An international panel of scientists has found with near certainty that human activity is the cause of most of the temperature increases of recent decades, and warns that sea levels could conceivably rise by more than 3 feet by the end of the century if emissions continue at a runaway pace.
The scientists, whose findings are reported in a draft summary of the next big U.N. climate report, largely dismiss a recent slowdown in the pace of warming, which is often cited by climate change doubters, attributing it most likely to short-term factors.
The report emphasizes that the basic facts about future climate change are more established than ever, justifying the rise in global concern. It also reiterates that the consequences of escalating emissions are likely to be profound.
“It is extremely likely that human influence on climate caused more than half of the observed increase in global average surface temperature from 1951 to 2010,” the draft report says. “There is high confidence that this has warmed the ocean, melted snow and ice, raised global mean sea level and changed some climate extremes in the second half of the 20th century.”
The draft comes from the Intergovernmental Panel on Climate Change, a body of several hundred scientists that won the Nobel Peace Prize in 2007, along with Al Gore. The coming report will be the fifth major assessment from the group, created in 1988. Each report has found greater certainty that the planet is warming and greater likelihood that humans are the primary cause.
On sea level, the new report goes well beyond the assessment published in 2007. The report lays out several possibilities.
In the most optimistic, sea level could be expected to rise as little as 10 inches by the end of the century. That is a bit more than the 8-inch increase in the 20th century, which proved manageable.
At the other extreme, the report considers a chain of events in which emissions continue to increase at a swift pace. Under those conditions, sea level could be expected to rise at least 21 inches by 2100 and might increase a bit more than 3 feet, the report said.
Hundreds of millions of people live near sea level, and either figure would represent a challenge for humanity, scientists say. But a 3-foot rise in particular would endanger many of the world’s great cities – among them New York; London; Shanghai; Venice, Italy; Sydney, Australia; Miami and New Orleans.
