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A doesn’t necessarily say the sky is falling, but portrays a complex world that it is clearly undergoing great change. Some change has been wrought by humans and some seems unrelated to our presence on the planet: The Southwest may be drying up, although we didn’t necessarily do it; Greenland and Antarctica are melting, we didn’t necessarily do it but we are certainly contributing; warm, salty currents in the Atlantic Ocean that circulate heat probably won’t collapse this century, but they could, and the catastrophic methane release some scientists have predicted is unlikely to happen anytime soon, but methane, a greenhouse gas significantly more potent than carbon dioxide, will surely continue to increase in the atmosphere.

The report illustrates a problem with climate change, what refers to as “the perfect problem;” monumental global change is likely happening, but the globe changes slowly, and it's difficult for humans, who live day-to-day, to take notice. “Large changes in sea level have occurred in the past, extensive droughts have occurred in past, extensive changes in the pump that transfers heat to high latitudes have occurred in the past and methane outflow has happened in the past too,” said lead author , who presented the report at a meeting of the , yesterday. Despite this precedent, that all these changes are occurring simultaneously seems significant. Whether or not they have occurred simultaneously at other times in the past is an area of intense research, said .

Weaver is another lead author of the report, which was compiled by a group that includes researchers from the United States and Canada. The project, which is part of the within the , evaluated previous research regarding ice sheet fluctuations, Southwest hydrology, current circulation and methane release to draw their conclusions.

Perhaps the most striking conclusions the report makes are regarding the Greenland and Antarctic ice sheets, both of which were expected to grow in some past models. However, what researchers found this time around was different. “Instead, we are seeing shrinking,” said Clark.

“There are no smoking guns that things are happening now caused by human activity but there are different lines of evidence to say the system has the possibility of tipping over,” said researcher , regarding drought in the American Southwest. “If that happened again it would have catastrophic effects on human activities and populations.”

The news about methane was equally alarming and quelling, depending on how you looked at it. “It is very unlikely that there will be a catastrophic release,” said Clark, “but very likely that emissions from these natural sources will increase through this century.”

After the presentation one reporter asked why the report did not include a section detailing ways to curb climate change.

“It is not really the intention of this report to provide mitigation strategies,” answered one of the authors. “It is more intended to be a snapshot in time of where we are with the science.”