{"id":19507,"date":"2021-08-25T10:34:24","date_gmt":"2021-08-25T14:34:24","guid":{"rendered":"http:\/\/www.cr2.cl\/eng\/?p=19507"},"modified":"2021-09-21T10:35:50","modified_gmt":"2021-09-21T13:35:50","slug":"ipcc-climate-report-earth-is-warmer-than-its-been-in-125000-years-nature","status":"publish","type":"post","link":"https:\/\/www.cr2.cl\/eng\/ipcc-climate-report-earth-is-warmer-than-its-been-in-125000-years-nature\/","title":{"rendered":"IPCC climate report: Earth is warmer than it\u2019s been in 125,000 years (Nature)"},"content":{"rendered":"

Landmark assessment says that greenhouse gases are unequivocally driving extreme weather \u2014 but that nations can still prevent the worst impacts.<\/strong><\/p>\n

By Jeff Tollefson<\/p>\n

Modern society\u2019s continued dependence on fossil fuels is warming the world at a pace that is unprecedented in the past 2,000 years \u2014 and its effects are already apparent as record droughts, wildfires and floods devastate communities worldwide \u2014 according to a landmark report from the United Nations on the state of climate science<\/a>. The assessment from the UN\u2019s Intergovernmental Panel on Climate Change (IPCC) says things are poised to get worse if greenhouse-gas emissions continue, and makes it clear that the future of the planet depends, in large part, on the choices that humanity makes today.<\/p>\n

\u201cThe evidence is everywhere: if we don\u2019t act, the situation is going to get really bad,\u201d says Xuebin Zhang, a climatologist at Environment Canada in Toronto, Ontario, and a coordinating lead author on the report, released on 9 August.<\/p>\n

Compiled by more than 200 scientists over the course of several years and approved by 195 governments during a virtual meeting last week, the report is the first in a trio assessing the state of climate change and efforts to mitigate it and adapt to it. The document \u2014 part of the IPCC\u2019s sixth climate assessment since 1990 \u2014 arrives less than three months before the next major global climate summit in Glasgow, UK. There, governments will have the opportunity to make pledges to reverse course and decrease their emissions.<\/p>\n

If global emissions hit net zero by around 2050 \u2014 a target that many countries have committed to over the past year \u2014 then the world can achieve the goal laid out in the 2015 Paris accord and limit global warming to 1.5 \u00b0C above pre-industrial levels over the course of the twenty-first century, says Val\u00e9rie Masson-Delmotte, a climatologist at the Laboratory of Climate and Environmental Sciences in Gif-sur-Yvette, France, and co-chair of the physical-science working group that produced the current report. \u201cThe climate we experience in the future depends on our decisions now,\u201d she says.<\/p>\n

Hotting up<\/strong><\/p>\n

Earth\u2019s global surface temperature has increased by around 1.1 \u00b0C compared with the average in 1850\u20131900 \u2014 a level that hasn\u2019t been witnessed since 125,000 years ago, before the most recent ice age. This is just one of the blunt facts appearing in a summary released with the IPCC report that is intended for policymakers.<\/p>\n

The overall assessment underscores efforts to pin down how much more temperatures will rise if atmospheric emissions continue, and provides climate scientists\u2019 most confident projections yet<\/a> for the twenty-first century. One key metric that researchers use to make their projections is \u2018climate sensitivity\u2019, a measure of how much long-term warming would be expected on Earth from a doubling of atmospheric carbon dioxide concentrations compared with pre-industrial levels. Although the IPCC\u2019s best estimate remains at 3 \u00b0C, the report reduces the uncertainty in that figure, narrowing the probable range to 2.5\u20134 \u00b0C, using evidence such as modern and ancient climate records. This compares with 1.5\u20134.5 \u00b0C, the wider range for sensitivity reported in the IPCC\u2019s last climate assessment, released in 2013.<\/p>\n

This narrowing of climate sensitivity bolsters scientists\u2019 confidence in their projections for what will happen on Earth in a number of different scenarios. In a moderate emissions scenario that features little change from today\u2019s global-development patterns, for instance, average global temperatures will rise by 2.1\u20133.5 \u00b0C, according to the IPCC report. This is well above the 1.5\u20132 \u00b0C limit laid out as a goal by the nations that signed the 2015 Paris climate agreement. Even in a scenario in which governments aggressively cut their greenhouse-gas emissions, the report projects that global temperatures are likely to surpass the 1.5 \u00b0C threshold in the coming years, before dropping back below it towards the end of the century.<\/p>\n

\u201cIs it still possible to limit global warming to 1.5 \u00b0C? The answer is yes,\u201d says Maisa Rojas, a coordinating lead author on the report and director of the University of Chile\u2019s Center for Climate and Resilience Research in Santiago. \u201cBut unless there are immediate, rapid and large-scale reductions<\/a> of all greenhouse gases, limiting global warming to 1.5 \u00b0C will be beyond reach.\u201d<\/p>\n

