What does the latest authoritative knowledge on climate change say?

Week of 9 August 2021

What does the latest authoritative knowledge on climate change say?

Our key takeaway: Climate change is “widespread, rapid, and intensifying” according to the consensus of the world’s leading scientists. The only time for transformational action is … now.

The latest analysis of the science of global warming has been released by the UN’s Intergovernmental Panel on Climate Change (IPCC). ‘Climate Change 2021: the Physical Science Basis’ is the IPCC’s sixth report and has been approved by 195 governments:

    • The attribution of extreme climate change to human influence is clear, and no region will be left untouched. The IPCC relies on new and updated data to state that the human influence on climate is “unequivocal.” Specifically, 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.” The attribution of extreme climate change to human influence is stronger than previously known, when compared to the Fifth Assessment Report (AR5). These extremes include “heatwaves, heavy precipitation, droughts, and tropical cyclones.” The IPCC provides new and extensive region-specific information on climate change. In short, every region will be impacted differently, but no region will be spared. Impacts include increased droughts and fires in Southern Africa, the Mediterranean, the Amazon, the western United States and Australia; changes in snow, ice and river flooding in North America, the Arctic, Europe, the Andes; and intense storms in North America, Europe and the Mediterranean.
    • The worst is yet to come – with every fraction of a degree making a difference. “Global surface temperature will continue to increase until at least the mid-century under all emissions scenarios considered.” We are currently at an average warming of 1.1 degrees C, and the IPCC finds that there is a more than 50% chance that the 1.5 degrees C target is reached or crossed between 2021 and 2040 (with a central estimate of the early 2030s). This means that the extreme weather events we are seeing this year are set to intensify – regardless of which scenario we find ourselves in. The IPCC finds that “the proportion of emissions taken up by land and ocean decrease with increasing cumulative CO2 emissions”, in other words, our land and ocean carbon sinks become less and less effective, the more carbon is emitted (with sinks eventually starting to emit CO2 rather than absorb it, leading to runaway warming). In addition, “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.”
    • The necessary transformation ahead. Looking ahead, and as depicted by WRI here, the IPCC finds that if we take aggressive action today, we can limit temperature rise to 1.6 degree C by 2050, and reduce to 1.4 degree C by 2100; however, if we take a high-carbon pathway, temperatures could rise to 2.4 degree C by 2050 and 4.4 degree C by 2100. The IPCC finds that “reaching net zero anthropogenic CO2 emissions is a requirement to stabilize human-induced global temperature increase at any level, but that limiting global temperature increase to a specific level would imply limiting cumulative CO2 emissions to within a carbon budget.” We need “immediate, rapid and large-scale reductions” in emissions, failing which curbing global warming to 1.5 degree C or 2 degree C above pre-industrial levels by 2100 would be “beyond reach.” In addition to a dramatic reduction of emissions, enhanced focus needs to be placed on adaptation, and building resilience of communities to the floods, fires and storms that are inevitable in the future.

For more information, see The UN’s Intergovernmental Panel on Climate Change (IPCC), Climate Change 2021: The Physical Science Basis Summary for Policymakers, Summary for Policymakers (August 2021).