Prehistoric Climate Provides Clues to Future Changes

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Patricia Jellison: Hello and welcome to USGS CoreCast. I'm Patricia Jellison. New data on a pre-historic warm period are available that will help understand today's global warming and refine models used to estimate future climate. Today we are joined by USGS scientists Harry Dowsett and Marci Robinson to discuss this research and its implications. Thanks for joining us today, Harry, Marci.

Harry Dowsett: It's a pleasure to be here.

Marci Robinson: It's great to be here.

Patricia Jellison: First, can you tell us about the data that you are releasing?

Harry Dowsett: Sure. We just completed a comprehensive reconstruction of climate conditions on the Earth for a time period known as the Mid-Pliocene Warm Period or about 3.3 to 3 million years ago. These data, which are really the first reconstruction of a period as warm as that it's predicted for the end of this century, are required to help refine climate models and reduce the uncertainty of future climate projections. Initial research on this data show the sensitivity of the climate system to changes in the carbon dioxide levels as well as a strong influence of ocean temperatures, heat transports from equatorial regions, and greenhouse gases on temperature.

 01:12

Patricia Jellison: Why did you study the climate system during this particular period of time?

Harry Dowsett: Well, the latest projections from the Intergovernmental Panel on Climate Change or IPCC are suggesting that mean temperature on the Earth will rise by about 2 to 3 degrees by the end of this century. A lot of climate research is focused on the historical period or even, say, the last 10,000 years, but if you want to really go back and find something, a climate of equivalent magnitude, you need to go back three million years ago to the Mid-Pliocene.

Exploring the Mid-Pliocene is going to tell us a lot about ocean circulation changes, energy transport, the sensitivity of the climate system. All these things are very important for modeling the future planet. Possibly the most important reason for some via global reconstruction for this time period is that it can be used to test or refine climate models that are used to estimate future warming.

 02:03

Patricia Jellison: Tell us a little bit about the team. Who conducted this research?

Harry Dowsett: Research was conducted here at the U.S. Geological Survey by the Pliocene Research, Interpretation and Synoptic Mapping or PRISM Project, but we have collaborators all over the world and all over the country. We rely heavily on colleagues at Columbia University, Duke University, University of Leeds in the U.K. and the British Antarctic Survey. A global reconstruction requires collaborators worldwide and it's a lot of work.

Patricia Jellison: What are the most significant findings?

Harry Dowsett: There are several. This is the first time we actually have temperature estimates from the Arctic Ocean itself and we're seeing maybe 16 degrees Celsius temperatures in the Arctic, which would suggest a great deal of heat being transported by the surface circulation from the tropics to the poles. And in the Pacific Ocean, many other workers have documented what they call a permanent El Niño situation during the Mid-Pliocene, but our new data are the first to show the spatial distribution of these temperatures.

 03:09

The most exciting or important part of the reconstruction is our deep ocean temperature reconstruction. There was seen warming in deep water masses that make a lot of sense with our surface temperatures and they're showing an enhancement of the conveyor belt or thermohaline circulation. We're able to use these data to look at numerical models of climate and these are the models that we use to project future climate conditions. So for the first time, we're going to have a better understanding of how the ocean works during this possible best analog to future climate conditions.

Patricia Jellison: So now we'll turn to Marci. Marci, can you tell us a little bit about the science behind this research?

Marci Robinson: Sure. First, we rely very heavily on fossil plants and animals to tell us what the Earth was like in the Mid-Pliocene. Harry and I study fossil plankton or the organisms that live on the surface of the ocean. We have many other scientists who work with us to study different types of fossil plankton, also fossils that lived on the ocean floors and also pollen.

 04:14

The idea is that if we assume that the plants and animals of the Mid-Pliocene are for the same type of environments as they do today, then we can reconstruct the environment three million years ago. Now remember, three million years ago wasn't that long ago in geologic terms. The continents were in their positions that they are now, oceanic circulation was much the same, but most importantly, the plants and animals that were alive three million years ago are still alive today for the most part.

So in order to do the reconstruction, we start with deep-sea cores or cores from on land and we start with sediment cores. We take them to the lab, we wash them to get the microfossils out, we look at the different species of plants or animals that live at these specific locations three million years ago. We can get an idea of what environment they lived in then.

 05:15

We can also look at the shells themselves to get the different ratio of elements inside. That also gives us an indication of not only temperature but also the amount of ice on the planet. We look at the organic molecules in the sediment, too, and that can also relate to temperature. On land, we don't get a temperature signal as much as we get a distribution of vegetation. We can also reconstruct sea level. We can look at the ancient shorelines and we can know how much ice there was. We can also adjust the topography. For example, the Great Lakes and other glacial features weren't there because those are features left over by the ice ages, and the Mid-Pliocene was from before the ice ages.

Patricia Jellison: From your perspective, could you share with us the most interesting part of the research and your view of the importance of it?

Harry Dowsett: I'm a geologist, so Earth history is fascinating. But I guess the most interesting part of this kind of research for me is seeing how the data and reconstruction is being used by climate modeling groups to refine the computer models. That's how they reduce uncertainty in future climate projections.

 06:07

Climate change is happening. It's something our children are going to have to deal with in a very real way. Knowing what we're doing is making a difference is both rewarding and a reason to produce the very best science that we can.

Marci Robinson: I also want to add how exciting it's been to bring together so many different disciplines to work on one project that's such a global scale. It's also very exciting to work on this time period because it's the last warm interval before the Ice Age has started and a very pivotal part of our climate history.

Patricia Jellison: Well it's been a pleasure speaking with you. Thank you for joining us. And thanks to all of you for listening to this episode of CoreCast. To learn more about this research and to view the compiled data, visit geology.er.usgs.gov/eespteam/prism. As always, CoreCast is a product of the U.S. Geological Survey, Department of the Interior.

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Mentioned in this segment:

• PRISM: Global Warming Analysis