Posted on 17 January 2019 by John Abraham

Last year was the hottest ever measured, continuing an upward trend that is a direct result of manmade greenhouse gas emissions.

The key to the measurements is the oceans. Oceans absorb more than 90% of the heat that results from greenhouse gases, so if you want to measure global warming you really have to measure ocean warming.

There are other ways to measure climate change, but none are as convincing as the oceans. Air temperatures are most commonly reported in the media as evidence of global warming, but the problem with these is they are very erratic. While there is certainly a long-term trend of higher air temperatures, any given year may be warmer or colder than the last.

So oceans are key, and they are telling us a clear story. The last five years were the five hottest on record. The numbers are huge: in 2018 the extra ocean heat compared to a 1981-2010 baseline amounted to 196,700,000,000,000,000,000,000 joules. The current rate of ocean warming is equivalent to five Hiroshima-size atomic bombs exploding every second.

The measurements have been published in the journal Advances in Atmospheric Sciences in an article by Lijing Cheng, the lead author, and his colleagues from the Institute for Atmospheric Physics in China. His collaborators, of which I am one, included researchers from around the world. The article charts ocean heat back to the late 1950s, showing a steady increase.

Ocean warming is incontrovertible proof of global warming, and there are real consequences to a warming ocean. Firstly, warmer water expands, and this expansion causes sea levels to rise. Approximately a third of the rise in ocean waters is a result of the heat absorbed by the oceans. Scientists expect about one metre of sea level rise by the end of the century, which would be enough to displace 150 million people worldwide.

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