Problems With Catastrophic Global Warming Shown in Two Charts

OK, I understand that perhaps my worst flaw in trying to make a point is in being too loquacious.  In a previous post, I showed why estimates of climate catastrophe were overblown by using the earth's experience over the last 100 years as an empirical guide.  Today, I shall try to make the same point with fewer words and just two charts instead.

Scientists have a concept called climate sensitivity which refers to the amount of global warming in degrees Celsius we might expect from a doubling of CO2 concentrations from a pre-industrial 280ppm to 560ppm  (we are currently at about 380ppm today and will reach 560ppm between 2065 and 2100, depending on how aggressive a forecast you want to adopt).

A simple way to estimate sensitivity is from experience over the past century.  At the same time CO2 has gone up by 100ppm, global temperatures have gone up by at most 0.6 Celsius (from the 4th IPCC report).  I actually believe this number is over-stated due to uncorrected urban effects and other surface temperature measurement issues, but let's assume 0.6ºC.  Only a part of that 0.6ºC is due to man - some is likely do to natural cyclical effects, but again to avoid argument, let's assume man's CO2 has heated the earth 0.6 Celsius.  From these data points, we can project forward:


As you can see, the projection is actually a diminishing curve.  For reasons I will not go into again (you can read much more in my original post) this relationship HAS to be a diminishing curve.  It's a fact accepted by everyone.  True climate consensus.  We can argue about the slope and exact shape, but I have chosen midpoint values from a reasonable range.  The answer is not that sensitive to different assumptions anyway.  Even a linear extrapolation, which is clearly wrong scientifically, would only yield a sensitivity projection a few tenths of a degree higher.

What we arrive at is a sensitivity of about 1.2 degrees Celsius for a CO2 doubling (where the blue line crosses 560ppm).  In other words, we can expect another 0.6ºC increase over the next century, about the same amount we experienced (and most of us failed to notice) over the last century.

But, you are saying, global warming catastrophists get so much higher numbers.  Yes they do, with warming as high as 9-10C in the next century.  In fact, most global warming catastrophists believe the climate sensitivity is at least 3ºC per doubling, and many use estimates as high as 5ºC or 6ºC.  Do these numbers make sense?  Well, let's draw the same curve for a sensitivity of 3ºC, the low end of the catastrophists' estimates, this time in red:


To get a sensitivity of 3.0ºC, one has to assume that global warming due solely to man's CO2 (nothing else) would have to be 1.5ºC to date (where the red line intersects the current concentration of 380ppm).  But no one, not the IPCC or anyone else, believes measured past warming has been anywhere near this high.  So to believe the catastrophic man-made global warming case, you have to accept a sensitivity three or more times higher than historical empirical data would support.  Rather than fighting against climate consensus, which is how we are so often portrayed, skeptics in fact have history and empirical data on our side.  For me, this second chart is the smoking gun of climate skepticism.  We have a lot of other issues -- measurement biases, problems with historical reconstructions, role of the sun, etc -- but this chart highlights the central problem -- that catastrophic warming forecasts make no sense based on the last 100+ years of actual data.

Global warming catastrophists in fact have to argue against historical data, and say it is flawed in two ways:  First, they argue there are positive feedbacks in climate that will take hold in the future and accelerate warming; and second, they argue there are other anthropogenic effects, specifically sulphate aerosols, that are masking man-made warming.  Rather than just repeat myself (and in the interest in proving I can actually be succinct) I will point you to my original post, the second half of which deals in depth with these two issues. 

As always, you can find my Layman's Guide to Skepticism about Man-made Global Warming here.  It is available for free in HTML or pdf download, or you can order the printed book that I sell at cost.  My other recent posts about climate are here.


  1. Mr. Mercy Vetsel:

    That was brilliant, brilliant, brilliant, as always and also this time starkly concise. I stumbled across this blog from Mankiw's blog and it has quickly become my favorite source for understanding why so many bright scientists are skeptical of climate crisis claims made by political activists like NASA's Hansen.

    I love the way the blog is tailored towards scientifically literate laymen. The post on the scale of the temperature fudge factors was also illuminating.

    I don't have anything to add to article above, but I've thought of a create way to illustrate the magnitude of NASA's Y2K error. Over the next 50 years the consensus among Kyoto advocates is that it will reduce global temperature by 0.07 degrees Celsius. That number is probably overly optimistic, but for the sake of comparison let's say it's correct.

    That means McIntyre has single-handedly reduced the effect of global warming on the United States by TWICE AS MUCH in one day as Kyoto will do in 50 years!

    Here's the chart:


    Kyoto (50 years, projection): *******
    McIntyre (1 day, actual): ***************

    Maybe the countries that got suckered into Kyoto should have spent more money on people like McIntyre who think independently and understand statistics.


