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Phase I: Imaging the Greenhouse World

Phase II: Drilling the Greenhouse World

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Looking back into Our Future

A growing body of knowledge indicates that these changes are due to increased concentrations of greenhouse gases such as CO2 in our atmosphere. Predictions of future atmospheric CO2 levels expected to occur by the end of this century range from 500 to 900 ppm.

The figure on the left is ice volume estimates from Pekar and Christie-Blick (2008) between 16 and 34 Ma and Miller et al. (2005) between 34 and 45 Ma.

The figure on the right are pCO2 estimates from Pagani et al. (2005) that show decreasing values during the Oligocene, reaching pre-industrial levels by the latest Oligocene and continuing into the early Miocene. The range shown in pCO2 is due to the uncertainty involved in using carbon isotopic composition of sedimentary alkenones (13C 37:2). The green and red lines represent pre-industrial values (280 ppm) and present-day levels (385 ppm, respectively, while the shaded box represent values that are predicted for the present to occur this century (Watson et al., 2001).

The last time that atmospheric CO2 levels were this high occurred between 25 and 40 million years ago. During this time, the Antarctic ice sheet was far more dynamic, retreating hundreds of miles inland during warm periods, which resulted in sea level rises of over a hundred feet, while during colder periods, the ice sheet expanded across the Antarctic shelf and grew in some case to larger than today. Additionally, it was also during this period (~34 million years ago) that one of the most dramatic and permanent climatic changes occurred of the last 100 million years: the abrupt change from greenhouse world conditions (older than 34 million years ago) in which ice sheets were either absent of ephemeral in nature to an icehouse world in which large continental sized ice sheets expanded across Antarctica (<34 million year ago). Scientists are still struggling to understand what were the causal mechanisms that resulted in this tipping point that switched the world climate dramatically especially in Antarctica. State-of-the-art climate models, combined with paleoclimatic proxy data suggest that the main triggering mechanism for initial inception and development of the Antarctic Ice Sheet were the decreasing levels of CO2 concentration in the atmosphere and that the opening of critical Southern Ocean gateways only played a secondary role. Additionally, as this time interval is the last time that atmospheric CO2 was as high as what is predicted for this century and was considerably warmer than today, studying this period may be able to provide us with a glimpse of our future.

 

 

 

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