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Climate Change and Public Health

  • Authors:Brian S. Schwartz, MD, MS
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  • Brian S Schwartz, MD, MS

    Professor, Departments of Environmental Health Sciences and Epidemiology, Johns Hopkins Bloomberg School of Public Health, Baltimore, Maryland; Professor, Department of Internal Medicine, Johns Hopkins School of Medicine and Johns Hopkins Hospital, Baltimore, Maryland


    Disclosure: Brian S. Schwartz, MD, MS, has disclosed no relevant financial relationships.


  • Peggy Keen, PhD, RNC

    Editorial Director, Medscape Public Health and Ob/Gyn & Women's Health


    Disclosure: Peggy Keen, PhD, RNC, has disclosed no relevant financial relationships.

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Climate Change and Public Health

Authors: Brian S. Schwartz, MD, MSFaculty and Disclosures


Overview: Climate Change, Peak Petroleum, and Public Health

There was great interest in activities surrounding global environmental health issues at the 135th Annual Meeting of the American Public Health Association (APHA), as well as evidence that the APHA will increase attention on these issues in the coming years. For example, APHA announced that the focus of National Public Health Week 2008 will be "Climate Change: Our Health in the Balance," and the goal will be to educate Americans on climate change issues.

At this year's APHA conference, presentations highlighting global environmental health issues included not only climate change, which has implications for temperature and the hydrologic cycle, but also elated issues occurring worldwide with health implications that are global in scale. These include land use (ie, the built environment, urbanization and sprawl), food production and distribution, water use, energy use (and the implications of entering the era of "after peak oil"), ecosystem degradation (eg, deforestation, desertification, declining coral reefs), and species extinctions. This report will summarize and build on 12 oral presentations presented in 3 sessions devoted to global environmental health issues.[1-3]

The Main Drivers Are Interconnected

Many presenters highlighted the interconnectedness among land use (the built environment), water use, food production and distribution, and energy issues, and how these have contributed -- alone and in combination -- to climate change, ecosystem degradation, and species extinctions. For example, increased land use over the past 3-4 decades has vastly outstripped population growth in the United States. This has resulted in a built environment characterized by suburbs that consist of low-density, single-use developments, with high-speed roadways and without walkable, highly connected street networks -- an environment centered on automobiles and requiring cheap and plentiful petroleum to keep the system moving.[4]

This type of built environment contributes to climate change because of the high carbon dioxide emissions required for living in such places, and to associated water problems when land required to recharge aquifers and handle extreme weather events without flooding are paved over and thus compromised.[5] Additionally, as the proportion of impervious surface areas in communities increases, runoff associated with paving degrades surface water and therefore decreases ecosystem quality.

Currently, food production and distribution systems in the United States are also highly reliant on cheap, plentiful oil (eg, fossil fuels are used for fertilizers, pesticides, irrigation, harvesting, and transportation of foods, often over very long distances). Several speakers expressed concern that the "green revolution" in agriculture over the last 50 years was really about the increasing use of fossil-fuel energy to produce food energy.[5-7] For example, some foods require 10 times more fossil-fuel energy to produce than the energy derived when the food is consumed. As cheap and plentiful petroleum disappears, there are concerning implications for food systems worldwide.[8] Animal production also contributes to global climate change and ecosystem degradation in several ways, including emissions of carbon dioxide and methane, and via methods of concentrated animal feeding operations (CAFOs, also known as "industrial" animal production) that directly degrade local and regional environments.[9]

After Peak Oil

If communities and food production were designed to rely on cheap and plentiful oil, what happens when this is no longer available? Several presentations discussed the implications of what has been referred to as "after peak oil."[5,6,10] In 1956, M. King Hubbert, a petroleum geologist, predicted that the fossil fuel era would be of very short duration, and that US petroleum production would peak in 1970. At the time, the United States was the world's biggest producer of petroleum, pumping almost 10 million barrels per day. Therefore, Hubbert's prediction was considered an outrage and was widely denounced.

However, in 1970, the United States did pass peak petroleum production, and daily production numbers have declined steadily ever since. This allowed the center of the petroleum world to shift to producers in the Middle East that have excess capacity.[11] In turn, these producers could control production and prices, resulting in petrodollars that have been linked to international terrorism and wars over access to petroleum resources.

"After peak oil" is the point where daily petroleum production can no longer be increased further. The world market currently produces approximately 84 million barrels of oil per day, with demand increasing at 2% to 3% per year. When peak is exceeded, as predicted to occur within a decade and perhaps sooner, daily production will decline by 3% to 5% per year. This will create a huge mismatch between supply and demand, and will make all climate-change-related problems much worse for many reasons.

If we attempt to solve the energy problem by using oil sands from Canada, or oil shale from Colorado, climate-change-associated problems will most likely accelerate. These fuels are much more carbon intensive, more environmentally degrading to produce, and have a much less favorable ratio of energy returned to energy invested to obtain. Politicians will be in a very difficult position as gasoline and other energy prices soar and constituents find that life as they previously knew it is no longer possible. Many analysts believe that there are no rapidly scalable alternatives to petroleum, that we needed to start planning for this eventuality decades ago, and that we are simply not prepared for the challenges that will soon be here.

