Research Fellows Directory
Professor Gavin Foster
University of Southampton
The Earth’s climate varies naturally on a number of timescales. The longest and most grandest of climate cycles is the icehouse/greenhouse cycle when the Earth switches from warm climate states with no continental ice (a greenhouse) to colder states with continental ice (an icehouse, like today) every 300 million years or so. By studying these long, slow, natural cycles in climate I have demonstrated last year that the most recent transition from greenhouse to icehouse around 50 million years ago was associated with a decline in atmospheric CO2. This not only underlines the importance of this greenhouse gas in driving Earth’s climate, but also offered us an opportunity to determine that the sensitivity of climate system to CO2 change was similar in the warm Eocene to what is expected given the output of climate models. By looking further back in time and considering the last 420 million years, that contain two such greenhouse/icehouse cycles, I also demonstrated this year that this association with CO2 change remains strong. However, an additional insight provided by this longer term view concerns the context of future climate change. If we continue to burn fossil fuel at an ever increasing rate the IPCC predict that by 2250 atmospheric CO2 levels will be 2000 ppm or more. This is likely higher than any time in the last 65 million years, and we have to go back to 200 million years ago to the Triassic when early dinosaurs roamed the Earth until CO2 was as high as this. But what was different then was the Sun’s output was reduced compared to today. When we factor in the combined effect of solar forcing and CO2 forcing, the climate system of this business-as-usual future has no analogue in the last 420 million years as far as we can tell. What does this mean? Well, we are not only changing the climate much faster than natural processes operate but if we carry on, we are going to enter a climate state that complex life has never experienced.
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