Climate Change and Population Health

Posted on: September 6, 2015 Topics: dean's note

deansnote1President Obama traveled to Alaska this week to call for action to tackle climate change, aiming for a global agreement in December at a United Nations summit in Paris. As might be expected, his engagement with the issue triggered competing protests, alternately between those urging the US government to do more on the issue and those conversely suggesting that we are over-privileging the issue above energy production concerns. Taking a cue from the public conversation on this issue, a few thoughts on climate change and how it intersects with the health of populations.

First, a note on global environmental climate change itself. Over the last hundred years, the global temperature on the surface of the earth rose by approximately 0.85 degrees Celsius, while the global sea level rose by approximately 0.19 meters. In addition to rising global temperatures and sea levels, key features of climate change include increases in temperature variability, extreme precipitation, and heat waves; acidification of the oceans; and the reduction of glacier mass and sea ice. Critically, climate change will amplify the effects of existing climatologic risks to human, plant, and animal ecosystems and create new risks. Figure 1, below, from the Intergovernmental Panel on Climate Change (IPCC) summarizes key global risks and mitigation capacities, by region and timescale.

FIGURE 1 : Pachauri, R. K., Allen, M. R., Barros, V. R., Broome, J., Cramer, W., Christ, R., & van Vuuren, D. (2014). Climate Change 2014: Synthesis Report. Contribution of Working Groups I, II and III to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change;

Figure 1.
Pachauri, R. K., Allen, M. R., Barros, V. R., Broome, J., Cramer, W., Christ, R., & van Vuuren, D. (2014). Climate Change 2014: Synthesis Report. Contribution of Working Groups I, II and III to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change;

Given the broad influence of global environmental climate change on all global systems, it is not at all surprising that climate change will have an effect on human health. I would refer to some very good reviews on the topic, including a chapter by professor Marie O’Neill in a book I edited more than seven years ago that remains relevant today. By way of illustration, I will focus here on two pathways through which climate change can be expected to affect population health: disasters and forced migration. Both disasters and forced migration will increase over time as a result of climate change, and both pose significant threats and challenges to the well-being of populations worldwide. In the last two decades, the number of natural disasters doubled from approximately 200 to 400 per year. Related, migration patterns have shifted populations toward coastal regions, which are most vulnerable to severe weather events.

I have written a recent Dean’s Note about the consequences of disasters, including mortality, physical morbidity, and psychiatric problems. Among those who survive disasters, there may be exacerbations of pre-existing health problems and the onset of new problems. Among the new problems that can arise, some will manifest in the immediate aftermath of the disaster, such as injuries and acute renal failure; other problems, such as gastrointestinal symptoms, musculoskeletal pain, and psychiatric disorders, will arise in the weeks following the disaster; and still other problems, such as increased risk of cardiovascular disease and diabetes, may be elevated in the longer term (≥1 year) post-disaster.

Mental health consequences of disasters include post-traumatic stress disorder (PTSD), depression, substance use disorders, and suicidality. For example, following Hurricane Katrina, the inspiration for last week’s Dean’s Note, approximately 49.1 percent of those in the New Orleans Metropolitan Area (who were most directly exposed to hurricane related trauma) were estimated to have had any DSM-IV anxiety or mood disorder in the prior 30 days, compared to 26.4 percent in less directly exposed areas. Similarly, 30.3 percent of those in the New Orleans Metropolitan Area were estimated to have PTSD, while the estimate in other areas was less than half that at 12.5 percent.

Forced migration at an unprecedented scale and complexity is emerging as one of the sentinel consequences of climate change. Natural disasters, desertification of previously arable land, and rising sea levels will all contribute to more forced migration. Bangladesh has already experienced forced migration as a consequence of climate change and is poised to experience a great deal more, given its coastal location and vast river delta network.

Forced migration and the attendant processes of adaptation constitute a powerful set of stressors that may exacerbate pre-existing health problems and increase risk of new-onset health problems. Relations between health and the process of migration can be conceptualized in terms of the stage of migration. Lack of access to medical care is a particular feature of the migration process that places those with pre-existing health problems at risk of disease progression, and those with minor problems that arise during migration at greater risk of long-term problems. Migrants are highly vulnerable to circumstances of deep exploitation, both physical (e.g. sexual trauma, violence, forced labor) and financial. These traumas are themselves associated with increased risk of health problems, including psychiatric disorders such as PTSD and depression.

Particularly relevant to our goals in public health is a central concern that, as the consequences of climate change unfold, we shall see a disproportionate harm of climate change among the poor and disadvantaged. Poverty and relative disadvantage are fundamental causes of health disparities in populations. Wealth and social position also affect risk of exposure to harm, as more vulnerable low-lying coastal areas tend to be occupied by the poor whereas the wealthy tend to occupy safer, more elevated areas. In addition, as in Hurricane Katrina, those who were black and had lower pre-disaster income had elevated risks of PTSD. Thus, in the context of climate change, social and financial resources buffer both the risk of exposure to natural disasters and the deleterious effects that follow such exposure. Similarly, financial resources insulate and protect against forced migration by providing a safer base and more contingency options. Broadly, as concluded in the IPCC report, risks associated with climate change are “generally greater for disadvantaged people and communities at all levels of development.”

Climate change is unequivocally progressing, and is emerging as one of the greatest threats to population health in the 21st century. To my mind, climate change represents a quintessential example of a structural driver of population health, where, despite our best efforts to identify opportunities to understand and mitigate the public health risks associated with climate change (as, for example, in Figure 1), core attention to the fundamental issue at hand—climate change driven by energy consumption patterns—is essential for any long-term solution, and a si ne qua non for the improvement of population health.

I hope everyone has a terrific week. Until next week.

Warm regards,


Sandro Galea, MD, DrPH
Dean and Professor, Boston University School of Public Health
Twitter: @sandrogalea

Acknowledgement: I am grateful for the contributions of Greg Cohen, MSW to this Dean’s Note.

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