CO2 and the formation of the Antarctic ice sheet

2009-10-02

in Geek stuff, Science, The environment

Plant with pond scum

Research published in Nature explores the origins of the Antarctic ice sheet during the Oligocene transition, 33.5 to 34 million years ago. The formation of the sheet was apparently triggered by a drop in the atmospheric concentration of carbon dioxide (CO2) below a critical level. The researchers were able to estimate CO2 levels in this time period by examining boron isotope rations in fossils from Tanzania, an approach that was necessary since it is not possible to go so far back on the basis of data from ice core samples. The researchers estimate that the CO2 concentration during this transition period was about 760 parts per million (ppm). That is about twice the level of current atmospheric CO2 concentrations. If the world carries along on its current trajectory of greenhouse gas emissions, the atmospheric concentration of CO2 will be above 1000ppm by 2100.

The operation of the global climate is highly complex, with many significant inputs and internal feedbacks. The researchers specify that the ice sheet displays “a nonlinear response to climate forcing during melting.” Nonetheless, it is worrisome to think that we are on track to exceed the atmospheric CO2 concentration at which the Antarctic ice sheet started to form, and do so well before the end of this century. That being said, even if we do push the climate into a state where the serious or total melting of Antarctica becomes an inevitability, the process may take hundreds or thousands of years to occur. Such long-term impacts seriously complicate economical and ethical analysis of climate change.

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{ 4 comments… read them below or add one }

Sarah October 2, 2009 at 5:43 pm

It might just be that I’m having a stupid day, but this post wasn’t at all self-explanatory to me on the first (or even second) reading. I presume what you are saying is that a fall in CO2 concentrations to level x occurred, meaning a change in temperature at which point the Antarctic ice sheet started to form. The ice sheet presumably then contributed to feedback effects which further lowered temperatures via changes in albido etc. We are currently way below level x in CO2 concentrations, but the concern is that we will reach or exceed level x – at which point by inference the temperature will be too high for ice accumulation in Antarctica and we can be pretty sure the ice sheet will melt. What we don’t know from this research is how fast the ice sheet will recede in response to a given CO2 concentration. Correct?

I am also unclear about this statement: “Nonetheless, it is worrisome to think that we are on track to exceed the atmospheric CO2 concentration at which the Antarctic ice sheet started to form”. Could you expand to say in layman’s terms why this is worrisome, how worrisome, and how this changes our existing understanding of climate change?

Milan October 2, 2009 at 5:50 pm

The study itself doesn’t stress the implications of the research for climate change mitigation planning.

Your summary is right: there was a period before the ice sheet when CO2 concentrations were above 760 ppm. When they were around that level, it started to form. As such, there is reason for thinking that there may be a threshold around there, when it comes to the existence of the Antarctic ice sheet.

Of course, conditions then were different in other ways. Various orbital characteristics were different and (perhaps quite importantly), the continents were arranged a bit differently. Because of that, we can’t say “go above 760 ppm and the Antarctic ice sheet is doomed.” That being said, there is some sense in worrying about whether 1000 ppm risks eventually melting the thing and raising sea level by tens of metres.

Milan February 3, 2010 at 10:55 am

This post is relevant here: Climate change: the solar hypothesis

It discusses the paleoclimatic record before and after Antarctic glaciation.

Peer reviewed science! July 14, 2011 at 10:35 pm

Chen, J. L., Wilson, C. R., Blankenship, D. and Tapley, B. D. 2009. Accelerated Antarctic ice loss from satellite gravity measurments. Nature Geoscience 2:859-862

New satellite data using gravity measurements indicate that ice sheet volume is currently declining over East Antarctica as well as West Antarctica. These results independently support similar conclusions of a previous study using radar data, but contradict earlier results that implied that the East Antarctic ice sheet was stable or slightly increasing in volume.

In 2008, researchers using satellite-based radar technology concluded that there has been a decline in ice volume of both the East Antarctica and West Antarctica ice sheets in recent years. Their results contradicted those from earlier studies that suggested that, while West Antarctica was losing ice, the East Antarctica ice sheet volume was stable or increasing slightly. In a recent issue of Nature Geoscience, researchers from the University of Texas report on new results that independently support the evidence from the radar data. These researchers employed a satellite based gravity measuring instrument to monitor the change in total ice mass over Antarctica since 2002. The results show that, between April 2002 and January 2009, West Antarctica experienced a net average annual loss of 132 billion tonnes of ice. However, East Antarctica also lost a net average of 57 billion tonnes of glacial ice per year, mostly from coastal regions. Most of the loss occurred after 2006. These results suggest that melting Antarctic ice sheets may be contributing more to global sea level rise than previously estimated.

Summary courtesy of Environment Canada

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