The Coming Health Crisis

By Samuel S. Myers and Aaron Bernstein The Coming Health Crisis Indirect effects of global climate change threaten the health of hundreds of millions of people. The very uncertainty that shrouds this issue must serve as an organizing principle for adaptation to its ill effects.

By | January 1, 2011

The Coming Health Crisis

Indirect effects of global climate change threaten the health
of hundreds of millions of people. The very uncertainty that shrouds this issue must serve as an organizing principle
for adaptation to its ill effects.

Heading to the water hole, northern Namibia
Alexander Nesbitt

Human activity is disrupting Earth’s climate, and the rising emissions of greenhouse gases are accelerating that disruption. (See “Our Changing Climate” box below) Some of the health consequences of climate change are straightforward: warmer temperatures, changes in the hydrologic cycle, increased ground-level ozone, and enhanced pollen production will increase exposure to heat stress, alter patterns of infectious disease, and compromise air quality. These and similar direct impacts of climate change have been well covered in the scientific literature, and what we know of their likely considerable effects is discussed in the sidebar “1 Enormous uncertainties surround predictions regarding how climate change may affect human well-being. Acknowledging these uncertainties is a critical component of designing optimal approaches to mediating the health impacts of climate change.


Water scarcity is already a major global issue that carries heavy adverse health sequelae, and climate change will further destabilize access to fresh water.

A sampling of four current crises illustrates the gravity of the situation. One: In the North China Plain, where half of China’s wheat is grown, the water table is falling by as much as 3 meters/year. Two: Certain states in India are using half of their electricity budget to pump water from depths as deep as one kilometer to irrigate crops. Three: Roughly 300 million Chinese and Indians are eating food grown on “fossil” water that is not replenished. Four: In the Middle East and North Africa, current rates of freshwater use are equivalent to 115% of total renewable runoff.

Given such unsustainable use around the world, the number of people living in water-scarce countries is expected to rise six-fold from 470 million to 3 billion between 1990 and 2025.

Future trends are of even greater concern. Rapid human population growth combined with economic development begets increased water demand from homes, industry, and agriculture. In agriculture alone, the amount of water required to keep pace with global food demand—roughly 2,000–3,000 km3—represents a tripling of water used for irrigation. This is water that, in many parts of the world, simply is not available.

The availability of adequate potable water is a pillar of public health without which human well-being falters. In addition to hindering food production inadequate access to water and sanitation has direct effects on human health. Today half of the urban populations of Africa, Asia, Latin America, and the Caribbean suffer from diseases associated with inadequate access to water and sanitation, and roughly 1.7 million people die every year from these diseases.

Climate change is expected to exacerbate water scarcity in several ways. Scientists predict that the hydrologic cycle will be altered with, generally speaking, wet areas becoming wetter while dry areas become dryer. Precipitation will likely fall in greater amounts and cause more rapid runoff. Heavy precipitation events and associated runoff may make water supplies less reliable and may also make conditions favorable to outbreaks of water-borne disease. In the United States, for example, over 50% of water-borne disease outbreaks in the second half of the 20th century were preceded by precipitation events that were above the 90th percentile.2

Warmer temperatures will also increase evapotranspiration, increasing water requirements for agriculture. At the same time, the availability of water during the height of the growing season may be less owing to earlier melting of winter snowpack in the spring, leaving less water for summer irrigation. Agricultural systems dependent on glacial melt, such as the Andean nations of South America or much of Asia that receives water from the Tibetan plateau, may suffer such a fate as glaciers melt away. As these glaciers dwindle they will provide ever less dry season water flow into many of the world’s great rivers. The Indus River, for example, receives 40–50% of its dry season flow from glaciers that are rapidly receding. Finally, sea-level rise and more extreme storms will lead to coastal inundation and intrusion of salt water into freshwater aquifers, further reducing coastal freshwater supply.


Perhaps even more problematic to human welfare in the coming century than a further diminution in the availability of fresh water is the impact of climatic disruption on the supply of food. As with water, global access to food is already tenuous. In 2009 the number of people suffering from protein-calorie malnutrition exceeded one billion after reaching a low of around 830 million in the 1990s. (See Figure 1) In poor countries around the world malnutrition underlies roughly one-third of the entire burden of disease, and roughly 2 to 3 billion people—almost half the human population—already suffer from micronutrient deficiencies.

3–5 As temperatures rise 2 to 6°C over the next century, the reduction in agricultural yield will depend, in part, on our capacity to adapt and, in part, on how temperature variability changes; but, in general, yields are expected to drop.

