rocks and can’t be released. What I was trying to explain in that section (maybe not all that clearly) is that because the rise in CO2 levels is a consequence of our use of fossil fuels, there’s no feedback mechanism that can cause the CO2 levels to start dropping if the Earth were to enter a cooling phase. If we were to do nothing, the CO2 levels would continue to rise and the global surface temperatures would, eventually continue to rise too. We will presumably run out of fossil fuels at some point in the future and it is likely (as you suggest) that that would happen before a runaway process started.

  7. Yes, that was kind of what I was expecting but couldn’t really find much about it. What Pierre Gosselin said in his post was that CO2 remained at 280 ppm while temperatures dropped by 6oC. I can’t find anything that suggests that this was indeed the case.

  8. Rachel says:

    This article puts the CO2 at 270ppm –
    It doesn’t give a global mean temperature but says that temperatures over Europe in summer were higher than today and that this can be explained by orbital parameters (which I assume means orbital forcing).

  9. Rachel says:

    Have you got a source for the Eemian 260ppm and a temperature drop of 6C?

  10. Rachel says:

    This is a question for P Gosselin btw.

  11. Yes, the abstract certainly says exactly that fairly explicitly.

  12. Rachel says:

    I asked him for a source on his own blog post at – – and he gives the graph in your post above. The temperature does appear to drop by about 6C or so. I know very little about this topic but am guessing this marks the end of the Eemian interglacial due to the Milkanovitch cycle. Correct me if I’m wrong.

  13. I see, so he’s referring to that relatively short period where the temperature appears to drop faster than the CO2 levels. Overall, the correlation appears quite strong, so this seems to be cherry-picking one portion where it may not be as strong as at other times.

  14. That’s a great video. Explains it all very clearly.

  15. Rachel says:

    I’m slowly trawling my way through all of his videos and they’re all equally compelling. The Monkton Bunkum series is particularly entertaining and really highlight what an idiot Monkton is.

  16. I notice you’ve referred to me as a warmist on your blog. I’ve tried to avoid labeling people as deniers (or as anything really). Pity others don’t see any value in doing the same.

  17. Rachel says:

    Sorry to hijack your comments like this but I think I’ve misunderstood that graph and I think P Gosselin has too. That graph is the Vostok Ice Core record and it is showing temperatures for the last 400,000 in ANTARCTICA. It does not show global mean temperatures. CO2 lags Antarctic temperatures but leads Arctic temperatures.

  18. No need to apologise. All (or at least most) comments appreciated. Yes, you’re correct. This is simply the Vostok ice core record. As I also learned in the video, the CO2 lags in the Vostok record, but leads in northern hemisphere records.

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