20.5: The Oceans and Climate Change
The Oceans and Climate Change
The oceans influence the weather on local to global scales, while changes in climate can fundamentally alter many properties of the oceans. Heat is transported across the Earth’s surface through wind currents, storms, and ocean currents (Figure 20.8). Large circular ocean currents, called gyres Links to an external site., appear to have a significant impact on the geographic distribution of heat on Earth and large-scale climate change in Earth’s history. These currents are particularly effective in melting polar ice as they melt the sea ice from below.
Figure 20.8: This map of heat content trends in the upper 700 meters (2,300 feet) of the world ocean shows where the oceans gained or lost heat between 1993 and 2019. Large parts of most ocean basins are gaining heat (orange)—and the global average trend is positive—but some areas have lost heat. Places with gray shading have trends that are not statistically significant. (Public Domain; NOAA/Climate.gov, via State of the Climate (2019) Links to an external site.)
More than 90% of the warming that has happened on Earth over the past 50 years has occurred in the ocean. Ocean heat content not only determines sea surface temperature, but also affects sea level and currents. Scientists have determined that global sea level has been steadily rising since 1900 at a rate of at least 0.04 to 0.1 inches per year. Sea level can rise by two different mechanisms with respect to climate change: 1) as the oceans warm due to an increasing global temperature, seawater expands, taking up more space in the ocean basin and causing a rise in water level, and 2) as ice melts on land and drains to the ocean, increased volume of water in the ocean basin causes a rise in sea level. Rising sea-level has major implications for our coastal states and communities, including flooding and the way we manage our coastal resources.
Lastly, the oceans absorb 30% of atmospheric carbon dioxide. As these carbon dioxide levels rise and more is absorbed by the oceans, the average pH of the ocean changes, a process called ocean acidification Links to an external site.. The higher acidity affects the balance of minerals, like calcite and aragonite, in the water, which can make it more difficult for certain marine animals to build their skeletons or shells.