Approved by 195 governments and based on more than 14,000 studies, the report is the most comprehensive summary of the physical science of climate change to date. It will be a focus when diplomats meet at a UN summit in Glasgow in November to discuss how to step up their emissions reduction efforts.
A growing number of world leaders, including President Biden, have advocated the goal of limiting global warming to 1.5 degrees Celsius, although current policies in major polluting countries are still a long way from achieving that goal to achieve. The top 10 greenhouse gas emitters are China, the United States, the European Union, India, Russia, Japan, Brazil, Indonesia, Iran and Canada.
The new report leaves no doubt that humans are responsible for global warming and concludes that essentially all of the rise in global mean temperature since the 19th and methane trapping the heat.
The previous climate changes have hardly any parallels in human history, the report says. The last decade is probably the hottest on earth in 125,000 years. The world’s glaciers are melting and receding at a rate “unprecedented for at least 2,000 years”. Atmospheric carbon dioxide had not been this high in at least 2 million years.
Sea levels have risen an average of 8 inches over the past century, and the rate of rise has doubled since 2006. Heat waves have gotten significantly hotter since 1950 and last longer in much of the world. Forest fire weather has worsened in much of the world. Extreme ocean heat bursts – which can kill fish, seabirds, and coral reefs – have doubled since the 1980s.
In recent years, scientists have also been able to draw clear connections between global warming and certain storm events. Many of the deadly new temperature extremes the world has seen – such as the record breaking heat wave that scorched the Pacific Northwest in June – “would have been extremely unlikely without human impact on the climate system,” the report said. Greenhouse gas emissions are noticeably exacerbating some droughts, downpours and floods.
