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The health impacts of climate change are already apparent


“Climate change is the greatest global health threat facing the world in the 21st century” This according to a new report published in The Lancet, a world leading medical journal. The Lancet Countdown on health and climate change, released Dec. 2nd, 2020, is the fifth annual publication of an international collaboration established to provide an independent, global monitoring system to track the relationship between climate and human health.

In 2015, countries committed to limit global warming to “well below 2°C” as part of the landmark Paris Agreement. The annual Countdown report provides an independent assessment of progress towards the goals of the Paris Agreement, and represents the findings and consensus of 35 leading academic institutions and UN agencies

The Lancet Countdown tracks changes in five broad focus areas:

  • Climate change impacts, exposures and vulnerabilities
  • Healthcare-oriented adaptation, planning and resilience
  • Mitigation actions and health co-benefits
  • Economics and finance
  • Public and political engagement

This post focuses on The Lancet Countdown health-based assessment of climate change – its current status and near-future projections – as the main driver for changes in the other focus areas.

From a human health perspective, the report identifies five areas of global concern directly related to the changing climate:

  • Heat and heatwaves
  • Extreme weather
  • Infectious diseases
  • Food security and undernutrition
  • Population migration or displacement due to sea level rise

Heat and Heatwaves – a Worsening Problem

This year’s Countdown report finds that vulnerability to extreme heat is increasing everywhere.

Increasing vulnerability is driven by aging populations, the widespread rise of chronic respiratory disease, cardiovascular disease and diabetes, and the increasing fraction of the population living in urban areas. So far, Europe and the Eastern Mediterranean are the most vulnerable regions, but vulnerability is increasing worldwide.

As the population ages and the climate warms, there has been a steady increase in the number of person-days of exposure to heatwaves. 2019 racked up a record number of heatwave exposure days for people over 65, a global total of approximately 2.8 billion person-days.

Not surprisingly, heat-related mortality for the over 65 age group has been rising in parallel with heatwave exposure, reaching 296,000 deaths in 2018. Europe was hardest hit in 2018, with more than 104,000 deaths, while U.S. deaths totaled nearly 19,000.

The effects of heat exposure on younger age groups is seen in a decline in labor productivity. The report estimates that more than 300 billion work-hours were lost in 2019 due to heat exposure (nearly 53 hours per person), an increase of 103 billion work-hours over 2018. Less developed countries where agriculture employs much of the labor force are most vulnerable, with Cambodia losing over 200 hours of labor per person. In contrast, the 2019 U.S. impact of heat exposure is only 7.1 hours per person.

Extreme Weather – Investing in Health Care Pays Off

The Countdown program tracks the health impacts of a variety of extreme weather events, including wildland fires, floods, storms and droughts.

No one in the U.S. or Australia will be surprised to hear that there has been a steady increase in the number of days people were exposed to very high or extremely high wildland fire risk. They might be surprised to hear that the same can be said of 126 other countries, largely due to increasingly persistent droughts in many areas and increased human activity in previously undeveloped areas.

As we have discussed in previous posts, climate warming is having a profound effect on weather patterns – often altering rainfall distribution and frequency to create localized flood events or droughts. In 2018, extreme drought events were recorded in every populous continent, and large areas (more than double the area in the study’s historical baseline) saw unusually lengthy periods of excess drought.

Overall, the study notes that in the 10 years through 2019 “there were clear, significant, increasing trends in the number of occurrences of weather-related disasters” – and that was before 2020’s explosive Atlantic hurricane season! However, there was not a significant change in the overall number of people affected or the number of fatalities per event.

From a health-care perspective, the results show a clear difference between countries that invested heavily in health care and those that did not. The former showed a decline in the number of people affected by extreme weather events, despite the increased frequency of events. Countries that showed little or no increase in health care investment experienced a significant increase in the number of people affected by extreme weather events.

Infectious Diseases – Spreading to New Areas

As we’ve discussed before, global climate warming is creating conditions that are accelerating transmission of infectious diseases. The Countdown study is following changes in climate favoring the spread of dengue, malaria and pathogenic Vibrio bacteria.

The 2020 report shows a global increase in climate suitability for transmission of all three diseases. The spread of dengue, which is transmitted by the Aedes aegypti and Aedes albopictus mosquito vectors, is being boosted by climate change in previously inhospitable areas. Both subtropical species are increasingly common in Florida and the southeastern U.S., earning Aedes albopictus (the Tiger mosquito) a place in this post’s headline image.

While improving health care systems in vulnerable areas was largely successful in containing dengue until 2016, subsequent years have shown early indications of its resurgence. As climate warming continues, expanding areas suitable for these infectious diseases and their transmission vectors, stopping their spread will become increasingly difficult and expensive.

Food Security and Undernutrition – Warning Signs

While global food production is sufficient to support current population growth, inefficient distribution and poor management are leaving increasing numbers of people hungry. In ten years time, more than 840 million people are predicted to be undernourished.

Climate change, accompanied by higher temperatures, changing precipitation distribution, droughts, and warming oceans, is poised to upset the food security apple cart.

The Countdown report notes that over the last 40 years, the yield potential for four key crops: corn, wheat, soybeans and rice has slowly but steadily declined. Corn, for example, has seen a reduction in the growing season in the U.S., South Africa and Europe of more than 20 days over the 1981-2010 global average.

In much of the world, people rely on fish as their principal source of protein. The Countdown investigators use sea surface temperature as an indicator of marine food security. As we know, climate warming has increased ocean temperatures significantly in most areas of the world. The report notes that over 70% of the territorial waters monitored by the UN Food and Agriculture Organization experienced an increase in sea surface temperature since 2003, coupled with a decline in fishery production. So far, fish farming has offset the drop in the wild catch. However, the study notes that more than 70% of countries are exposed to declining dietary levels of seafood omega-3 fatty acids – a key preventative for cardiovascular disease.

Sea Level Rise – When Your Home Becomes Uninhabitable

The study team added this metric for the first time in 2020. The health impacts of rising sea levels are significant, including:

  • Changes in water quality and supply
  • Changes in soil quality
  • Livelihood and housing security
  • Disease – waterborne and via wetland vectors
  • Flooding
  • Saltwater intrusion

Given the current levels of climate warming and the slow response rate of oceans to external input, we are already likely to see an average global sea level rise of 1m by 2100. Applied to today’s population distribution, a 1m sea level rise would affect 145 million people worldwide, a number that is likely to be considerably larger by the turn of the century.

Should we fail to limit climate warming to the Paris Agreement target of 1.5 – 2.0°C, many more people are likely to be displaced by sea level rise well in excess of 1m.

Not mentioned in the report is displacement and migration instigated by other consequences of climate warming, such as persistent drought.

Where Do We Go From Here?

The Lancet Countdown researchers provide a much needed human health perspective on the impact of climate warming. The publication of this 5th Countdown report during the peak of the COVID pandemic, with its devastating impact on our healthcare infrastructure, further strengthens the already compelling case for integrating public health in our climate change strategies. As the U.S. prepares to re-enter the 2015 Paris Climate Accord, and the world looks forward to the 2021 UN climate conference, we have a unique opportunity to make this happen.


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