/ 27 September 2013

IPCC report: 95% certainty that humans drive climate change

It is "very likely" anthropogenic greenhouse gas emissions have contributed to more than half of all global warming since the middle of the previous century
It is "very likely" anthropogenic greenhouse gas emissions have contributed to more than half of all global warming since the middle of the previous century

The Intergovernmental Panel on Climate Change released its fifth big report on Friday, which has confirmed that it is 95% certain that humans contribute to climate change.

The report said: "It is extremely likely that human interference has been the dominant cause of the observed warming since the mid-20th century."

The evidence supporting this – which led to an increase from the prediction in its 2007 report that it was "very likely" – had been gathered by more, and better observations, as well as "an improved understanding of the climate system response and improved climate models".

Extremely likely means there is a 95% certainty, which is as high a certainty as science can provide. Very likely meant a 90% certainty. The panel is a UN body that is tasked with giving comprehensive reports on the science around climate change. It takes all the reports out there and creates an overview of what scientists are thinking on climate change.

The report, "Climate Change 2013: the Physical Science Basis", has been several years in the making and is the work of over 600 scientists from 32 countries. They looked at 9 200 peer-reviewed articles on climate change, backed by two-million gigabytes of data. This week the scientists and government representatives gathered in Stockholm to create a final document that would give the consensus view on climate change. 

The last three decades have been successively warmed in the lower layers of the atmosphere – the ones where life exists. 

The highlighted projections are that the average global temperature will increase by a minimum 1.5C by the end of this century, and is likely to exceed 2C. The climate will also change. Heat waves will be more frequent and last longer, rainfall will be harder and more sporadic. Wet places will get wetter and dry places will get drier – which is a huge problem for South Africa given that it is the 30th driest country in the world.

'Oceans have warmed'
The intergovernmental panel defended against criticisms of the way it had gotten its evidence by saying: "Observations of changes in the climate system are based on multiple lines of independent evidence." It concluded that the atmosphere and the oceans have warmed, and the total amount of snow and ice had diminished. Global average sea levels had risen, and the concentration of greenhouse gases in the atmosphere had increased. 

Thomas Stocker, the co-chair of the group in Stockholm that created the summary, said, "Continued emissions of greenhouse gases will cause further warming and changes in all components of the climate system." Action had to be taken now, backed by political will. "Limiting climate change will require substantial and sustained reductions of greenhouse gas emissions."

Sceptics have attacked the panel for what they see as 15 years of no warming – an attack based on tinkering with statistics. The panel addressed this, saying that temperatures increases had been lower than predicted because heat was being stored in the ocean. "The report finds with high confidence that ocean warming dominates the increase in energy stored in the climate system, accounting for more than 90% of energy accumulated between 1971 and 2010."

Stocker warned that current and historical emissions of greenhouse gases meant that humanity was locked into temperature increases. "As a result of our past, present and expected future emissions of carbon dioxide, we are committed to climate change, and effects will persist for many centuries even if emissions of carbon dioxide stop."

This Summary for Policymakers will be used by governments around the world to inform their policy decisions.