A summary of the IPCC’s summary report

Nina van Rijn

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4 minutes

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Industry news

No time to read the 3.949 page IPCC report or the 42-page summary for policymakers? Read this 1 page summary of the summary.

September 21, 2021
Image: 
USGS

No time to read the 3.949 page IPCC report or the 42-page summary for policymakers? Read this 1 page summary of the summary.

The current state of the climate

  • There is no doubt about the fact that human activity has warmed our atmosphere, ocean and land. Widespread and fast changes is our atmosphere and biosphere have occurred.
  • The current state and scale of recent changes across the climate system as a whole and many separate aspects of the climate system, are unprecedented in the past hundreds or thousands of years.
  • Human-induced climate change is already affecting many weather and climate extremes in every region across the globe. No region can escape these effects. Evidence of weather extremes include heatwaves, heavy rain, drought and cyclones.
  • Improved knowledge on climate systems and insights in our climate’s response to human activity, gives an estimate that a doubling in the atmospheric carbon dioxide will lead to a 3 C temperature rise.

Possible climate futures

  • Global surface temperature will continue to increase until at least mid-century, under all emissions scenarios considered by the IPCC. Global warming of 1.5 C and 2 C (the latter agreed as maximum global temperature rise under the Paris Agreement, the former agreed as the preferred path under the Paris Agreement) will be exceeded unless deep reductions in CO2 and other greenhouse gas emissions occur in the coming decades.
  • Many changes in the climate system will become worse as a result of global warming, including the frequency and intensity of hot extremes, marine heatwaves, heavy rain, droughts, cyclones, reductions of Arctic sea ice, snow cover and permafrost.
  • Continued global warming is expected to further intensify the global water cycle, including monsoon rain and the severity of wet and dry events.
  • If CO2 emissions continue to rise, the ocean and land carbon sinks – that is, the capacity of ocean and land to capture and retain CO2 – are expected to become less effective at slowing the accumulation of CO2 in the atmosphere.
  • Many changes as a result of greenhouse gas emissions are irreversible for centuries to millennia, especially changes in the ocean, ice sheets and global sea level.

Climate information for risk assessment and regional adaptation

  • Natural drivers and inherent variability of weather and climate interact with human-caused changes, especially at regional scales. This interaction is important to consider in planning for the full range of possible changes that could occur in terms of our climate.
  • With further global warming, every region is projected to increasingly experience changes in climatic impact-drivers – that is, events or trends that may have an impact on society or on ecosystems. Changes in these drivers would be more widespread at 2 C increase than at 1.5, and even more widespread of we go beyond 2 C.
  • Low-likelihood outcomes, such as ice sheet collapse, abrupt ocean circulation changes and larger warming than the very likely range cannot be ruled out.

Limiting future climate change

  • From a science perspective, limiting human-induced global warming requires limiting accumulation of CO2 in the atmosphere by reaching at least net zero CO2 emissions, together with strong reductions in other greenhouse gas emissions. Strong reduction in methane emissions – for example – would limit the warming effect and would improve air quality.
  • Scenarios with low or very low greenhouse gas emissions will lead within years to an observable effect on aerosol concentrations, GHG-concentrations and air quality, compared to high or very high scenarios. We would begin to notice the difference within around 20 years.

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