Q&A: Keeping a Watchful Eye on Earth
From the baking hot savannahs of Africa to the icy cold wastelands of Greenland and Antarctica, Andrew Shepherd has worked in some of the most extreme environments on Earth. In college, he studied astrophysics, and flirted with the idea of pursuing it as a career. But a professor’s warning that few of his classmates would find a permanent job in that field turned him off. Instead he took advantage of a new department of Earth observation science at Leicester University in the UK to follow a career studying our planet’s climate. Now, rather than pointing satellites towards space to observe the stars, Shepherd flips them around to monitor the Earth. He has studied the arid land in Zimbabwe and the ice sheets at Earth’s poles. (From his fieldwork in these places, Shepherd has concluded that it is far better to bundle up warm for the cold than to boil in the heat.) As the director of the Centre for Polar Observation and Modeling in the UK and a professor at Leeds University, Shepherd also has a hand in designing and building new satellites. Physics spoke to Shepherd to learn more about his work.
–Katherine Wright
Your current focus is measuring changes in the amount of ice stored in Antarctica and Greenland. How did you get involved in that?
There are dozens of estimates for how much ice is being lost from the polar ice sheets, some of which my group has produced. But climate scientists and policy makers don't want to pick and choose between different estimates; they need a single, authoritative one. I worked with the European Space Agency (ESA) and the National Aeronautics and Space Administration (NASA), and the world’s leading experts, to pull together all the satellite measurements and deliver a single assessment of polar ice sheet losses. The project, called IMBIE—the Ice Sheet Mass Balance Inter-comparison Exercise—has been really well received. Now the space agencies want us to generate yearly assessments of ice sheet loss to chart its impact on global sea-level rise.
What techniques are used to monitor polar ice?
People have been exploring the polar regions for centuries, but Antarctica and Greenland are simply too large to track on foot. Satellites have solved this problem. We can now measure changes in the flow, thickness, and mass of the polar ice sheets routinely from space. These data have revolutionized our understanding of how Antarctica and Greenland interact with the climate system. Although most satellite orbits don't cover the highest latitudes, some—such as ESA’s CryoSat—have been specially designed for that purpose.
Unfortunately, we can’t measure everything from space. For example, the radio frequencies that we use to survey the bedrock beneath ice sheets can interfere with satellite television and telecommunications, so instead we rely on aircraft measurements.
What questions about polar ice are you trying to answer?
The headline science question is, how much ice is being lost from Antarctica and Greenland? It’s an important question, but there are many other things that we are interested in finding out. For example, how fast can ice sheets flow? Ask a glaciologist today and they'll tell you that some glaciers flow at speeds greater than 15 km per year—you can sit next to Greenland’s Jacobshavn Isbrae glacier during your lunch break and watch it move; it’s that quick. But 10 years ago we thought the maximum speed was only 4 or 5 km per year. The speed is a useful piece of information because it’s an indication of how much ice [is available to] contribute to a future rise in sea level.
Your group is part of several international collaborations. What’s your experience of working with so many other people towards a common goal?
I enjoy it. As scientists, we are able to rely on the expertise of other people; we don't have to have the answer to every problem. In climate and Earth science, problems are often much larger than any one group, or even institution, can solve alone, so teamwork is important.
What’s it like to work in a field that’s often in the political and media spotlight?
This adds excitement to our work: it’s great to know that people are interested in what we do. But it also adds an element of caution. Science moves forward by people challenging what has come before them. It can be daunting to do that in climate science, because it’s easy to be labeled an extremist. If you discover glaciers that aren't shrinking, people assume you are going against an immense body of science. If you find evidence that the future sea-level rise will be higher than the latest predictions, you get labeled an alarmist. But often the worst option is to adopt a central position. If we assume that everyone else is right, and that there is no need to change the way we look at a problem, then we can rapidly slip into a situation where our knowledge ceases to expand.
Know a physicist with a knack for explaining his or her research to others? Write to physics@aps.org. All interviews are edited for brevity and clarity.