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It's the sun
Climate's changed before
There is no consensus
Surface temp is unreliable
Models are unreliable
It's cooling
Ice age predicted in the 70's
Al Gore got it wrong
CO2 lags temperature
We're heading into an ice age
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Friday, 12 October, 2007

What does CO2 lagging temperature mean?

With a recent British court case critiquing An Inconvenient Truth and the news that Al Gore just won the Nobel Peace Prize, the attacks on Gore and his slideshow have stepped up in recent times. A common criticism is his use of the CO2/temperature record to show that in the past, CO2 caused temperature increase. A close look at ice core records finds that CO2 actually lags temperature. In fact, a study came out just a few weeks ago (Stott 2007) that confirms CO2 increases around 1000 years after temperature rise. This raises an important question - does temperature rise cause CO2 rise or the other way around? The answer is both.

http://www.adobe.com/designcenter/thinktank/womack/tt_womack_2.jpg

The dominant signal in the temperature record (the white line in the above figure) is a 100,000 year cycle where long ice ages are broken by short warm periods called interglacials. This cycle coincides with a change in Earth's orbit as it evolves from a more circular orbit to a more elliptical orbit. When springtime insolation (incoming sunlight) increases in the southern hemisphere, this causes temperature to rise in the south. The warming is amplified as retreating Antarctic ice means less sunlight is reflected back into space.

As the southern oceans warm, they give up more CO2 to the atmosphere as the solubility of CO2 in water falls with rising temperature. The CO2 mixes through the atmosphere, amplifying and spreading the warming to the tropics and northern hemisphere. This is why warming in the southern hemisphere precedes warming in the northern hemisphere (Caillon 2003). This is confirmed by marine cores that show tropical temperatures lag southern warming by ~1000 years (Stott 2007). CO2 warming also explains how the relatively weak forcing from orbital cycles can bring the planet out of an ice age.

So where does that leave Al Gore? What he says in An Inconvenient Truth is this:

"The relationship is very complicated but there is one relationship that is far more powerful than all the others and it is this - when there is more carbon dioxide, the temperature gets warmer because it traps more heat from the sun inside."

This statement, while an oversimplification, is essentially correct. A more accurate and informative statement would've been

"A change in Earth's orbit warmed the southern oceans which released more CO2 into the atmosphere. The extra CO2 trapped more heat from the sun and amplified the warming. It also mixed through the atmosphere, spreading the warming to the tropics and northern hemisphere"

Of course, the audience may have dozed off by the end of the explanation and slept through all the pretty pictures of polar bears and glaciers.

Note - I've posted more info as well as links to many peer reviewed studies on this topic on our CO2 lags temperature page.

Posted by John Cook at 19:36 PM

Comments

  1. You are going to have to actually FIND evidence for a feedback effect. Alleging it or quoting someone who is alleging it isn't the same thing. There's insufficient evidence here not to assume a negative feedback effect on longer time scales.
  2. Wondering Aloud at 08:51 AM on 4 January 2008
    GMB seems someone disconnected from the topic of this post.

    But, what I still want to know is what is currently happening with the Earth's orbit? What causes the sudden dramatic cool down and is it expected to happen soon? If not, why not? looks to me like the interglacial is due to end at least in terms of the last 4.
  3. What theory that explains how the miniscule variations in the earths orbit could produce the initial temperature rise? How is this theory reflected in climate models? BY contrast, there is a well-proven theory of how variations in solar flux are amplified to produce not only the initial temperature rise. Basically, the solar flux affects cloud cover, and clouds reflect radiation whereby the earth cools. This explains not only interglacial warming, but the up and down climate variations of the past century - warming then cooling then warming again, and for the last seven years cooling.

    How do atmospheric scientists model solar flux and cloud formation in climate models? These are critical because only a 4% variation in cloud cover would account for climate change. They do not model it at all. Instead they assume an unknown mechanism by which carbon dioxide effects are amplified. The dominant green house gas is water vapor. CO2 is less than 5%, so of course some magic is required to make CO2 dominate.

  4. Philippe Chantreau at 14:40 PM on 15 February 2008
    Roy, there was no Arctic ice cap until the Isthmus of Panama closed. Changes in oceanic circulation, no TSI involved for the start of the first ice ages is a very plausible possibility. The most constant thing in Earth climate over the past half million years is solar energy input.

    That 4% variation would have to persist to trigger climate change. Look at the CERES and ERBE pages and see how many papers are there about clouds. There is nothing magic about CO2, the physics of it are very well known.
  5. Wondering Aloud at 06:17 AM on 8 March 2008
    What Gore should have said is that one relationship is clear... When it gets warmer carbon dioxide increases. Than he would have been correct and we wouldn't have to be discussing it.
    [ Response: Gore oversimplified. It's like when you're explaining complicated science to kids - you dumb it down so they can understand it. Plus Gore is not only trying to explain but also entertain - he doesn't want to get bogged down.  Personally, I find the CO2 cycle fascinating and would've like to have heard more. And he opened himself up to criticism by oversimplifying. But the overall assertion "when there is more carbon dioxide, the temperature gets warmer" is correct. The criticism is more a framing question than a question of whether he got the science right or wrong. ]
  6. Wondering Aloud at 23:20 PM on 16 May 2008
    To quote the late Reg Newell on this topic "I'm saying that's not at all evident."
  7. Wondering Aloud at 23:27 PM on 16 May 2008
    http://www.geocraft.com/WVFossils/Carboniferous_climate.html

    The CO2 temperature connection leaves much to be desired on any time scale I can find, 800 years wrong way over the last 600K years is only a bit of it. It is clear that temp increase can cause carbon dioxide to increase. The converse being true is your working hypothesis but it is questionable because it just doesn't fit the record. We have warm periods with low CO2 and ice ages with high CO2.

    Maybe convection and cloud effects simply overwelm the supposed radiative issues.

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