According to a new study published in the journal Nature Climate Change, the world’s oceans absorbed about the same amount of heat in the last two decades as they did over the previous 130 years.
For reasons as yet undetermined about a third of that buildup has occurred at depths of 700 meters or greater; well beyond the penetration of the suns rays.
As has been suggested in this forum on numerous occasions this is the most likely explanation for the recent pause in surface temperatures observed by scientists in recent years.
Although the laws of thermodynamics predict that heat will flow from a warm surface to a cold deep, this effect is offset by the buoyancy of less dense, warm, water.
Scientific American reinforces the opinions expressed previously on these pages here, here, here, here and here that winds and currents have driven trapped heat that has eluded surface temperature measurements to deep water, fueling the claims of a “hiatus” or “pause” in global warming from 1998 to 2013.
The subsequent subsidence of the trade winds in the southern hemisphere has allowed for the return of considerable amounts of this heat.
A prior study cited in the Nature study suggests that between 67 to 98% of this warming occurred in southern, extratropical, oceans, which are in fact the largest bodies of water.
It is well understood that the oceans are able to retain vastly greater quantifies of heat than the atmosphere due to their heat capacity and as Peter Gleckler, an oceanographer at the Lawrence Livermore National Laboratory and the lead author in the new study points in the Washington Post, “Ninety, perhaps 95 percent of the accumulated heat is in the oceans”.
“As the upper oceans have been warming over time, more and more of this heat is finding its way down into the deeper ocean, and our results indicate that the fractional amount of heat that is trapped in the deeper ocean is increasing as well,” Gleckler said.
“We find that the heat uptake of the global oceans has doubled since about 1997, compared to what took place prior to that over the industrial era. And that was a surprising result to us,” he added.
Global warming is generally perceived to be an overall upward trend in air temperature but this is because that is how we experience the change. Scientists however define global warming in terms of an energy imbalance between the Earth and space, with less heat escaping and more being retained within the planet’s system as a result of the greenhouse effect.
Where that trapped heat ends up makes a huge difference as to its impact on the systems upon which our survival depends.
In a recent RealClimate post, Gavin Schmidt, Director of the NASA Goddard Institute for Space Studies, refers to ocean heat as “a measure of the unrealised radiative imbalance”.
In other words it is global warming that has limited direct impact on our lives.
“The heat capacity of the Earth’s entire atmosphere is equaled by the top 3.5 meters [11 feet] of the ocean,” explains a fact sheet released by Lawrence Livermore National Laboratory to accompany the new study.
Since the ocean on average is over 1000 times deeper than 3.5 meters it has over 1000 times the capacity to absorb trapped heat that the atmosphere has.
John Shepherd, a researcher at the University of Southampton’s National Oceanography Centre, who was not involved in the study, says it is unclear if the extra heat absorbed by the oceans will return to the atmosphere or stay in the depths. “It’s certainly not a cure for climate change, nor any reason to be less concerned with it,” he said in a statement on ocean warming.
Although the natural movement of heat to deep water is not a cure for climate change, such a movement, through a heat engine can be.
Heat trapped in the ocean can safely be removed through conversion to productive work. Although this conversion is only about 5 percent each cycle of an ocean thermal energy conversion system, the remaining heat moved to the deep will cycle back to the surface in about 250 years and can be returned to the depths at that point with the conversion of another 5 percent to work at that time. Not only does this insure the unconverted heat remains in the deep, the surface effects are avoided and over the millennia all of the heat currently trapped in the ocean can be converted to productive use.
The energy potential of this heat is 125, 25 and 71 times the IAEA estimate for reserves of oil, coal and natural gas.
The ‘hiatus’ is a surface phenomenon. “The Earth is still warming, and the oceans have been taking up the bulk of that heat,” says Matt Palmer, a climate scientist at the British Met Office Hadley Centre.
Tropical storms are also surface effects that are avoid by the movement of the heat that drives them to deep water and heat at the surface causes twice the thermal expansion and therefore sea level rise that it does at a depth of 1000 meters.
John Shepherd says, if the extra heat remains in the ocean it could disturb sea and atmospheric circulation, playing havoc with weather patterns.
Its conversion to work is the only way that heat can safely be removed and that the havoc he describes can be mitigated. As Shepherd points out, its release back into the atmosphere could accentuate warming already poised to punch through the threshold for dangerous impacts.
Last month, almost 200 governments agreed at Paris to avoid those impacts. It is time the heat is turned up on them to live up to those commitments by taking the heat out of global warming which can only be done by sequestering some in the deep ocean and converting the balance to productive use. The carbon dioxide driving global warming stays in the atmosphere for centuries therefore the oceans will continue to heat up long after we stop burning fossil fuels as will the atmosphere unless we convert and sequester that heat.
The science is clear; the oceans are saving us from catastrophe and have the capacity to continue to do so if their ability to produce energy through ocean thermal energy conversion and to absorb heat at depth is exploited.
No other replacement for fossil fuels alleviates the escalating problem of ocean heat, by far the greatest manifestation of global warming, and in fact virtually all other energy sources exacerbate this problem.