Unlocking the Past for Clues to the Future of Greenland’s Ice Sheet


Glacial geologists Maggie Jackson (left), Lauren Farnsworth (center) and Gordon Bromley (right) hiked long miles over bouldery terrain every day, in search of ideal glacial features to be sampled for cosmogenic surface exposure dating.  Dates on glacial landforms help to clarify how the Greenland Ice Sheet and local ice caps responded to past climate change in the Thule region. Photo by Alex P. Taylor. What can the past tell us about the future? That’s the question ice core specialist Erich Osterberg and a multi-disciplinary team of scientists is trying to answer. Their project, Response of the Northwest Greenland Cryosphere to Holocene Climate Change, is supported by the National Science Foundation.

Osterberg, an assistant professor at Dartmouth College, and his colleagues Meredith Kelly (Dartmouth), Yarrow Axford (Northwestern) and Sean Birkel (University of Maine) have spent the past two years gathering ice core, sediment core and landscape data to help them reconstruct past climate-driven changes in the region and understand how glaciers responded to those changes.

This month Osterberg explains how what they learn about the past will be used to help us understand how the Greenland ice sheet may respond under different climate scenarios many years from now.

Field Notes (FN): How far back in to Greenland’s climate history are you interested in studying?

Erich Osterberg (EO): Our focus is on the last 10,000 years, when the climate was not too dissimilar from today’s climate. Records tell us that around 6,000 years ago, the climate in Greenland was a little bit warmer than today by a degree or two. We are able to see how the ice sheet responded then and that will allow us to tune our models and run them in to the future.

Ryan O'Grady (right), Eric Lutz (center) and Fredrik Eriksson (left) recover a sediment core from a frozen lake during the spring expedition. The small rock at the bottom of the core (in Ryan's hand) suggests that the entire Holocene record was recovered in this 1 m core. Photo: Erich Osterberg.

FN: Why focus on northwest Greenland’s ice sheet versus other ice-covered areas?

EO: When we are thinking about changes in climate, melting glaciers and rising sea level, Greenland is where a lot of change is happening right now. Over the last 10 years or so, the ice sheet on Greenland has started to melt more rapidly due to rising temperatures. That melting started in the southern part of the ice sheet and has been slowly migrating northward, up the coast.

We decided to go to northwest Greenland because it appeared—from other published reports—that northwest Greenland was just about to start responding to this warming. So we could see it moving up the west coast through published papers and we wanted to get in there and see if we could find evidence about what happened when climate had been warmer in the past. Then we could use that as a window to what we think will happen in the future.

Professor Yarrow Axford (right) Jamie McFarlin (left) and Everett Lasher (center) show off a sediment core recovered from a small non-glacial lake near the Greenland Ice Sheet margin.  Photo: Alex P. Taylor.

FN: What types of data do you and your partners collect in order to tell you how northwest Greenland looked over the last 10,000 years?

EO:What’s really neat about this project is that we are a collaborative group of four project leaders—Meredith Kelly and I here at Dartmouth College, Yarrow Axford at Northwestern University and Sean Birkel at the University of Maine. We each have different areas of expertise that can come at this problem from a slightly different direction.

My specialty is looking at past climate using ice core records. We’ve collected ice cores from the coastal areas of the northwest Greenland ice sheet, as well as from independent ice caps that are right on the coast. These will help us better understand how climate has changed in the past.

Yarrow Axford has expertise collecting and studying sediment core records from lakes in front of the ice sheet. Her records give us a good understanding about how summertime climate varied in the past, especially temperature.

Meredith Kelly looks at how the landscape has changed over time. She tracks the edges of the ice sheet and glaciers back through time by studying and dating the materials the glaciers leave behind as they retreat.

Finally, Sean Birkel is a glacier and climate modeler. He can take all these data that we collect in the field and use them to calibrate his models and better understand what happened in the past, and then predict what will happen in the future under different scenarios.

FN: How far in to the future can the models project?

EO: We tend to run the models for about 100 years in to the future, until the end of the 21st century - and that’s the convention in climate change science. But there’s no particular reason why models should stop there. Because Greenland is such a huge piece of ice, it’s a little misleading because it can take hundreds of years or more for the ice to come in to balance with the higher temperatures that we are predicting. So we’ll do the traditional analysis going out to the year 2100, and then we’ll probably extend that a little bit further to see what will happen over the next several hundred years.

FN: How can delving in to an area’s climatologic past tell you about its future?

EO: The past is our record of how the earth really behaved. It’s what keeps us grounded in reality of how the climate system works. If we can understand what happened with climate in the past, and we can understand how the Greenland ice sheet responded to these changes, then it really improves our fundamental understanding of how the climate system works.

Looking to the past is also important for our climate models. We need the models to project in to the future. However, the only way we can confirm that these models work well is by using them to look in to the past and see if they can reproduce what we see in the field. So it’s a way for us to improve our understanding and it’s also a way for us to test the models that we are going to use to forecast the future.

FN: This project also has an education component to bring climate science to K-12 students. Tell us more about that.

EO: Yes, the PIs and our graduate students meet with local K-12 students to talk about climate change and glaciers, and we also participate in national science and engineering festivals where K-12 students from all over the country come to learn about science.

Project PI Sean Birkel also developed a really amazing online K-12 teaching tool called the Environmental Change Modelthat’s accessible to anyone. Typically the climate models we use are extremely complex. But Sean has simplified his climate model into a web interface where students can adjust different factors and see how the climate responds. They don’t need to take somebody’s word for what happens when temperature goes up; they can ramp up temperature in the model themselves and witness the response. This gives them a much more fundamental understanding of how the climate system works and makes them more informed citizens. Ultimately, changes in the environment will have an impact on all of us and it’s up to us to decide how we want to respond.

FN: What’s next?

EO: We have reams of fantastic data both from the 2012 season and this past season. So the next phase is pulling all of these different data sets together to get a really comprehensive understanding of what’s going on. That’s the exciting part of the project and what we’ve been waiting to do! The stress of collecting the records from Greenland is over. Now we have the records and get to sit down and put it all together.

Click here for more information on Erich Osterberg’s collaborative project.