IPCC says human activity is undoubted cause of climate change in stark new report
The latest report from the Intergovernmental Panel on Climate Change (IPCC) says that "it is unequivocal that human influence has warmed the atmosphere, ocean and land" and that "widespread and rapid changes in the atmosphere, ocean, cryosphere and biosphere have occurred".
The IPCC is a representative group of a wide range of scientists and experts whose findings are endorsed by the world's governments.
The headline summary says that the scale of recent changes across the climate system as a whole and the present state of many aspects of the climate system are unprecedented over many centuries to many thousands of years.
Human-induced climate change is already affecting many weather and climate extremes in every region across the globe. Evidence of observed changes in extremes such as heatwaves, heavy precipitation, droughts, and tropical cyclones, and, in particular, their attribution to human influence, has strengthened since the Fifth Assessment Report (AR5).
The report identifies a range of 'Possible Climate Futures'. It says that global surface temperature will continue to increase until at least the mid-century under all the emissions scenarios considered.
It baldly states that global warming of 1.5°C and 2°C will be exceeded during the 21st century unless deep reductions in carbon dioxide (CO2) and other greenhouse gas emissions occur in the coming decades.
It also notes that many changes in the climate system become larger in direct relation to increasing global warming. They include increases in the frequency and intensity of hot extremes, marine heatwaves, and heavy precipitation, agricultural and ecological droughts in some regions, and the proportion of intense tropical cyclones, as well as reductions in Arctic sea ice, snow cover and permafrost.
Continued global warming is projected to further intensify the global water cycle, including its variability, global monsoon precipitation and the severity of wet and dry events.
If CO2 emissions continue to rise, the report says that ocean and land carbon sinks are projected to be less effective at slowing the accumulation of CO2 in the atmosphere.
The IPCC says that many changes due to past and future greenhouse gas emissions are irreversible for centuries to millennia, especially changes in the ocean, ice sheets and global sea level.
With further global warming, every region is projected to increasingly experience concurrent and multiple changes in climatic impact-drivers and these would be more widespread at 2°C compared to 1.5°C global warming and even more widespread and/or pronounced for higher warming levels.
Extreme events such as ice sheet collapse, abrupt ocean circulation changes, some compound extreme events and warming substantially larger than the assessed very likely range of future warming are low likelihood but cannot be ruled out the report says.
The IPCC says that rapid reductions in CO2 emissions are essential to mitigate the most dangerous effects. Limiting human-induced global warming to a specific level requires limiting cumulative CO2 emissions, reaching at least net zero emissions, along with strong reductions in other greenhouse gas emissions. The report highlights the need for strong, rapid and sustained reductions in CH4 (methane) emissions which would also limit the warming effect resulting from declining aerosol pollution and also improve air quality.
The Working Group I contribution to the Sixth Assessment Report addressed the most up-to-date physical understanding of the climate system and climate change, bringing together the latest advances in climate science.
The report "is a code red for humanity", says UN Secretary General António Guterres.
"If we combine forces now, we can avert climate catastrophe. But, as today's report makes clear, there is no time for delay and no room for excuses. I count on government leaders and all stakeholders to ensure COP26 is a success."
Their report is the first major review of the science of climate change since 2013. Its release comes less than three months before the COP26 climate summit in Glasgow.
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