The reduction of greenhouse gases that cycle through the atmosphere more quickly than carbon dioxide could significantly reduce potential sea level rise this century, according to a study in which the National Center for Atmospheric Research was a major contributor.
Although carbon dioxide emissions into the atmosphere remain the most significant contributor to continued increase to the Earth's sea level increase, four other heat-trapping pollutants also have a damaging effect, according to NCAR's Aixue Hu, first author on the study, published this week in the journal Nature Climate Change.
"If we can effectively cut emissions of these short-lived climate pollutants -- methane, tropospheric ozone, hydrofluorocarbons and black carbon -- it will reduce the overall global temperature increase by 0.6 degrees C(elsius) by 2050, and by the end of the 21st century, it will reduce the overall increase by over 1 degree C(elsius)," said Hu.
However, said, Hu, "The cutting of these short-lived climate pollutants only gives us a short-term fix to the increase of global mean temperature and the seal level. If we really want to reduce the global warming effect due to greenhouse gas emissions, we still have to cut the CO2 emissions."
It is estimated by the study that reductions in those four pollutants could forestall the rate of sea level rise by about 25 percent to 50 percent. Stemming the increased level of the planet's ocean is a key concern of climate scientists, with massive population centers ranging from New York to Mumbai to Tokyo established in low-lying areas.
Melting glaciers and ice sheets on Greenland and Antarctica and thermal expansion of the oceans has triggered an annual increase to sea levels by about 3 millimeters, or, just more than one-tenth of an inch. With continued global warming, global sea levels are predicted to rise between 18 to 59 centimeters (7 to 23 inches) this century, according to a 2007 assessment by the Intergovernmental Panel on Climate Change.
"Once CO2 is released into the air, it will last there for a long time, potentially for centuries or longer," said Hu. But the four shorter-lasting pollutants targeted by the study, he added, "only stay in the atmosphere for weeks, months, to at most, a decade."
A sharp reduction in those comparatively short-lived pollutants, starting in 2015, could offset warming temperatures by up to 50 percent by 2050, the study indicated.
The study assumed a decrease in the emission of the four targeted gases and particles by 30 percent to 60 percent over the next several decades. It showed a resulting projected reduction in sea level rise of 22 percent to 42 percent by 2100, depending on the actual level of emissions reduction that might be achieved.
Hu credited Veerabhadran Ramanathan of the Scripps Institution for Oceanography, who led the study, for his support of a project in India which is reducing the emissions of black carbon.
"So there is some action that we are taking, but it is on a smaller scale," Hu said. "If the governments of the world can do this on a much larger scale, in a more effective way, the benefits would be realized in a more significant way.
"The technology to reduce the emissions of these short-lived climate pollutants exists, but we just need to get people to start acting on it and use it," Hu added. "I certainly hope that governments can take action as soon as possible, but the reality is that we still have a long way to go."