A century and a half of reconstructed data is helping scientists paint a picture of how much energy the world’s oceans are absorbing from human-made greenhouse gas emissions (GHG) and, as a result, how temperatures have changed since the 19th century. Estimates suggest that from 1871 until now, global warming of our oceans is at 436 x 10^21 Joules, which, if you’re not a physics buff, is roughly 1,000 times the amount of energy used by humans every year.
The Guardian reports that its staff crunched the numbers and found that the “average heating across that 150-year period was equivalent to about 1.5 Hiroshima-size atomic bombs per second.” They say that figure has accelerated over time as emissions continue to rise, now equaling between three and six atomic bombs per second.
IFLScience reached out to study author Laure Zanna for her take on the analogy. She said, "we prefer to avoid this analogy and favor a comparison between the heat absorbed by oceans and annual human energy consumption, or how many cups of tea one can make that amount of heat." (It's unclear exactly how many cups that equates to.)
“But obviously, we are putting a lot of excess energy into the climate system and a lot of that ends up in the ocean. There is no doubt,” she added. Prior to now, a lack of records has limited researchers in their ability to estimate historic temperature fluctuations in oceans around the world. Now, researchers have employed a new method that takes on a mathematical approach.
“Our approach is akin to ‘painting’ different bits of the ocean surface with dyes of different colors and monitoring how they spread into the interior over time. We can then apply that information to anything else – for example humanmade carbon or heat anomalies – that is transported by ocean circulation,” explained study author Samar Khatiwala in a statement. “If we know what the sea surface temperature anomaly was in 1870 in the North Atlantic Ocean, we can figure out how much it contributes to the warming in, say, the deep Indian Ocean in 2018. The idea goes back nearly 200 years to the English mathematician George Green.”
The team used ocean circulation models with observed surface temperatures to reconstruct the full profile of temperature changes over the last 150 years. They found that since 1955, up to half of warming in the low- and mid-latitudes of the Atlantic Ocean can be attributed to ocean circulation that has accumulated heat in the area.
Publishing their work in the Proceedings of the National Academy of Sciences, the authors note that uncovering ocean circulation changes can help predict future patterns of warming and sea level rise, but there is still work to do to validate their method and provide even more accurate estimates. Their technique applies to human-made carbon transported by ocean currents, but heat doesn’t always behave in this way. Instead, it affects circulation by changing the density of seawater.