Climate change is having significant effects on the ocean. Sea levels are rising. The ocean is becoming warmer, and because the ocean absorbs chemically reactive carbon dioxide, its pH is dropping. Hurricanes, typhoons, and other coastal storms are becoming stronger on average. Marine species are on the move, generally shifting toward the poles and, to a lesser extent, deeper. Coral reefs are dying.
Clearly, the climate impacts on the ocean are cause for concern. Between 2013 and 2016, the ocean along United States' west coast experienced a three-year surge of hot water that National Geographic dubbed "The Blob that Cooked the Pacific." Perhaps most fittingly, on Halloween 2018, Nature published a new study indicating that the ocean is warming 60 percent more per year than the Intergovernmental Panel on Climate Change (IPCC) had projected.
So, yes, there is cause for serious concern. And it's not just the health of ocean creatures we should be concerned about; it has huge implications for public health, as well.
In the "Oceans and Coasts" chapter (Chapter 8) of a new book called Climate Change, Public Health, and the Law, I lay out the connections between climate change impacts on the ocean and coasts and various kinds of public health threats.
Throughout most of the world, the coasts are becoming more crowded, and human migration to the coast is projected to continue throughout this century. As a result, more people are moving into harm's way. The increasing threats to public health – not to mention human life – are perhaps most obvious when we think about growing coastal populations facing higher numbers of increasingly severe coastal storms at the same time that sea levels are rising in most places, making storm surge ever worse.
As we know even from recent experiences in the United States – Hurricane Katrina in 2005; Superstorm Sandy in 2012; Hurricanes Harvey, Irma, and Maria in 2017; and Hurricanes Florence and Michael in 2018 – sewage treatment systems regularly fail, "contaminating waters – including drinking water supplies – with raw sewage and increasing the risks of outbreaks of waterborne diseases such as cholera and typhoid fever" (pp. 213-214). Post-storm reliance on emergency generators can lead to carbon monoxide poisoning, while loss of power from a storm causes failure of medical equipment and increases in foodborne illness. Storm floodwaters expose residents to a toxic soup made up of sewage, animal feces, oil, and hazardous chemicals from coastal businesses, industrial sites, Superfund sites, and hazardous waste treatment facilities. As Hurricane Harvey demonstrated particularly memorably, a storm can also lead to fires and toxic air pollution. Finally, storms expose populations to disease vectors. In the United States, they generally include Aeromonas bacteria, which cause gastroenteritis and wound infection; Vibrio cholerae, which causes cholera, and Vibrio vulnificus, which causes gastroenteritis and wound infection; and fecal coliform, especially E. coli, with typhoid fever also a risk.
In developing countries, the number and severity of waterborne diseases spread in coastal storms multiply and include leptospirosis, hepatitis A, typhoid, cholera, poliomyelitis, rotavirus, and paratyphoid. In addition, flooded conditions can increase the spread of mosquito-borne illnesses such as malaria, West Nile virus, and dengue fever and rodent-borne diseases such as Hanta virus.
If coastal storms represent the most dramatic of public health threats that climate change is making worse, several other but more insidious risks are also emerging. Sea level rise and storm surge pose direct threats to coastal water supplies by inundating coastal rivers and aquifers with salt water. Existing groundwater pumping along the coast often speeds the process by effectively pulling saltwater into aquifers. The sea is also invading coastal farmland in many places, threatening local – and for some island nations, national – food security. At the extreme, sea level rise and coastal inundation force people from their homelands, a reality already for many Native Alaskan and Pacific Islander villages. Population displacements and migrations come with their own health costs, both physical and mental, especially when the migration is not well-planned in advance of actual emergency.
A changing ocean also increases certain disease vulnerabilities. For example, cholera has an ocean phase, and in certain parts of the world, cholera outbreaks have been linked to warming and rising seas. Cholera's cousin, Vibrio vulnificus, also flourishes in warm oceans and has been spreading up the Atlantic coast of the United States as temperatures warm. Warming contaminated oceans are more likely to experience blooms of toxic algae, which can both contaminate shellfish and sometimes aerosolize in wind-driven surf, causing respiratory problems for people on shore. Increasing numbers of pools of stagnant, brackish water as the ocean invades the land also are perfect breeding grounds for disease-bearing mosquitoes.
Finally, one risk that seems almost to be a product of science fiction is exposure to old diseases as ice melts. Notably, in 2016, a 12-year-old boy died from exposure to anthrax when a thaw exposed an infected reindeer that had been frozen for 75 years. In addition, researchers found the 1918 H1N1 pandemic influenza virus – the virus that caused so much death worldwide right after World War I – in frozen corpses in Alaska.
Adaptation to climate change's impacts on ocean and coasts, therefore, is not just a matter of deciding whether to build seawalls or to retreat. Instead, these impacts bring with them a suite of increased risks to public health that need to be evaluated on a community-by-community basis and then incorporated into more comprehensive adaptation plans. As one example, coastal retreat may become more politically viable in some communities if inhabitants realize that both their drinking water and their farmland will become too salty to use long before the ocean permanently invades. As another, acknowledgement of public health risks may provide many coastal communities with an additional incentive to detoxify the coast, cleaning up existing contamination and changing land use plans, building codes, and permit requirements to help prevent new contamination from occurring. Finally, assessing changing coastal health risks may dictate that additional training for medical personnel and different kinds of emergency preparedness are more warranted than previously thought.