"After peak oil" further contributes to these problems because many of the solutions to climate change will require petroleum. Several presenters and authors[5,6,10] have discussed how converging catastrophes -- "after peak oil", climate change, ecosystem degradation, and species extinctions -- recently called "The Triple Crisis" at a conference sponsored by the International Forum on Globalization[6,10] will be the prime public health challenges of the coming decades.

Health Impact

The projected implications of climate change for human health are many, diverse, and wide-ranging in magnitude. Several speakers[5-7, 10] defined the commonly used term "catastrophic climate change" which was used by climatologist James Hansen and others.[12] Catastrophic climate change is defined as climate change that would result in extinction of up to 50% of terrestrial and marine species, sea-level rise leading to the displacement of tens to hundreds of millions of people, and changes in regional climate that would cause profound disruption to regional food production and the hydrologic cycle (eg, worse droughts, more severe rain events with flooding and consequent damage).[11] There was recognition and agreement[5-7, 10] with the many climatologists who have maintained that there are less than 10 years remaining to change "business as usual" with respect to reducing carbon emissions, or else catastrophic climate change will be unavoidable.

There was emphasis[5,7] on the necessity of decreasing greenhouse gas emissions by 20% by 2020, by 80% by 2050, and then establishing a zero-emissions economy thereafter. Concern that much of the current information about climate change may in fact be harsh underestimates of what could occur was also recognized.[5,7] First, the Inter-governmental Panel on Climate Change (IPCC) had used a conservative, consensus-driven, politically influenced, slow-moving (eg, 4 assessment reports in 20 years), lowest-common-denominator scientific approach.[13] Second, worldwide emissions are rising faster than expected.[7]

Third, we are currently experiencing several important "tipping points" that will produce positive feedback that could vastly accelerate climate changes. Examples include, but are not limited to, melting Artic sea ice and tundra.[13] Melting Artic sea ice causes the cooling influence of the reflection of light off the ice (termed "albedo") to be lost and replaced by the heat-absorbing, dark ocean left behind. In turn, this accelerates further melting and warming. As the tundra melts, it will release copious quantities of methane, a greenhouse gas with a warming potential approximately 20 times more potent than carbon dioxide. As oceans warm and acidify, plankton, a primary organism that facilitates oceanic levels of carbon dioxide, will die, thus limiting the future effectiveness of this carbon sink and the ability of the oceans to absorb carbon.

Finally, the IPCC expressly decided not to factor ice-sheet melting into its most recent sea-level-rise projections, because ice-sheet melting is less predictable (ie, a nonlinear or chaotic system) and relies mainly on contribution of thermal expansion of the oceans to sea-level rise. However, ice-sheet melting appears to be happening much faster than previously projected.[7]

Although climate change will result in increased climate variability, average temperature and precipitation changes will not be the key problems. Rather, the activity in the tails (eg, the number of days that exceed a certain temperature threshold is more important to climate change's effects than is the increase in the average temperature for an area or the planet) of the temperature and hydrologic event distributions are what will be most dangerous. These will result in extreme weather events -- an increase in severe hurricanes and storm surges, thermal stress (especially for the urban populations because of the urban heat island effect), floods, and droughts. Such changes will thus have a profound impact on public health.

Climate change will also increase the risk for many infectious diseases worldwide, including vector-borne diseases (eg, West Nile virus, Lyme disease, malaria), water-borne diseases, and infections prevalent in refugees fleeing from extreme weather events. Temperature changes and interactions with air pollution will increase the risk for cardiovascular and pulmonary disease, as will an expected increase in wildfires. Mental health outcomes -- posttraumatic stress disorder, anxiety, and depression -- would be of concern due to the expected social upheaval and the increased number of refugees created by climate change.[5]

Climate change will also affect population health and human settlements. Although there is considerable uncertainty about how species and ecosystems will fare under climate change, food production could be affected in ways that lead to famine and malnutrition. Social upheaval could result from large population shifts resulting from sea-level rise, prolonged droughts, and severe weather events. Environmental scarcities could also contribute to conflict that would further increase social upheaval.[14]

Climate change could also degrade ecosystem services. Examples include the ability of ecosystems to collect, purify, and store water; mitigate flooding; purify the air; and contribute to food production in terrestrial and marine environments. Human settlements could be affected by extreme temperature (with resultant increased energy demand) via drought, leading to strain on municipal and agricultural water supplies, storms leading to disruption of infrastructures, and wildfires causing property destruction and community disruption.

Several presentations[5,6,10] highlighted the concern that vulnerable populations will be affected most by climate change, and addressed issues of disparities. Individuals in developing countries will be more affected than those in developed countries; urban dwellers more than rural dwellers; those of low socioeconomic status more than those of higher status; children, the elderly, pregnant women, the socially isolated, and persons with chronic conditions and comorbidities will be more vulnerable to increased temperatures and air pollution.