Climate change has further relevance to agricultural yields. As discussed above, climate change is expected to alter the timing and quantity of water available for agriculture while increasing the needs of plants as temperatures rise. Increased production of ground-level ozone curtails agricultural yields, as ozone is a potent plant toxin. When ozone concentrations reach 30 to 45 ppb (parts per billion), yield losses for the major grains approach 10 to 40%. By 2030 mean annual ozone concentrations in South Asia are expected to exceed 50 ppb. Increasingly intense tropical cyclones, sea level rise, more frequent forest fires, droughts, and floods will also conspire to diminish local harvests.

Despite strong evidence that climate change will increase the risk of numerous challenges to agricultural production, the net effect of climate change on global food production is difficult to quantify. Little is known, for example, about how climate change may alter the relationships between plants and their pests and pathogens, though several worrying examples indicate that climate change may promote infestations of plant pests as higher winter minimum temperatures enable insects to overwinter more effectively. Also poorly understood is how climate change will impact the extent and pattern of cloud cover which, to some degree, determines the solar radiation available to plants for photosynthesis.

In addition to these impacts on the quantity of food produced, it appears that rising concentrations of atmospheric carbon dioxide also affect nutritional quality. Grains grown at elevated concentrations of carbon dioxide appear to have reduced concentrations of protein, iron, zinc, and perhaps other nutrients. As with other examples already cited in this article, these potential decrements in plant nutritional content are of particular concern given the current state of affairs: iron and zinc deficiency account for roughly 63 million years of life lost annually, and the major grains are a critical source of these nutrients for many populations around the world.6,7 Taken together these additional threats to food production may very well have extensive impacts on human nutrition and global health.


Population displacement may be the final common pathway for many of the climate change impacts discussed above. Regional changes in precipitation leading to increased droughts and flooding, increased incidence of natural disasters like tropical cyclones and forest fires, local crop failures, and severe water scarcity are all likely to force people around the world to abandon their homes. (See Figure 2) In addition to these threats, coastal vulnerability puts many people at risk for displacement. More than one-third of the human population lives in coastal areas and on small islands that are within 100 kilometers of the shore and less than 50 meters above sea level. The combination of sea-level rise, increasingly intense storms, and destruction of coastal barriers (mangroves, wetlands, vegetated dunes, and coral reefs) leaves these populations extremely vulnerable. By 2050 an estimated 200 million to 1 billion people may be displaced due to climate change. These estimates are highly uncertain in part because many of the biophysical changes that contribute to displacement remain hard to quantify.8,9

Despite this uncertainty, a significant fraction of the human population will undoubtedly be displaced in this century, and displaced persons face stark health realities. Nonimmune populations migrating into endemic areas are more susceptible to a variety of infectious diseases. Poor housing, sanitation, and access to safe drinking water combined with poor nutrition lead to disease epidemics, particularly diarrheal disease, measles, and acute respiratory infections. Malnutrition plagues displaced populations, with rates as high as 50% seen in refugee populations in Africa.10 In addition to infectious disease and malnutrition, displaced people suffer from high rates of violence, sexual abuse, and mental illness. Post-traumatic stress disorder has been diagnosed in 30 to 75% of resettled refugee children and adolescents.11 Finally, displacement may lead to civil strife and violent conflict as large numbers of people with few resources move into areas where they frequently are not welcome.

Infectious Disease
• Climate change will alter the distribution of malaria, dengue fever, schistosomiasis, and others that are transmitted by an insect vector or those that have animal reservoir hosts.

• The range of these diseases is limited geographically by the range of the insects and/or animal reservoirs that effect their transmission to humans. As temperature and precipitation patterns change, so too will the geography conducive to the survival of these other species.

• Warming temperatures increase the rates of reproduction, development, survival, and biting of blood-feeding vectors as well as shortening the parasite development time inside these vectors.

• Geographic shift from one locale to another may introduce pathogens into novel and nonimmune human populations who may be far more susceptible to infection than those now living in endemic areas.

Heat Stress
• Increased extreme heat events can exact a heavy human health toll.

• Hyperthermia may cause relatively mild illness such as heat rash, exhaustion, or heat syncope (fainting), but may also precipitate severe sequelae including heat stroke, which is often fatal.

• Survivors of heat stroke experience a marked increase in illness and mortality in years subsequent to the extreme heat event.

• An additional 2.5 billion people will be added to the planet’s population over the next 40 years and nearly all of them will live in cities. Cities tend to be warmer due to the urban heat-island effect.

• The human population is aging, and the elderly are particularly sensitive to heat stress.

