The oceans are major drivers of climate change. Ocean temperatures shape storms, and large-scale regional climate cycles such as El Nino/La Nina. Our seas are also a sink for carbon dioxide, but can only soak up a finite amount of the excess CO2 we pump into the air before fundamentally changing the properties of the ocean. However, the warmer the surface water becomes, the harder it is to mix the surface layers with the deeper layers making the ocean less effective as a CO2 sponge.
Ocean habitats help mitigate climate change. Better conservation of these habitats, which also support mangroves, salt marshes, and seagrass meadows store some of this “blue carbon”. However, this vegetation is being rapidly cleared for agriculture, aquaculture, and other forms of coastal development. Better conserving these habitats, which also support fish and protect the coasts from storms, holds the promise of reducing greenhouse gas emissions.
Sea level rise is one of the clearest ways that global warming brings its impacts right to our cities and homes. For coastal American cities with populations above 50,000 people, about nine percent of the land lies below 3.3 feet in elevation – and scientists expect about one 3 feet or more of sea level rise this century. About 36 percent of the land lies below 20 feet – and scientists expect enough global warming this century to potentially commit us to a 20 feet sea level rise over the next centuries. Though the ice sheets of Greenland and Antarctica take time to respond to warming temperatures, these expansive ice fields are losing mass at an accelerating pace. Watch how Savannah, Georgia may change with sea level rise.
There are two main reasons why sea level is rising as the world gets warmer. First, as ice sheets and glaciers melt they send ice and water pouring into the oceans. Second, like most substances water expands as it heats up — and as greenhouse gases warm the atmosphere, some of that heat is slowly warming the oceans as well.
Coastal and marine ecosystems are changing because of climate change, impacting people as well as nature. Coastal marshes tend to absorb the energy of waves and surges. If they disappear under the rising sea, that buffer will be gone, making the land more vulnerable to flooding and erosion. Underground supplies of fresh water can become salty due to sea level rise.
Fish are moving to colder waters in response to climate change. The boundaries of the ranges of some North Sea fish have already shifted further north as the waters have warmed. Smaller fish, with shorter life cycles, have been more likely to shift ranges. It is possible that larger fish, with slower life cycles may be less able to move their ranges in response to climate change. Additionally, climate change affects fish habitat - for example, causing coral bleaching and the flooding and erosion of coastal marshes. Ocean acidification, by making it harder for marine creatures to build their shells, is changing the marine food web. A recent preliminary report from the International Programme on the State of the Ocean (IPSO) examined the combined impact of all of the stressors currently affecting the oceans and listed ocean warming, along with ocean acidification and anoxia (lack of oxygen that causes "dead zones"), as the top historical factors contributing to mass extinctions. The panel warns that the combination of these factors will inevitably lead to mass extinctions if conditions are not mitigated.
The House Select Committee on Energy Independence and Global Warming examined many oceanic and coastal climate change Impact Zones, including Florida, New Orleans, Alaska, California, New England, the Netherlands, Ireland, Greenland, the Artic and Antarctic, and Australia. Coastal communities must adapt to become resilient to sea level rise, storm surges, and more frequent and intense coastal storms.