THEGREENGROK    Statistically Speaking

Our Climate Future: Looking Back to See Ahead

by Bill Chameides | January 20th, 2011
posted by Erica Rowell (Editor)

Permalink | 2 comments


Conditions millions of years ago may tell us where we are headed.

Climate models can be used to predict future climate trends but, as has been pointed out many, many times, models are far from the real thing. How accurate are such predictions? Hard to say.

But models are not the only way to peek into the future. There’s an old saw that the past is the key to the future and that is almost certainly true of the climate. For example, consider the question on most climate scientists’ minds these days:

How will the climate respond in the coming decades to rising carbon dioxide (CO2) concentrations from burning fossil fuels?

One answer comes from looking at past climatic conditions when CO2 concentrations were as high as we expect them to grow now.

A Look at Some Past Climate Numbers

So what does such a look into the past tell us? In a Policy Perspective piece published last week in the journal Science, Jeff Kiehl, of the National Center for Atmospheric Research, provided a pretty stark picture of rather hot times ahead. How so? Here are some of the numbers.

  • Current global average temperature (in degrees Fahrenheit): 58.12 1
  • 20th century average global temperature (in degrees Fahrenheit): 57 1
  • Current CO2 concentration (in parts per million): 389 2

  • CO2 concentration in 2100 under business as usual (in parts per million): 900–1100 3

  • Last time on Earth CO2 reached ~1000 ppm: about 35 million years ago 4
  • Global average temperature 35 million years ago (in degrees Fahrenheit): 88 5


The kicker? Climate models predict much less warming from a CO2 concentration of 1000 ppm. In other words, the empirical data from 35 million years ago suggest that the climate models underestimate the climate’s sensitivity to greenhouse gases like CO2.

Predicting future climate using models may put us on thin ice. But past climatic variations suggest the ice may be a whole lot thinner than we thought.



1. “State of the Climate Global Analysis Annual 2010,” NOAA’s National Climatic Data Center.

2. “Trends in Atmospheric Carbon Dioxide,” November 2010, NOAA’s Earth System Research Laboratory.

3. “Climate Change 2007: Working Group I: The Physical Science Basis,” IPCC Fourth Assessment Report.

4. “A Climate Debate,” September 29, 2010, TheGreenGrok.

5. “Early Palaeogene Temperature Evolution of the Southwest Pacific Ocean,” Peter Bijl et al., August 2009, Nature.

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  1. Ken Towe
    Jan 24, 2011

    Bill… You state that the global average temperature 34 million years ago was 88°F, citing a paper by Bijl et al. in SCIENCE, the results of which were based on just ONE core sample and a host of assumptions. Actually, the figure of 88°F (= 31°C) comes from Kiehl’s Perspective in SCIENCE (subscription required). A look at Bijl et al’s. Figure 1 shows the value of 31°C to be off the chart. A subscription to SCIENCE is not needed to view this chart. Go here: Where did Kiehl’s off-the-chart figure of 88°F come from? It was modeled “using proxy temperature data and assuming to first order that latitudinal temperature can be fit with a cosine function in latitude”. Might there just be a tad of circularity in these studies? It might have been pointed out that geological and geochemical evidence also suggests that the Antarctic ice sheet formed during the late Eocene. Some believe that the maximum ice-sheet growth occurred when CO2 was between 450 and 1500 ppm. See Pearson et al. NATURE, vol 461, p. 1110, October 2009. And, if the CO2 concentration in 2100 is near 1000 ppm, the global population, unless checked, will be near 18 billion…a lot of carbon footprints. Of course, if it is checked, the CO2 will also be checked. Submitted 1/24

  2. Jim
    Jan 21, 2011

    From what I’ve read, the models don’t take into account some of the feedbacks, mainly because they are not well understood, such as methane release. Also, they put the models on the conservative end. If temperatures are above that fine (not really, but you get the idea), but if they are below what are predicated, then the scientists will be raked over the coals with shouts of “Conspiracy!” and will never be believed again, a classic shouting Wolf scenario, whether or not it’s warranted. My uneducated guess is that we will experience temperatures above what the IPCC reports. A world at 88 degrees would not be fun. I won’t be around then, but I’ll hopefully be around for a while and I’m sure things will be bad enough in 30-40 years time frame.

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