FIRST WORLD OCEANS REPORT REVISITED; Theme 1: Climate change and its impact on the oceans

FIRST WORLD OCEANS REPORT REVISITED; Theme 1: Climate change and its impact on the oceans

22 scientists from around the world—including Silliman University’s Hilconida Calumpong, Ph.D.—submitted to the United Nations General Assembly in late 2015 their report on the state of the world’s oceans after their appointment by the U.N. in 2010 to constitute the Ad Hoc Working Group on the Regular Process for Global Reporting and Assessment of the State of the Marine Environment.

The First World Ocean Report consists of ten topics/themes. We wish to share some details of each theme in the report (verbatim), beginning with Theme No. 1:

Climate change and related changes in the atmosphere have serious implications for the ocean, including rises in sea level, higher levels of acidity in the ocean, reduced mixing of ocean water and increasing deoxygenation.

Ocean warming
Average ocean temperature from 1971 to 2010 are positive over most of the globe. The warming is more prominent in the northern hemisphere, especially in the North Atlantic. (But) average upper ocean temperature trends show warming at nearly all latitudes and depths.
The ocean’s large mass and high heat capacity enable it to store huge amounts of energy, more than 1,000 times than that found in the atmosphere for an equivalent increase of temperature. The earth is absorbing more heat than it is emitting back into space, and nearly all that excess heat is entering the ocean and being stored there.

The ocean has absorbed about 93 per cent of the combined extra heat stored by warmed air, sea, land, and melted ice between 1971 to 2010. During the past three decades, approximately 70 per cent of the world’s coastline has experienced significant increases in sea-surface temperature. That warming is resulting in increasing poleward distribution of many marine species.

Sea-level rise
Average global sea level has risen by 3.2 mm a year for the past two decades, about a third of which is derived from thermal expansion. Some of the remainder is due to fluxes of freshwater from the continents, which have increased as a result of the melting continental glaciers and ice sheets. (Through a combination of many natural factors and changes in land use and coastal development), sea levels will rise more than the global mean in some regions, and will actually fall in others. A 4?C warming by 2100 (high-end emissions scenario in the IPCC report) would lead by the end of that period a median rise of 1 meter above 1980 to 1999 levels.

Ocean acidification
Rising concentrations of carbon dioxide in the atmosphere are resulting in increased uptake of that gas by the ocean. The ocean is absorbing 26 per cent of the increasing emissions of anthropogenic carbon dioxide, which reacts with seawater to form carbonic acid. The resulting acidification of the ocean is generally decreasing the levels of calcium carbonate dissolved in seawater, thus lowering the availability of carbonate ions, which are needed for the formation by marine species of shells and skeletons.

Alongside broad-scale ocean warming, shifts in ocean salinity (salt content) have also occurred. Variations in the salinity of the ocean around the world result from differences in the balance between freshwater inflows (from rivers and glacier and ice-cap melt), rainfall and evaporation, all of which are affected by climate change. The shifts in salinity suggest that at the surface, high-salinity subtropical ocean regions and entire Atlantic basin have become more saline, while low-salinity regions, such as the western Pacific Warm Pool, and high-altitude regions have become even less saline. Since variations in salinity are one of the drivers of ocean currents, those changes can have an effect on the circulation of seawater and on stratification, as well as having a direct effect on the lives of plants and animals by changing their environment.

Differences in salinity and temperature among different bodies of seawater result in stratification, in which seawater forms layers, with limited exchanges between them. Increases in the degree of stratification have been noted around the world. Increased stratification brings with it a decrease in vertical mixing in the ocean water column. This decreased mixing, in turn, reduces oxygen content and the extent to which the ocean is able to absorb heat and carbon dioxide, because less water from the lower layers is brought up to the surface, where such absorption takes place. Reductions in vertical mixing also impact the amount of nutrients brought up from lower levels into the zone that sunlight penetrates, with consequent reductions in ecosystem productivity. (to be continued)—SU Research and Environmental News Service

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