Rising CO2 Levels Linked to Global Warming During Last Deglaciation

[Vergent]

http://www.sciencedaily.com/releases/2012/04/120404133702.htm

http://www.nature.com/nature/journal/v484/n7392/full/nature10915.html

[dabize]

Nice to see this come out as concrete science (as opposed to the only reasonable assumption).

Unfortunately, anyone capable of ignoring the contribution of CO2 levels to warming despite a) the physical reality of the CO2 mediated greenhouse re-emission of longwave radiation and the tightly linked changes between temp and CO2 levels (never mind which comes first) will have no trouble ignoring this as well, I fear.

You'll get pseudoarguments like "Stone age humans couldn't have caused the post YD warming!"

[PhillipS]

http://www.scienceda...20404133702.htm

http://www.nature.co...ature10915.html

Thank you for the links. That's an interesting article and it will be very interesting to see how the conclusions hold up. Ideally, this would quiet some of the endless pseudo-skeptical chanting of "CO2 lagged temperatures so it can't have much effect!". Nah, that's just wishful thinking on my part - pseudo-skeptics will continue their willful ignornce of actual climate science. (sigh)

I have long been leery of the so-called lag between the paleo temperature record and the paleo CO2 record because of the difference in the data collection methods. The CO2 data are direct measurements of the CO2 levels in tiny bubbles in the ice cores, and have small error bars. On the other hand, the paleo temperature reconstructions are all derived from proxy measurements (oxygen isotopes in the ice cores, IIRC) and have much larger error bars - particularly when regional measurements are extrapolated to global values. The apparent 800 year lag fell into the grey area of data uncertainty between different data series..

And now this study concludes that CO2 doesn't lag global temperatures after all, corroborating the theory that CO2 levels are a major driver of climate change.

[dabize]

Thank you for the links. That's an interesting article and it will be very interesting to see how the conclusions hold up. Ideally, this would quiet some of the endless pseudo-skeptical chanting of "CO2 lagged temperatures so it can't have much effect!". Nah, that's just wishful thinking on my part - pseudo-skeptics will continue their willful ignornce of actual climate science. (sigh)

I have long been leery of the so-called lag between the paleo temperature record and the paleo CO2 record because of the difference in the data collection methods. The CO2 data are direct measurements of the CO2 levels in tiny bubbles in the ice cores, and have small error bars. On the other hand, the paleo temperature reconstructions are all derived from proxy measurements (oxygen isotopes in the ice cores, IIRC) and have much larger error bars - particularly when regional measurements are extrapolated to global values. The apparent 800 year lag fell into the grey area of data uncertainty between different data series..

And now this study concludes that CO2 doesn't lag global temperatures after all, corroborating the theory that CO2 levels are a major driver of climate change.

Good summary. I was thinking that even if the CO2 levels followed the temp rise a little, the tight link suggested sonme kind of synergistic link between the two consistent with the status of CO2 as a GHG.

but this paper (and your summary) make it much more definite than that......

[TerryM]

Good summary. I was thinking that even if the CO2 levels followed the temp rise a little, the tight link suggested sonme kind of synergistic link between the two consistent with the status of CO2 as a GHG.

but this paper (and your summary) make it much more definite than that......

If anyone comes across a free copy of the paper I 'd like to spend some time with it. I've been interested in the Younger Dryas, and have been following the 'black band' across the continent. I'd have to see how this new study compares with what i think I already know about the period.

Terry

[donsutherland1]

Very interesting paper.

The conclusion:

Our global temperature stack and transient modeling point to CO₂ as a key mechanism of global warming during the last deglaciation. Furthermore, our results support an interhemispheric seesawing of heat related to AMOC variability and suggest that these internal heat redistributions explain the lead of Antarctic temperature over CO₂ while global temperature was in phase with or slightly lagged CO₂. Lastly, the global proxy database suggests that parts of the northern mid to high latitudes were the fist to warm after the LGM, which could have initiated the reduction in the AMOC that may have ultimately caused the increase in CO2 concentration.