The crucial need for public health messages to be positive and optimistic to avoid arousing fear, complacency, and inaction was also highlighted.[5,10] Many actions can be taken to help prevent climate change and its effects -- what the IPCC termed mitigation and adaptation, respectively. Solutions were offered on the individual, community, regional, national, and international levels.

It is crucial to help citizens "reconnect the disconnect" between current lifestyles and potential environmental effects in order to meet future challenges.[6] "Lifestyles" in the future will, by necessity, likely look very different from what they are now, but there will be many benefits to establishing different sustainable patterns of living. For example, as more walkable communities are built, there will be decreased carbon emissions, less air pollution, more opportunities for physical activity, less reliance on the automobile, and more opportunities for interacting with neighbors.[15] In turn, these changes could lead to a decreased burden from diseases associated with the previous exposures and behaviors (eg, osteoporosis and depression risk could decline with increased physical activity; cardiovascular and pulmonary diseases could decline with increased physical activity and lower levels of air pollution.[10] In December 2007, the international community convened in Bali to try to determine a path that can actually solve these problems. The time to get engaged in helping the world achieve these goals is now.[16]


The projections and signs of global environmental changes are worrisome, and there are reasons to believe that related information may have been conservatively interpreted and presented in the recent past. Although the challenges are great, there are many opportunities for devising beneficial solutions at individual, community, and global levels. It is essential for public health professionals to become involved in advocating for change at all of these levels, as well as through professional organizations. We must begin "greening" our own lives and clinical practice, and start talking about these issues with patients. As we build walkable neighborhoods, change methods of energy production, and make water use and food production and distribution more sustainable, the benefits to improved air quality, a stabilized climate, social support, and individual and community health will be dramatic.[5,10]



  1. Global Climate Change and the Public Health Community: Mobilizing for Precautionary Action. Program and abstracts of the American Public Health Association 135th Annual Meeting; November 5, 2007; Washington, DC. Session 3115.
  2. Built Environment I: Health in the Greenhouse: Global Climate Change and the Built Environment. Program and abstracts of the American Public Health Association 135th Annual Meeting; November 5, 2007; Washington, DC. Session 3406.
  3. Climate Change: A Challenge to Public Health. Program and abstracts of the American Public Health Association 135th Annual Meeting; November 6, 2007; Washington, DC. Session 4077
  4. Balbus J (substituting for Frank LD). Urban form's influence on transportation related greenhouse gas emissions: putting sprawl in the hot seat. Program and abstracts of the American Public Health Association 135th Annual Meeting; November 5, 2007; Washington, DC. Presentation 3406.2.
  5. Patz JA. Defining the current and future health risks of climate change. Program and abstracts of the American Public Health Association 135th Annual Meeting; November 6, 2007; Washington, DC. Presentation 4077.2.
  6. Schwartz BS. Role of health care professionals in raising clinician and public awareness around global climate change: importance of individual behaviors. Program and abstracts of the American Public Health Association 135th Annual Meeting; November 5, 2007; Washington, DC. Presentation 3115.1.
  7. Flavin C. Coping with climate change: the way forward. Program and abstracts of the American Public Health Association 135th Annual Meeting; November 6, 2007; Washington, DC. Presentation 4077.1.
  8. Pfeiffer DA. Eating fossil fuels: oil, food and the coming crisis in agriculture. Gabriola Island, British Columbia, Canada: New Society Publishers; 2006.
  9. McMichael AJ, Powles JW, Butler CD, Uauy R. Food, livestock production, energy, climate change, and health. Lancet. 2007;370:1253-1263.
  10. Frumkin H. Coping with climate change: what the public health community needs to do. Program and abstracts of the American Public Health Association 135th Annual Meeting; November 6, 2007; Washington, DC. Presentation 4077.3.
  11. Simmons M. Twilight in the Desert: The Coming Saudi Oil Shock and the World Economy. Hoboken, New Jersey: John Wiley & Sons, Inc; 2005.
  12. Hansen J. Defusing the global warming time bomb. Sci Am. 2004;290:68-77.
  13. Flannery T. The Weather Makers: How Man is Changing the Climate and What it Means for Life on Earth. New York: Grove Press; 2005.
  14. Homer-Dixon TF. Environment, Scarcity, and Violence. Princeton, New Jersey: Princeton University Press; 1999.
  15. Chen D (substituting for Jackson RJ). Prevention and our planet: public health needs to lead. Program and abstracts of the American Public Health Association 135th Annual Meeting; November 5, 2007; Washington, DC. Presentation 3406.4.
  16. Profeta T. Finding new partners: identifying new opportunities for APHA to advocate for improved climate policy. Program and abstracts of the American Public Health Association 135th Annual Meeting; November 5, 2007; Washington, DC. Presentation 3115.4.