July 17, 2013
Greenhouse Gas Emissions Will Plague Us For Thousands of Years With Sea Level Rise
Susan Bowen for redOrbit.com - Your Universe Online
Current levels of greenhouse gas emissions will have far-reaching effects, even if the levels decrease in the near future. According to a new study published in the Proceedings of the National Academy of Sciences, the greenhouse gases emitted today will cause the sea level to rise for centuries to come. It is estimated each degree of global warming will raise sea levels by more than two meters.
This new study, completed by an international team of scientists, is the first to combine evidence from early Earth's climate history with comprehensive computer simulations using physical models that take into account four major contributors to long-term global sea-level rise. According to a Science Daily report on this topic, these four contributors are expansion of the oceans themselves due to warmer temperatures, melting mountain glacial ice, melting of the Greenland ice sheet and melting of the Antarctic ice sheet. Some of the factors considered in compiling the climate history are data from sediments from the bottom of the sea and from ancient raised shorelines found on various coastlines around the world.
Currently, the largest contributor to sea level rise is thermal expansion followed by melting mountain glaciers. Over the next two millennia, melting ice sheets in Greenland and Antarctica will likely produce most of the rise. One reason for this is that the mountain glaciers will shrink to the point that they are no longer much of a factor.
Initially, the two large ice sheets will be less of a factor because their huge masses slow their temperature change. "The problem is: once heated out of balance, they simply don't stop," says Levermann. When they do begin to melt, their behaviors will be very different." In Greenland, not only will the warming earth eventually cause melting, but as the ice reaches a lower latitude, the latitudinal increase in temperature will accelerate the rate of melt. The Greenland ice sheet could completely disappear.
The Antarctic ice sheet, in contrast, will continue to be so cold that latitudinal changes will not have a significant effect. The majority of its melting will be the result of the calving of icebergs. In all likelihood, the ice sheet will not melt completely, but it will be much smaller.
Scientists are fairly confident about the accuracy of these models as they are the first ones to combine the basic laws of physics with all four factors that contribute to sea level rise.
"The Antarctic computer simulations were able to simulate the past five million years of ice history, and the other two ice models were directly calibrated against observational data - which in combination makes the scientists confident that these models are correctly estimating the future evolution of long-term sea-level rise," says Peter Clark in describing some of the factors considered. Clark is a paleo-climatologist at Oregon State University and co-author on the study. He also added, "The simulations of future scenarios we ran from physical models were fairly consistent with evidence of sea-level rise from the past. Some 120,000 years ago, for example, it was 1-2 degrees warmer than it is now and sea levels were about five to nine meters higher. This is consistent with what our models say may happen in the future."
These changes are not expected to happen at a steady rate. "Keep in mind that the sea level rise projected by these models of 2.3 meters per degree of warming is over thousands of years," emphasized Clark, "If it warms a degree in the next two years, sea levels won't necessarily rise immediately. The Earth has to warm and hold that increased temperature over time."
In concluding his report, Levermann states, "Continuous sea-level rise is something we cannot avoid unless global temperatures go down again. Thus we can be absolutely certain that we need to adapt. Sea-level rise might be slow on time scales on which we elect governments, but it is inevitable and therefore highly relevant for almost everything we build along our coastlines, for many generations to come."
This study was funded primarily by the National Science Foundation and the German Federal Ministry of Education and Research.