Sea Level Rise Pioneer to Receive 2020 Vetlesen Prize

The 2020 Vetlesen Prize for achievement in the Earth sciences will be awarded to French geophysicist Anny Cazenave. Cazenave pioneered the use of satellite data over the past 20-plus years to chart rises in the surface of the oceans. Her work has tied together many previous loose threads linking sea level rise with climate change.

Cazenave will receive the $250,000 prize and a gold medal at Columbia University in April. The triennial award is administered by Columbia’s Lamont-Doherty Earth Observatory. The ceremony will mark the 60th anniversary of the Vetlesen Prize, which was established by the G. Unger Vetlesen Foundation.

Global mean sea level has risen 8 to 9 inches (21 to 24 centimeters) since the 1880s, and this is accelerating; recently, it has been about 0.14 inches a year (3.6 millimeters) – two and a half times the rate during most of the 20th century. The rise is not even; some regions are seeing more, others less. Scientists have determined that the increase is coming from two basic sources:  melt water from glaciers and ice sheets, and expansion of seawater itself as it warms.

It was Cazenave and her colleagues who quantified much of the sources of the rise by harnessing satellite data to analyze the height and mass of Earth’s land and waters in unprecedented detail, and tease out how they interact.

Cazenave received her Ph.D. in geophysics from the University of Toulouse in 1975. She went into space geodesy, the use of satellites to track changes in Earth’s surface, gravity field and orientation in space. She first focused on the dynamics of the oceanic crust and the mechanically strong layer of the uppermost mantle below it. Among other things, she used early space-borne radars to show that the ocean surface is not flat, but subtly mimics the topography of the ocean floor.

Until the 1990s, sea levels were recorded mainly by tidal gauges anchored at coastal ports; levels in the open ocean were largely a black hole. Then, European and American space agencies launched a new series of satellite radar altimeters capable of monitoring sea and land levels. Cazenave and her colleagues quickly developed ways to analyze the data and combine them with other information. By the early 2000s, they had determined that global sea level was going up about 3 millimeters a year – in some places three times that. The variations are due to regional factors including wind and wave patterns, and subsidence or rebound of the land itself.

Quantifying the sources of the rise, they used altimetry measurements of the polar ice sheets, and newly available satellite data of changes in the ice sheets’ gravity fields, which are linked with mass. Satellites, ships and, most recently, oceangoing robots, can now also track the salinity and temperature of ocean waters across the globe. Combining this information, Cazenave and her colleagues found that about half the sea level rise in recent decades has come from expansion of ocean waters, and half from melting glaciers and ice sheets.

However, she and her colleagues have also found that a small part is now also coming from a shift of water from rivers, lakes, soils and aquifers into the oceans. This appears due to a combination of factors including humans’ increased pumping of surface and underground water, and intensifying evaporation caused by rising temperatures.

The techniques pioneered by Cazenave “continue to transform and deepen our appreciation of the seriousness of the climate crisis which we are experiencing,” said physics professor W. Richard Peltier of the University of Toronto, who received the Vetlesen Prize in 2004.

Cazenave is director of Earth sciences at the International Space Sciences Institute in Bern, Switzerland. She previously was based at France’s National Center for Space Studies. She was lead author of the sea level sections of the Intergovernmental Panel on Climate Change’s most recent full reports, in 2007 and 2014.

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