Air pollution
• The formation of ground-level ozone, the major cardiorespiratory toxin in smog, is coupled to temperature particularly as temperatures rise above 90°F (32°C).

• Climate change has brought about an earlier start to spring and later end to fall, and these changes to seasonality, along with higher CO2 concentrations, yield both longer pollen seasons and more pollen production from many allergenic plants.

• Allergic respiratory disease, particularly asthma, is already associated with a quarter of a million deaths annually worldwide.

• The frequency and extent of forest fires is expected to rise, generating large amounts of air pollutants, including potent lung irritants (such as acrolein and other aldehydes), carcinogens (such as formaldehyde and benzene) and fine particulates (PM 2.5) which are known to increase risk of cardiorespiratory disease and death.

Living with uncertainty

There is no doubt that climate change will have important impacts on human health, but we are uncertain about what those impacts will be and where and when they will be most severe. The most consequential health effects of climate change will come about from interactions between biophysical changes to the natural environment, demographic trends, and human adaptations. (See Figure 3) The biophysical changes—such as temperature variability or sea level rise—are difficult to predict with accuracy today, and the capacity for adapting to these changes is largely unknown.

1. Intergovernmental Panel on Climate Change (IPCC), “Climate Change 2007: Impacts, adaptation and vulnerability. Contribution of Working Group 2,” Intergovernmental Panel on Climate Change (IPCC), 2007.
2. F.C. Curriero et al., “The association between extreme precipitation and waterborne disease outbreaks in the United States, 1948-1994,” Am J Public Health, 91:1194-99, 2001.
3. D.S. Battisti, R.L. Naylor, “Historical warnings of future food insecurity with unprecedented seasonal heat,” Science, 323:240-44, 2009. Free F1000 Evaluation
4. D.B. Lobell et al., “Prioritizing climate change adaptation needs for food security in 2030,” Science, 319:607-10, 2008.
5. S. Peng et al., “Rice yields decline with higher night temperature from global warming,” PNAS, 101:9971-75, 2004.
6. L.E. Caulfield, R.E. Black, “Zinc Deficiency,” in Comparative Quantification of Health Risks: Global and Regional Burden of Disease Attributable to Selected Major Risk Factors, Vol. 1, M. Ezzati, et al., eds, Geneva: World Health Organization, 2004, pp. 257-79.
7. R.J. Stoltzfus, L. Mullany, R.E. Black, “Iron Deficiency Anemia,” in Comparative Quantification of Health Risks: Global and Regional Burden of Disease Attributable to Selected Major Risk Factors, Vol. 1, M. Ezzati, et al., eds, Geneva: World Health Organization, 2004, pp. 163-209.
8. L.C. Johnstone, “Planning for the inevitable, the humanitarian consequences of climate change,” in “Linking Climate Change Negotiations and Disaster Risk Reduction” Copenhagen, 2008.
9. K. Warner et al., “In search of shelter: mapping the effects of climate change on human migration and displacement,” Cooperative for Assistance and Relief Everywhere (CARE), New York, NY, 2009.
10. M.J. Toole, R.J. Waldman, “Refugees and displaced persons. War, hunger, and public health,” JAMA, 270:600-05, 1993.
11. L.A. McCloskey, K. Southwick, “Psychosocial problems in refugee children exposed to war,” Pediatrics, 97:394-97, 1996.


Avatar of: Mike Waldrep

Mike Waldrep

Posts: 155

January 4, 2011

Avatar of: anonymous poster

anonymous poster

Posts: 3

January 4, 2011

Most of the article is categorized as sensationalistic journalism, which in it self is an oximoronic description. Most of the information has already been either withdrawn or proven incorrect or at the very least, not quite right. Generally this falls under the category of the "Stupid Human Theory"; ie: humanity won't survive because man stays in one place and dies.
Avatar of: anonymous poster

anonymous poster

Posts: 1

January 4, 2011

It boils down to too many people on this planet. If we don't do something to curb over-population, Mother Nature will. Simple as that.
Avatar of: Andrew Russo

Andrew Russo

Posts: 5

January 4, 2011

Just let me reply to anonymous who posted under the title NOT. Do you watch much Fox News Network? I guess the authors are affiliated with Harvard because they are incompetent and do not know how to check facts. And all the cited references have simply got to be wrong.
Avatar of: Timothy Ray

