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August 9, 2021
by Marlowe Hood and Patrick Galey
The first major scientific assessment by the UN Intergovernmental Panel on Climate Change since 2014, published on Monday, clearly shows that global warming is developing faster than feared and that it is almost entirely human.
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Here is an overview of some of the key findings from the IPCC Working Group 1 report on physics:
The Earth’s average surface temperature is projected to be around 2030 in all five greenhouse gas emission scenarios – from very optimistic to reckless – which are taken into account in the report, reach 1.5 or 1.6 degrees Celsius above pre-industrial levels. That is a whole decade earlier than the IPCC forecast three years ago.
By the middle of the century, the 1.5C limit will have been broken across the board, by a tenth on the most ambitious route and by almost a whole degree in the opposite extreme.
There is a silver lining: In the most ambitious scenario, if we do everything right, global temperatures will drop to 1.4 ° C by 2100 after “overshooting” the 1.5 ° C target.
Since around 1960, forests, soils and oceans have absorbed 56 percent of all CO2 that mankind emitted into the atmosphere – even though these emissions have increased by half. Without the help of nature, the earth would be much hotter and less hospitable.
But these allies in our fight against global warming – known in this capacity as carbon sinks – are showing signs of saturation, and the percentage of man-made carbon they ingest will likely decline over the century.
The report highlights the amazing advances made by a new field, attribution science, in quantifying the extent to which man-made global warming increases the intensity and / or likelihood of a particular extreme weather event such as a heat wave, hurricane or hurricane Wildfire increased.
For example, within a few weeks scientists discovered that the record breaking heat wave that devastated British Columbia in June would have been « practically impossible » without the impact of climate change.
More broadly, the IPCC report contains In 2021 there will be far more “high confidence” results than before.
The world’s oceans have increased about eight inches (20 centimeters) since 1900, and the increase has nearly tripled in the past decade. Crumbling and melting ice sheets over Antarctica, and especially Greenland, have replaced glacier melting as the main driver.
If global warming is limited to 2 ° C, the ocean’s watermark will rise by about half a meter in the 21st century. It will rise to almost two meters by 2300 – twice as much as the IPCC forecast for 2019.
Due to the uncertainty about the ice sheets, scientists cannot rule out a total increase of two meters by 2100 in a worst-case emission scenario.
For example, the last time the planet’s atmosphere was as warm as it is today, about 125,000 years ago, global sea levels were likely 5 to 10 meters higher – a level that would submerge many large coastal cities.
Three million years ago, when atmospheric CO2 concentrations were the same as they are today and temperatures were 2.5 to 4 ° C higher, sea levels were up to 25 meters higher.
The report contains more Data than ever on methane (CH4), the second most important greenhouse gas after CO2, and warns that if emissions are not contained, the Paris Agreement targets could be undermined.
Man-made sources are roughly divided between leaks from natural gas production, coal mining and landfills on the one hand, and livestock farming and manure handling on the other.
CH4 only lingers one in the atmosphere Fraction of as long as CO2, but far more efficient at capturing heat. The CH4 value is the highest in at least 800,000 years.
Although all parts of the planet – from the oceans to the land to the air we breathe – are warming, some areas warm faster than others. In the Arctic, for example, the average temperature of the coldest days is projected to increase by three times the global warming of the entire planet.
Sea levels are rising everywhere, but are likely to rise up to 20 percent above the global average on many coastlines.
The IPCC warns of « low probability, high impact » abrupt shifts in the climate system that if they are irreversible, are referred to as tipping points. Crumbling ice sheets that contain enough water to raise the seas a dozen meters; the melting of permafrost soils laden with billions of tons of carbon; the transition of the Amazon from tropical forest to savannah – are all examples.
« Abrupt reactions and tipping points of the climate system … cannot be ruled out, » states the report.
The Atlantic Meridional Overturning Circulation (AMOC) – a large system of ocean currents that controls global heat transfer from from the tropics to the northern hemisphere – slowing down, a trend that is “very likely” to continue into the 21st century.
Scientists have only « medium confidence » that the AMOC will not come to a complete standstill as it has in the past. If it did, European winters would be much harsher, monsoons would likely be interrupted, and sea levels in the North Atlantic Basin could rise significantly.
© 2021 AFP
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