Changes in Ocean Climates

A new study by researchers Katie E. Lotterhos, Áki J. Láruson & Li-Qing Jiang quantifies changes in ocean climates between the years 2000 and 2100.


To predict how ocean climates change in the future from greenhouse gases, researchers implemented the Representative Concentrations Pathway (RCP). The RCP predictions model different climate change outcomes for the near future (until the year 2100). Each RCP scenario estimates a different future temperature depending on the levels of greenhouse gas concentrations in the atmosphere. The RCP scenario estimates assume that temperature is linearly related to the cumulative total of anthropogenic greenhouse gas emissions.

Some scenarios are optimistic, in that they predict future emissions to be much lower than they are today. The worst-case scenarios, on the other hand, are pathways which have the highest estimated future greenhouse gas emissions; and therefore the highest temperatures.

Katie E. Lotterhos, one of the studies lead researchers

Lotterhos and her colleagues used pathways RCP 4.5 and RCP 8.5. RCP 4.5 is a future scenario in which human beings curb their greenhouse gas emissions and moderate our warming trajectories. RCP 8.5, sometimes considered the ‘business as usual scenario’, is a future scenario in which humans do not reduce their emissions statistics and greenhouse gases are emitted at current rates throughout the 21st century.

RCP 8.5 has the highest global mean temperature increases of all pathway scenarios. The sea water near and along the ocean’s surface heats in response to the warming atmosphere above. Airborne gases like carbon dioxide and methane are absorbed by ocean water at depths hundreds of feet down below the surface. The buildup of atmospheric greenhouse gases inevitably increases average ocean surface temperatures.

Researchers used the RCP models to quantify ocean surface climates. Ocean climates are defined by temperature, pH acidity and carbonate chemistry. The temperature and chemistry models the years between 1800, and project out to the year 2100. Of the climates that were analyzed, no novel extremes of global ocean surface temperature were judged to have occurred until the year 2000. In the RCP 4.5 scenario, 35.6 percent of sea surface climates may be lost by 2100. On the other hand, the RCP 8.5 scenario is projected to lose 95 percent of surface level climates.

Lotterhos and colleagues concluded that aquatic lifeforms may survive climatological changes by “dispersing” themselves. ‘Dispersal’ is the process by which organisms relocate. Organisms that do not disperse into a suitable area or adapt in some other way will face population declines. As carbon dioxide increases, the number of suitable climates for these organisms decreases. The loss of these climate zones effectively contributes to the loss of marine biodiversity.

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