Belize Barrier Reef: photographed April 2006.
With respect to oceans and climate change there are principally four concerns: 1) ocean acidification; 2) changes in ocean currents, most notably the thermohaline circulation; 3) sea-level rise and 4) damage to ecosystems such as coral reefs.
The first two changes are of particularly grave concern, as they threaten to touch off feedbacks that could result in abrupt and catastrophic changes in the climate. (There is good evidence in the climate record that such deadly, rapid changes have happened before). Ocean acidification refers to changes in the ph balance of the ocean thought to be caused by the ocean’s absorption of carbon dioxide. Current rate of acidification is the fastest in 65 million years, according to a recent study. This could cause mass extinctions events and other major disturbances. Ocean currents are one of the primary drivers of climate on the planet. Any significant change to those currents (for example through ocean warming or introduction of sizeable cold water melt from icecaps) could likewise cause relatively sudden and drastic changes. Much speculation exists about the possibility of altering or shutting off the thermohaline circulation, which accounts for our current distribution of heat and cold. The impact of this happening would be to throw some northern latitudes into a deep freeze. While there is little doubt that global warming will have some impact on currents, it is unknown how much and how fast.
Loss of ecosystems such as coral reefs due to ocean warming and other human impacts is yet another part of the story concerning climate change and the oceans. It is worth remembering that the issue is not the loss of beauty but the broader impact that loss of such ecosystems has on the current balance of the earth. Ocean research has been largely neglected in climate research, “despite its enormous importance in regulating global climate and its sensitivity to the impacts of climate change and ocean acidification,” according to the International Union for the Conservation of Nature, which published a recent report on oceans and climate change that is addressed to a general public (see first link above).