The UN's Intergovernmental Panel on Climate Change delivered its first comprehensive report on the state of the planet's climate since 2013 on Monday. In a gesture of unity, representatives from all 95 member nations endorsed the conclusions found in the report, which directly linked human activity to recent waves of volatile weather and redefined the sensitivity of the earth's climate to human emissions, among other things.
"We've known for decades that the world is warming but this report tells us that recent changes in the climate are widespread, rapid and intensifying, unprecedented in thousands of years," said Ko Barret, one of the panels vice chairs and a senior climate advisor at the National Oceanic and Atmospheric Administration. "Further, it is indisputable that human activities are causing climate change."
The IPCC report distilled the findings of 14,000 individual climate studies to reach its conclusions, some of which were grimmer than others. For example, Climate scientists now believe that a hypothetical doubling of human emissions would lead to a temperature spike of 2.4-5 ° C, a much narrower range than previously thought. Said findings dash any remaining hope that the effects of unmitigated climate change would fall toward the moderate end of the spectrum.
The IPCC found that enough pollutants are currently circulating in the atmosphere to warm the earth by 1.5 ° C, the limit set by the Paris Climate Agreement. However, fine particle pollution is currently mitigating the impact of these greenhouse gases by diffusing sunlight in the atmosphere and causing cooling.
Nevertheless, the data shows that the 2010s were the hottest decade in 125,000 years. Meanwhile, CO2 levels are at a 2 million high while concentrations of more potent greenhouse gases, methane and nitrogen dioxide are both at an 800,000-year peak. At the same time, global sea levels continue to rise at a rate of roughly 0.1 inches annually.
The report finds that human impact on sea ice might not be reversible for millennia, and that sea levels will likely climb for centuries. Under every scenario, global temperatures are expected to get hotter until mid-century. At which point, depending humanity's effort to curb emissions, temperatures could continue to climb by 1.5-2 °C until the end of the century.
There is hope, however. After a few decades of near-zero-emissions, the earth's climate should stabilize, the report finds.
Climate science is ever advancing, and decades of heatwaves, droughts, and unprecedented hurricanes have sharpened the tools of researchers to such a degree that individual weather events can now be confidently attributed to human activity. For example, in the case of this summer's heatwave that has broiled the U.S. West Coast, research group World Weather Attribution concluded that the record highs reached during that time would be "virtually impossible," if not for human-caused climate change.
"When you see what has happened this summer with heat waves in Canada and the heavy precipitation in Germany, I think this is showing that even highly developed countries are not spared," Sonia Seneviratne, a senior scientist at ETH Zurich in Switzerland and a lead co-author of the report told the Wall Street Journal. "We don't really have time to adapt anymore because the change is happening so quickly."