‘It is clear that the next decade is going to be pivotal to securing the future of our planet,’ says UK prime minister Boris Johnson
The target for limiting global heating set out in the Paris Agreement is slipping beyond reach, the world’s leading authority on climate science warns, with the crisis already affecting every region of the planet.
Some of the impacts, such as global sea level rise, could be “irreversible for centuries to millennia”, according to the most comprehensive assessment yet from the UN’s Intergovernmental Panel on Climate Change (IPCC).
The group of 234 scientists from 66 countries found “it is more likely than not” that the world will reach 1.5C above pre-industrial levels sometime over the next 20 years – with the risk of far greater global warming if little is done to tackle rapidly rising greenhouse gas emissions. Temperatures currently stand at around 1.2C above pre-industrial levels.
And there is “unequivocal” evidence that humans are to blame for rapidly rising land and ocean temperatures – the strongest statement yet from the IPCC after its last assessment report in 2013 said people were the “dominant cause” of global heating.
“We’re already experiencing climate change, including more frequent and more extreme weather events,” Prof Ed Hawkins, a climate researcher at the University of Reading one of the scientists behind the milestone report, told a press briefing.
“The consequences will continue to get worse for every bit of warning and – for many of these consequences – there’s no turning back.”
The summary findings, from the first chapter of the IPCC’s sixth assessment report, come just three months before world leaders are due to meet in Glasgow for the global climate summit, 警察26. The “summary for policymakers”, a 41-page overview of the report released on Monday morning, will play an important role in informing high-level discussions on how to cut emissions.
UK prime minister 鲍里斯·约翰逊 said the report’s findings made “sobering reading”.
“It is clear that the next decade is going to be pivotal to securing the future of our planet,“他在一份声明中说. “We know what must be done to limit global warming – consign coal to history and shift to clean energy sources, protect nature and provide climate finance for countries on the frontline.”
“The IPCC report underscores the overwhelming urgency of this moment. The world must come together before the ability to limit global warming to 1.5C is out of reach,” said the US Special Presidential Envoy for Climate John Kerry.
他加了: “We can get to the low carbon economy we urgently need, but time is not on our side. This is the critical decade for action, and Cop26 in Glasgow must be a turning point in this crisis.”
The report reflects major progress in the field of attribution – the science of how human-caused climate change is influencing the frequency and intensity of extreme weather events. Hundreds have died in recent heatwaves from the US and Canada to India, along with Iraq and elsewhere in the Middle East.
Flooding has devastated regions of Nigeria, 印度, 中国, 德国, Belgium and the UK, while wildfires have exploded across the Brazilian Amazon, Siberia, parts of southern Europe and the American West.
The report says “it is virtually certain” that heatwaves have become more intense and more frequent over the past 70 years and that many other types of extreme weather events are also becoming more likely.
“Climate change is not a problem of the future – it’s here and now and affecting every region of the world,” added Dr Friederike Otto, a report author and associate director of the Environmental Change Institute at the University of Oxford.
Almost all countries agreed to keep global temperatures below 2C by 2100, with an aspiration of limiting warming to 1.5C under the historic Paris Agreement in 2015. 一个 interim IPCC report 在 2018 found that the additional half a degree of heating would spell disaster for low-lying island nations, tropical coral reefs and glaciers.
The new report looks at five possible futures for the Earth’s climate over the coming decades, ranging from a scenario with very low greenhouse gas (GHG) emissions to one with very high GHG emissions.
It finds that, under every scenario, “it is more likely than not” that the world will reach 1.5C sometime between 2021 和 2040. 和, under a scenario of very high GHG emissions, it is “very likely” that temperatures will exceed 1.5C in the near term.
然而, if the world successfully cuts GHG emissions to very low levels and rolls out techniques to remove CO2 from the atmosphere, it is more likely than not that temperatures will decline back to below 1.5C towards the end of the century, the report adds.
“[If we] go past 1.5C degrees, that doesn’t necessarily constitute a failure of our climate policies,” said Prof Piers Forster, a report author and director of the Priestley International Centre for Climate at the University of Leeds.
“We want to clearly get across that every bit of additional warming we can prevent is really a success.”
The IPCC’s 2018 interim report found that the world will reach 1.5C at a later period of between 2030 和 2052. 然而, the report authors said the two estimates are based on different methodologies and so are not directly comparable.
分析 by the research group Climate Action Tracker shows that current pledges and targets put forward by countries would cause around 2.4C of global heating by 2100. Most countries do not have the policies in place to meet these targets.
The report also warns that potential tipping points in Earth’s climate – thresholds where a small change could lead to dramatic change – “can’t be ruled out”. Such tipping points could include ice sheet collapse or abrupt changes to ocean circulation patterns, it adds.
然而, taking urgent action to address greenhouse gas emissions would minimise the likelihood of such tipping points occurring, the scientists said.
The report adds that oceans and forests, which have long acted as buffers to the climate crisis by absorbing CO2 from the atmosphere, are projected to be less effective if greenhouse gas emissions continue to rise rapidly.
Along with the goal of net-zero CO2 emissions by 2050, the report highlights that dramatic and rapid cuts in super-potent methane would have a significant impact, not just on global heating but more immediately on air quality.
Methane has a shorter lifespan that CO2, which remains in the atmosphere for centuries, but has about 80 times the warming power over the first 20 年.
一种 UN report published in May found that if methane is cut in half by the end of this decade, around half a degree of warming could be prevented by 2050.
This is highly achievable and relatively cheap, researchers found, as it requires plugging leaky oil and gas pipelines, sealing abandoned wells and capturing gas from landfill along with the more complex issues of reducing methane burps from livestock and in the agricultural sector.
Climate activists, policy experts and environmental groups called for immediate action in light of the report’s findings.
Mohamed Adow, director of Nairobi-based think tank Power Shift Africa, 说: “Those of us living in Africa have been aware of the urgency of the climate crisis for many years. Lives and livelihoods have been shattered by overwhelming heat, rising seas and extreme weather. It is vital that governments heed the warning of the IPCC’s scientists and act with speed and boldness to make our world safer, cleaner and greener.”
Helen Mountford, vice president of climate and economics at the World Resources Institute, 说: “If this IPCC report doesn’t shock you into action, it should. The report paints a very sobering picture of the unforgiving, unimaginable world we have in store if our addiction to burning fossil fuels and destroying forests continues.
“While the IPCC’s findings are alarming, they most certainly should not translate to hopelessness or inaction… This report should galvanize every country, 公司, city and citizen to fight like hell to avoid every bit of warming we can.”
The remaining chapters of the IPCC’s sixth assessment report, including detailed assessments of how the world can mitigate greenhouse gas emissions and adapt to worsening climate impacts, are due to be published in 2022.