Will a warming world directly damage human health?

Question

It is widely believed that a warming world will be a worse world (but see this question for a discussion of the minority view: Could Global Warming be good for life?)

The medical community seems to feel it has a responsibility to do something to help stop warming. But many of their attempts to link warming directly to health seem tenuous if not ridiculous. This news report from the British Medical Journal (BMJ), for example, reports 350,000 climate change deaths a year but as my response to the article points out:

The major causes of death that climate change is supposed to exacerbate are malaria, diarrhoeal disease and malnutrition. As the report point out these deaths are entirely preventable with simple cheap actions (mosquito nets, rehydration solutions and basic dietary supplements). None of these have anything to do with climate change and any effort spent trying to reduce carbon dioxide emission is likely to be millions of times less effective in saving lives than spending on these simple, cheap remedies.

Other articles in the BMJ (e.g. this one by Roberts and Stott) have argued for strong connections between climate change and health and that doctors have a strong responsibility to engage:

Responding to climate change could be the most important challenge that health professionals face.

But all the measures they propose are things that would be good health measures even if global warming was not happening. Again a skeptical response argues:

The authors (Roberts and Stott) seem to want us to focus our public health attention on climate lobbying ("Responding to climate change could be the most important challenge that health professionals face"). This is where being part of a bandwagon starts to damage public health. Every good measure they propose (eat less meat, walk more, drive less) is irrelevant to global warming. We should lobby for those anyway, and might be more effective if we didn't pretend that the climate was involved.

It looks to me as though medics are grasping at straws in an attempt to join the global warming bandwagon. I have a point of view already, but in the spirit of skepticism I ask this question to give space for a proper case to be made: are there any well documented areas where human health will be damaged because of a warmer climate?

Answer 1

The Lancet published a series of papers on health and climate change in 2009.

The series is framed from the perspective of: how does climate-change mitigation provide a health dividend? And that's pretty much the same question as asked here, "Will a warming world directly damage human health?", from a different perspective. Either we mitigate climate change successfully, and get the health benefits; or we don't, and health suffers.

Haines et al summarised the findings of the whole series, and is the best place to start in grasping the breadth of issues, summarising the findings across all the papers. I'll give a quick overview below: first of the most directly-relevant paper, and then of three of the context-relevant papers.

On the specifics:

One of the most significant papers in that series relates directly to the question:

Chan found that:

Several health consequences of a changing climate have been identified with a high degree of certainty. Malnutrition, and its devastating effects on child health, will increase. Worsening floods, droughts, and storms will cause more deaths and injuries. Heat waves will cause more deaths, largely among people who are elderly. Finally, climate change could alter the geographical distribution of disease vectors, including the insects that spread malaria and dengue.

The other papers looked at additional health benefits of climate-change mitigation:

Here, the causal linkage is one step back: climate-change mitigation measures will reduce global warming, and bring health benefits. Absence of these mitigation measures will lead to worse global warming, and worsened health. So, in addition to the direct causal links identified by Chan above, there are several links between a warming world and worsened health, that come about via the common cause of absence of mitigation:

Wilkinson et al found that for household energy, on the subject of interventions to prevent global warming:

interventions were generally beneficial for health. For a strategy of combined fabric, ventilation, fuel switching, and behavioural changes, we estimated 850 fewer disability-adjusted life-years (DALYs), and a saving of 0·6 megatonnes of carbon dioxide (CO2), per million population in 1 year

Woodcock et al found that, in a study of Delhi and London:

In both cities, we noted that reduction in carbon dioxide emissions through an increase in active travel and less use of motor vehicles had larger health benefits per million population (7332 disability-adjusted life-years [DALYs] in London, and 12 516 in Delhi in 1 year) than from the increased use of lower-emission motor vehicles (160 DALYs in London, and 1696 in Delhi). However, combination of active travel and lower-emission motor vehicles would give the largest benefits (7439 DALYs in London, 12 995 in Delhi), notably from a reduction in the number of years of life lost from ischaemic heart disease (10–19% in London, 11–25% in Delhi). Although uncertainties remain, climate change mitigation in transport should benefit public health substantially.

