SOURCE: Inside Climate News
DATE: December 26, 2017
SNIP: When the UN’s Intergovernmental Panel on Climate Change issued its 5th Climate Assessment in 2014, it formally declared that observed warming was “extremely likely” to be mostly caused by human activity.
This year, a major scientific update from the United States Global Change Research Program put it more bluntly: “There is no convincing alternative explanation.”
The most ominous of its chapters addressed the risks of surprises like “tipping points” or “compound extremes”—sucker punches, combination punches, and even knockout punches. “The more the climate changes, the greater the potential for these,” it said.
“Uncertainty is not our friend here,” said Penn State climate scientist Michael Mann. “We are seeing increases in extreme weather events that go well beyond what has been predicted or projected in the past. We’re learning that there are factors we were not previously aware of that may be magnifying the impacts of human-caused climate change.” Among those are “subtle mechanisms involving the behavior of the jet stream that may be involved in explaining the dramatic increase we’ve seen in floods, droughts, heat waves and wildfires,” he said.
“Increasingly, the science suggests that many of the impacts are occurring earlier and with greater amplitude than was predicted,” Mann said, after considering new research since the milestone of the IPCC’s Fifth Assessment, which served as the scientific basis for the Paris Agreement.
“We have literally, in the space of a year, doubled our assessment of the potential sea level rise we could see by the end of this century. That is simply remarkable. And it is sobering,” he said.