Hope For an Energy Rich, Sustainable Future
- Sep 17, 2014 12:00 am GMT
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In the 2011 paper Earth’s energy imbalance and implications Hansen et al. state, “The rate of ocean heat uptake determines the planetary energy imbalance, which is the most fundamental single measure of the state of Earth’s climate.”
The conclusion of the paper was most climate models mix heat too efficiently into the deep ocean and as a result underestimate the negative forcing by human-made aerosols.
As Hansen et al. point out the Earth is absorbing more energy from the Sun than it is radiating to space as heat. If the ocean could absorb all of this heat there would be no noticeable impact on our climate and thus no concern about greenhouse gases. At least until such time as the oceans could absorb no more heat and the imbalance had to be taken up by the atmosphere.
The essence of the paper is existing models are putting too much emphasis on ocean heat uptake and thus are underestimating the climate risk.
For entirely the opposite reason Norm Rogers, a climate skeptic, in a paperIs Ocean Heat Storage Presently Knowable? presented to the December 2012 meeting of the American Geophysical Union, trys to make the case that the deep oceans cannot be absorbing as much heat as climate models suggest.
He points out; heat enters the ocean from the surface and is diffused downward. The mixed layer, commonly taken as being 100 meters thick, quickly comes into equilibrium. Below that, except near the poles, heat transfer is much slower, taking around 100 years to penetrate 500 meters below the mixed layer. This slow movement of heat is confirmed by the distribution of tracers such as chlorofluorocarbons that have only been present in the atmosphere for about 60 years.
If one looks below about 200 or 300 meters for missing heat, as S. Levitus et al. does (see figure below) in the paper World ocean heat content and thermosteric sea level change (0–2000 m), 1955–2010 this heat started going missing decades if not a century ago.
Rogers uses the following diagram to show the penetration of heat into the ocean with time in years shown on the left of the chart and depth in meters on the bottom.
The conclusion Rogers seems to draw is if the atmosphere hasn’t warmed appreciably over the past 15 years and the ocean can’t be taking up heat as rapidly as existing models claim then global warming isn’t the problem it has been made out to be.
This goes against the scientific consensus however, which if right suggests two alternatives possibilities. First there are other factors at play with respect to the hiatus. Second if the deep ocean could be forced to accept more heat more rapidly, the climate threat could be forestalled.
Cowtan & Way have claimed that effectively there has been no atmospheric warming hiatus. They suggest that measurements simply haven’t been taken in the 16 percent of the world, including the poles and Africa, where temperatures have risen over the period of the so-called hiatus. Their reconstruction of global averages with these temperatures included showed the global surface warming trend for 1997–2012 was approximately 0.11 to 0.12°C per decade; more consistent with a warming planet.
Pauses are also part of natural climate variability, and their existence does not refute long-term climate change trends. Other proposed causes for the hiatus include increased sulfur emissions from volcanic activity, the emission of pine-smelling vapors from pine forests, which have been shown to turn into aerosols, and the ban on chlorofluorocarbons as a result of the Montreal Protocol, since they were potent greenhouse gases.
There are also indications other factors are at play driving heat into the ocean over and above the diffusion Rogers points to. Matthew England of the Australia Research Centre of Excellence for Climate System Science at the University of New South Wales points to dramatically increased trade winds driving heat into the western Pacific.
Tung, University of Washington, and Xianyao Chen of Ocean University of China in Qingdao suggest the missing heat has gone into the deep waters of the Atlantic Ocean, carried there by the ocean conveyor system which moves from the Caribbean to the North Atlantic, where the water becomes colder and saltier, sinks and flows south again.
According to Tung, if intensified trade winds, related to the El Niño-La Niña cycle, are sinking heat into relatively shallow layers of the Pacific, then the current hiatus could be over as soon as the next El Niño occurs. If the heat is ending up deeper in the Atlantic Ocean however, then we may have another 10 to 15 years before global warming resumes with its previous intensity, buying us a little more time to deal with the problem—but also giving skeptics like Rogers more ammunition.
As I have argued however, there is a better alternative. We can move heat almost instantaneously into the deep ocean with a heat pipe and produce all of the energy the world requires in the process. Currently the world operates on about 16 terawatts of primary energy. To produce this with ocean thermal energy conversion systems of the heat pipe design, 16 terawatts of surface heat would be converted to energy and approximately another 300 terawatts of heat would be moved to the deep. The heat pipe would deposit this heat at a depth of 1000 meters.
According to Rogers the rate of return of heat from the depths is approximately 4 meters per year thus it would take 250 years, rather than 10 to 15 for Atlantic heat, for this heat to return. Since the energy provided by this method is carbon free the climate would be a long way along the road to recovery before the subducted heat could start flowing back into the atmosphere.
If the rate of ocean heat uptake is the most fundamental single measure of the state of Earth’s climate, then ocean thermal energy conversion using a heat pipe is the single hope for an energy rich sustainable future given, as I believe is the case, 97 percent of climate scientists are right.