Overview of the “Extreme Humidity and Heat Days–Map” and “Extreme Heat Days–Map” in En-ROADS.


Big messages:

  • As global temperatures rise, extreme humidity and heat events become more frequent and intense in many regions. 
  • Strong climate policies that lower emissions rapidly can reduce the frequency and intensity of extreme heat events in the future compared to the Baseline Scenario. 
  • Combinations of high humidity and heat impair the human body’s ability to self-cool through sweating, which increases the risk of life-threatening conditions such as heat stress and heat stroke.
  • Policies to expand access to cooling resources (like air conditioning and shaded areas) and raise heat-risk public awareness (like reducing time outdoors during the hottest hours of the day) can mitigate the effects of extreme heat. However, the ability to adapt to extreme heat becomes more difficult as global temperature increases.


Key Dynamics:

  • Adaptation measures can increase emissions. Increasing demand for cooling can lead to further greenhouse gas emissions, both from increasing energy demand to power cooling resources (like air conditioners and refrigerators) and from leaking coolants in cooling equipment (F-gases).


Facilitator Tips:

  • Use the search function to zoom in on the location relevant to the audience. Compare the Baseline Scenario in a recent year (e.g., 2020) to a future year (e.g., 2100) to highlight the increase in extreme humidity and heat events for that location. After creating a reduction scenario, compare the Baseline and Current Scenario in the future to highlight the impact of mitigation efforts and the need for adaptation measures. 
  • Use these maps in combination with the “Outdoor Labor Losses from Extreme Heat”, “Deaths from Extreme Heat”, and “Deaths from Extreme Heat by Region” graphs to highlight how global increases in temperature will have disproportionate extreme heat outcomes in different regions. 
  • Wet-bulb temperature is a measure of temperature and humidity. A 26°C (78°F) wet-bulb temperature occurs at 26°C with 100% humidity or at different temperature and humidity combinations such as: 30°C (86°F) air temperature and 75% relative humidity, or 38°C (100°F) and 36% humidity. 
  • Explainer: How is climate change driving dangerous 'wet-bulb' temperatures? (Reuters, 2023) 


Equity Considerations:

  • As global temperatures rise, regions closest to the equator and populations in the Global South will face disproportionate increases in extreme heat and humidity events. 
  • The impacts of extreme heat and humidity events compound on pre-existing risks and vulnerabilities, and present inequitable impacts to underserved and marginalized populations, in turn further intensifying social inequities.


Technical Clarifications:

  • These maps are sourced from Probable Futures. E.g., “Days above 26°C (78°F) wet-bulb” map. 
  • The light gray area indicates regions where data is either unavailable.
  • The maps are divided into squares that are approximately 22 square kilometers (km2) in area.
  • The maps only show changes of 0.5°C between 0.5-3.0°C of global temperature increase.