Rainforest Response to Pennsylvanian Global Warming

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If global warming runs its course, what will be the effects on our planet? More specifically, how will the Earth's richest ecosystems - the tropical rainforests - cope with future changes? Some of the answers to these questions may lie in the ancient geological past. Three hundred million years, the Earth experienced global warming on a massive scale, completely melting the polar icecaps. About the same time, the tropical rainforests began to dieback. Did global warming trigger extinction? Not everyone agrees. Others point the finger at the jostling of the Earth's tectonic plates that forced up a Himalayan-scale mountain belt on the edge of the tropics. They claim that changes in elevation and geomorphology caused rainforest wipeout. From 2008-2013, I plan to lead a large team of international experts to investigate this important sequence of events in enormous detail. We want to know exactly how and why rainforest dieback occurred. Was it a slow protracted decline or an abrupt crunch, and was global warming or mountain building responsible? To achieve this end, we intend to work in the underground coalmines of Illinois, Kentucky and Indiana, USA. Here spectacular fossilized forests are preserved that date from the crucial time period. When we first reported these amazing discoveries back in April, they really captured the public imagination and triggered something of a 'media frenzy'. The extraordinary thing about these fossil forests is that they have been unearthed over thousands of hectares (the size of a city). This allows geologists like me to literally walk through the forests and see how species make-up changed across the ancient landscape. This shows us the forests were very complex, patchy ecosystems much like rainforest today. My team has now identified seven fossil forests stacked on top of each other. The fossil forests span a period of about two million years and crucially date from before and after the rainforest dieback. By studying these forests we can learn exactly how dieback occurred. What species were lost? How did ecosystems reorganize? How abrupt was the change? Of course, understanding rainforest dieback in this kind of detail doesn't tell us the cause. However, our North America rainforests were located more than a thousand kilometers from the nearest mountain belt, so we can rule out that option that a cause of change. So what about global warming? To find out what the climate was doing during the extinction event we plan to study pores in the leaves of the fossil trees called to stomata. Stomata allow plants to absorb carbon dioxide. Studies have shown that the more carbon dioxide there is the air, the less stomata plants produce. So, in effect, fossil leaves allow us to detect changes in the carbon dioxide levels. As carbon dioxide is an important greenhouse gas, changes in its concentration will affect climate. My colleagues will use other techniques using fossil soils to get independent estimates of past carbon dioxide levels. Together we will put together a high-resolution record of climate change through the key time interval. We will then see how the timing of climate change corresponds with the timing of rainforest dieback. Of course, even if it turns out that two events coincide, it doesn't necessarily mean that climate change caused rainforest dieback. You can never prove 'cause and effect' in the fossil record. However, colleagues will input our findings into computer climate simulations. This will test to see whether our observed climate change would lead to the observed rainforest dieback. This will help support any inferences we make about climate change and extinction. Although our three hundred million year old rainforests are not directly comparable to modern rainforests, our work will generally contribute to discussion on the nature and rate of rainforest dieback in the face of climate change, and help us better predict future changes.