How ancient warm periods can help predict future climate change

Several more decades of increased carbon dioxide emissions could lead to melting ice sheets, mass extinctions and extreme weather becoming the norm. We can’t yet be certain of the exact impacts, but we can look to the past to predict the future.

We could start with the last time Earth experienced CO2 levels comparable to those expected in the near future, a period 56m to 34m years ago known as the Eocene.

The Eocene began as a period of extreme warmth around 10m years after the final dinosaurs died. Alligators lived in the Canadian Arctic while palm trees grew along the East Antarctic coastline. Over time, the planet gradually cooled, until the Eocene was brought to a close with the formation of a large ice sheet on Antarctica.

During the Eocene, carbon dioxide (CO2) concentrations in the atmosphere were much higher than today, with estimates usually ranging between 700 and 1,400 parts per million (ppm). As these values are similar to those anticipated by the end of this century (420 to 935ppm), scientists are increasingly using the Eocene to help predict future climate change.

We’re particularly interested in the link between carbon dioxide levels and global temperature, often referred to as “equilibrium climate sensitivity” – the temperature change that results from a doubling of atmospheric CO2, once fast climate feedbacks (such as water vapour, clouds and sea ice) have had time to act.

To investigate climate sensitivity during the Eocene we generated new estimates of CO2 throughout the period. Our study, written with colleagues from the Universities of Bristol, Cardiff and Southampton, is published in Nature.

Reconstruction of the 40m year old planktonic foraminifer Acarinina mcgowrani.
Richard Bizley ( and Paul Pearson, Cardiff University, CC BY

As we can’t directly measure the Eocene’s carbon dioxide levels, we have to use “proxies” preserved within sedimentary rocks. Our study utilises planktonic foraminifera, tiny marine organisms which record the chemical composition of seawater in their shells. From these fossils we can figure out the acidity level of the ocean they lived in, which is in turn affected by the concentration of atmospheric CO2.

We found that CO2 levels approximately halved during the Eocene, from around 1,400ppm to roughly 770ppm, which explains most of the sea surface cooling that occurred during the period. This supports previously unsubstantiated theories that carbon dioxide was responsible for the extreme warmth of the early Eocene and that its decline was responsible for the subsequent cooling.

We then estimated global mean temperatures during the Eocene (again from proxies such as fossilised leaves or marine microfossils) and accounted for changes in vegetation, the position of the continents, and the lack of ice sheets. This yields a climate sensitivity value of 2.1°C to 4.6°C per doubling of CO2. This is similar to that predicted for our own warm future (1.5 to 4.5°C per doubling of CO2).
Our work reinforces previous findings which looked at sensitivity in more recent time intervals. It also gives us confidence that our Eocene-like future is well mapped out by current climate models.

Fossil foraminifera from Tanzania – their intricate shells capture details of the ocean 33-50m years ago.
Paul Pearson, Cardiff University, CC BY

Rich Pancost, a paleoclimate expert and co-author on both studies, explains: “Most importantly, the collective research into Earth history reveals that the climate can and has changed. And consequently, there is little doubt from our history that transforming fossil carbon underground into carbon dioxide in the air – as we are doing today – will significantly affect the climate we experience for the foreseeable future.”

Our work also has implications for other elements of the climate system. Specifically, what is the impact of higher CO2 and a warmer climate upon the water cycle? A recent study investigating environmental change during the early Eocene – the warmest interval of the past 65m years – found an increase in global precipitation and evaporation rates and an increase in heat transport from the equator to the poles. The latter is consistent with leaf fossil evidence from the Arctic which suggests that high precipitation rates were common.

However, changes in the water cycle are likely to vary between regions. For example, low to mid latitudes likely became drier overall, but with more intense, seasonal rainfall events. Although very few studies have investigated the water cycle of the Eocene, understanding how this operates during past warm climates could provide insights into the mechanisms which will govern future changes.
The Conversation
This blog was written by Cabot Institute member Gordon Inglis, Postdoctoral Research Associate in Organic Geochemistry, University of Bristol and Eleni Anagnostou, Postdoctoral Research Fellow, Ocean and Earth Science, University of Southampton

This article was originally published on The Conversation. Read the original article.

India-UK scientific seminar: Developing new records of global change

The Royal Society of London, which was founded in November 1660, is the oldest existing scientific society with a long history of working internationally. Indeed, in 1723, the Royal Society established the post of Foreign Secretary, nearly 60 years before the British government did. In 2014, science remains a global endeavour which requires both international discussion and collaboration. In order to facilitate international and collaborative study, the Royal Society recently funded a three-day seminar for Indian and UK climate scientists. The aim of the proposal was to help develop new records of past global change in India using a variety of geological and geochemical techniques.

The seminar, hosted by Professor Paul Pearson (Cardiff University) and Professor Pratul Saraswati (IIT Bombay), was held in Bhuj between the 15th and 18th of January. Bhuj is a relatively small city in the district of Kutch and is located approximately 100km from the Indian-Pakistan border. In 2001, Bhuj was devastated by a magnitude 7.7 earthquake. The death toll approached 20,000 and over 600,000 people were made homeless. However, since then, Bhuj has become an outstanding example of a town rebuilt from scratch thanks to government support and corporate involvement. The city has become the focal point of western India’s growth and more than 200 companies have been established in the region since 2001. Of particular importance is the cement manufacturing industry which exploits the abundance of lime- and clay-containing materials (e.g. limestone and shale).

The UK was represented by five scientists whose research encompassed the major disciplines in past climate research. Attendees were selected from a range of universities, including two participants from the Cabot Institute at the University of Bristol (Dr. Dan Lunt, a climate modeller based in the School of Geography, and myself, Gordon Inglis, an organic geochemist based in the School of Chemistry). Ten Indian scientists were also in attendance, including members from academia and industry. The primary aim of the seminar was to develop stronger international collaborations between India and the UK, with an emphasis upon developing new climate records from the Indian continent. The first two days were designated for individual presentations and focused upon the regional geology of India and a variety of analytical techniques available to both parties. The third day was spent in the field and allowed participants to visit the geological successions discussed in the seminar.

A particular highlight was a visit to the Deccan Traps. Encompassing most of central and western India, the Deccan Traps is the world’s largest continental flood-basalt province outside Siberia. The eruption is thought to occur between 68 and 65 million years ago, approximately coinciding with the Cretaceous-Paleogene mass extinction event, and is associated with the demise of the dinosaurs and other marine and terrestrial species. Although the event has been attributed to a large bolide impact in Mexico, the Deccan Traps were almost certainly a major contributor to this extinction. Ken Caldeira, an atmospheric scientist who works at the Carnegie Institution, has argued that the Deccan Traps may have been responsible for a 75ppm increase in carbon dioxide during this interval. Although this is relatively small in geological terms, it is comparable to the increase in CO2 that has occurred over the past 50 years as a result of anthropogenic climate change. In more recent times, geologists are studying whether the Deccan Traps can store CO2 derived from coal-fired power stations in an attempt to reverse anthropogenic climate change.

Although the visit to India was brief, the seminar was a success and both Indian and UK scientists showed a great deal of enthusiasm for developing future collaborations. In particular, there is great scope to reconstruct past climate records over the past 70 million years and how that has corresponded to major biotic events.

This blog was written by Gordon Inglis, a PhD student in the School of Chemistry.
You can follow Gordon on Twitter (@climategordon)

For information on Royal Society funding opportunities, click here.