CLIMATE CHANGE AND HEALTH
CONCERNING CLIMATE Few nations are as vulnerable to the health effects of climate change as Bangladesh, where a research institute headed by FSPH’s Dr. John Clemens is helping to define the challenges and develop solutions.
HIGHER TEMPERATURES, extreme weather events, sea-level rise and more frequent outbreaks of vectorand water-borne infectious diseases are among the effects of climate change that threaten the health of populations in many parts of the world. Few countries are as vulnerable to these effects as Bangladesh, where Dr. John Clemens, Fielding School epidemiology professor, serves as executive director of the International Centre for Diarrhoeal Disease Research, Bangladesh (icddr,b), one of the world’s leading global health research institutes. “Bangladesh is among the most climate-vulnerable countries in the world,” Clemens says. “The combination of high and increasing population density, geography, poverty and weak infrastructure make Bangladesh especially vulnerable to the adverse impacts of climate change.” The icddr,b team on addressing climate change, led by senior scientists Dr. Quamrun Nahar and Dr. Peter Kim Streatfield, is grappling with wide-ranging concerns. In Bangladesh, the mean temperature increase per year between 1970 and 2010 was significantly greater than the global average, with an accompanying decrease in the number of cool nights and an increase in the number of warm nights during the country’s hot and cool seasons. In analyzing five decades of mortality data from Matlab, icddr,b’s major rural field site in Bangladesh, in conjunction with daily weather data, icddr,b researchers are learning about the health impacts of high temperatures and the physiological adaptation to exposure to heat waves. Sea-level rise is also accelerating 14
at a much faster rate in Bangladesh — two to five times the global average, Clemens notes. This is a particular problem given that Bangladesh sits in a low-lying region at the intersections of the Ganges, Meghna and Brahmaputra rivers in the Ganges-Brahmaputra delta, and its southern coast lies on the Bay of Bengal, making it susceptible to increased flooding related to storm surge and sea-level rise. In the Global Climate Risk Index for 2019, the annual report issued by the Berlin-based environmental organization Germanwatch, Bangladesh ranked seventh among the nations most affected by extreme weather events over the last 20 years; a tropical cyclone hits the country once every three years on average. Beyond these risks, the sea-level rise is having a major impact through saltwater intrusion in the drinking water aquifer — affecting approximately 20 million people living along the coast. Clemens’ group has begun exploring the links between the highly saline drinking water and the risk of hypertension among populations living in coastal areas of Bangladesh. The rising salt level in the coastal soil is also damaging agriculture, which is driving more people from the coastal areas to the already dense urban centers. Climate change is increasing the risk of vector-borne diseases — infectious diseases that are transmitted between humans or from animals to humans by insects, most commonly mosquitoes — in many parts of the world, including Bangladesh. Dhaka, the country’s capital and home of icddr,b, has seen a significant emer-
U C L A F I E L D I N G S C H O O L O F P U B L I C H E A LT H M AG A Z I N E
gence of dengue in recent years, and 2017 saw the first major outbreak of chikungunya, another mosquito-borne infection. “Studies done in Bangladesh showed that transmission of malaria and dengue is associated with variability in temperature, rainfall, and humidity,” Clemens says. His group is investigating the influence of climatic factors on dengue in Dhaka, and has long-running surveillance systems monitoring malaria and kala azar in specific regions of Bangladesh to determine how weather variables contribute to outbreaks of these diseases. The icddr,b team has carried out detailed studies for decades on the environmental correlates of the waterborne infectious disease cholera, which have produced evidence that cholera outbreaks in Bangladesh are associated with increases in sea-surface temperatures, another effect of climate change. This appears to be a consequence of the fact that higher sea-surface temperatures result in a greater concentration of phytoplank-