L'Association pour la santé environnementale du Québec / Environmental Health Association of Québec

A Quick Summary of the IPCC’s AR6: Summary for Policymakers, Section C

Section C of the Intergovernmental Panel on Climate Change’s (IPCC) Sixth Assessment Report (AR6), titled Climate Information for Risk Assessment and Regional Adaptation, discusses the importance of knowing the range of possible climate responses to anthropogenic influences, natural factors, and internal variability. Understanding what could be expected in climate responses allows us to better prepare, respond, and adapt to these possible future changes. 

This section touches upon three points, listed below:

Natural drivers and internal variability will modulate human-caused changes, especially at regional scales and in the near term, with little effect on centennial global warming. These modulations are important to consider in planning for the full range of possible changes” (p.23).

  • Internal variability can be expected to either amplify or reduce anthropogenic-induced changes to the climate system
  • It has been found that decadal variability in global surface temperature has amplified and also concealed anthropogenic-induced changes. This can be expected to continue in the future
  • A large volcanic eruption (which has been projected to likely occur sometime in the 21st century) would obscure anthropogenic-induced changes to the climate system by cooling the global surface temperature, impact the global monsoon circulation, etc.

With further global warming, every region is projected to increasingly experience concurrent and multiple changes in climatic impact-drivers. Changes in several climatic impact-drivers 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” (p.24).

  • It is predicted that regions will experience increases in hot climate system conditions (events and extremes) while cold climate system conditions are expected to decrease
  • 2°C of global warming presents a greater level of confidence in the likelihood that precipitation and flooding events, as well as droughts, will amplify and become more frequent in certain regions when compared to what is projected at 1.5°C of warming
  •  Agricultural and ecological droughts will be more frequent and severe in all continents (except Asia) when compared to 1850-1900
  • Tropical cyclones, river floods, aridity, fire weather, and other physical climate system conditions are expected to increase and/or become amplified at 2°C global warming, while hail, ice storms, dust storms, heavy snowfall, and landslides have a low likelihood of going through drastic changes
  • Sea level rise will continue throughout the 21st century, resulting in the increase of coastal flooding events and coastal erosion (p.33). Extreme sea level events that have occurred once per century in the past are expected to now occur annually in many regions
  • The combination of urbanization with hot extremes augment the intensity of heatwaves

Low-likelihood outcomes, 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 cannot be ruled out and are part of risk assessment” (p.27).

  • A scenario with a low probability of occurring still needs to be under our radar as it could always occur. Essentially, we need to understand that anything could happen, even if a certain scenario or outcome has been categorized in the IPCC’s AR6 as having a very low likelihood of occurring
  • Rare and unforeseeable natural events that have the potential to take place could result in outcomes and scenarios that have not been taken into account in the IPCC’s AR6


IPCC, 2021: Summary for Policymakers. In: Climate Change 2021: The Physical Science Basis. Contribution of Working Group I to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change [Masson- Delmotte, V., P. Zhai, A. Pirani, S.L. Connors, C. Péan, S. Berger, N. Caud, Y. Chen, L. Goldfarb, M.I. Gomis, M. Huang, K. Leitzell, E. Lonnoy, J.B.R. Matthews, T.K. Maycock, T. Waterfield, O. Yelekçi, R. Yu, and B. Zhou (eds.)]. Cambridge University Press. In Press.