Hothouse climates of the past – lessons for the future

Some of the world’s leading climate change scientists will be in Bristol next week to discuss extreme warm climates throughout the history of the earth and how they help us understand the future of our planet.

The workshop on May 22 and 23 will be hosted by the University of Bristol’s Cabot Institute which carries out fundamental and responsive research on risks and uncertainties in a changing environment.

When people think of climate change, we typically think of global warming and higher sea levels.

However, to fully understand the consequences of climate change – and how it will most affect life on Earth including human society – we must understand a vast variety of physical, biological and chemical processes.

How, when and where will rainfall change? How will more extreme weather events affect our cities but also the landscape and its soil? How will changes in acidity, temperature and runoff from land affect coral reefs and other marine ecosystems?

The workshop, at Bristol’s M Shed and funded by a European Research Council grant – The Greenhouse Earth System (TGRES) – will explore those processes through the lens of ancient climate systems that could be analogues for our future.

Professor Rich Pancost , the Principal Investigator of the project in the Organic Geochemistry Unit and Director of the Cabot Institute, said the past is not a perfect representation of the future but it can help us understand it and discover the processes that will become important as the world warms.

He added: "We think that it has been about three million years since the atmosphere had 400 ppm (parts per million) carbon dioxide and 30 to 50 million years since it had 1,000 ppm. We are now beginning to understand the consequences of a more than 400 ppm CO2 world because we have reached it (at this moment atmospheric CO2 levels are 410 ppm compared to 280 ppm prior to the industrial revolution).

"Extreme weather events are increasing, Artic sea ice is disappearing, and coral reefs are being devastated. If we want to anticipate what will happen if we reach 1,000 ppm CO2, looking deep into the past is a very useful tool."

Professor Dan Lunt from the School of Geographical Science’s BRIDGE Group and lead of a new project that will explore past temperature change explained: "One of the most important questions is the temperature response to a change in carbon dioxide concentrations.

"Our approaches generally confirm that this was about the same in the past as anticipated for the future – about 3⁰C of warming for every doubling of carbon dioxide concentrations."

Gavin Foster of the University of Southampton and a keynote speaker added: "We have recently made great strides in understanding climate sensitivity. By and large, the models have it right; higher atmospheric CO2 means higher temperatures. But the models seem to consistently underestimate reconstructed past polar warming. So although the models are broadly correct with respect to the magnitude of change, questions remain regarding how accurately they simulate the patterns of this change."

The workshop is being led by Dr David Naafs , a Research Fellow in the School of Chemistry Organic Geochemistry Unit.

He said: "It is important to understand the extent of warming but the workshop wants to move beyond that to explore the impacts of warming.

"The Earth system is diverse and complex and we cannot explore all of these possible consequences, but we are looking at some of the major ones: changes in the water cycle, in erosion and the land surface, the cycling of other important greenhouse gases such as methane, and the impact of these land-based processes on the oceans."

The workshop will feature many UK and international scientists, including Sarah Feakins of the University of Southern California.

She said: "We know that ancient warm times offer important lessons. What’s important about this workshop is that it brings together those who study Earth’s past, but not for purely ’academic’ reasons.

"Our mission is to shine light on the climate problems of the future. We know it’s getting warmer and we know why, but we have critical gaps in our understanding, for example, about water. In many places models can’t yet predict whether it will get wetter or drier – and that’s obviously a big problem for readying society for change. The past can really help to nail down how and why rain-belts shift, and that’s why I study rainfall across warm periods of the past 20 million years."

Professor Pancost said: "Increased carbon dioxide concentrations will cause global warming. The past confirms that.

"This global warming will likely exacerbate extreme weather, disrupt ecosystems and undermine food production. The past does not confirm that those things will happen but it certainly confirms that they have happened – and could happen again. They are real and potentially devastating risks. Our goal is to better understand those risks."