Scientists are more certain than ever that humans are causing climate change, prompting calls for renewed focus on developing renewable energy.
The first part of the Intergovernmental Panel on Climate Change's (IPCC) fifth assessment report, released today, shows that global warming is "unequivocal" and human influence on the climate is clear.
The report, which has been published in Stockholm after line-by-line scrutiny by scientists and policymakers, found it is "extremely likely", or 95 per cent certain, that the majority of the warming since the 1950s is down to human activity, up from a 90 per cent certainty in the last IPCC study in 2007.
As a result of the warming, ice sheets are losing mass, glaciers are shrinking, sea ice cover has reduced in the Arctic and the permafrost is thawing in the northern hemisphere, the report – which draws on thousands of scientific papers – warns.
Experts said the report was a "wake-up call" that activities such as burning fossil fuels would have a profound effect on society today and in the future and campaigners called for immediate action to cut greenhouse gas emissions.
Maf Smith, deputy chief executive of renewable energy trade association RenewableUK, the trade said: “The scientific community is sending a clear and unequivocal message to policymakers that urgent action is needed to reduce our carbon emissions and set in place paths to create a future of clean, carbon reducing sources of energy if we are to reduce our negative impacts on our environment.”
“Wind has a vital role to play in this, given that as a result of wind power deployment in the UK we are reducing by 10 million tonnes every year the amount of carbon that we pump in to the atmosphere.
“This report shows that we cannot rest on our laurels though, we have to make sure that we hit our 2020 carbon reduction targets as well as looking beyond 2020 so we can create a decarbonised economy fit for the future.”
Lord Stern, who authored the key review on the economics of climate change, said: "Delay is dangerous because greenhouse gases are accumulating in the atmosphere and because we are locking in high-carbon infrastructure and capital."
To have a 50 per cent chance of keeping temperature rises to no more than 2C, there is a limit to how much greenhouse gas can be emitted in the 21st century, and at current rates the world will have hit the limit in 15 to 25 years, he said.
Lord Stern said he expected nations, businesses and communities to increase the urgency and scale of emissions reductions in the light of the report and that the emissions "budget" would focus the minds of governments taking part in international negotiations on a new global climate deal.
"The transition to a low-carbon economy, led by private sector investment, in the context of sound public policy, will be full of opportunity, discovery, innovation and growth," he added.
But Professor Richard Dawson, chair of Earth System Engineering at Newcastle University’s School of Civil Engineering and Geosciences, said that simply focusing on reducing emissions is not enough – work must be done to prepare for the negative impacts of climate change.
"More than half of the world’s population now lives in urban areas, many of them located in low-lying coastal or delta areas,” he said.
“Urban areas concentrate people, infrastructure and economic activity, making them disproportionately vulnerable to weather extremes like heat waves or flooding. Furthermore, they are major consumers of resource and producers of pollutants both within and outside their boundaries.
“The latest IPCC findings highlight that in the face of continued global change it remains an international priority to adapt urban areas and infrastructure to be more resilient to a wider range of environmental conditions, and to reduce their contribution towards emissions through more efficient use of resources and reduced greenhouse gas emissions."