Frontiers of Knowledge award for detecting, understanding and projecting anthropogenic sea level rise

In its citation, the jury underscores how their contributions have been pivotal for “detecting, understanding and projecting the response of global and regional sea level to anthropogenic climate change.” Due to the dramatic consequences of rising sea levels, it is essential to understand the key factors that are driving this change. “Interpreting and projecting sea-level change is a tremendous scientific challenge,” notes de citation. A challenge for the scientific community in which the laureates are pioneers: “Their findings have been instrumental in testing our understanding of how the Earth system works, enabling better grounded projections.”

Thanks to the laureates’ work, it has been possible to establish that the rate at which this rise is taking place is increasing. “Collectively, their research demonstrated the recent acceleration of regional and global sea-level change and quantified the relative contributions of the different causes of sea-level rise, most importantly ocean thermal expansion and the melting of ice sheets and glaciers driven by anthropogenic global warming,” in the words of the citation.

Anny Cazenave, a geophysics specialist, is a pioneer in interpreting satellite measurements. Her allowed to correct errors in previous estimates to deliver the first accurate and reliable set of data on sea level globally.  As she explains, “observations from space have had a key role. Before the satellite altimetry era that began at the start of the 1990s, the only information we had about sea-level rise was from an instrument installed in ports, which gave no data on the open ocean. So very little was known about the phenomenon.”

John Church, an oceanographer, and Cazenave were able to reconcile the new satellite data with existing local registers, and by this means build a solid record of sea-level change in the recent period.  The next steps were to extend their records into the past and draw up projections for the future, and it was here that Gregory’s numerical models came into their own.

Jonathan Gregory is an expert in calibrating climate sensitivity to diverse factors, be it the rise in atmospheric CO2 or the speed of ice melt.  “What I have done mostly is work on how to put together models that include all components of sea-level change, in order to make projections for the future and to improve understanding of the past,” he explains.

Understanding the problem to find a solution

“Our confidence has improved because we have gained a greater understanding of the past, such that we can now explain how and why sea level has changed over the past 150 years,” says Gregory. Although they remain optimistic, the three laureates have emphasized the gravity and urgency of the problem, and the need for a political response.

“Sea level is rising at an increasing rate. If it is business as usual, and we fail to curb our emissions, we could see a sea-level rise of up to a meter, perhaps more by the end of the century.  But with urgent and significant mitigation, we could reduce that rise to maybe a little over half a meter.  The rise in any case will be ongoing for many centuries, says Church. “About 100 million people live within one meter of current high tide level, so in a century we could have 100 million people having to adapt in some way, either protecting their houses, retreating from the coastline or protecting the coastline.”

Even if the rise is unavoidable, Gregory says that we can do things to slow down the process: “We can have an influence on how much and how fast it will happen. We can’t stop the increase, but we are not too late to do something to mitigate it and reduce its impact.”

Cazenave calls for further action: “It is clear that we are not doing enough to combat climate change. Sea-level rise is just one consequence of global warming. There are many others, like extreme weather events, that are becoming more intense.  We have to change the model of our society and way of life, consuming less fossil fuels.  In Europe the general public is aware of the problem, but at government level we are still waiting for concrete action.”

“To skeptics I would say compare the current climate in 2019 to that of 10 or 15 years ago.  I would simply say to them to look at the facts and observations,” she concludes.