A leaked draft of the U.N.'s next major climate change report warns that global sea levels could rise more than three feet by the end of the century if greenhouse emissions continue unabated, The New York Times reported Monday.
The Intergovernmental Panel On Climate Change (IPCC) report is also more confident that human activities, like the burning of fossil fuels, are the chief cause of the atmospheric warming seen since the 1950s. The report's authors say it is at least 95 percent likely that humans are behind this warming, according to an initial report from Reuters last Friday.
This confidence is reflected in the study's language. It's "extremely likely" that humans caused "more than half of the observed increase in global average surface temperature from 1951 to 2010," the Times quoted from the draft report.
The IPCC outlines several sea level rise scenarios for the end of the century, based on efforts to limit emissions in the coming decades. The most optimistic emissions reductions could bring only a 10-inch rise, explains the Times, on top of the eight inches seen in the last century. If emissions continue at a runaway pace, sea levels could rise "at least 21 inches by 2100 and might rise a bit more than three feet."
The National Atmospheric and Oceanic Administration's 2012 State of the Climate report, released earlier this month, showed global greenhouse gas emissions reached a new record high in 2011, and estimates suggest the record was broken again in 2012.
"It's good to see that the IPCC has moved in the right direction this time by at least trying to account for the key contribution to sea level rise from melting ice sheets," director of Pennsylvania State University's Earth System Science Center Michael Mann told The Huffington Post in an emailed statement, explaining that it was ignored in the previous IPCC report from 2007.
"However, the projections they provide are still overly conservative, with an upper limit of roughly one meter by 2100, when there is published work that suggests the possibility of as much as two meters (six feet) sea level rise by 2100," he added.
"This fits a pattern of the IPCC tending to err on the side of conservative, in part--I believe---because of fear of being attacked by the climate change denial machine."
Describing the IPCC's projections, Climate Progress' Joe Romm wrote on Sunday, "Like every IPCC report, it is an instantly out-of-date snapshot that lowballs future warming because it continues to ignore large parts of the recent literature and omit what it can’t model."
A recent study published in the journal Nature Climate Change shows that with only 15.75 inches of sea level rise by mid-century, losses due to flooding in 136 of the world's coastal cities may approach $1 trillion annually, reported Climate Central.
IPCC spokesman Jonathan Lynn cautioned against drawing too many conclusions from the leaked drafts, but told the BBC on Monday, "We are not trying to keep it secret." He said, "After the report is finished we are going to publish all the comments and response so that people can track the process."
Reuters' breakdown of the IPCC draft also draws attention to the apparent slowdown in warming observed since 1998, despite rising greenhouse gas emissions. Romm contends the slowdown "turns out to be only true if one looks narrowly at surface air temperatures, where only a small fraction of warming ends up."
The Times emphasizes the international scientific panel's further confidence in the future effects of unchecked emissions and notes, the experts "largely dismiss a recent slowdown in the pace of warming, which is often cited by climate change contrarians, as probably related to short-term factors."
The IPCC's Fifth Assessment Report is set to be released in four parts between September 2013 and November 2014.