November 27, 2018 — The Fourth National Climate Assessment is a landmark report that was published last week on the day after Thanksgiving. It summarizes the impacts of climate change in the United States as well as potential mitigation and adaptation measures. The report states that the combined effect of burning fossil fuels, developing natural landscapes, and deforestation have increased the concentration of greenhouse gases (GHGs) in Earth’s atmosphere* and emphasizes that drastically reducing GHGs is necessary to prevent the most catastrophic consequences of climate change.
According to the report, climate change is modifying the ocean environment in three primary ways: warming, oxygen loss, and acidification. These “stressors” have large implications for ocean ecosystems and marine fisheries. Globally, ocean surface temperatures have increased by nearly 1.3°F over the past century and “… more than 90% of the extra heat linked to carbon emissions is contained in the ocean.” As the ocean warms, seawater not only expands and causes sea levels to rise, but it also loses its ability to hold gases – including oxygen. Additionally, as carbon dioxide (CO2) emitted by human activities dissolves in seawater, it undergoes a series of chemical reactions that are gradually causing the ocean to become more acidic.
While warming, oxygen loss, and acidification will likely reduce the diversity of life in the sea, they will also impact fisheries, seafood farming, and recreational activities. These stressors will also interact and can have complex impacts. For example, as climate change progresses, hurricanes will become more frequent and intense. These hurricanes may redistribute nutrients that cause massive algal blooms that are sustained by warmer temperatures. When the blooms die off, microbes respire as they assist in the algae’s decomposition, simultaneously producing CO2 and consuming oxygen that cause ocean acidification and oxygen loss. The severe red tide along the Florida coast this year was likely a product of this series of events.