What is Causing Ocean Warming?

by: Davis Yancy Clegg


Melting Glasier


There are a number of factors that influence patterns of change in sea levels around the globe. Ocean basin levels are maintained by the pressure in the atmosphere, and are affected by circumstances such as wind stress on the surface waters. Also, levels of heat and fresh water concentrations from runoff play as factors. As the waters begin to warm, the density is lowered. Thus, the overall volume of the oceans water content increases.

This process is termed as thermal expansion, or steric sea level rises. This relatively new science has been one of the most profound contributors to sea level changes over the past 115 years. Most vulnerable to expansion, water kept at a high temperature (shallows) or under a greater amount of pressure (deep water) will expand at greater rates. It’s by using these measurements that we are able to arrive at the average expansion rate for the globe’s ocean waters as a whole. While the salt levels (salinity) in ocean waters can also take part in the density, they are of little consequence in determining causes of sea level change.


Looking at climate change in reverse, the rate of change is affected by the rate at which heat is taken away from the surface waters. If heat is taken up more efficiently, the change in climate is slowed, but the sea level will rise more quickly. The ocean’s impressive ability to withstand changes in temperature on multi-level scenarios where depth is concerned means that there will be a very long delay before the absolute effects of surface warming are felt throughout the depth of the ocean. This delayed response will result in the ocean not being in equilibrium and the global average measurements for rises in sea levels will continue to increase for hundreds of years after atmospheric greenhouse gases have eventually stabilized.

The most crucial factor to remember when reacting to news of ocean level or global climate changes is the rate at which they fluctuate. There is no one constant direction that can be said has been unchanged throughout time. Some points in history show rises. Adversely some show decreases in numbers. In the past two years, regional measurements have shown that some areas have seen a foot –give or take – of decreased sea levels. However, the 20 years prior to 2015 showed a consistent increase. While there is no complete existence of evidence to support a distinct conclusion, there are widespread indications that pin the proverbial “tail” on thermal expansion as being the majority contributor to sea level change since the early 1900s. The evidence is most convincing as it pertains to the North Atlantic, but it extends to the Pacific and Indian Oceans as well. The only area where cooling has been recorded is in the sub-polar gyre of the North Atlantic, and possible the North Pacific. Science continues to grow in the area and much knowledge remains to be gained.


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