Cook: “When someone mentions to you that CO2 lags temperature, remind them they’re actually invoking evidence for a positive feedback that further increases global warming by an extra 15 to 78%.”

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"Cook: “When someone mentions to you that CO2 lags temperature, remind them they’re actually invoking evidence for a positive feedback that further increases global warming by an extra 15 to 78%.”"

Physicist John Cook of Skeptical Science has a good piece on “The significance of the CO2 lag” that I’m reposting here, followed by a discussion of the best-studied feedbacks and their likely impact (with links to the literature).

When we examine past climate change using ice cores, we observe that CO2 lags temperature. In other words, a change in temperature causes changes in atmospheric CO2. This is due to various processes such as warmer temperatures causing the oceans to release CO2. This has lead some to argue that the CO2 lag disproves the warming effect of CO2. However, this line of thinking doesn’t take in the full body of evidence. We have many lines of empirical evidence that CO2 traps heat. Decades of lab experiments reveal how CO2 absorbs and scatters infrared radiation. Satellite measurements find CO2 trapping heat and surface measurements confirm more radiation at CO2 wavelengths returning to the Earth’s surface. So the full body of evidence gives us these two facts: warming causes more CO2 and more CO2 causes warming. The significance should by now be obvious. The CO2 lag is evidence of a climate positive feedback.

The magnitude of this positive feedback is calculated in Positive feedback between global warming and atmospheric CO2 concentration inferred from past climate change (Scheffer 2006). In this paper, they use reconstructions of past CO2 and temperature to empirically calculate the positive feedback between global warming and CO2. First, they look at pre-industrial CO2 variations during glacial cycles and the Little Ice Age. The relationship between CO2 and temperature is roughly linear.

CO2 vs Temperature: Little Ice Age and Last Glacial Maximum
Figure 1. Relationships between past atmospheric CO2 concentrations and reconstructed temperatures. (a) Reconstructed Northern Hemisphere temperatures of the period 1500-1600 plotted against CO2 levels 50 years later from the Law Dome record. (b) CO2 vs temperature for a 400.000 years period of glacial cycles reconstructed from the Vostok ice core.

Over these periods, changes in CO2 are assumed to be primarily driven by temperature. This is because mechanisms other than changing CO2 (such as changes in solar output) drove temperature over these periods. So looking at Figure 1, we can calculate the effect that temperature change has on CO2 levels. However, this is complicated by the fact that different carbon cycle processes operate on different time scales. On a time scale of years, warming has an effect of around 3 ppm of CO2 per degree Celsius. On a scale of centuries, the effect is much larger – around 20 ppm of CO2 per degree Celsius.

What we’re interested in is the expected global warming by the end of the 21st century so century time-scales are the focus. The most important period for estimating sensitivity of CO2 to temperature on century time-scales is the Little Ice Age. Figure 1a shows how CO2 levels dropped (with a time lag of 50 years) in response to the drop in temperature in this period. From this is calculated a positive feedback of between 15 to 78% on a century-scale.

The benefit of this study is it provides an independent, empirical method of calculating the positive feedback from the CO2 lag. These results are consistent with what’s been found in simulation studies. So when someone mentions to you that CO2 lags temperature, remind them they’re actually invoking evidence for a positive feedback that further increases global warming by an extra 15 to 78%.

– John Cook

JR:  We continue to learn about the dangerous positive carbon-cycle feedbacks that threaten to amplify the impacts of human-caused GHGs:

Indeed, the best evidence is that the climate is now being driven by amplifying feedbacks — see, most notably:

The most worrisome of the by amplifying feedbacks is the defrosting of the permafrost:  Using the first “fully interactive climate system model” applied to study permafrost, the researchers found that if we tried to stabilize CO2 concentrations in the air at 550 ppm, permafrost would plummet from over 4 million square miles today to 1.5 million. If concentrations hit 690 ppm, permafrost would shrink to just 800,000 square miles.  See also “Science shocker: Vast East Siberian Arctic Shelf methane stores destabilizing and ventingNSF issues world a wake-up call: “Release of even a fraction of the methane stored in the shelf could trigger abrupt climate warming.”

High emissions levels + positive feedbacks = climate catastrophe:

The time to act was a long time ago, but now is much better than later — and infinitely better than too damn late.

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32 Responses to Cook: “When someone mentions to you that CO2 lags temperature, remind them they’re actually invoking evidence for a positive feedback that further increases global warming by an extra 15 to 78%.”

  1. Rabid Doomsayer says:

    Is the timing of the CO2 lag to do with the Meridonal Overturning Circulation? If so we are going to be in deep trouble within the next 800 years, even if we get our act together now.

