Let us be absolutely clear: scientists are in no doubt that climate change is happening, that it’s being caused by the build-up of heat-trapping gases in the atmosphere, that humanity is largely to blame for these concentrations and that the impacts will become more severe and widespread if we continue burning fossil fuels on an unrestricted basis. That’s what the UN’s Intergovernmental Panel on Climate Change (IPCC) has concluded in the final part of its Fifth Assessment Report, summarising the findings of three volumes of work following a review of some 30,000 pieces of peer-reviewed scientific literature on climate change over the five years to 2013. Its 13 main findings are a remarkable distillation of critical issues; what faces Planet Earth and what needs to be done.
Not only is warming of the climate system "unequivocal", but the human influence "clear". Atmospheric concentrations of carbon dioxide and other greenhouse gases are at their highest level for 800,000 years; the last time CO2 reached such a peak, humans didn't exist. In the northern hemisphere, for which better records exist, the past three decades have been the warmest for 1,400 years – a century or so after St Patrick brought Christianity to Ireland. Surface temperatures are projected to rise during the 21st century under all emission scenario, threatening more intense and frequent heatwaves, storms and other extreme weather events.
The IPCC’s report makes it clear tackling climate change will require “substantial and sustained reductions” in emissions. Indeed, these will need to fall to zero by 2100 if we are to have any chance of limiting global warming below the potentially dangerous threshold of 2 degrees – the internationally agreed target. If average global surface temperatures were to rise 4 degrees, life on Earth would be dramatically changed, with “substantial species extinction” as well as global and regional “food insecurity”, slower economic growth and more people condemned to live in abject poverty, notably in developing countries that are least to blame.
As UN secretary-general Ban Ki-moon said at the report's launch "science has spoken yet again, and with much more clarity". If the world maintains a "business-as-usual" stance, the opportunity to achieve the 2-degree target "will slip away within the next decade," he warned. "Time is not on our side . . . leaders must act." Indeed they must, not least by availing of the forthcoming UN climate conference in Lima, Peru, to devise a draft negotiating text for the international agreement that's meant to be concluded in Paris before the end of next year. Given the IPCC conclusions, any further delay in a process that's been going on for 20 years would be an unconscionable disservice to humanity and the entire natural world.