A Warmer Ocean
The burning of fossil fuels such as coal, oil and gas is warming Earth’s atmosphere – and also its ocean: Average sea surface temperature has increased by 0.4 degrees Celsius since the 1950s.
Because warm water is lighter than cold water, the warmer sea surface is less able to sink and mix with the colder waters beneath it, limiting the flow of oxygen and nutrients from surface to deep water and vice-versa, and creating expanses of ‘ocean desert’. As temperatures change, some species will adjust their range – generally away from the tropics and toward higher latitudes – while the range of other species will expand and still others will contract.
Additionally, as water warms, it expands, and such thermal expansion of the ocean is the primary reason why, since 1880, sea level has risen by an average of 22 centimeters; increased warming, combined with groundwater extraction, the melting of glaciers and some melting of the massive sheet of ice covering Greenland, is likely to cause sea levels to rise by a meter, or possibly even significantly more, by 2100.
Some areas and environments will be affected more than others. In the Arctic Ocean, for example, sea ice extent is declining by an average of 12 percent per decade, profoundly altering Arctic marine ecosystems and threatening the survival of species such as ringed seals, walruses, and polar bears. Coral reefs are particularly susceptible, as they have a very narrow temperature band in which they can thrive; once the temperature exceeds the upper limit of that band, the corals become stressed, and when they do so they expel the symbiotic zooxanthellae that give them most of their color, a frequently-fatal phenomenon known as ‘coral bleaching.’ A widespread bleaching event took place in 2010, with bleaching observed in every ocean and major sea in which coral occurs, from the Persian Gulf to southeast Asia, the Central Pacific to the Caribbean. In the Caribbean, more than 80 percent of corals surveyed by researchers had bleached and in many places 40 percent or more had died.
Back to top