Climate Change, Health, and the Marine Environment

Climate Change, Health, and the Marine Environment

Caleb Dresser, M.D. & Samuel Truesdell, Ph.D.

Climate change is altering the chemistry, temperature, weather, and ecology of the world’s oceans. Seas are rising at an accelerating rate, causing saltwater intrusion, shore erosion, flooding, and disappearance of low-lying land, all of which are expected to intensify during the 21st century.

Changes in the marine environment alter weather patterns and create new opportunities for marine pathogens and biological toxins that can cause health problems. Destabilization of ecosystems can also indirectly harm human health via economic hardship caused by disruption of coastal economies.

Despite the specter of uncertainty that climate change presents to human health, we are fortunate to have many tools at our disposal. The more we understand about how climate change is impacting various dimensions of human health, the better equipped we are to mitigate negative consequences. To do so, it is critical that we understand the mechanisms by which evolving ocean conditions impact human health so that anticipated future conditions, rather than historical norms, become the basis for policy decisions.

Health Effects

Climate change is leading to a range of marine dynamics that can cause health problems for humans. The most important common pathway linking these is rising ocean temperatures. Warmer waters are more hospitable to the growth of a variety of microorganisms, some of which are infectious or toxic to humans.

Rising temperatures in brackish coastal environments such as the Chesapeake Bay and salt marshes in New England are making these habitats increasingly hospitable to Vibrio bacteria (1,2). These bacteria cause severe necrotizing soft tissue infections and sepsis and can be contracted from either minor skin injuries exposed to contaminated water or consumption of contaminated shellfish (3). Infections carry a high mortality rate (4) and the number of cases reported to the CDC has increased dramatically over the past 20 years (5).

Warming oceans also increase the occurrence of toxic algal blooms (red tide). In addition to leading to hazardous conditions for swimmers and shellfishing closures, the toxins produced during these events can affect respiratory function. Emergency Department utilization rates increase significantly among people living near the coastline, even if they avoid beaches and contaminated water (6).

Warming water in the tropics can also lead to increased growth of the plankton that produce ciguatoxin, which bio-accumulates in pelagic fish and causes ciguatera poisoning in humans when the fish is eaten (7). There is concern that such poisonings may increase among people who consume tropical pelagic fish in coming decades (8).

Hurricanes

Climate change is making hurricanes more dangerous, increasing the risk to human health both through direct impacts such as bodily injury and the resulting losses to infrastructure and economies. Warmer oceans provide additional potential energy, and warmer air holds more moisture that can later fall as rain (9). While it is challenging to study this system because of its complexity and interactions with other climatological features such as El Niño and the North Atlantic Oscillation, hurricane scientists have found evidence of several concerning trends.

Hurricane rainfall and intensity are both expected to increase (9,10). Storm centers may be moving more slowly, meaning longer impact duration in affected locations (11). There is some evidence that the latitude of average peak intensity is moving poleward, increasing risk in temperate zones (9,12). Finally, rapid intensification - a sudden and dramatic increase in power within 24 hours - appears to be on the rise (13,14). Together, these changes are profoundly concerning, particularly for temperate zone coastal areas that are at risk from sea level rise, such as the coastlines of New England.

Impacts on Fisheries

Climate impacts are already occurring regionally over perceptible time frames. In recent years, the Gulf of Maine has warmed at a faster rate than most of the world’s oceans and experienced marine heat waves (15,16). Such environmental change has downstream effects on marine ecosystems, impacting fisheries on which communities depend; climate variability has been linked to decreases in regional fisheries revenue and employment (17). Diminished economies have negative repercussions for human health.

Scientists expect distributional changes and productivity impacts on numerous important regional marine populations as a result of climate change (18). For example, both American lobster and Atlantic sea scallops are expected to experience shifts in optimal habitat (19). Further, lobsters have seen settlement declines with increasing temperatures in nursery grounds (20) and increased incidence of shell disease linked to warming waters (21,22). There is also concern that ocean acidification may reduce productivity of sea scallops in the future (23).

Fishing will continue to contribute to coastal economies as the impacts of climate change are realized, but to effectively utilize these resources and avoid negative socioeconomic impacts, and by association negative health effects, it is important to integrate our understanding of environmental change into fishery policy. Policy that understates the risks of overfishing remains the greatest threat to fishery performance regardless of climate change (24), but in order to fully support coastal economies it will be critical to incorporate the implications of environmental change into fisheries management.

Conclusion

Climate change is transforming the world’s oceans, destabilizing ecosystems and fisheries, and contributing to the growth of harmful plankton and bacteria that can affect human health. Policies based on historical precedent rather than an understanding of the trajectory of these processes will inevitably fail to meet their goals. In addition to dramatically reducing greenhouse gas emissions, we must understand both the changes our oceans are undergoing and the mechanisms by which they affect human health, and begin taking steps to address these impacts as - or before - they occur.

Caleb Dresser, M.D. is a Fellow in Climate and Human Health in the Department of Emergency Medicine at Beth Israel Deaconess Medical Center. He is affiliated with Harvard C-Change and the FXB Center for Health and Human Rights at Harvard, and supported by the Climate and Health Foundation. Email: cdresser@bidmc.harvard.edu.

Samuel Truesdell, Ph.D. is a Stock Assessment Specialist at the Massachusetts Division of Marine Fisheries. E-mail: samuel.truesdell@mass.gov.

References

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