Mankind is to blame for climate change, UN report argues

Humans are "extremely likely" to have made more than half of the contribution to increased temperatures from 1950 to 2010 and more and longer heat waves are expected, according to a new report from a UN-endorsed global research organization.

"It is extremely likely that human influence has been the dominant cause of the observed warming since the mid-20th century," said the Inter-governmental Panel on Climate Change in its latest assessment report.

Intergovernmental Panel on Climate Change Chairman Rajendra Pachauri (left) and Co-chairman Thomas Stocker present the UN IPCC Climate Report during a news conference in Stockholm on Friday. Leading climate scientists said they were more certain that mankind was the main culprit for global warming. Bertil Enevag Ericson / reuters

"Continued emissions of greenhouse gases will cause further warming and changes in all components of the climate system."

More than 800 scientists and researchers from 39 countries contributed to the report, the panel's fifth since the Stockholm organization was established in 1988. The previous one was published in 2007.

The scientists said the evidence for human influence on global warming has grown, thanks to increased observations, improved understanding of climate system response and better climate models.

According to the report, global warming is not a myth. Since 1950 many unprecedented changes have been observed throughout the climate system. Each of the last three decades has been successively warmer at the Earth's surface than any preceding decade since 1850.

"Observations of changes in the climate system are based on multiple lines of independent evidence," said Qin Dahe, co-chair of the plan's Working Group I, which is devoted to the scientific report.

"Our assessment finds that the atmosphere and ocean have warmed, the amount of snow and ice has diminished, the global mean sea level has risen and the concentrations of greenhouse gases have increased."

Thomas Stocker, the other co-chair of Working Group I, said: "Continued emissions of greenhouse gases will cause further warming and changes in all components of the climate system."

Stocker said limiting climate change will require substantial and sustained reductions of greenhouse gas emissions. "Global surface temperature change for the end of the 21st century is projected to be likely to exceed 1.5 C relative to 1850 to 1900 in all but the lowest scenario considered, and likely to exceed 2 C for the two high scenarios," said Stocker. "Heat waves are very likely to occur more frequently and last longer."

Stocker said that as the earth warms, wet regions will receive more rainfall and dry regions will receive less, although there will be exceptions.

As the report was published, the Stockholm-based think tank Global Challenges Foundation organized an international seminar, inviting the global risk experts to discuss possible risks of global warming and what can be done to reduce human impact.

"This report has included more specific data than ever on the probability of high-impact scenarios, and it is time to factor in the possibility of these scenarios in a scientific way," said Dennis Pamlin, project manager of the foundation. "The impacts of climate change and global warming are so catastrophic that we need to take actions."

Projections of climate change are based on a new set of four scenarios of future greenhouse gas concentrations and aerosols, spanning a wide range of possible futures. The Working Group I report assessed global and regional-scale climate change for the early, mid and late 21st century.

"As the ocean warms, and glaciers and ice sheets reduce, global mean sea level will continue to rise, but at a faster rate than we have experienced over the past 40 years," said Co-Chair Qin.