'Severe' climate change predicted
The world faces "severe, widespread and irreversible" impacts of climate change without urgent action to cut emissions, a major international report has warned.
While there are solutions to climate change, experts warned there was little time before the window of opportunity to limit dangerous temperature rises closed, and that delaying action would greatly increase costs.
Significant and swift cuts to greenhouse gases are needed, with the phasing out fossil fuelled power plants without technology to capture and store their carbon by the end of the century, and a shift away from investment in oil, coal and gas towards renewables.
The stark warning comes from the UN climate body's final report of its latest assessment on the science of climate change, which draws together three studies published in the past year.
The Intergovernmental Panel on Climate Change's (IPCC) report showed global warming was "unequivocal" and human influence on the climate was clear. It was "extremely likely" or more than 95% certain that the majority of the warming since the 1950s was down to human activity.
Climate change was already having an impact on every continent, affecting human health, agriculture and wildlife, and increasing weather extremes, the Synthesis Report said.
Massive cuts to greenhouse gas emissions are needed in the coming decades to curb temperature rises to no more than 2C - the level at which it is thought dangerous impacts of climate change will be felt.
A failure to take more action than is already planned to curb greenhouse gases leaves the world at risk of temperatures soaring 3.7C to 4.8C, or even higher, by 2100.
The planet would face rising temperatures and sea levels, species extinctions, more heatwaves and intense storms, worsening health and poverty, water shortages and damage to food security, the report warned.
Pledges made by countries to cut greenhouse gases by 2020 were not enough and delaying action until 2030 would make it much harder to keep temperature rises to below 2C, it said.
But efforts to tackle emissions would not have a major impact on economic growth, as ambitious moves on climate change were likely to curb global growth by just 0.06 percentage points.
The figure does not take into account the economic impacts that runaway climate change would have, or other financial benefits that action could deliver, such as reduced costs of ill health due to air pollution.
Rajendra Pachauri, chairman of the IPCC said: "We have the means to limit climate change. 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."
He said the scientific case for prioritising action on climate change was clearer than ever.
But he warned: "We have little time before the window of opportunity to stay within 2C of warming closes.
"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.
"We have that opportunity, and the choice is in our hands."
Launching the report in Copenhagen, UN secretary general Ban Ki-moon said: "Science has spoken, there is no ambiguity in their message. Leaders must act. Time is not on our side."
But he said: "The good news is that if we act now immediately and decisively we have the means to build a better and more sustainable world.
"Many tools and technologies are already available, renewable energy sources are increasingly economically competitive, energy efficiency has long proven its value.
"Action on climate change can contribute to economic prosperity, better health and more liveable cities while reducing the risks of future environmental degradation."
The report comes as efforts build towards securing a new global treaty on climate change, which it is hoped can be agreed in Paris at the end of next year.
It prompted calls from environmental campaigners for the world to shift away from fossil fuels, while business leaders called on governments to secure an ambitious deal to give them certainty to invest in a low-carbon future.
The Synthesis Report brings together the three parts of the IPCC's fifth assessment on climate change, an analysis which involves thousands of scientists and experts and drew on 30,000 scientific papers, and has been subject to scrutiny and approval by governments.