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The Intergovernmental Panel on Climate Change (IPCC) has been keeping a close eye on rising sea levels and has released several reports outlining the forecasts for the future of our world’s oceans. In its fourth assessment report, released in 2007, the IPCC estimated sea levels were rising at a rate of 0.08 inches per year based on satellite data.
But new research from the Potsdam Institute for Climate Impact Research, Tempo Analytics and Laboratoire d’Etudes en Géophysique et Océanographie Spatiales (LEGOS), shows that sea-levels are rising much faster than the IPCC’s 2007 projections. These latest observations show that seas are rising at a rate closer to 0.125 inches per year (about a 60 percent increase).
The researchers believe that these findings are important for keeping track of how well past projections match observational data, especially as projections made by the IPCC are increasingly being relied upon for decision making.
“Global temperature continues to rise at the rate that was projected in the last two IPCC Reports. This shows again that global warming has not slowed down or is lagging behind the projections,” said Stefan Rahmstorf, the lead author in the study, published today in IOP Publishing’s journal Environmental Research Letters.
The researchers compiled data from five global land and ocean temperature measurement mechanisms and compared them to projections made by the IPCC. To allow for an accurate comparison, the scientists accounted for short-term temperature variations due to El Nino events, solar variability and volcanic eruptions. Their results confirm that global warming, first predicted by scientists in the 1960s as a consequence of increasing greenhouse concentrations, continues to climb at about 0.3F per decade, which also follows IPCC projections closely.
For sea-level rise projections, the researchers turned to satellite data. Satellites measure sea-level rise by bouncing radar waves back and forth off the sea surface and have proven much more accurate than tidal gauges. Tidal gauges typically only measure coastal sea levels, whereas satellites can make measurements on a global scale. Tidal gauges also include variability that has nothing to do with changes in global sea level, but rather with how the water moves around in the oceans.
The researchers noted the increased rate of sea-level rise is unlikely attributable to temporary episodic ice discharge from Greenland and Antarctic ice sheets or other internal variabilities in the climate system, because it correlates very well with the increase in global temperature.
“In contrast to the physics of global warming itself, sea-level rise is much more complex,” Rahmstorf said in a statement. “To improve future projections it is very important to keep track of how well past projections match observational data.”
Rahmstorf stressed that “the new findings highlight that the IPCC is far from being alarmist and in fact in some cases rather underestimates possible risks.”
The IPCC, which has released a climate assessment report four times in the past (the last in 2007), is scheduled to release its fifth report in 2014.