Guest post by David Middleton
When the observations don’t match the models, adjust the observations…
Satellite snafu masked true sea-level rise for decades
Revised tallies confirm that the rate of sea-level rise is accelerating as the Earth warms and ice sheets thaw.
17 July 2017
The numbers didn’t add up. Even as Earth grew warmer and glaciers and ice sheets thawed, decades of satellite data seemed to show that the rate of sea-level rise was holding steady — or even declining.
Now, after puzzling over this discrepancy for years, scientists have identified its source: a problem with the calibration of a sensor on the first of several satellites launched to measure the height of the sea surface using radar. Adjusting the data to remove that error suggests that sea levels are indeed rising at faster rates each year.
“The rate of sea-level rise is increasing, and that increase is basically what we expected,” says Steven Nerem, a remote-sensing expert at the University of Colorado Boulder who is leading the reanalysis. He presented the as-yet-unpublished analysis on 13 July in New York City at a conference sponsored by the World Climate Research Programme and the International Oceanographic Commission, among others.
Nerem’s team calculated that the rate of sea-level rise increased from around 1.8 millimetres per year in 1993 to roughly 3.9 millimetres per year today as a result of global warming. In addition to the satellite calibration error, his analysis also takes into account other factors that have influenced sea-level rise in the last several decades, such as the eruption of Mount Pinatubo in the Philippines in 1991 and the recent El Niño weather pattern.
The view from above
The results align with three recent studies that have raised questions about the earliest observations of sea-surface height, or altimetry, captured by the TOPEX/Poseidon spacecraft, a joint US–French mission that began collecting data in late 1992. Those measurements continued with the launch of three subsequent satellites.
“Whatever the methodology, we all come up with the same conclusions,” says Anny Cazenave, a geophysicist at the Laboratory for Studies in Space Geophysics and Oceanography (LEGOS) in Toulouse, France.
“As records get longer, questions come up,” says Gavin Schmidt, a climate scientist who heads NASA’s Goddard Institute for Space Studies in New York City. But the recent spate of studies suggests that scientists have homed in on an answer, he says. “It’s all coming together.”
If sea-level rise continues to accelerate at the current rate, Nerem says, the world’s oceans could rise by about 75 centimetres over the next century. That is in line with projections made by the Intergovernmental Panel on Climate Change in 2013.
“All of this gives us much more confidence that we understand what is happening,” Church says, and the message to policymakers is clear enough. Humanity needs to reduce its output of greenhouse-gas emissions, he says — and quickly. ”The decisions we make now will have impacts for hundreds, and perhaps thousands, of years.”
So… They accomplished accelerated sea level rise by slowing down the past…
Of course, Bill Cosby invented the word “riiiiight” in a sketch about accelerated sea level rise…
Oddly enough, Dr. Nerem and company predicted that they would soon detect the irascible acceleration in sea level rise. So, I guess the soon-to-be-detected acceleration will be tacked on the the adjusted acceleration and Bill Cosby will probably not get credit for the inundation of our coastlines when they are submerged under 7.5 meters of adjusted sea levels.
Until then, sea level rise looks just as tame as it ever did…
Featured Image: Cartoons by Josh