800 scientists behind the "most comprehensive assessment of climate change ever undertaken" have come to the conclusion that humans' influence on our climate is already apparent and growing, with impacts now observable on all continents.

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Amongst the report’s key findings are that measures to tackle climate change are affordable, but that delaying action will make future moves much costlier, that global poverty and climate change are inextricably linked, and action on one will require action to tackle the other, and that emissions from fossil fuels will have to fall to zero by the end of the current century.

The final Synthesis Report, released on Sunday, follows the gradual publication of findings from the IPCC's working groups over the past 13 months. Though the pronouncements are grave, the IPCC experts maintain that "options are available to adapt to climate change" and ensure that the impacts remain "Within a manageable range."

"We have the means to limit climate change," elaborated IPCC chair Rajendra Pachauri. "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."

However, some scientists, notably Kevin Anderson, former head of the UK's Tyndall Centre for Climate Change Research has warned that such mitigation is now unlikely and that only radical reforms and de-growth policies in richer countries can lead to the changes in emissions needed to avoid disastrous climate change. Given the gulf between political rhetoric and action on climate issues, Prof Anderson said last month, "I think it very likely we will choose to fail, but this is a choice – not a fait accompli."

'Unequivocal' evidence of global warming

The IPCC Report will be used to inform world leaders meeting for climate talks in Paris next year. It confirms that there is "Unequivocal" evidence that the global climate is warming. Since the 1950s many of the observed changes are unprecedented over decades to millennia, the IPCC authors warn, and they are certain that this is the result of human activity.

"Our assessment finds that the atmosphere and oceans have warmed, the amount of snow and ice has diminished, sea level has risen and the concentration of carbon dioxide has increased to a level unprecedented in at least the last 800,000 years," Summarised Thomas Stocker, Co-Chair of IPCC Working Group I.

The disastrous effects of these changes pose a disproportionate threat to those living in poorer countries, given their locations and limited ability to cope. IPCC authors said "People who are socially, economically, culturally, politically, institutionally, or otherwise marginalized are especially vulnerable to climate change."

In the words of IPCC chair Pachauri, recognition that "Many of those most vulnerable to climate change have contributed and contribute little to greenhouse gas emissions," has given rise to arguments for Climate Justice – that views climate change as an ethical issue.

Pachauri added, "Addressing climate change will not be possible if individual agents advance their own interests independently; it can only be achieved through cooperative responses, including international cooperation."

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Though IPCC experts recommend that effective adaptation measures be developed immediately, which have a greater focus on equity and cooperation, they are clear that adaptation alone is not enough. "Substantial and sustained" reductions of greenhouse gas emissions are needed to limit the risk of disastrous climate change. Since mitigation reduces the rate as well as the magnitude of warming, they warn, it also increases the time available for adaptation to a particular level of climate change, potentially by several decades.

Working Group III chair Youba Sokona said, "It is technically feasible to transition to a low-carbon economy, but what is lacking are appropriate policies and institutions. The longer we wait to take action, the more it will cost to adapt and mitigate climate change."

"Compared to the imminent risk of irreversible climate change impacts, the risks of mitigation are manageable."

The IPCC authors maintain that moves to tackle climate change need only have minimal impacts on growth, and even provide some benefits, such as cutting damage to public health and the environment from pollution.

Illustrating once more that an immediate response would be the most cost-effective and least disruptive course of action, Pachauri added, "We have little time before the window of opportunity to stay within 2ºC of warming closes. To keep a good chance of staying below 2ºC, and at manageable costs, our emissions should drop by 40 to 70 percent globally between 2010 and 2050, falling to zero or below by 2100. We have that opportunity, and the choice is in our hands."

However, responding to last week's EU commitments to source at least 27 percent of energy from renewable sources, reduce greenhouse gas emissions by 40 percent and drive a 30 percent increase in energy efficiency by 2030, Tyndall Centre's Kevin Anderson warned, "There is little time to convert a sow's ear into a silk purse – and the omens are not looking good if the EU's decision to adopt a leaky 40% target by 2030 is anything to go by."

Countering EU Climate Commissioner Connie Hedegaard's claim that "The [EU] policies work," Prof Anderson wrote on his blog, "If we are serious about repeated international commitments to reduce emissions in line with the 2°C obligation… the EU will need to reduce its emissions by over 80% by 2030 – with the rapid phase out of all fossil fuels soon after," arguing that thus far the easily achievable targets and seemingly empty rhetoric on climate action amount to "Elaborate ruses for inaction."