NOTE:

AMOC = Atlantic Meridional Overturning Circulation

LGM = Last Glacial Maximum

[cmc0605]

Thank you for the links. That's an interesting article and it will be very interesting to see how the conclusions hold up. Ideally, this would quiet some of the endless pseudo-skeptical chanting of "CO2 lagged temperatures so it can't have much effect!". Nah, that's just wishful thinking on my part - pseudo-skeptics will continue their willful ignornce of actual climate science. (sigh)

I have long been leery of the so-called lag between the paleo temperature record and the paleo CO2 record because of the difference in the data collection methods. The CO2 data are direct measurements of the CO2 levels in tiny bubbles in the ice cores, and have small error bars. On the other hand, the paleo temperature reconstructions are all derived from proxy measurements (oxygen isotopes in the ice cores, IIRC) and have much larger error bars - particularly when regional measurements are extrapolated to global values. The apparent 800 year lag fell into the grey area of data uncertainty between different data series..

And now this study concludes that CO2 doesn't lag global temperatures after all, corroborating the theory that CO2 levels are a major driver of climate change.

You're misunderstanding the study a bit (and I agree the "skeptics" misrepresentation of the ice core records for a decade now never helped the public understanding in paleoclimate or climate change).

What the study suggests is that CO2 did in fact lag Antarctic temperatures, just as previous studies (e.g., Caillon et al., 2003) suggested, though the "800 year" number referred to a different deglacial period, not the most recent one, and has been revised downward a bit (e.g., see Luthi et al 2008 in Nature). But CO2 provides a good globalizer of climate change, and so probably led global temperatures (since Antarctica led the Northern Hemisphere and the global average). This is pretty consistent with what a few other recent papers have shown. The pacing for this comes from orbital forcing (via Milankovitch cycles) though the authors propose interesting communications between boreal summer insolation, the ocean, and Antarctic temperatures, though I agree with the commentary that supplemented the paper in Nature that there's still a lot of work to be done to connect this with previous interglacials and to find a robust mechanism for the CO2 change.

[PhillipS]

You're misunderstanding the study a bit (and I agree the "skeptics" misrepresentation of the ice core records for a decade now never helped the public understanding in paleoclimate or climate change).

What the study suggests is that CO2 did in fact lag Antarctic temperatures, just as previous studies (e.g., Caillon et al., 2003) suggested, though the "800 year" number referred to a different deglacial period, not the most recent one, and has been revised downward a bit (e.g., see Luthi et al 2008 in Nature). But CO2 provides a good globalizer of climate change, and so probably led global temperatures (since Antarctica led the Northern Hemisphere and the global average). This is pretty consistent with what a few other recent papers have shown. The pacing for this comes from orbital forcing (via Milankovitch cycles) though the authors propose interesting communications between noreal summer insolation, the ocean, and Antarctic temperatures, though I agree with the commentary that supplemented the paper in Nature that there's still a lot of work to be done to connect this with previous interglacials and to find a robust mechanism for the CO2 change.

I stand corrected. Thanks!

[donsutherland1]

What the study suggests is that CO2 did in fact lag Antarctic temperatures, just as previous studies (e.g., Caillon et al., 2003) suggested, though the "800 year" number referred to a different deglacial period, not the most recent one, and has been revised downward a bit (e.g., see Luthi et al 2008 in Nature). But CO2 provides a good globalizer of climate change, and so probably led global temperatures (since Antarctica led the Northern Hemisphere and the global average).

The paper offers an explanation as to why Antarctica was an exception. Elsewhere, CO2 did not lag the temperature rise. The skeptics typically used Antarctica as a proxy for global temperatures. The paper shows that Antarctica was an exception and not representative of what happened globally.

[cmc0605]

Indeed, though note they do report some small changes elsewhere before CO2 levels rose, but you do need the CO2 to get the big global warming you see coming out of the LGM to the Holocene. The orbital forcings themselves are very small globally.

[WeatherRusty]

Indeed, though note they do report some small changes elsewhere before CO2 levels rose, but you do need the CO2 to get the big global warming you see coming out of the LGM to the Holocene. The orbital forcings themselves are very small globally.

This is what the science has long been assuming. The small orbital forcing needs to be augmented by the full assortment of feedback mechanisms including CO2, H2O and shifts in albedo. In order for this to work, net feedback must be significantly net positive and equilibrium climate sensitivity in the range so far determined. ~2 to 4.5C for a forcing equal to that of a doubling of CO2 or 3.7W/m^2.

[bluewave]

Another paper this week links PETM warming to the release of CO2 and methane from thawing permafrost.

http://www.umass.edu...cles/150355.php

http://www.nature.co...ature10929.html

"The standard hypothesis has been that the source of carbon was in the ocean, in the form of frozen methane gas in ocean-floor sediments," DeConto says. "We are instead ascribing the carbon source to the continents, in polar latitudes where permafrost can store massive amounts of carbon that can be released as CO2 when the permafrost thaws."