  2. homunq says:

    If we can get our act together now, we can handle an 800-year threat. If not… well, I think some humans will survive (ironically, Darwin, Australia is one of the best places for it), but most dystopian science fiction will look utopian.

  3. homunq says:

    We’re going way off the charts compared to the historical record, which adds uncertainty to the “15%-78%” number. That’s almost all downside, since the difference between (say) 15% and 5% is negligible, while the difference between 78% and 234% is probably noticeable.

  4. Nell Reece says:

    Sorry, but unless some technology like the STEP Carbon Capture is successful, I think it’s already too late.

  5. That’s profoundly sad news for humankind. I really believe that climate change is like a freight train going down a steep mountain without any brakes. The stable climate which made civilization possible isn’t going to exist any longer within a century and whatever comes next isn’t going to be compatible with the future survival of the human species.

    The really sad news is that our government and the world are doubling down on their gamble by increasing coal and oil consumption in the hopes of resurrecting the economy and causing it to grow again and keep on growing forever since economic growth is the secret to eternal prosperity for humankind (just as there is also a hidden pot of gold underneath the rainbow!).

    Humankind is in a bad place and the only reason why there remains an argument on the side of the denialists is because some illusion of normalcy remains. It won’t continue for too much longer, though, and humankind will witness some major catastrophes in the years ahead. The United States isn’t going to escape from suffering, either (imagine a heat wave on the scale of the Russian heat wave in America’s breadbasket, imagine the Mississippi suffering a flood of the same type as afflicted Pakistan, imagine Las Vegas and Phoenix running out of water).

    The future ain’t pretty. Technological civilization isn’t leading humankind to any sort of utopia.

  6. Prokaryotes says:

    “On a time scale of years, warming has an effect of around 3 ppm of CO2 per degree Celsius. On a scale of centuries, the effect is much larger – around 20 ppm of CO2 per degree Celsius.”

    So this is just a mean and does not account for abrupt release. Tipping points create emission spikes in the earth climate history. Depending on the magnitude of abrupt events, overall climate setup and ultimately biosphere pump condition you have either one or two polar ice disintegration.

  7. Wit'sEnd says:

    Another amplifying feedback not being calculated into predictions – vegetation is CURRENTLY dying off, in a rapidly accelerating ecosystem collapse, especially in the northern hemisphere, because of the toxins in the atmosphere.

    Details are here:

    http://witsendnj.blogspot.com/2010/08/i-cant-keep-up.html

    Scores of scientific studies have shown that tropospheric ozone, the levels of which are inexorably rising from fuel emissions, is poisonous to plants, by damaging the stomata, interfering with the ability to photosynthesize and produce chlorophyll – as well as increasing the amount of water lost by foliage. Take a look outside. Leaves on trees already turning fall color because they are losing their green pigment – the streets and sidewalks are already littered with dead leaves. Look at any garden – the leaves of crops exhibit characteristic chlorosis from exposure to ozone – stippling, spotting, singing, wilting, holes, discoloration.

    We are in for mass famine if we don’t stop polluting the air, and soon, and in industrialized nations, not just impoverished places like Pakistan.

    Add to that:

    “Climate changes will also lead to increases in the emission of CO2 and methane from wetlands, nitrous oxides from soils, volatile organic compounds from forests, and trace gases and soot from fires. All these emissions affect atmospheric chemistry, including the amount of ozone in the lower atmosphere, where it acts as a powerful greenhouse gas as well as a pollutant toxic to people and plants.

    Although our understanding of other feedbacks associated with climate-induced ecosystem changes is improving, the impact of these changes is not yet accounted for in climate-change modelling.

    An international consortium of scientists, led by Almut Arneth from Lund University, has estimated the importance of these unaccounted ‘biogeochemical feedbacks’ in an article that appears as Advance Online Publication on Nature Geoscience’s website.”

  8. Peter Mizla says:

    # 2 homunq

    Curious–why Darwin AU? Darwin is a tropical savanna climate (Koppen AW)
    Hot with a dry and wet season-what makes an AW climate like Darwin survivable with catastrophic climate change?

  9. Recent briefing I did on climate feedbacks as part of an effort we are ramping up at Climate Solutions to dial back CO2 concentrations in the atmosphere.

    http://climatesolutions.org/solutions/reports/biocarbon-briefs/the-biocarbon-imperative-reaching-target-350

  10. Wit'sEnd says:

    #8, Patrick, darn…somewhere I saw a comment and of course I can’t remember where – maybe here on CP – that 350 was a politically expedient choice of a number as goal – and what we really need for a stable climate is well under 280, pre-industrial levels.

