One of the lesser known aspects of climate change is the role played by oceans as a "heat sink." Oceans absorb a lot of heat from the atmosphere with currents and prevailing surface winds sometimes driving that captured heat deep into the ocean depths.
We might think that oceanic heat goes down into the cold depths and just disappears only it doesn't. The first law of thermodynamics, the law of conservation of energy, holds that energy can not be created or destroyed. It can merely be converted from one form to another. In other words oceans absorb that surface energy, heat from direct sunlight and from the warming atmosphere, and, in the right circumstances, store it in very deep water until, again in the right circumstances, it may be returned to the surface. This stored ocean heat is believed to be a driving force behind the Pacific Decadal Oscillation.
Climate scientists have been keeping a close eye on ocean temperatures, especially the rapid pace of ocean warming. Their concern is that a powerful positive phase could see much of that heat energy released back into the atmosphere creating a big spike in global warming.
The science types now have even more cause for concern. A new study finds that the oceans are warming 13% faster than previously estimated and that the rate of increase is accelerating.
Since about 2005 a new type of sensing device has been deployed (the Argo float system). These floats (approximately 3500 in total at any time) are spread out across oceans where they autonomously rise and fall in the ocean waters, collecting temperature data to depths of 2000 meters.
When they rise to the ocean surface, they send their data wirelessly to satellites for later analysis. Hence we can now map the ocean heat content quite well. But what about the past, when we mainly had measurements from expendable bathythermographs deployed mainly along major shipping routes and largely confined to the northern hemisphere? Putting data from these various sensors together has been a struggle and has been a major impediment to an accurate quantification of the ocean’s temperature history.
Lead author, Lijing Cheng says:
"We know that ocean observations were very sparse until the Argo era. There were major gaps in data, particularly in the Southern Hemisphere. Our challenge was to assess the changes to global ocean heat and fill data gaps. A major issue is to ensure gap-filling is reliable. It is this issue that motivated the study. We proposed an advance gap-filling strategy and used it to attain near global coverage. We rigorously evaluated the reliability of our approach and as a result, we have much higher confidence that the ocean and the Earth are warming at a faster rate than previously thought."
One of the co-authors, John Fasullo added:
"This study shows that more heat is likely to have been absorbed by the oceans over the past 50 years than had previously been reported. With upward revisions in our estimates of the climate’s sensitivity to greenhouse gases and the associated resultant sea level rise."
Our team’s press release noted:
"we know the oceans are much warmer now and they contain the memory of climate change. Higher sea surface temperatures are continually reinforced by the extra heat beneath the ocean surface. The oceans are affecting weather and climate through more intense rains. This process is a major reason why 2016 was the hottest year ever recorded at the Earth’s surface, beating out 2015 which was the previous record. Additionally 2015 was a year with record hurricanes, heat waves, droughts, and wild-fires around the world."
It is these changes that affect storms, such as the deluges that have recently affected California, or which have led storms to produce “thousand year floods” as has been seen in the Carolinas with Hurricane Matthew, or the Louisiana floods in August last year, or the Houston floods in April, and so forth. This kind of knowledge and understanding has profound consequences.
Of course this new data on the degree and rate of ocean warming means a lot of other temperature based projections, notably sea level rise, will have to be recalculated - and not in a good way.