Australia: The Land Where Time Began

A biography of the Australian continent 

Climate Change - The Atlantic Ocean

According to the authors1 climate change is the climate system's response to anthropogenic forcing, as distinguished from the natural variability of the climate. As a change in the MOC of the Atlantic in response to anthropogenic forcing would presumably result in a change in the amount of ocean heat being transferred to the high northern regions, there is great interest in knowing if it is actually changing, As in the northern North Atlantic there is a large amount of natural variability, mostly associated with the NAO, and also possibly the EAP, and it has not yet been possible to attribute variations of circulation and local water mass to anthropogenic forcing, as a result of the short length of observational records (Bindoff et al., 2007). It has only been possible for properties averaged over very large areas to to be studied to detect long-term trends that indicate climate change.

Over the last several decades the heat of the Atlantic ocean has increased overall. The upper part of the ocean warmed, with the exception of the latitudes between 50-60oN, where cooling related to a positive trend in the NAO index occurred, which peaked in the early 1990s - positive NAO is associated with cooling in the Labrador Sea and Irminger Sea. The deep penetration of warming in the North Atlantic in the subtropics resulted from warming Mediterranean Water and reduced LSW production. As a whole, the world ocean warmed over those 5 decades, the overall trend being contributed to most by the Atlantic Ocean (Levitus, Antonov & Boyer, 2005). Coupled climate model simulations that were run with and without anthropogenic forcing have been used to attribute the warming in the North and South Atlantic to anthropogenic change (Barnett et al., 2005).

Regions in which the salinity increased and decreased were included in salinity trends in the Atlantic Ocean during the same 5 decades. In the northern North Atlantic between 45oN and 75oN freshening began in the mid-1970s, though this has reversed the increasing salinity since 2000. The salinity of the Atlantic has increased overall, that of the Indian Ocean has also increased, and the salinity of the Pacific Ocean has decreased, resulting in the overall global net salinity balance remaining unchanged. The evidence for the attribution of the observed changes in salinity to anthropogenic forcing is more indirect than that for temperature change. According to the authors1 salinity changes are consistent with anthropogenic change as more moisture can be held by warmer atmosphere.

Sources & Further reading

  1. Talley, Lynne D., Pickard, George L., Emery, William J., and Swift, James H., 2011, Descriptive Physical Oceanography: An Introduction 6th ed.., Academic Press.
Author: M. H. Monroe
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