Even if humanity manages to reduce greenhouse gas emissions to near-zero levels, the damage may have already been done, with sea levels expected to rise over the next 1,000 years regardless of what actions humans take, according to a new study published Monday.
Under a best-case scenario, where carbon emissions fell immediately to near-zero levels, the world's oceans will rise 1.1 meters over the next 1,000 years as a direct result of greenhouse gases already emitted by humans, according to the model, published in Environmental Research Letters. Under more likely scenarios endorsed by the Intergovernmental Panel on Climate Change, a sea level rise of up to 6.8 meters could happen over the next 1,000 years if human carbon emissions remain unchecked until the year 2100.
Because greenhouse gases stay in the atmosphere for many years, their warming impacts can last for hundreds or thousands of years. This creates a phenomenon known as "irreversible warming" that is already locked in.
"Any realized warming is very likely irreversible on human time scales," according to the authors, of the University of Brussels, Manchester Metropolian University, and the Université catholique de Louvain in Belgium.
"Anything we do now that changes the forcing in the climate system will necessarily have long consequences for the ice sheets and sea level," Philippe Huybrechts, one of the study's authors, said.
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Under each of the four models the team looked at, most of the sea level rise was attributed to melting of Greenland's ice sheet. In July, a heat wave in that country melted nearly all of that ice sheet, but much of it reformulated days later. At the time, Waleed Abdalati, a NASA scientist, said that the event was "seriously unusual" and was the most severe melt NASA satellites have ever monitored.
According to the Environmental Research letters study, if polar ice sheets completely melted, sea levels would rise up to 65 meters.
"If climatic warming [is] severe and long-lasting, all ice will eventually melt," Huybrechts said. "Mankind should limit the concentration of greenhouse gases at the lowest possible level as soon as possible. The only realistic option is a drastic reduction of the emissions. The lower the ultimate warming [is], the less severe the ultimate consequences will be."