Timothy Ray

Posts: 2

January 4, 2011

Avatar of: PAUL STEIN


Posts: 61

January 4, 2011

For Andrew Russo and all anonymous posting folks, I'll state the same thing I say every eight to twelve months on The Scientist forums: I've learned to simply ignore anything from anyone called "Anonymous". Oftentimes, posts from these people are rude, ignorant, ill-informed, or worse, and add absolutely nothing logical or constructive to the conversation. If a person doesn't have the guts or good manners to place his or her good name out there, then I am wasting my valuable time reading the drivel that is coming out from under some rock.
Avatar of: stephen black

stephen black

Posts: 2

January 5, 2011

The trouble with global warming is that it appears to be possible to talk nonsense as long as you bolster the case for doing something about it. Hence weak if not completely misleading arguments about the likely impacts on health. You don't need to be a climate denier to see why these arguments mostly suck.\n\nOne example: diseases like malaria are, we are told, going to spread further because of warming. But the limiting factor in malaria's spread is effective public health, not climate. Cold Northern european countries had endemic malaria as recently as the 1940s and it wasn't eliminated because they got colder but because their public health systems got better. \n\nAnother example. The article argues more people will die from heat stress as the world warms (especially in cities as a higher proportion will live there). But more people now die from cold than heat so warming might bring a net benefit! Also, cities are easy and cheap to cool by more than any projected amount of warming.\n\nEssentially all the supposed deadly health problems of warming are actually problems that would be easy and cheap to solve by simple interventions we already know how to make. Spending money to avoid warming is thousands or millions of times less effective at dealing with the problems than directly addressing the problems now. But attaching them to the warming agenda just distracts us from that.
Avatar of: Michael Holloway

Michael Holloway

Posts: 55

January 5, 2011

stephen black:\n"One example: diseases like malaria are, we are told, going to spread further because of warming. But the limiting factor in malaria's spread is effective public health, not climate. Cold Northern european countries had endemic malaria as recently as the 1940s and it wasn't eliminated because they got colder but because their public health systems got better. "\n\nWatch Fox News much? How it is eradictated is irrelevant. The fact that it needs warm temperatures to spread isn't legitimately arguable. The spread of the parasite in Northern Europe was contingent on the warmth of the previous summer. More warmth = more mosquitos.\n\n
Avatar of: Michael Holloway

Michael Holloway

Posts: 55

January 5, 2011

Sorry, missed the point of Stephen's post. As in creationism anti-science, climate change denyiers are adept at moving the goal posts. One fall back is to claim that higher average temperatures are a good thing, and therefore no effort needs to be expended to curb carbon emissions. Haven't actually heard any suggest that it be accelerated, but that may be because of my sheltered existance. The fact remains though that if there was a concerted effort to decrease use of fossil fuels it would certainly be cheaper and more logical than burning more fossil fuels in order to power increased air conditioning.\n\nstephen black:\n"But more people now die from cold than heat so warming might bring a net benefit!"\n\nNot if you happen to be the person dying from the heat.
Avatar of: PAUL STEIN


Posts: 61

January 6, 2011

Let's all behave here. Stephen Black brings up important concepts that need to be thought about carefully. So, everybody focus on Figure 3. It points out that while all of the problems associated with global warming can be initially countered to some, most, or every extent and in some, most, or all places given enough capital outlay for technology, etc., the basic problem this article points out is that, at some point in time, if global warming gets so bad, there will eventually not be enough resources everywhere to handle things.\n\nIn that vein, concerning one example Stephen Black brings up, the increasing incidence of malaria will eventually outcompete all of the public health systems that Society at large will be able to throw at it. In another, because humans, as well as all land animals, have limited behavioral and homeostatic mechanisms to handle higher and higher temperatures, there just won't be enough resources to air condition every place day and night to preserve everyone's lives.\n\nWhile Stephen Black is correct that "Essentially all the supposed deadly health problems of warming are actually problems that would be easy and cheap to solve by simple interventions we already know how to make." Yes, for now, but only for now...focus on Figure 3. "Spending money to avoid warming is thousands or millions of times less effective at dealing with the problems than directly addressing the problems now." Yes, that is also true, but it misses the point of the necessity of looking beyond right now.\n\nAt some point in time, if we don't spend the thousand or millions of times to stave off the problems mentioned in the article, and many more, we absolutely will be spending billions and trillions of times when things are totally, catastrophically out of control.\n\nPersonally, I would rather pay for the large investment in technology to reduce the threat than to shovel our entire collective monetary futures in a futile battle.\n