The new view is supported by calculations estimating interactions of variables such as greenhouse gas levels, changes in the Earth’s tilt and orbit, ancient distributions of vegetation, and carbon stored in rocks and in frozen soil.

While the amounts of carbon involved in the ancient soil-thaw scenarios was likely much greater than today, implications of the study appear dire for the long-term future as polar permafrost carbon deposits have begun to thaw due to burning fossil-fuels, DeConto adds. "Similar dynamics are at play today. Global warming is degrading permafrost in the north polar regions, thawing frozen organic matter, which will decay to release CO2 and methane into the atmosphere. This will only exacerbate future warming in a positive feedback loop."

[WeatherRusty]

Another paper this week links PETM warming to the release of CO2 and methane from thawing permafrost.

http://www.umass.edu...cles/150355.php

http://www.nature.co...ature10929.html

"The standard hypothesis has been that the source of carbon was in the ocean, in the form of frozen methane gas in ocean-floor sediments," DeConto says. "We are instead ascribing the carbon source to the continents, in polar latitudes where permafrost can store massive amounts of carbon that can be released as CO2 when the permafrost thaws."

The new view is supported by calculations estimating interactions of variables such as greenhouse gas levels, changes in the Earth’s tilt and orbit, ancient distributions of vegetation, and carbon stored in rocks and in frozen soil.

While the amounts of carbon involved in the ancient soil-thaw scenarios was likely much greater than today, implications of the study appear dire for the long-term future as polar permafrost carbon deposits have begun to thaw due to burning fossil-fuels, DeConto adds. "Similar dynamics are at play today. Global warming is degrading permafrost in the north polar regions, thawing frozen organic matter, which will decay to release CO2 and methane into the atmosphere. This will only exacerbate future warming in a positive feedback loop."

The permafrost is in much more proximate danger for out gassing massive quantities of methane gas. The land surface is warming faster than the seas. This permafrost source is set to go before any such major release from trapped methane clathrates within the sea floor, although they would be next in line.

We may be relatively safe for a while though, the last interglacial period appears to have reached about 1C warmer than today without triggering a serious run away out gassing. That would likely change however as temp rises to levels 2,3,4,5C above what has occurred for many millions of years.

[dabize]

The permafrost is in much more proximate danger for out gassing massive quantities of methane gas. The land surface is warming faster than the seas. This permafrost source is set to go before any such major release from trapped methane clathrates within the sea floor, although they would be next in line.

We may be relatively safe for a while though, the last interglacial period appears to have reached about 1C warmer than today without triggering a serious run away out gassing. That would likely change however as temp rises to levels 2,3,4,5C above what has occurred for many millions of years.

I am wondering whether the recent changes in sea ice formation pattern (open Barents(z), Kara in February etc.) and thickness http://neven1.typepad.com/blog/2012/04/piomas-april-2012.html (good discussion of thickness pattern change) are suggesting that the thermohaline overturning pattern is changing in a way that would bring a current of warmer water to the sea floor in the ESAS.

I know that conventional calculations suggest that the sea floor clathrates would take a long time to be reached by the 0C isotherm, but I suspect that these calculations do not take convection into account. Convection of 1C+ water past the thawing sea floor would greatly speed up the thaw rate and penetration (think of the convection oven principle).

I believe that this is thought to have been the trigger for the sharp warming spikes that occurred during the PETM, but that it occurred in the North Pacific rather than the Atlantic side Arctic.

[TerryM]

I am wondering whether the recent changes in sea ice formation pattern (open Barents(z), Kara in February etc.) and thickness http://neven1.typepa...april-2012.html (good discussion of thickness pattern change) are suggesting that the thermohaline overturning pattern is changing in a way that would bring a current of warmer water to the sea floor in the ESAS.

I know that conventional calculations suggest that the sea floor clathrates would take a long time to be reached by the 0C isotherm, but I suspect that these calculations do not take convection into account. Convection of 1C+ water past the thawing sea floor would greatly speed up the thaw rate and penetration (think of the convection oven principle).

I believe that this is thought to have been the trigger for the sharp warming spikes that occurred during the PETM, but that it occurred in the North Pacific rather than the Atlantic side Arctic.

I recall linking to a paper that claimed 3C temperature increases in seafloor temperatures in the ESAS back on the 'This is not good' thread. We've had no news on that front recently, and it's easy (or at least comforting) to put it out of mind.

S&S are heading out again this summer and hopefully will bring some kind of clarity to the boiling sea questions.