In its 2007 assessment, the Intergovernmental Panel on Climate Change (IPCC) estimated a sea level rise of between 18 to 59 centimeters (about 7 to 23 inches) by the end of the century.
This March at the International Scientific Congress on Climate Change in Copenhagen, scientists presented new data that suggests sea levels will likely rise at least 50 centimeters (more than a foot-and-a-half), with a possible rise of more than one full meter (over 3 feet).
Studying fossil corals, researchers have determined that the last time the Earth grew warmer than it is today, melting ice caused a sudden rise in sea levels. The sea level rise studied happened about 125,000 years ago at the end of the last ice age according to Paul Blanchon, one of the researchers on the study published in yesterday’s issue of Nature.
We know there was less ice” (back then), Blanchon told reporters at CBCNews.ca, “and we know sea level was higher. And we know that’s what’s going to happen in the future [if greenhouse gas emissions continue to grow].”
Blanchon, a geoscientist at the National Autonomous University of Mexico in Cancun, along with colleagues at the Leibniz Institute of Marine Sciences in Kiel, Germany, say the study shows that a sudden and substantial sea level rise has happened before. A similar rise now would affect homes, drinking water, and the lives of millions of people living in coastal areas, the conseuquences of which Blanchon describes as “catastrophic.”
Blanchon and his colleagues are able to determine ancient sea levels by examining coral “crests.” Corals grow about one meter every three hundred years, rising up in layers. The highest part of a reef is the crest, and is home to specialized reef-crest corals. The position of a reef-crest coral is an indicator of sea level, since coral cannot grow above the water.
The team studied two separate reef-crests, one higher and one lower, both connected at their base, indicating they grew from the same coral bed. Chemical dating measurements determined the approximate age of the coral bed at 125,000 years and suggested that the lower reef crest was older, and the higher reef crest younger.
By examining the growth of the reef crests, they were able to determine that the corals grew toward the shore over time. At one point the lower reef crest suddenly died. Evidence suggests that it was killed by stirred-up sediment. Blanchon believes rising sea levels allowed waves to crash over and past the reef, stirring up the sediment in the lagoon behind it.
Once the lower crest had died, the upper crest began growing two to three meters (six and-a-half to nearly ten feet) above the previous sea level.
By further studying the band of coral reefs stretched below both crests, noting the change in coral types through the layers of the reef, and based on their knowledge of growth rates, Blanchon and his team estimate that the two-to-three meter rise in sea levels happened in a span of 50 years.
If this turns out to be the case, I think that we should be closely monitoring the events on the Antarctic and Greenland ice sheets, as well as doing all we can to reduce our greenhouse gas pollution, and fast,” he said in a statement, “before the marine portions of these ice sheets start an irreversible slide into the ocean.”