The second-hottest year recorded at Earth’s surface was the hottest in its oceans
Among scientists who work on climate change, perhaps the most anticipated information each year is how much the Earth has warmed. That information can only come from the oceans, because almost all heat is stored there. If you want to understand global warming, you need to first understand ocean warming.
This isn’t to say other measurements are not also important. For instance, measurements of the air temperature just above the Earth are really important. We live in this air; it affects us directly. A great commentary on 2017 air temperatures is provided by my colleague Dana Nuccitelli. Another measurement that is important is sea level rise; so too is ocean acidification. We could go on and on identifying the markers of climate change. But in terms of understanding how fast the Earth is warming, the key is the oceans.
This important ocean information was just released today by a world-class team of researchers from China. The researchers (Lijing Cheng and Jiang Zhu) found that the upper 2000 meters (more than 6000 feet) of ocean waters were far warmer in 2017 than the previous hottest year. We measure heat energy in Joules. It turns out that 2017 was a record-breaking year, 1.51 × 1022 Joules hotter than any other year. For comparison, the annual electrical generation in China is 600 times smaller than the heat increase in the ocean.
The authors provide a long history of ocean heat, going back to the late 1950s. By then there were enough ocean temperature sensors to get an accurate assessment of the oceans’ warmth. Their results are shown in the figure below. This graph shows ocean heat as an “anomaly,” which means a change from their baseline of 1981–2010. Columns in blue are cooler than the 1981-2010 period, while columns in red are warmer than that period. The best way to interpret this graph is to notice the steady rise in ocean heat over this long time period.
Ocean heat content change since 1958. Illustration: Cheng and Zhu (2018), Advances in Atmospheric Sciences |
It’s interesting to look at the top five years on record in terms of ocean heat; they are listed below.
- 2017: 19.19 × 1022 J
- 2015: 17.68 × 1022 J
- 2016: 17.18 × 1022 J
- 2014: 16.74 × 1022 J
- 2013: 16.08 × 1022 J
The authors went a bit further and investigated how the heat was input into the oceans by region. They found that in 2017, a lot of heat was deposited in the Atlantic and Southern Oceans. The authors also calculated that all this heat resulted in approximately 2 mm rise in sea level (as water warms, it expands and so that ocean levels rise).
Ocean heat content data. Illustration: USGCRP report, originally from Cheng et al., 2017 |
The consequences of this year-after-year-after-year warming have real impacts on humans. Fortunately, we know why the oceans are warming (because of human greenhouse gases), and we can do something about it. We can take action to reduce the heating of our planet by using energy more wisely and increasing the use of clean and renewable energy (like wind and solar power).
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