Climate Change’s Impacts on Human Health

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The “Policy Brief for the United States of America” that accompanies the Lancet Countdown report shows how climate change affects human health in every measurable way.

Climate change has unequal health impacts, affecting historically marginalised groups and communities in the US, people of colour, the elderly and the poor (The Lancet Countdown, 2021).

The burning of fossil fuels has warmed the world by 1.1°C above pre-industrial levels. The long-predicted consequences for these are already unfolding – climate change is directly affecting millions across the globe.

According to the brief:

  • Climate change worsens heatwaves, amplifies droughts, intensifies wildfires, supercharging hurricanes, and increases flood risk through more frequent heavy rainfall events and rising sea levels.
  • The economic costs from these climate-related events are in the billions of dollars from infrastructure and property damages, crop failure, and lost productivity.
  • In 2020, 22 climate-related disasters caused billions of dollars in damage in the US Floods are getting worse – the flash floods from Hurricane Ida in September this year have trapped people in the subways, their cars and homes.
  • This summer, record-breaking heatwaves in the Pacific Northwest, which scientists thought is impossible without climate change, have killed hundreds of people.

The report focuses on three interrelated hazards – extreme heat, droughts and wildfires and highlights the complexities and varying risks and impacts of climate change.

Extreme heat

Health risks from extreme heat are growing, varying by population and geography. Heat kills people, result in poor sleep, worsens mental health, increases suicide rates and crime rates. People susceptible to extreme heat are outdoor workers, incarcerated persons, people of colour, historically redlined communities, the poor, and the elderly. Heat exposure is due to the following reasons poorly designed infrastructure and limited access to air conditioning.


Droughts have increased significantly across the Western and Central U.S. since 2020. Harmful effects from drought include respiratory and infectious diseases, worsening water quality, and exacerbating mental health issues, especially in rural areas. Droughts can also cause food insecurity, water shortages, and job losses, affecting 65% of farmworkers that identify as Hispanic and affecting indigenous communities who depend on land and water supplies for their cultural medicines and traditional food.


Wildfires in the Western U.S. are linked to hotter temperatures, and the report has shown that the wildfire season has been lengthening. By September 2020, the annual wildfire incidence peaked at approximately 80,000 wildfires, eight times great than the total incidence in 2001.

Wildfires also release several harmful air pollutants – particulate matter, carbon monoxide, etc. Emerging evidence shows that wildfire smoke can be up to 10 times more harmful to human health. It can increase the risk of heart and lung diseases, premature deaths, worsen mental health, and increase the chances of preterm birth.

Wildfire can also worsen air quality up to thousands of miles from the origin of the fire. This is due to smoke becoming more toxic over time through oxidation and people not recognising the danger of the air quality.

To deal with the inequalities of climate change impact on health, the United States needs to implement an evidence-informed response to climate change that prioritises health and equity in three key areas:

  1. Adaptation or intervention to improve health and equity. For example, improving access to air conditioning to prevent heat-related fatalities and health problems.  Policies should increase funding for local, climate-specific health research
  2. Economics and Finance. The health-related costs of fossil fuel are substantial and must be factored into fiscal analyses and decision-making across all levels and sectors.
  3. Mitigation through urgent economy-wide GHG reductions that is consistent with the 1.5°C temperature rise limit by 2030. Policies to slash emissions should focus on shifting away from high-polluting fossil fuel infrastructure in and adjacent to low-income communities and people of colour – who have had high exposure to air pollution across the states due to biased and discriminatory infrastructure and housing policies.

Click the link to read more about the Lancet Countdown on Health and Climate Change report.

Source Citation:

The Lancet Countdown on Health and Climate Change. Policy Brief for the United States of America. (2021). Retrieved from

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