Chapter 11 of the IPCC report (yes, I’ve skipped a few chapters since my last post on this topic) is about Human health: impacts, adaptation and co-benefits. This is all about us so I think it deserves a post all on its own.
Climate change will affect human health in three ways:
- Weather: Directly through higher temperatures, heat waves, floods, droughts and fires.
- Natural systems: Environmental changes such as the contamination of freshwater resources and the spread of mosquitoes and ticks that carry diseases like malaria.
- Human systems: Impacts arising from climate-change induced crop failures which lead to undernutrition and mental illness; violent conflict arising from human migration and economic losses caused by inability to work due to high temperatures (heat exhaustion).
The health impacts of climate change do not increase linearly with temperature. A 4°C increase in temperature does not equate to double the impact when compared to an increase in 2°C; it will be more than double. Part of the reason for this is that the latitudes where people will benefit from less cold, the far north of the Northern Hemisphere, are less populous than the areas expected to suffer the most with extreme heat.
However, It’s not just the temperature that is important but also temperature variability – there’s evidence that deaths from heat waves are more likely early in the season before people have had a chance to acclimatise – and so winter mortality may not decrease in a warmer climate that is also more variable. What is clear though, is that the negative heath impacts of a hotter climate will outweigh any benefits from fewer cold-related health impacts.
The human body has limits to what it can tolerate temperature-wise. Body temperatures above 38°C lead to heat exhaustion and cognitive impairment. Body temperatures above 40.6°C lead to heat stroke, with risks of organ damage and loss of consciousness. The human body cannot tolerate wet bulb (100% humidity) temperatures above 35°C for long. If temperatures were to rise by 7°C, parts of the earth would become uninhabitable to humans as our bodies would not be able to dissipate metabolic heat. If the temperature were to rise by 11-12°C, most areas occupied by humans today would become uninhabitable. These are conservative estimates.
Hot days are particularly risky for those who work outdoors. They also lower economic productivity as those people will need breaks to avoid heat stress. Crop failures will lead to undernutrition and stunting in children and food insecurity. If populations are forced to migrate as a result of disasters or food insecurity then there’s a risk of violent conflict. There’s also evidence of a link between drought and psychological distress.
The frequency of floods is expected to increase with climate change and the populations most at risk are those in Asia, Africa, Central and South America. The impact on human health is through drowning, injuries, hypothermia and the spread of infectious diseases. But there is also a psychological impact: anxiety and depression. There’s also expected to be an increase in intense tropical cyclones later this century.
More people are projected to be at risk of malaria because of climate change even when disease control efforts are factored in. There are no projections that it will spread to Europe or North America but once upon a time it was prevalent in these regions. The geographic area suitable for dengue fever is expected to increase with climate change as well. There may be regions which see improvements as some mosquitoes cannot tolerate temperatures above 40°C.
There’s lots that can be done to reduce the impact of climate change on human populations. These adaptive measures include improvements in public heath services, identifying at-risk populations, implementing early warning systems for things like heat waves and malaria outbreaks. Local interventions are also useful like increasing urban green spaces to counter the heat island effect.
The burden of climate change will fall heaviest on the world’s poor and will exacerbate diseases already in existence. The best adaptation strategy for these areas in the near term is to improve health services to these places to alleviate diseases already in place. Improving access to clean water, sanitation and taking steps to lift people out of poverty are other important adaptation strategies. But these strategies have their limits. Under business as usual, some of these places could see temperatures by the end of the century which for parts of the year are too high for the human body to tolerate work outdoors and this will have implications for the economy and productivity as well as health.
Human populations will benefit from some greenhouse gas reduction strategies. These are referred to as co-benefits and include things like reducing harmful pollutants from coal-fired power plants and solid fuel stoves which cause respiratory illness, lung cancer and cardio- and cerebrovascular disease; increasing access to contraception; eating less meat (which may reduce ischemic heart disease and some cancers); encouraging more active transport alternatives like walking and cycling; increasing urban green spaces.
Some populations will benefit. For instance, people living in temperate zones may see improvements in agricultural productivity, at least initially. But for the world as a whole, the impact will be negative particularly as time goes on.