'No Ambiguity' on Climate Change, UN Says in IPCC Report

http://preview.weather.com/science/environment/news/climate-change-un-ipcc-report-20141102

Climate change is here and human caused and the time to act is now, the U.N.'s panel on climate science said Sunday.

The fourth and final volume of the Intergovernmental Panel on Climate Change's giant climate assessment didn't offer any surprises, nor was it expected to since it combined the findings of three earlier reports released in the past 13 months.

But it underlined the scope of the climate challenge in stark terms. Emissions, mainly from the burning of fossil fuels, may need to drop to zero by the end of this century for the world to have a decent chance of keeping the temperature rise below a level that many consider dangerous. Failure to do so, which could require deployment of technologies that suck greenhouse gases out of the atmosphere, could lock the world on a trajectory with "irreversible" impacts on people and the environment, the report said. Some impacts are already being observed, including rising sea levels, a warmer and more acidic ocean, melting glaciers and Arctic sea ice and more frequent and intense heat waves.

"Science has spoken. There is no ambiguity in their message. Leaders must act. Time is not on our side," U.N. Secretary-General Ban Ki-moon said at the report's launch in Copenhagen.

Amid its grim projections, the report also offered hope. The tools needed to set the world on a low-emissions path are there; it just has to break its addiction to the oil, coal and gas that power the global energy system while polluting the atmosphere with heat-trapping CO2, the chief greenhouse gas.

"We have the means to limit climate change," IPCC chairman Rajendra Pachauri said. "All we need is the will to change, which we trust will be motivated by knowledge and an understanding of the science of climate change."

The IPCC was set up in 1988 to assess global warming and its impacts. The report released Sunday caps its latest assessment, a mega-review of 30,000 climate change studies that establishes with 95-percent certainty that nearly all warming seen since the 1950s is man-made.

Today only a small minority of scientists challenge the mainstream conclusion that climate change is linked to human activity.