Extreme impacts<\/strong><\/p>\n

The report lists a dizzying array of impacts that climate change has had on Earth \u2014 and that are already evident from pole to pole. The coverage of sea ice in the Arctic during the late summer has been lower over the past decade than it has been in at least 1,000 years. The ongoing global retreat of glaciers is unparalleled in at least 2,000 years. And oceans are heating up at a pace not seen since the end of the most recent ice age, 11,000 years ago.<\/p>\n

Beyond these sobering measurements, the IPCC report emphasizes some of the most significant scientific advances in understanding the regional effects of climate change, including where extreme heat, precipitation and drought have hit hardest. Extreme drought, for instance, has affected various regions around the globe, with particularly widespread impacts in the Mediterranean region and in southwest Africa.<\/p>\n

As temperatures rise in the future, says Zhang, extreme weather events will become increasingly severe. Over land, an extreme temperature event that occurred once every 50 years in centuries past will probably occur every 3\u20134 years if Earth reaches 2 \u00b0C above pre-industrial temperatures, according to the report. The world should also expect more compound events, such as heatwaves and long-term droughts occurring simultaneously.<\/p>\n

\u201cWe are not going be hit just by one thing, we are going to be hit by multiple things at the same time,\u201d says Zhang.<\/p>\n

Irreversible changes<\/p>\n

Global warming\u2019s impact on bodies such as glaciers, ice sheets and oceans, which adjust slowly to rising temperatures, will continue to be felt for centuries or even millennia, according to the report. Sea levels around the world are projected to rise by 2\u20133 metres over the next 2,000 years, even if temperatures are held in check at 1.5 \u00b0C of warming, and up to 6 metres with 2 \u00b0C of warming, which would alter entire coastlines currently inhabited by hundreds of millions of people.<\/p>\n

The report warns that some of the most severe impacts of climate warming \u2014 such as ice-sheet collapse, massive forest loss or an abrupt change in ocean circulation \u2014 cannot be ruled out, particularly in scenarios in which high emissions and significant warming occur towards the end of the century. But it notes that the biggest uncertainty in all climate-change projections is how humans will act.<\/p>\n

Although the IPCC has been warning about the perils of global warming for three decades, governments have yet to take the kind of action necessary to transition to clean-energy sources and halt greenhouse-gas emissions. But perhaps things are about to change, says Zhang, if only because people all over the world are starting to seeing the impacts of climate change around them.<\/p>\n

\u201cClimate change is happening, and people actually feel it,\u201d says Zhang. \u201cThe report just provides scientific validation to the general public that, yes, what you feel is actually true.\u201d<\/p>\n

But the IPCC report also states something even more important: many of the most dire effects of climate change can still be avoided if aggressive action is taken now. Every degree of warming matters, says Rojas. \u201cThat is a very powerful idea,\u201d she says. \u201cThe future is in our hands.\u201d<\/p>\n

Read at\u00a0Nature<\/a>.<\/p>\n","protected":false},"excerpt":{"rendered":"

Landmark assessment says that greenhouse gases are unequivocally driving extreme weather \u2014 but that nations can still prevent the worst impacts. By Jeff Tollefson Modern society\u2019s continued dependence on fossil fuels is warming the world at a pace that is unprecedented in the past 2,000 years \u2014 and its effects are already apparent as record […]<\/p>\n","protected":false},"author":3,"featured_media":19508,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[12,25],"tags":[],"_links":{"self":[{"href":"https:\/\/www.cr2.cl\/eng\/wp-json\/wp\/v2\/posts\/19507"}],"collection":[{"href":"https:\/\/www.cr2.cl\/eng\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.cr2.cl\/eng\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.cr2.cl\/eng\/wp-json\/wp\/v2\/users\/3"}],"replies":[{"embeddable":true,"href":"https:\/\/www.cr2.cl\/eng\/wp-json\/wp\/v2\/comments?post=19507"}],"version-history":[{"count":1,"href":"https:\/\/www.cr2.cl\/eng\/wp-json\/wp\/v2\/posts\/19507\/revisions"}],"predecessor-version":[{"id":19509,"href":"https:\/\/www.cr2.cl\/eng\/wp-json\/wp\/v2\/posts\/19507\/revisions\/19509"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/www.cr2.cl\/eng\/wp-json\/wp\/v2\/media\/19508"}],"wp:attachment":[{"href":"https:\/\/www.cr2.cl\/eng\/wp-json\/wp\/v2\/media?parent=19507"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.cr2.cl\/eng\/wp-json\/wp\/v2\/categories?post=19507"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.cr2.cl\/eng\/wp-json\/wp\/v2\/tags?post=19507"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}