    David Mathews, you might like this exceedingly clever cartoon of a coal-fueled train out of control “Runaway”!

    http://witsendnj.blogspot.com/2010/08/runaway.html

  11. David B. Benson says:

    Patrick Mazza & Wit’sEnd — Hansen et al. worked out 350 ppm or likely less. While none can be certain, my best estimate is around 300 ppm CO2-equivalent as nearly optimal for humans and civilization.

  12. Robert says:

    Wit’s end #7

    How do you know that your green bean problem is not just a virus? I grow runner beans and French beans and have noticed some leaf spots and discoloration on the runners this year. We have still had a very good crop of beans.

    http://vegetablemdonline.ppath.cornell.edu/factsheets/Virus_Beans.htm

  13. Robert says:

    Just found this:

    http://nsidc.org/images/arcticseaicenews/20100817_Figure3.png

    The sea ice area in the northern route of the northwest passage has fallen far below any previous year.

  14. Chad says:

    It always amazes me how many otherwise intelligent people can’t quite figure out that order doesn’t matter in a positive feedback loop. If A causes B causes A, then B causes A causes B. This ain’t rocket science, folks.

    It only goes to show how little critical thinking deniers actually undertake.

  15. Sen Comn, S.E. says:

    CO2 is a greenhouse gas and does indeed heat the atmosphere, that much even deniers admit. The amount of warming it causes in different concentrations and temperatures is however under debate. A simple question which I’m sure has to have an answer before the deniers can be shown to be wrong is this:

    If CO2 is a serious cause of warming, how then has the atmosphere historically started to cool when CO2 concentrations were much higher than now and still rising?

    Vostok data shows CO2 rising time and again for hundreds of years after the temperature has already started to decline. That is where we need to address the lag, not going up, since “deniers” are agreeing that CO2 indeed causes warming. Until we can do that, the issue remains.

  16. Prokaryotes says:

    Last time carbon dioxide levels were this high: 15 million years ago

    “We can now have confidence in making statements about how carbon dioxide has varied throughout history,”

    “We have shown that this dramatic rise in sea level is associated with an increase in carbon dioxide levels of about 100 parts per million, a huge change,” Tripati said. “This record is the first evidence that carbon dioxide may be linked with environmental changes, such as changes in the terrestrial ecosystem, distribution of ice, sea level and monsoon intensity.”

    Today, the Arctic Ocean is covered with frozen ice all year long, an ice cap that has been there for about 14 million years.

    “Prior to that, there was no permanent sea ice cap in the Arctic,” http://newsroom.ucla.edu/portal/ucla/last-time-carbon-dioxide-levels-111074.aspx

  17. Raul M. says:

    Back in early 40′s before dad went to WW2,
    mom had taken pictures of his canoe filled
    with turtles he was taking back to UF to the
    biology class from the Itchtucknee river.
    When I first saw those pictures many years
    later I was amazed at how many large river
    turtles there were. They said yes the river
    had been filled with them.
    Going down the river in receint times, I may
    say, there are no large numbers of large or
    otherwise turtles.
    Times have changed.

  18. Prokaryotes says:

    The Sixth Extinction

    Can we stop the devastation of our planet and save our own species? We are in a biodiversity crisis — the fastest mass extinction in Earth’s history, largely due to:

    * human destruction of ecosystems
    * overexploitation of species and natural resources
    * human overpopulation
    * the spread of agriculture
    * pollution

    Harvard biologist E.O. Wilson estimated that Earth is currently losing something on the order of 30,000 species per year — which breaks down to the even more daunting statistic of some three species per hour. Some biologists have begun to feel that this biodiversity crisis — this “Sixth Extinction” — is even more severe, and more imminent, than Wilson had supposed. http://www.actionbioscience.org/newfrontiers/eldredge2.html

    Now add climate change …

  19. Colorado Bob says:

    ScienceDaily (Aug. 17, 2010) — The Wildlife Conservation Society has released initial field observations that indicate that a dramatic rise in the surface temperature in Indonesian waters has resulted in a large-scale bleaching event that has devastated coral populations.

    http://blogs.cqpolitics.com/trailmix/2010/08/open-thread-tuesday-1.html

  20. Colorado Bob says:

    Sorry for the wrong link -
    Massive Coral Mortality Following Bleaching in Indonesia

    http://www.sciencedaily.com/releases/2010/08/100816170839.htm

  21. jorleh says:

    It´s obvious that plus 1C more with the ensuing catastrophes brings us to wars which put end to our species.