January 7, 2011

the article suffers from the same problems as the vast majority of climate-change-related ones. Uncertainties are glossed over, speculation is presented as fact, positive aspects of the purported change are neglected altogether, and a good opportunity to seriously start talking about risk management is squandered in self-righteous pseudoscientific babble. Please try again!
Avatar of: stephen black

stephen black

Posts: 2

January 10, 2011

Just in case people assume from previous comments that I'm some climate change denier: no I'm not. But the fact that people think I am is a symptom of the problem I was trying to highlight. Just because the climate is getting warmer doesn't justify any and every argument (no matter how scientifically dubious) to persuade people to do something about it. Nor does it avoid the need to debate the cost/benefit ratio of potential responses to it.\n\nWhat I was trying to argue against in my first post was partially the tendency of scientists use dubious arguments to make what they believe to be a stronger case for action on warming. But this is a poor long term strategy as the weakness of the arguments will eventually leak, taking the rest of climate science with it. Besides, it is incredibly slipshod if not downright dishonest to use some of the arguments as presented.\n\nThe other, related, point was that the debate on what to do about climate change has been buried in a religious crusade where any action--no matter how poor the gain per dollar spent--is justified. \n\nLet me illustrate by answering some of the specific points raised. Michael Holloway, for example, links me with climate deniers (a purely ad hominem attack) because I chose to question the estimated health effects of a warming word. But my criticism is not based on some general belief that a warmer world is better but on a specific criticism of the supposed costs of warming. It is a dishonest argument, for example, to count the cost of increased heat stress on mortality and not to mention the decreased mortality from excessive cold. \n\nThe use of arguments around water stress is similar. It sounds plausible to a layperson that a warmer world will be a drier world, so this argument is co-opted into the "warming and global health" debate. But climate models of a warming world don't show a uniformly drier world: rain is redistributed so some countries gain and others lose. But when the argument about health and warming is made only the downside is mentioned. This is either careless or dishonest.\n\nBut the other problem of treating the case for doing something about climate change as a religious crusade is that we can't have sensible debates about costs and benefits of actions. It is impossible to differentiate between crippling and complex actions that would cost trillions but save few lives and simple easy interventions that would save millions of lives for millions of dollars of spend. Hence the debate about whether warming spreads malaria. Even if it did (and there is little evidence that it will) spending money avoiding warming is not a sensible way to deal with the problem. We can tell public health in colder countries won't be overwhelmed by warming (as Paul Stein argued in one response) because countries with ideal malarial climates (like Singapore) have eliminated it. So even if the whole of North America warmed to Singaporean levels, malaria wouldn't spread there.\n\nThe poor quality of evidence used in some arguments about warming damages science. The poor quality of arguments about the health impact of warming (seemingly generated so health experts can get on the global warming bandwagon) just serve to distract attention from soluble problems now.\n\nPS I hate Fox News, alongside most Europeans.\n\n\n\n
Avatar of: Joan Hanley-Hyde

Joan Hanley-Hyde

Posts: 4

January 11, 2011

Human beings are successful in organizing their environments because they can adapt more quickly to stressors than most other organisms. Any debate about future actions of our species should deal with the best outcome for most people and tolerable ones for the rest. Where is there any room for debate about that concept? We are seeing the increased intensity of storms occurring globally. At the vary least we should decide upon contingencies, should more disasters arise. I don't expect that there is any doubt that disasters have been coming rather rapidly, of late.
Avatar of: anonymous poster

anonymous poster

Posts: 1

February 2, 2011

An excellent article. However, it's not quite true to say that the indirect effects of climate change have not been researched or discussed in the professional press. A particularly interesting report on precisely this issue is The Lancet / UCL Commission Report on Managing the Health Effects of Climate Change (2009).\nI am an architect working in a Boston hospital system on 'sustainability' and I have found this to be an excellent document for contextualizing the challenges we face in the healthcare sector.
Avatar of: DAN FERBER


Posts: 1

April 22, 2011

Stephen Black argues that "the limiting factor in malaria's spread is effective public health, not climate." That's only half the picture, and it doesn't mean climate change is not contributing. It is.\n\nYes, mosquito control, which is a part of effective public health, is an essential tool that has helped us control malaria in the United States and Europe. \n\nBut, as Paul Epstein, MD, and I document clearly in our new book, Changing Planet, Changing Health (, a warming climate has contributed to malaria's spread in the highlands of central Kenya. We document this with both science and on-the-ground reporting. The area had no malaria; it got warmer; malaria-carrying mosquitoes appeared there, and now there's endemic malaria. \n\nIn Changing Planet, Changing Health (University of California Press, April 2011), we profile people working on many of the health threats mentioned in Dr. Bernstein and Dr. Myers' piece, and we present a suite of solutions. If you're interested in this subject, we hope you'll check it out.

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