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How Fast Are the Oceans Warming?

By Rosie Oakes, PhD

Ocean
The ocean is vast, covering 71 percent of the Earth’s surface, which makes it difficult to measure changes in ocean temperature. Photo by Rosie Oakes


February 15, 2019

The greenhouse gases in the Earth’s atmosphere make our planet habitable, taking it from an average global temperature of -18 degrees C (zero degrees F) to a balmy 15 degrees C (60 degrees F). Current human activities, such as fossil fuel burning and deforestation, are increasing the concentration of these greenhouse gases, increasing the amount of the sun’s energy that is getting trapped.

It should be getting hotter. A lot hotter. Although we are seeing increased surface temperature, the oceans are stepping in to save the day, absorbing a whopping 93 percent of the excess energy.

That’s great for us at the surface, but not so good for the oceans. That excess energy is causing the oceans to warm. A recent paper in Science demonstrates that this is happening faster than we previously thought.

Because it takes more energy to heat the water than to heat the air, the temperature of the world’s oceans are less affected by daily variability than the atmosphere, making it a faithful recorder of temperature change.

There’s just one problem. The oceans are huge. Covering 71 percent of Earth’s surface with an average depth of 3,800 meters (12,000 feet), there is a lot of water to measure.

Before 2000, scientists had to base their calculations of ocean warming on a sparse set of data points taken from research cruises. Let’s think of it in terms of the New Jersey coast: If you measure the water temperature while at the beach in Cape May, and your friend measures the water temperature at the beach in Asbury Park, would the two of you be able to calculate the water temperature along the whole New Jersey coastline?

You’d probably want some more information first. What time of day did you take the measurements? How far from the beach? How deep in the water? What was the weather like? Did you and your friend use the same brand of thermometer? The list goes on.

Scientists asked these same questions of the sparse ocean temperature datasets and so had to make a lot of assumptions when estimating the temperature of the seawater. But over the last 20 years, scientists have worked out how to correct measurements taken using different instruments, and how to improve their calculations by using ocean models.

In addition, over 3,000 automated floats called Argo floats have been deployed throughout the world’s oceans collecting over 100,000 temperature records per year.

With all this new data at hand, scientists now can answer the question: How fast is the ocean warming? So, we know for a fact that it is faster than we expected. Four recent studies have found that ocean warming is occurring at two times the rates predicted in the fifth climate report from the Intergovernmental Panel on Climate Change back in 2014.

Why does this matter? And what does it mean for us? As the oceans warm, they become less habitable. Warm water can hold less oxygen, causing dead zones to form in the ocean where fish and other animals cannot survive. Warmer ocean temperatures also increase the likelihood of coral bleaching events.

Ocean warming also increases the rates of melting of ice caps in the polar regions, increasing global sea level, the implications of which are being studied by the Academy’s Wetlands Section Leader, Beth Watson, PhD, and her team on coastal marshes here in the Delaware and Barnegat Bays.

The good news is that we have the ability to slow this warming. The increase in ocean heat content is linked to increased level of greenhouse gases in our atmosphere.

To counter this, we have to start making changes at the individual level and at the national level to decrease our output of greenhouse gases. The Nature Conservancy has a great carbon calculator where you can calculate how changes in your lifestyle will impact your carbon footprint.

For example, I ride my bike to work each day, four miles each way, five days a week. Compared to driving a car, I will save one ton of carbon dioxide emissions this year. What can you do to help reduce your carbon footprint?

Rosie Oakes, PhD, is a post-doctoral researcher in the Department of Biodiversity, Earth and Environmental Science and a member of the Academy of Natural Science’s Inverterbrate Paleontology Lab.

Read more from Academy of Natural Sciences blog