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Explain the causes and effects of ocean warming.

Causes of Ocean Warming

Climate change is caused by increases in greenhouse gases which trap more heat from incoming solar radiation. As temperatures on Earth warm due to climate change, oceans become warmer as well. Explore the graph below. Notice how, on average, sea surface temperatures are increasing. 2023 is very noticeable, as it was much warmer, especially in the second half of the year than any previous year.

But, it's not just surface temperatures that are increasing! Deep sea temperatures are usually relatively stable due to the high specific heat of water. Even still, these zones are warming. Explore the graph below, to see how the top 2000 meters (over 6561 feet!) of the world's oceans have warmed since 1955:

Essential Knowledge

Ocean warming is caused by the increase in greenhouse gases in the atmosphere.

Effects of Ocean Warming

A gif of the indian and southern oceans, showing the locations of the Argo floats in these oceans. — **Each dot on the map is an Argo float that moves with the ocean currents.** **Dots suddenly appearing in a line, represent new floats being deployed (float movement over a 6-month period in 2005)**.

The oceans are critical to our planet - covering over 70% of the planet. Interestingly, oceans were able to delay the onset of atmospheric warming because around 93% of the excess energy trapped in the Earth system by greenhouse gas pollution from 1971 to 2010 was absorbed by the oceans, 3% expanded melting ice and 3 percent warmed the land. Only 1% of the excess energy warmed the atmosphere.

The National Oceanic and Atmospheric Association (NOAA) is the primary governmental body monitoring our oceans, including ocean warming. Through a series of “Argo floats”, NOAA monitors ocean conditions worldwide. There are nearly 4000 Argo floats in the ocean.

Data collected from the Argo floats has helped NOAA identify several conditions thought to be caused by rising ocean temperatures.

Warmer water is less dense than cooler water, occupying more space. This thermal expansion accounts for about 42% of sea level rise since 1993.

Rising ocean temperatures can stress corals. When corals are stressed, they often expel their zooxanthellae and turn white. This is known as coral bleaching. Because these corals are the foundation of coral reef ecosystems, death of corals can dislocate or disrupt fish and other populations that rely on coral reefs.

This image illustrates the process of coral bleaching in three stages. — ***Coral bleaching is a process in which stressed corals expel their symbiotic algae partners, making it harder for these animals to obtain the nutrients they need to survive.***

Rising ocean temperatures can also increase vertical ocean stratification, reduce nutrients in surface water, and decrease dissolved oxygen at depth, all of which affect ecosystems, fisheries, and possibly even ocean carbon storage. Additionally, rising ocean temperatures can promote rapid intensification of tropical cyclones and hurricanes, which can result in increased infrastructure, ecosystems, fisheries, and possibly even ocean carbon storage. Additionally, rising ocean temperatures can promote rapid intensification of tropical cyclones and hurricanes, which can result in increased infrastructure, ecosystem, and economic damages from these storms.

Essential Knowledge

Ocean warming can affect marine species in a variety of ways, including loss of habitat, and metabolic and reproductive changes.

Ocean warming can cause coral bleaching, which occurs when the loss of algae within corals causes the corals to bleach white. Some corals recover and some die.

AP Exam Tip

The oceans were able to delay significant climate change for several years, but they cannot do this forever.

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