Last reviewed 3 October 2013

“Human influence on the climate system is clear and evident in most regions of the globe”, a new assessment by the Intergovernmental Panel on Climate Change (IPCC) has concluded.

“It is extremely likely human influence has been the dominant cause of the observed warming since the mid-20th century,” the IPCC said. “The evidence for this has grown, thanks to more and better observations, an improved understanding of the climate system response and improved climate models.”

Qin Dahe, Co-Chair of IPCC Working Group I, said: “Observations of changes in the climate system are based on multiple lines of independent evidence. Our assessment of the science 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. 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. Heatwaves are very likely to occur more frequently and last longer. As the Earth warms, we expect to see currently wet regions receiving more rainfall, and dry regions receiving less, although there will be exceptions.

“As a result of our past, present and expected future emissions of carbon dioxide (CO2), we are committed to climate change, and effects will persist for many centuries even if emissions of CO2 stop.”

Discussing the report, Professor Sir Brian Hoskins, Director of the Grantham Institute for Climate Change, said: “This report significantly strengthens the consistent message from the four previous IPCC assessment reports: climate change is happening and we are conducting a dangerous experiment with our planet.

“It presents comprehensive evidence of change in many different aspects of the climate system, from the ice sheets to the deep ocean, as well as providing scenario-based projections of how the climate might evolve for the rest of this century and beyond.”

Nilay Shah, Professor of Process Systems Engineering at Imperial College London, said: “Energy systems will take decades to change but we need to start now with major drives to improve energy efficiency and a determined transition to a low-carbon energy system. This means lowering the carbon intensity of electricity, using renewables such as solar and wind, as well as carbon capture and storage and nuclear power.

“It also means an increased role for low-carbon electricity and other low-carbon fuels in the buildings, transport and industry sectors, and using carbon capture and storage to reduce CO2 emissions from industrial sources. Numerous studies have come to the conclusion that mitigation will probably cost around one or two per cent of GDP, with the important caveat that we have the right policies in place.”