    Natural catastrophes in China are the beginning, there are millions of square kilometers of land practically avoid of people in Siberia. Where are the Chinese people going?

  22. Colorado Bob says:

    Raul M. @ 17

    Why Do We Destroy the Nature We Love?
    The problem of environmental generational amnesia

    http://www.psychologytoday.com/blog/human-nature/200909/why-do-we-destroy-the-nature-we-love

  23. Raul M. says:

    Yes, Nature deficit disorder could be a somewhat
    neglected description.

  24. Robert says:

    Sen Comn #15

    “Vostok data shows CO2 rising time and again for hundreds of years after the temperature has already started to decline. That is where we need to address the lag, not going up, since “deniers” are agreeing that CO2 indeed causes warming. Until we can do that, the issue remains.”

    Vostok data does NOT show CO2 rising after temperature has started to fall. The only issue I see is why temperatures start to fall at all after CO2 has peaked. This pdf (from a “denier”) explains the issue. Temperatures typically decline over a period of 20K years or so, outpacing the decline in CO2. I searched the IPCC AR4 but could not find any info on it. Perhaps it’s not really of interest to how the climate reverts to a low CO2 / low temperature phase as we are more concerned about the sharp, fast upslope part of the cycle.

    http://icecap.us/images/uploads/CO2,Temperaturesandiceages-f.pdf

  25. Robert says:

    …following up on my last comment, I think the answer lies in the graph on the first page of the pdf link. Temperatures and CO2 fall for 100K years between cycles and the data is very noisy within these periods. The 20K year graphs are made up by aggregating data from all 4 cycles but the comparison of CO2 and temperature within the 20K year timeframe is flawed and only shows temp falling faster than CO2 due to noise in the data. The same comparison over the full 100K year period clearly does not show the same effect – CO2 and temp fall at proprtionately equal rates.

    If you have other data to shed light please post links.

  26. Prokaryotes says:

    It’s called natural carbon sequestration, such as azolla events – happening on timescales of hundred thousand years.

  27. Jeffrey Davis says:

    Milankovich forcings are around an order of magnitude smaller than those from today’s greenhouse gas emissions.

    So, the thing to take away from the graphs of CO2 concentrations and temps over the last hundreds of thousands of years is the fact that the line goes practically perpendicular to the x-axis. When atmospheric radiation equilibrium changes, it doesn’t mess around. The fall takes time, but getting to the peak just happens instantly. Geologically speaking.

  28. Wit'sEnd says:

    Robert, #12

    Scientific research using controlled experiments has demonstrated that ozone increases the incidence of attacks from fungus, disease, insects, and weather. So if bean have a fungus or virus it’s quite likely that the composition of the atmosphere has predisposed them to greater vulnerability. There are links to the research on my blog.

    Also, the damage is too universal. There is not a single species of vegetation that doesn’t show evidence of exposure to ozone, so it cannot be explained by species-specific blights. Grasses are supposed to be the most resistant and last year they looked normal. This year they are turning brown and there are patches of ground with nothing at all but dirt – not even weeds.

    Nature abhors a vacuum. That is not normal.

  29. As Administrator of the Space Coast Climate Change Initiative I have spoken to a broad range of organizations throughout peninsular Florida. So far, none of the attendees have mentioned the CO2 lag and for that I am grateful. I was hoping the Cook piece on the lag would provide a relatively simple answer to the question – but it did not.

    From what I gathered in reading that piece and related replies, CO2 does lag temperature. What am I missing?

  30. Prokaryotes says:

    “What am I missing?”

    The full body of evidence gives us these two facts: warming causes more CO2 and more CO2 causes warming.
    Actually you have to account for all carbon systems and interactions to understand the inter-connectivity of the climate system. The biggest factor seems to be the ocean – which will keep releasing Co2 even if we stop all emissions today.

  31. Robert says:

    Randall #29

    I read your site and was a bit surprised to find that it is all about adaptation. Shouldn’t there be something in there about reducing / halting emissions? Even those not entirely sold on AGW must appreciate that fossil fuels are finite and someday we will stop using them anyway because they will run out. A blind acceptance of rising sea levels and a bit of woolly stuff about developing policies to cope seems unambitious to say the least.

  32. Robert says:

    Wit’s end #28

    “Grasses are supposed to be the most resistant and last year they looked normal. This year they are turning brown and there are patches of ground with nothing at all but dirt – not even weeds.”

    No worries. Technology to the rescue.

    http://earthfirst.com/new-company-offers-green-spray-paint-service-for-dead-lawns/