By Nina Chestney and Alister Doyle LONDON (Reuters) -
International climate scientists are more certain than ever that
humans are responsible for global warming, rising sea levels and
extreme weather events, according to a leaked draft report by an
influential panel of experts. The early draft, which is still
subject to change before a final version is released in late
2013, showed that a rise in global average temperatures since
pre-industrial times was set to exceed 2 degrees Celsius by
2100, and may reach 4.8 Celsius. "It is extremely likely that
human activities have caused more than half of the observed
increase in global average surface temperatures since the
1950s," the Intergovernmental Panel on Climate Change (IPCC)
draft report said. "Extremely likely" in the IPCC's language
means a level of certainty of at least 95 percent. The next
level is "virtually certain", or 99 percent, the greatest
possible certainty for the scientists. The IPCC's previous
report, in 2007, said it was at least 90 percent ce