Signals from a drowning world
Melting ice sheets and glaciers – and the resulting rising seas - are a startling reminder of the rate of climate change. However, measuring ice loss was an inaccurate science... until Edinburgh experts helped change things.
The United Nations’s latest Intergovernmental Panel on Climate Change (IPCC) report made for sobering reading. The report’s authors – a group of the world’s leading scientists – were unequivocal in their predictions of extreme heatwaves, droughts and flooding to come as a “code red for humanity”.
Despite its grim forecast that the world would exceed the Paris climate agreement’s target of keeping the rise in global temperatures below 1.5C within less than a decade, the report did offer some hope. With colossal and coordinated effort between nations to drastically cut greenhouse gas emissions deeper and faster than ever before, it said we could avert a climate catastrophe.
The IPCC was also unambiguous on rising sea levels. No matter what we do, melting ice means our seas will rise. In a worst-case scenario, oceans will rise by as much as two metres before the end of this century and five metres by 2150.
Such a change would be disastrous for the more than 400 million people worldwide who live in zones less than five metres above sea level. It would also destroy precious land and marine habitats and could lead to dramatic changes in the weather, from disrupting the jet stream to causing hurricanes and typhoons.
Measuring the melt
“The numbers are not positive. No one can deny that,” acknowledges Dr Noel Gourmelen, a University of Edinburgh expert on the cryosphere, the technical term for Earth’s frozen water. “But the IPCC’s uncompromising tone is encouraging. I remember in the recent past when these issues were still not taken seriously. The fact that the latest report is so strongly worded and stimulates such interest is a clear indication of how far we’ve come to bring climate change to the public’s consciousness.”
Gourmelen has more than a passing interest in the IPCC’s findings. It is thanks largely to his and Edinburgh colleagues’ research that – for the first time – this year’s report includes accurate predictions on the impact of melting ice around the margins of Antarctica and Greenland and high-mountain regions such as the Himalayas, Iceland, and South America.
“It might surprise people to know, but until relatively recently, the scientific community has not been able to measure what’s happening to land ice accurately,” explains Gourmelen’s collaborator, glaciologist Professor Robert Bingham.
“We have a tremendous amount of geological evidence on how the ice sheet has grown and reduced in size during the past two million years, and for the past 50 years, we’ve been able to observe these changes from satellites. But what we’ve lacked until the past decade is the necessary level of precision to fully understand how our ice sheets and glaciers are changing or make useful predictions about how these changes will affect sea levels.”
Eyes in the sky
The University of Edinburgh’s team of ice-sheet and glacier scientists have spearheaded new methods to collect invaluable satellite and field data and developed new computer modelling techniques to monitor and predict changes in the Earth’s ice-covered regions.
Since its launch in 2010, the CryoSat satellite has used a radar altimeter instrument to measure the changing height of ice in Antarctica. The process works by firing a microwave signal to the ground and timing how long it takes to bounce back to the satellite. Differences in these return times indicate variations in the height of the ice’s surface below. Working with the European Space Agency (ESA), Gourmelen has developed new data analytic methods to supercharge CryoSat’s ability to ‘see’ the terrain at a much higher resolution.
“The satellite used to be able to determine features in the ice to within one or two kilometres. This new ‘swath’ process can measure the topography of ice to within 500 metres or less. This cryospheric processing technique also makes it possible to see the true shape of valleys and depressions, not only their rims. This level of detail is crucial to help us measure glaciers in mountainous terrain. Because the field of detection is much broader, it also reduces the time taken to map an ice sheet,” says Gourmelen.
This methodology has demonstrated that Greenland today is losing ice seven times faster than two decades ago, allowing Gourmelen and colleagues to pinpoint where the ocean is eroding ice under rapidly melting Antarctic ice shelves, identifying giant icebergs in the making. Sharing these data with the scientific community has significantly enhanced predictive modelling on melting ice and the sea level rises it causes. However, calculating the volume of sea-level rise resulting from ice-sheet and glacier melt means that scientists also need to measure ice thickness, which still requires travelling to some of the world’s most isolated locations.
“Frequencies of radar that can see through ice happen to be the same as those that the Earth’s atmosphere blocks, so, unfortunately, we cannot measure ice thickness from space. We’ve been trying to develop radar to overcome this for the past 50 years, and we’re getting closer, but until we crack this, we have to take a more hands-on approach,” says Bingham, himself no stranger to the ice.
Working with the British Antarctic Survey and UK Natural Environment Research Council, he has spent two three-month-long seasons traversing Pine Island Glacier - a vast area of the Antarctic ice almost the size of the UK - on a specially adapted snowmobile. Behind him – sometimes as far as a kilometre - he drags a radar antenna that measures the ice thickness below.
“Even to get to Pine Island Glacier requires travelling for several days in a succession of decreasingly small aircraft. Acquiring the measurements then involves spending most days driving slowly up and down the same largely featureless area,” he says. “But it provides essential complementary data to what we can understand from satellite images.”
Driving across the ice has significant benefits over the traditional approach of flying an aircraft over the area to take measurements every five kilometres and then estimate the topography between these points. Thanks to Bingham and his colleagues’ endeavours to measure the landscape accurate to metres, not kilometres, we now have a much more detailed understanding of how the landscape under the ice changes how it moves and melts.
Back in Edinburgh, the team combines the satellite data and field measurements to create detailed models of what could happen to the world’s ice sheets under different conditions in the future. These models were crucial to giving IPCC’s scientists the conviction to make firm predictions about future sea level rises.
A new frontier
The cryospheric processing techniques Edinburgh researchers have developed during the past decade also influenced the European Commission and ESA to launch a new ring of satellites specifically focused on polar ice and snow topography monitoring as part of its Copernicus Earth Observation programme. These dedicated satellites are the first to systematically monitor our planet and its environment for citizens’ benefit.
“We’re standing at a new frontier of discovery, and if anything, our projections are telling us the future remains uncertain, and there are still a lot of questions to answer,” says Gourmelen. “But what we do know is that the leaps we’ve made during the past decade have contributed to a much higher degree of public and political understanding about the possible futures we could have if we do nothing. If there were ever a moment to act, it is now.”
Photo credits: polar bear - NiseriN/Getty; waves - Moorefam/Getty; cryosat - ESA/P. Carril; glacier - ESA; Noel Gourmelen - Adam Clark