Monday's UN Intergovernmental Panel on Climate Change released its first major scientific assessment since 2014. It clearly shows that global warming is happening faster than expected and that humans are almost entirely responsible.Here's a summary of the key findings of the IPCC Working Group 1 Report on Physical Science:Goodbye 1.5 C, hello overshootThe report projects that the Earth's average surface temperature will rise to 1.5 to 1.6 degrees Celsius above preindustrial levels by 2030. This is in accordance with five different greenhouse gas emission scenarios. These scenarios range from extremely optimistic to reckless. This is a decade sooner than what the IPCC had predicted only three years ago.The 1.5 C threshold will be breached by midcentury. It will be broken by almost a full degree for the extremes and a tenth of an degree for the rest.There is a silver lining: in the most ambitious if-we-do-everything-right scenario, global temperatures - after "overshooting" the 1.5 C target - fall back to 1.4 C by 2100.The natural climate is weakeningThe Earth's forests, soil, and oceans have taken 56 percent of the CO2 humanity has released into the atmosphere since 1960. This is despite the fact that these emissions have increased by half. Earth would be much more hot and less welcoming without the help of nature.These allies in the fight against global warming - also known as carbon sinks – are starting to show signs of becoming saturated. The percentage of human-induced CO2 they absorb is expected to decrease as the century progresses.Climate change is indeed to blameThis report highlights the remarkable progress made by attribution science in quantifying how human-induced global warming increases the intensity or likelihood of extreme weather events such as a heatwave.Scientists proved that climate change was responsible for the record-breaking heatwave in British Columbia that decimated British Columbia in June. This was just weeks after scientists had established this.The 2021 IPCC Report contains many more findings that were "highly confident" than ever before.Sea rising higher, more quicklyThe global oceans have increased by 20 centimetres (8 inches) in the past century. This has almost tripled over the last decade. The main driver of global oceans' growth has been replaced by melting glacier melt.The ocean watermark will rise by about half a meter if global warming is stopped at 2 C. It will rise to almost two metres by 2300, twice what the IPCC predicted in 2019.Scientists cannot rule out two metres of total increase in emissions by 2100 due to uncertainty about the ice sheets.Deep past warningsRecent major advances in paleoclimatology, the science of Earth's natural climate in the past, have brought sobering warnings.For example, when the atmosphere of the planet was warmest, around 125,000 years ago. Global sea levels were most likely 5-10 metres higher. This would have put many coastal cities underwater.Three million years ago, when atmospheric CO2 concentrations were comparable to today's and temperatures were 2.5 C- 4 C warmer, sea levels were as high as 25 metres.Methane is in the spotlightThis report contains more data than ever on methane (CH4), the second-most important greenhouse gas after CO 2 and warns against ignoring Paris Agreement goals.The human-induced sources can be divided roughly into leaks from natural gas production and coal mining, landfills, and livestock and manure processing.CH4 is only half as long as CO2 in the atmosphere, but it traps heat far better. The highest levels of CH4 have been recorded in at least 800,000.Regional differences are the focusWhile all areas of the planet are warming, not all are as fast as others. For example, in the Arctic, the average temperature on the coldest days will rise at three times the global warming rate.The sea level is rising all over the globe, but it will likely rise by up to 20% along many coasts.Tipping points = sudden changeThe IPCC warns against sudden, "low likelihood and high impact" changes in the climate system. These are known as tipping points, which can be irreversible. There are many examples: melting permafrost with billions of tonnes of carbon, disintegrating ice sheets that hold enough water to raise sea levels a dozen meters; melting ice sheets that contain enough water to raise seas twelve metres; and the transformation of the Amazon from tropical forest into savannah.The report states that "abrupt responses and tipping point of the climate system... cannot not be ruled out."The global ocean conveyor beltThe Atlantic Meridional Overturning Circulation is (AMOC), a system of ocean currents that regulates global heat transfer from the tropics to the northern hemisphere, is showing signs of slowing down. This trend "very likely," will continue into the 21st Century.Scientists are confident that the AMOC won't stall completely, as it did in the past. It would make European winters more severe, disrupt monsoon season, and cause sea level to rise in the North Atlantic basin.Agence France-Presse
