Climate change is unequivocal, affects all continents and will continue to the end of the century regardless of even the toughest emissions cuts, warned a landmark UN science report today.
Greenhouse gases released by human activity have caused sea levels to rise, Arctic ice to melt and oceans to become more acidic, the report said.
One of climate science’s greatest controversies, the 15-year pause in global warming, is described as an example of natural variability which does “not in general reflect long-term climate trends”.
The UN’s Intergovernmental Panel on Climate Change [IPCC] released the fourth and final installment of its latest assessment on global warming in Copenhagen on Sunday after a week of intense discussions between scientists and politicians.
Sleep deprived delegates stayed up to 5am on Saturday morning to finalise the document, which will form the scientific basis of the UN’s negotiations for a new international climate change agreement, set to be signed off in in Paris next year.
“We have the means to limit climate change,” said Rajendra Pachauri, chair of the IPCC.
“The solutions are many and allow for continued economic and human development. All we need is the will to change, which we trust will be motivated by knowledge and an understanding of the science of climate change.”
The 116-page report brings together six years of work by 830 scientists, who have synthesized over 30,000 scientific papers on the cause, effects and possible solutions to climate change.
The IPCC’s last report came out in 2007.
Since then, the evidence of human influence on the atmosphere has increased, the scientists announced.
And despite more policies designed to limit greenhouse gases, the last decade has seen greater volumes of emissions than ever before, the report warned.
“The longer we wait to take action, the more it will cost to adapt and mitigate climate change,” said Youba Sokona, who chaired the IPCC’s report on options to reduce greenhouse gases.
“Compared to the imminent risk of irreversible climate change impacts, the risks of mitigation are manageable.”
Burning coal, oil and gas has been responsible for 78% of the increase in emissions since 1970, with growing populations and economies driving activity.
Greater use of coal – the dirtiest fossil fuel – has undermined attempts to create a cleaner energy system, it says. It warns that that the impacts have been felt across all continents and the oceans.
The burden on the global economy and sectors such as agriculture is expected to increase as the planet gets warmer.
Even with aggressive emissions reductions designed to keep the world from heating beyond the dangerous threshold of 2C, warming is inevitable until the end of the century, scientists said.
“A large fraction” of this will be irreversible for centuries, they warn, with impacts continuing to be felt across the natural world thousands of years after temperatures have stabilised.
“To keep a good chance of staying below 2C, and at manageable costs, our emissions should drop by 40 to 70% globally between 2010 and 2050, falling to zero or below by 2100,” said Pachauri.
To limit global warming to safe levels, humans can emit no more than 2900 gigatonnes of carbon dioxide. Of this budget, only around 1000 Gt remains.
Current fossil fuel reserves—the bedrock of the global economy—contain enough carbon dioxide to exceed this budget by up to seven times, the report said.
Dividing it up among countries will prove politically difficult.
The concept of the carbon budget was omitted from the IPCC’s “summary for policymakers”, the 40-page summary which politicians will read, after lobbying from a number of countries including the US and India.
Leading climate economist Lord Nicholas Stern said that the report should be “essential reading” for political leaders across the world.
Options are available to combat climate change, the scientists say. Reducing emissions now and in the future can “substantially reduce climate change impacts in the latter decades of the 21st century and beyond”.
To keep warming below dangerous levels, emissions will have to drop to near zero by the end of the century, the report says.
The solutions are not financially crippling. Economists involved in the report say that the policies and technologies required to keep global temperatures below 2C will reduce economic growth by around 0.06% every year over the century.
As growth itself is projected to be between 1.6-3%, this means that humans will still be richer in the future, even under the most stringent climate policies. And this doesn’t include the benefits of stopping climate change.
Since their previous 2007 report, there has been a “considerable increase” in national and sub-national governments implementing policies to both adapt to climate change and cut emissions.
The report released today will form the scientific basis of UN negotiations, as politicians prepare to sign off a new deal to address climate change in Paris next year.
“If we fail to act, we jeopardise efforts to reduce poverty and endanger food, water and livelihoods for many of the world’s poor,” said Samantha Smith, head of WWF’s climate and energy initiative.
“We also leave today’s youth and future generations with a nearly insurmountable challenge.”