  2. Alexander White:

    Another good post. I read your first post and I didn't think it was too long. I have run into one counter argument that you didn't address in this post or in the previous one. It goes something like this: Changes in temperature as a function of CO2 are not immediately seen. Rather, there is a sort of "climate inertia" at play which delay the full effects of carbon dioxide. At least that is the claim. If this were true, we could theoretically be closer on to the origin on the red curve. This seems like something one should be able to approximate with a back-of-an-envelope calculation. It would have to be a major inertial effect though, because 0.6 C change on the red curve looks like only about ~315 PPM CO2 (using just my eyeball on your second graph).

  3. TCO:

    A. It's a very nice explication. Kudos.

    B. Regarding McIntyre, I seriously recommend to take some skeptical looks. He has a delightful blog. But there are a lot of things wrong/skewed. You may get the wrong impression by reading things too much through a SM lense. I recommend reading the Huybers comment on Steve's GRL article. Reading that really explained to me what was going on and cut through a lot of defensive Steve argument (where he messes up a full factorial, obscures confounding factors) wrt correlation/covariance and centering/decentering. Also note that Steve's response to a correction on RE benchmarking by Huybers is to try to shift the argument to an all new benchmarking (like someone who can always adjust the DCF to give you an NPV even with changed inputs, corrected errors). Just do yourself the favor of reading Huybers FIRST, then read Steve's 3! blog posts about Huybers.

  4. Charles D. Quarles:

    I'd like to add a few points.

    1) The "pre-industrial" CO2 figure of 280 ppmv is suspect. It is suspect because the early CAGW people date back to the late 19th and early 20th Century and could essentially cherry pick a number. Why do you ask? Simple. Ice core data is subject to contamination. CO2, like H2O is a gas with a variable concentration. Using chemical methods, estimates varied from the 280 or so ppmv to 500 or so ppmv for the "pre-industrial" and/or "prehistoric" times. Even today's Mauna Loa IR derived figures are suspect because the measurements are made on a volcano. Some current best estimates, based upon plant physiology (C4 pathways vs C3 pathways) support past CO2 levels at or above current ones.

    2) There are a number of studies indicating an atmospheric residence time for CO2 of 5 years. This is because of Henry's Law and the fact that oceanic CO2 concentrations are 50 times the atmospheric ones. Given this, anthropogenic atmospheric CO2 is a small fraction of the current concentrations, and any CO2 signal will be dominated by other natural sources (human activity is just as natural as any other activity on this rock).

    3) Water is and will be for the forseeable future the main "greenhouse" gas in our atmosphere.

    4) Never forget ol' Sol and orbital mechanics.

    5) There is evidence that air and ocean temperatures have been warmer than the current estimated values.

    6) A major volcanic eruption can inject more CO2 in a day than human activity has for the last 50 years.

    7) Global warming is a misnomer if defined as global average temperatures. Climate, being statistical weather, will only warm globally (meaning everywhere on Earth's surface) if insolation increases. What is happening in the real world is areas of localized warming, areas of localized cooling, and areas of essentially no long term change.

  5. Pieter:

    Your diminshing curve makes a reasonable point look questionable, and the even more dramatically diminishing curve in chapter 5 of your skeptic's guide makes it look completely ridiculous.

    If you want to use a linear relationship to say that the .6C increase from 100ppm CO2 would only give about 1.8C for 280ppm CO2, that would be a reasonable argument. I'd still believe the guys with the PhDs in climatology, but I'd agree that they had some explaining to do.

    Your diminishing curve seems to have been pulled purely from your imagination. The limited piece you give in this post seems unjustified. The larger graph you present in your skeptic's guide shows an increase to 1500ppm CO2 is still about 1.5C of increase, and judging by the slope of the curve, it looks like it wouldn't even reach 1.6C by 3000ppm.

    I'd also like anyone reading this blog to think about your discussion of positive feedback. The simplest example of a positive feedback system that people will encounter in their everyday lives is a computer microphone too close to a set of speakers. An external noise can be picked up by the microphone and then played out of the speaker. If the microphone is too close to the speakers, the sound will be picked up by the microphone again and played out of the speaker, starting a feedback loop. According to your description of feedback, if the volume is set too high, a positive feedback loop will be formed, the sounds will increase in volume exponentially, there will be a "run away" in amplification, and the speakers will explode. This isn't what happens. Positive feedback systems (coupled to negative feedback systems) can produce an amplification -the sound played is louder than the original sound- without leading to unbounded, exponential growth. In short, it is not an insult to scientific intuition to say a .5C temperature increase from CO2 alone could lead to an overall increase of 1C because of positive feedback systems.

  6. Mhaze:

    Something I have not heard adequately explained by warmers. At first glance this may seem silly, but it is not. It has to do with what the natural trend line is or should be and thus is similar to a question on the subject of technical analysis of stock markets.

    Begin here. Go through (1), (2) and then answer the question.

    1. We were in a Little Ice Age until about the middle of the 1900s.
    2. We are not in a Little Ice Age now.

    Should temperatures have gone up, down, or stayed the same?

  7. Anna:

    We need to make a stop to global warming. Why do people know how bad this is going to get and then they still pollute? we need to do something big like Al Gore did to get people's attention.