Since the Industrial Revolution, hundreds of billions of tonnes of carbon have entered our atmosphere. Atmospheric carbon compared with a 20th-century average, parts per million Less carbon More carbon 1840 285 ppm 2018 405 ppm The surface of the sea is getting hotter. Sea-surface temperature compared with a 20th-century average, degrees Fahrenheit Cooler Hotter 1854 64 2018 65.2 Heat is penetrating into the depths of the ocean. Heat content down to 700 meters compared with a 1955-1985 average, 10^22 joules Ocean heat content up to 700 meters compared with a 1955-1984 average, 10^22 joules Less heat More heat 1955 -3.2 2018 16.7 Sea levels are rising. Sea level change compared with a 20th-century average, inches Lower Higher Sea level change compared with a 20th-century average, inches Lower Higher 1880 0 2015 8.9 The extent of our arctic sea ice is shrinking. Arctic sea-ice extent compared with a 1979-2008 average, millions of square miles Larger extent Smaller extent 1979 7.7 2018 6.4 The Greenland ice sheet is melting. Percent of ice sheet surface area that is melting compared with a 1979-2008 average Less melt More melt 1979 2.1 2018 3.3 And ocean water is becoming more acidic. Seawater pH level, compared with a 1988-2017 average Less acidic More acidic 1988 8.109 2017 8.065 Note: Acidity measurements taken from the ALOHA station. Source: Ted Scambos, University of Colorado Boulder; Boyin Huang, NOAA; Thomas L. Mote, University of Georgia; NOAA; NSIDC; University of Hawai’i at Manoa

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The massive amounts of carbon dioxide and other greenhouse gases that have entered our atmosphere since the Industrial Era began in the 18th century have had significant effects on the world’s oceans.

Solar energy striking Earth is either reflected back into space or absorbed and then radiated back as heat. Greenhouse gases trap some of that heat. Because they are accumulating in the atmosphere, excess heat is accumulating too, and the Earth is warming.

“Greenhouse gases like carbon amplify the amount of excess heat left over because they prevent heat energy from releasing from Earth’s system,” says oceanographer Tim Boyer of the National Oceanographic and Atmospheric Administration.

Excess heat trapped in the atmosphere by our greenhouse gases spreads into the oceans. They've absorbed about 90 percent of that heat. As a result, they've been warming steadily for a long time.

Sea surface temperatures over the last several decades reflect such warming, but are also sensitive to weather events like hurricanes and El Nino. That explains why temperatures fluctuated from one year to the next as far back as the mid-1800s.

Along with the warm air itself, the heat absorbed by the oceans melts ice in the polar regions, releasing fresh water that accounts for more than half of all sea level rise; the rest is attributed to the expansion of seawater as it warms. “This has obvious effects on coastal area flooding and real estate,” says NOAA oceanographer Andrew Allegra, as well as implications for marine life.

The oceans don't just soak up excess heat from the atmosphere; they also absorb excess carbon dioxide, which is changing the chemistry of seawater, making it more acidic. “Ocean acidification is one simple and inescapable consequence of rising atmospheric CO2 that is both predictable and impossible to attribute to any other cause,” says oceanographer John Dore of Montana State University.