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It's the sun
Climate's changed before
There is no consensus
Surface temp is unreliable
It's cooling
Models are unreliable
Ice age predicted in the 70s
Al Gore got it wrong
We're heading into an ice age
CO2 lags temperature
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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.
  8. Warm Penguin Eggs at 23:02 PM on 5 June 2008
    ...or perhaps the other drivers of climate explain a very high percentage of what has happened to temperature. With CO2 not only is there simultaneity but the amount of effect may simply be very much smaller than that proportion explained by solar activity.

    However, the sun's effects are being subjected to far greater standards of proof than CO2's effects. When the former is used as a single variable cause of temperature change over the long term, little mention is made of the closeness of fit over most of the period; the focus seems to be on "it hasn't worked since 1975". Well if I was the sun I would be a little upset at that summary dismissal.

    If I was CO2 looking to take plenty of credit for temperature change, I would feel very flattered by all the attention being lavished on me, especially as I had something of an inferiority complex on the matter of causality - was I the symptom or the cause, I had always wondered. Perhaps I had been appointed almost by default to fill the vacancy that has existed since 1975 (call it a change in the structure of the sun / temp relationship), rather than on my merits. My face happens to fit.

    Cynics might say that it's the fact that CO2 levels incorporate some element of human behaviour and the various urges of governments (humans can be taxed and regulated whereas the sun can't) or human beings (we are powerful creatures who must be having an influence on the world around us) explain the focus on CO2 rather than on solar activity.
    [ Response: That is a rather cynical approach. I take a simpler approach. Basic physics stipulates CO2 absorbs longwave radiation - it's a greenhouse gas. CO2 is increasing - it's the highest level in at least 800,00 years. The atmosphere is warming the amount we expect it to. ]
  9. Cynicism is just exaggerated sceptisism; I prefer the
    Get Your Nose Off The Canvas attitude....otherwise all you can see is the detail you are looking at and not how it fits into the overall picture. And that is un-scientific and potentially dangerous.
    CO2 lags temperature increases mostly because a warming period releases the gas from oceans, increased CO2 levels further moderate the heat flow process ( to what extent nobody is sure), add a few (minor) complexities like forest fires and volcanic outgassing to the equation.
    Ice starts melting ( latent heat of fusion) and cooling the biosphere, evaporation does the same, then biomass kicks in and CO2 starts getting locked up again further moderating the process.It all cools down and eventually the cycle repeats.
  10. The problem that I have with the man-made CO2 theory is, human contribution has been so slight by comparison to natural contribution. For example, in less than 10 years, the Kilauea Volcano in Hawaii has contributed more CO2 than humans have their entire existence. Kilauea alone pumps more CO2 in 1 day, than the entire US produces in a full year. So, how can man-made CO2 have any affect on climate change? Its like expecting the ocean to rise by spitting in it.
  11. Mizimi, you state "... Minor Complexities like volcanic ...", but the fact of the matter is, Volcanic CO2 contributions just during the past 10 years far exceeds that of human contribution. Perhaps you should go dig up some volcanic research material on the matter. Heck, even the Science Channel showed me this (and backed up by several research papers found about on the internet).
  12. Mizimi, you state "... Minor Complexities like volcanic ...", but the fact of the matter is, Volcanic CO2 contributions just during the past 10 years far exceeds that of human contribution. Perhaps you should go dig up some volcanic research material on the matter. Heck, even the Science Channel showed me this (and backed up by several research papers found about on the internet).
  13. squidly: It's a question of context, in this case time.
    The whole debate is about long term trends not short term. The point I was trying to make is concentrating on one factor stops us getting the 'picture' in proper perspective. For example, global methane emissions from all known sources is (guess)estimated at around 500+ Mtonnes/annum and its' greenhouse effect is equal to about 1/3 to 1/2 of all CO2 emissions. Worse, it breaks down into water and CO2!
    Now add a very recent discovery that green leaves ( on plants and in leaf litter) also produce methane but no empirical data is available. Factor in that methane emissions are rising faster than CO2 and in 10 years we may well forget about CO2 ...............
    Research on CO2 influence on plant growth shows a 1/3 increase in rate of growth if the other moderating factores (temperature, water, nitrogen) remain the same.
    If you maximise all these factors, growth rate increase can be as high as 85%.
    As humans, we try and look for a few major factors that we can pin 'the problem' on; climate is hideously complex process with a lot of unknowns and simply will not bend to simplistic analysis.
  14. Squidley: the CO2 emission from Kilauea has been relatively steady at 8000 -8500 tonnes/day until 2005 when they effectively tripled to 26,000t/day.

    http://hvo.wr.usgs.gov/volcanowatch/2006/06_02_23.html

    The current estimate for manmade CO2 emissions is 75 million tonnes/day (27 billion tonnes/year)and forecasts suggest this may rise to 40 billion tonnes by 2030. Somewhat more than volcanic contributions.

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