August 19, 2013
UN Report: Climate Change Is Man-Made, Exact Effects Difficult To Predict
Brett Smith for redOrbit.com - Your Universe Online
A new report from a United Nations panel on climate change scales back some previous predictions but still states humans are responsible for global warming with more certainty than ever, according to a version of the draft acquired by Reuters.
The upcoming report by the Intergovernmental Panel on Climate Change (IPCC) is the primary reference guide for governments considering energy, coastal infrastructure and agricultural policies. Reuters reported on Friday a copy of a draft of the report said, “it is at least 95 percent likely that human activities - chiefly the burning of fossil fuels - are the main cause of warming since the 1950s.”
That level of certainty is up from 90 percent in the last report in 2007, 66 percent in 2001, and slightly more than 50 percent in 1995.
“We have got quite a bit more certain that climate change is largely man-made,” Reto Knutti, a professor at the Swiss Federal Institute of Technology in Zurich, told Reuters. “We’re less certain than many would hope about the local impacts.”
Like anything surrounding climate change, the IPCC report is expected to face strong criticism when it is released. The new report comes after the panel admitted a claim in the 2007 report, which stated Himalayan glaciers would melt by 2035, was incorrect due to miscalculations. The new report is expected to scale back other assertions from the 2007 report, including the claim human activities have caused more droughts.
The IPCC is also looking to explain why global temperature have risen more slowly since 1998 even though greenhouse gas emissions have hit record highs due to emerging economies like China. In the draft, the panel said it has “medium confidence” that the slowing rise is the result of natural variations in the Earth’s weather and factors limiting the amount of sunlight reaching the planet’s surface.
The panel of experts said higher-than expected levels of volcanic ash could be blocking out sunlight – resulting in less planetary warming. They also theorized more heat is being absorbed by the deep oceans than previously thought or global climate could be less sensitive than expected to the heavier influx of greenhouse gas.
"It might be down to minor contributions that all add up," said Gabriele Hegerl, a professor at Edinburgh University.
The IPCC also said predicting specific or local events is particularly difficult given the wide array of influencing factors. While the draft toned down previous assertions hurricanes will be more intense due to human activity, the scientists did reiterate the fact warmer air is capable of holding more moisture.
"There is widespread agreement among hurricane scientists that rainfall associated with hurricanes will increase noticeably with global warming," said Kerry Emanuel, of the Massachusetts Institute of Technology. "But measuring rainfall is very tricky.”
The scientists also told Reuters predicting how climate change will impact nature or agriculture is also highly difficult because the necessary calculations go beyond physics.
"You can't write an equation for a tree," Knutti said.
Well, at least not yet.