Answers from space

Two images: satellite map of Antarctic ice sheet with patches of colour showing areas of elevation change (left) and Mal McMillan wearing running gear smiles to the camera from a hilltop with mountains behind (right) © European Space Agency
Antarctic ice sheet taken from CryoSat2 satellite (left)

Lancaster’s new professor combines his love of mountains and ice, with his mathematical skills and satellite data, to answer questions about how our ice sheets are responding to climate change.

Dr Mal McMillan, who recently became Professor of Earth Observation at the Lancaster Environment Centre, is co-director of the Centre of Excellence in Environmental Data Science (CEEDS), run jointly by Lancaster University and the UK Centre for Ecology & Hydrology.

He uses data from satellites to measure how polar ice sheets are changing, and how this is contributing to sea level rise, to provide evidence for policy makers who are responding to climate change.

“The great thing about satellite remote sensing is the scale and the coverage it gives you. If you want to observe ice sheets you can land on them and take measurements, which gives you the most accurate data but only at one point. What satellites allow you to do is to systematically survey the whole ice sheet.”

His aim is to “provide the best, credible and precise measurements, that provide the evidence base that leads to action in the policy sphere,” with his results informing influential reports, from bodies like the Intergovernmental Panel on Climate Change (IPPC).

Mal first became interested in the polar regions after a visit to Greenland when he was a student, studying maths and philosophy at Edinburgh University.

“I was struck by what an amazing, different environment it was. I enjoyed climbing and going to the Alps, so I think my interest in ice started then.”

Mal pursued his passion for snow and ice when he left university, learning to ski and spending two years in ski resorts in Canada and France. He then decided he wanted to find a way to combine his passion and skills and apply them to environmental problems at scale.

He decided to go back to Edinburgh to do a Masters in Remote Sensing – using images and other data from satellites. Because the European Space Agency and NASA make their data available free to academic researchers, there was a huge amount of information to work with.

For his dissertation, Mal used satellite images to study the hydrological system around the lakes which form on top of the Greenland Ice Sheet in summer, and their impact on the ice sheet. He had found his vocation.

A PhD followed, developing new techniques using radar imagery from satellites to measure changes in the ice shelves in the west of Antarctica, where the ice flows into the ocean.

“This is a region that is very dynamic, very sensitive to climate change. The ice sheet is moving faster and faster, losing a lot of ice to the ocean and so making a bigger contribution to sea level rise. So, if we want to monitor what is happening, we need to be able to measure it accurately.”

He used images from the ‘invisible’ microwave part of the spectrum, using a technique called Interferometric Synthetic Aperture Radar (InSAR), which measures tiny changes in the distance between the satellite and the ice surface.

He studied surface features like crevasses, and how the movement of tides interacted with the flowing ice.

“It still blows my mind that you have a satellite, hundreds of kilometres up, that can measure millimetre movements on Earth.”

Mal then moved to Leeds University, taking advantage of a newly launched European satellite, CryoSat-2, specifically designed to observe sea ice and the polar regions.

“The data from CryoSat-2 had much finer resolution, providing a more detailed picture of how the surface was changing and it also enabled us to observe the whole ice sheet. We were able to make more accurate estimates of how ice sheets were contributing to sea level rise, and to identify which regions are loss hotspots, which we might want to study more in detail.”

Mal also switched his focus to the other pole - to the Arctic and Greenland. "Greenland is more temperate with a lot more melting in the summer. The glaciers are smaller and more dynamic, so harder to measure from space."

As the available satellite data got larger and higher resolution, Mal realised he needed help from those with expertise in working with large data sets.

“How do you process this data better, how do you estimate the uncertainty of your measurements?”

So, he leapt at the ‘really exciting opportunity’ to come to Lancaster University in 2018, to help to set up the Centre of Excellence in Environmental Data Science.

As co-director of the new Centre, run jointly with the UK Centre for Ecology and Hydrology (UKCEH), he works out of a joint UKCEH office in the Lancaster Environment Centre.

“We are trying to bring together people who have shared interests, it might be about particular techniques that we use, or cross cutting methodological themes such as how do we store data or collect time series of ice sheet or river level changes.

“I now interact with a much broader field of researchers than I did previously, bringing a lot of different dimensions and avenues to explore in my own research.”

One such avenue is exploring how to use data science techniques like artificial intelligence and deep learning to process the images of ice sheets. Another, which he hopes to develop in the future, focusses on using the techniques he has developed for ice sheets to monitor changes in rivers, which is of particular interest to UKCEH.

“The opportunities excite me. I don’t feel we are taking full advantage of the data that is available. We need to figure out new methodologies and bring the right people in the room, then there are lots of opportunities to make big advances.”

CryoSat-2, the satellite mission that has provided the data for most of Mal’s research, is now at the end of its working life. Mal is part of an international advisory group advising the European Space Agency, and so can influence decisions about the satellite’s successor. He hopes the new mission, provisionally named CRISTAL, will provide more and better data, enabling his group to provide ever more accurate information about how climate change is impacting our ice sheets.

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