The impact of climate change on human health

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:

  1. Weather: Directly through higher temperatures, heat waves, floods, droughts and fires.
  2. Natural systems: Environmental changes such as the contamination of freshwater resources and the spread of mosquitoes and ticks that carry diseases like malaria.
  3. 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.

19 thoughts on “The impact of climate change on human health

  1. You certainly paint a pretty picture Rachel!!!
    Unfortunately what you have said is what the experts predict. If ALL nations, (of course meaning the rabbits that lead those nations), pull together collectively, instead of just caring about their own little dunghills, we may be able to mitigate some of the worst scenarios that have emerged from many of the climate models. My feelings are however that that will not take place until very extreme weather events start occurring…………………and then it may be too late!!!!

    1. ranmobiJohn,

      My feelings are however that that will not take place until very extreme weather events start occurring….

      Lots of people think this but I hope you’re wrong and that we take decisive action in the near future.

  2. I like that you list the simple measures that could be taken to lessen the impact, because there will be impact.

    ________________________________

    1. Thanks, Denise. I’ve read some astonishing statements from climate science contrarians over the past week or two who seem to think adaptation will just come naturally and there’s no need to study it or plan for it which sounds very unwise to me.

    1. Thanks, Sherri. I’ve been thinking it was a bit dry and boring. Maybe it needs a bikini photo or two? 🙂

      Yes, there was a bit about adaptation in this chapter and how important it is going to become. But they did emphasise in the report as a whole that adaptation will be much easier with mitigation, so first and foremost, we need to cut emissions. And not just lower them, emissions have to be zero.

  3. Rachel

    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

    Hansen has long warned of the Faustian bargain we have made with coal-fired power and the opposing CO2 and aerosol forcing from its emissions.

    Michael Mann has just pointed to this grim reality again. Burning less coal means a reduction in the cooling shield of aerosols it produces. But because the carbon cycle is slow to sequester, the GHG forcing just keeps on going.

    Mann’s SciAm article on climate sensitivity is here:

    http://www.scientificamerican.com/article/earth-will-cross-the-climate-danger-threshold-by-2036/

    The text captions for the main graphic are important.

    Greg Laden’s post on the role of coal and its aerosol negative forcing is here:

    http://scienceblogs.com/gregladen/2014/04/09/manns-false-hope-graphic-presentified/

  4. BBD,

    That’s interesting. The graphic you’re referring to (I presume it’s this one) says the only way we can keep below 3°C is to keep emitting polluting particles into the atmosphere. Really? I know aerosols have a cooling effect so I’m not contesting that, I’m genuinely interested. So if we stopped emissions completely over the next five years, we’re still going to hit 3°C or more?

    The chapter I read wasn’t really addressing climate sensitivity, only how climate change would impact human health. They made quite a big deal out of how much pollution already affects human health.

    Put into terms of disability-adjusted life years (DALYs), particle air pollution was responsible for about 190 million lost DALYs in 2010, or about 7.6% of all DALYs lost. This burden puts particle air pollution among the largest risk factors globally, far higher than any otherenvironmental risk and rivaling or exceeding all of the five dozen risk factors examined, including malnutrition, smoking, high blood pressure, and alcohol.

    .

    1. Rachel

      That’s interesting. The graphic you’re referring to (I presume it’s this one) says the only way we can keep below 3°C is to keep emitting polluting particles into the atmosphere. Really?

      I think the key word is ‘Faustian Bargain’. Or perhaps a nod towards the implacable law of unintended consequences.

  5. I know aerosols have a cooling effect so I’m not contesting that, I’m genuinely interested. So if we stopped emissions completely over the next five years, we’re still going to hit 3°C or more?

    See the second caption to the graphic: ‘Where to hold the line’.

    1. I think Steve Easterbrook has an analysis that suggests that if we were to stop emissions completely then the atmospheric GHG concentration would drop at a rate that roughly fixed temperatures at the values today. On the other hand, if we were to reduce emissions so that concentrations remain at today’s level, then temperatures would continue to rise, probably by up to a another degree.

      1. Yes, but I think RCP2.6 assumes CO2 concentrations rise to just over 450 by 2040 and then drop slowly to around 400ppm by 2100. So, it is – I think – quite an extreme mitigation scenario and is probably consistent with what I was saying above. If we were to fix concentrations now at 400ppm, temperatures would continue to rise by up to 1 degree.

      2. Ok, that sounds reasonable to me and is what I thought. Now that I look closely at the other graph I see a blue line which represents CO2 held constant at 405ppm and temperatures are just under 2°C.

  6. My feelings are however that that will not take place until very extreme weather events start occurring….

    If a heat wave that caused >30,000 deaths in Europe does not qualify as a “very extreme weather event,” I shudder to think what would.

    A runaway ice shedding event in Greenland that jumped MSL a meter or so in a decade might do it, I guess, but in the unlikely event of such a thing, would the propaganda and bribery efforts of the fossil fuel interests abate? I’d bet not and, that being the case, their stooges in the world’s governments would continue their stooging as diligently as ever.

    1. Dan L,

      If a heat wave that caused >30,000 deaths in Europe does not qualify as a “very extreme weather event,” I shudder to think what would.

      Good point. There are other examples of things like this too, particularly in my home country of Australia. It’s hard to see how people who live there can ignore the problem. The recent IPCC report mentioned Australia a couple of times in the context of drought – which causes enormous psychological distress to those affected – and also bushfires.

      I doubt vested interests will suddenly go silent but hopefully people will start to ignore them.

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