The Intergovernmental Panel on Climate Change (IPCC) has released the summary and final draft of its fifth assessment of the state of scientific knowledge on climate change. The authoritative panel, which examines the latest results from both observation and model-based studies, concludes that “warming of the climate system is unequivocal”. It goes on to state that human activity is “extremely likely” to be the dominant cause of this warming.
This is the phrase that the IPCC uses when it has 95% confidence in a conclusion. Importantly, it is five percentage points more confident that humans are driving climate change than when it published its fourth assessment report in 2007.
In addition to identifying the causes of the observed warming, the IPCC also examines the changes in the climate system that are happening as a result. It finds that:
• Almost the entire surface of the planet is warmer now that it was a century ago.
• The atmospheric concentration of carbon dioxide has increased by 40% since the start of the Industrial Revolution to a level that is unprecedented in at least 800,000 years.
• Land ice is melting at an increasing rate around the North and South poles.
• Global average sea level has risen by 19 cm since the start of the twentieth century due to expansion of the warming water, as well as fresh water input from melting land ice.
The report provides a bleak picture of the future. Continued emissions of greenhouses gases, the IPCC believes, will provoke changes across the entirety of the climate system. There is a reasonable chance that by 2100 the target of limiting warming to less than 2oC, thought to be necessary to avoid so-called dangerous climate change, will have been breached.
The only way to prevent the worst of the predicted changes from occurring is to make cuts to our greenhouse gas emissions that are “substantial and sustained”.
Dr. Tim Osborn of UEA’s Climactic Research Unit contributed to the writing of the summary during an international meeting in Stockholm. He highlighted the extent of human influence on climate as the “key finding” of the report. “Policy makers now have the latest independent and authoritative assessment to help guide their decision making”, he said. He added that the report does not present politicians with any easy choices.