Markandya et al found that:

Changes in modes of production of electricity to reduce CO2 emissions would, in all regions, reduce PM_2·5 and deaths caused by it, with the greatest effect in India and the smallest in the EU. Health benefits greatly offset costs of greenhouse-gas mitigation,

Answer 2

These days, what used to be referred to as global warming is more often referred to as global climate change, and sometimes global environmental change, as warming is not the only anthropogenically driven global scale change. The news article that you refer to gives a brief summary of a report, The Climate Vulnerability Monitor, which correctly identifies the threats to human health as being caused by "climate change" instead of simply "global warming."

Global climate change is mostly studied in departments of Earth System Science, because you simply cannot just separate out the anthropogenically driven changes, like warming, without considering the way that that change will effect the earth system. Yes, we're "only" looking at a global average temperature increase of 2°C, but that warming will directly cause changes in the earth system that will seriously effect human health.

Chapter 8 of the Contribution of Working Group II to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change, 2007 addresses the impacts of climate change on human health. Some of the most serious impacts on human health by the anthropogenically driven global environmental changes include loss of food sources due to biodiversity changes, lack of potable water, changing climate belts effecting the location of land suitable for food production, spread of pests that threaten food safety, poor air quality as well as the more direct effects of warming such as deaths due to changing temperatures and increasing storm frequency.

The way that global environmental change will effect human health is the the central reason to be concerned about mitigating anthropogenically driven climate change. There's nothing tenuous about the links between public health and changes to the environment.

Answer 3

There are definitely cases where global warming will damage human health.

If you live in the Maldives, then a rise in sea level of several feet will flood your country, drowning you (if it happens fast enough) but more likely turning you into a stateless refugee, with the well-documented health problems that go along with that.

In certain parts of the world climate change can affect the viability of crops, resulting in malnutrition for those unable to buy imported food. Malnutrition is definitely a health problem.

(I'm not going to get into the detailed arguments as to how likely these effects are to occur - see any question or discussion of climate change for arguments).

The point about the articles you quote isn't whether global warming can harm health. it's about whether it is politically sensible to focus on climate change as a means of advancing certain policies (walk more, drive less) that would definitely have a beneficial effect on British health (the main area of focus of the BMJ) while also providing minor benefits in terms of climate change.

Answer 4

Our understanding of how climate change will human health is still poorly understood. One thing is how humans are affected by climate variability; the variability in weather from one year to another. Climate change will take place over several decades, and this "slow" change is different from year-to-year variability.

For malaria, it was until recently believed transmission would increase up to 32 degrees C, while recent studies has shown that in Africa transmission peaks at 25 C. As temperatures increase beyond 25 C, the potential malaria transmission will decrease rapidly. See Lunde et al., Parasites & Vectors 2013, 6:20.

Answer 5

Many people die each year due to heat waves around the world, so for me it seems obvious that an overall warmer climate could result in more severe heat waves and more deaths due to that.

But what seems obvious to me maybe does not seem obvious to others. However according this research article: Toward a Quantitative Estimate of Future Heat Wave Mortality 
under Global Climate Change

Heat waves have had debilitating effects on human mortality, and global climate models predict an increase in the frequency and severity of heat waves.

The authors are trying to estimate a future increase in deaths due to heat waves in the city of Chicago using global climate models concluding that:

In this study, we have estimated future annual excess mortality attributable to heat waves for Chicago, Illinois, a major U.S. city, using several global climate models and climate change scenarios. We found considerable variability in the projections of annual heat wave mortality, with point estimates ranging from 166 to 2,217 deaths per year. In particular, the largest source of variation appeared to be the different climate model implementations, followed by variation due to statistical noise and the choice of SRES. Nevertheless, even in the presence of large intermodel variations, the results of our analysis suggest that annual heat wave mortality will increase in the future and that a mitigation of this projected increase may be expected through a lower pathway of future CO2 emissions.