The concerns with global warming notwithstanding, according to NASA the average temperature of the Earth is only 0.9 °C.
This is about 19 °C warmer than the surface temperature would be where there no greenhouse effect.
As shown in the following Atmospheric Infrared Sounder (AIRS) satellite image from April 2003, calibrated from a low of -81°C to a high of 47 °C, the highest temperatures are recorded in the deserts of the Middle East and Australia and the lowest is recorded on the Antarctic land mass.
Figure 2. The average temperature of the surface is 15°C or 288 degrees Kelvin or 75% up to the scale shown above.
The distance between the South and North Poles is about 20,003 kilometers, which is half the distance it takes for heat generated at the equator to dissipate to space at the poles. Assuming an average wind speed of about 4.5 meters/second, it takes therefore about a month for heat generated at the equator to reach one of the poles if the heat is transported through the atmosphere and closer to 500 years through the ocean, considering this half a cycle of the thermohaline circulation.
Figure 3 is a horizontal cross-section of the Pacific Ocean for the period March 1991 to October 1992 from the World Ocean Atlas showing that the surface is only a veneer of global heat picture.
Although the surface is predominantly red and yellow in Figure 2, it is the blues and purples of Figure 3 that dominate the ocean depths, where temperatures below a depth of 1000 meters are 4 °C or less and where the average temperature of the entire ocean is 3.9 °C.
If the objective is to distribute the excess heat of global warming, as the following graphic from the paper Warming the World’s Oceans by Hegerl and Bindoff suggests might be a worthwhile endeavour, given that solar radiation accumulates 30 degrees either side of the equator and dissipates at the higher and lower latitudes, then the path of least resistance would be to move surface heat to deeper water.
Figure 4 is a cross section of the Atlantic Ocean basin illustrating how atmospheric warming is transferred from the ocean surface to the ocean interior.
The stable configuration of a column of water is the same as the right-hand scale of Figure 4.
Wave action can create turbulence however, that stirs light, warm, water into the mixed layer of the ocean, which depending on the season and the surface temperature can reach to depths of 100 meters.
In this regard it should be noted that although Figure 1 shows 2017 was slightly cooler than 2016, Table 1, from the paper, 2017 was the Warmest Year on Record for the Global Ocean by Cheng and Zhu, shows that the oceans were almost 12% warmer in 2017 than in 2016 and that the last 5 years have been the warmest on record.
The Atlantic hurricane season in 2017 was the fifth most active since 1851 when record keeping started and anecdotally the 17 named storms were likely the reason for a slight cooling of the surface while the ocean got considerably warmer.
These storms are also the analogy the writer has been trying to convey for some time for how the ocean surface can anthropogenically be cooled by relocating the surface heat to deeper water.
Furthermore, such a relocation is happening inexorably and destructively rather we intervene or not.
The second way wind-driven currents move surface heat to deeper water is through what is known the El Niño–Southern Oscillation or ENSO. As indicated in Figure 5. Under normal conditions, Trade Winds blow heat across the Pacific from east to west and drive the surface heat and the thermocline into deeper waters. The winds that blow the heat are driven by what is known as Walker Circulation which is repeated around the globe but as Figure 6 indicates only impacts the Pacific and to a lesser extent the Atlantic because the surfaces of Asia, Africa, and North America produce less evaporation and thus cloud cover.
As shown in Figure 5, La Nina conditions drive heat deeper in the West-Pacific and the thermocline deeper while the East-Pacific cools as the thermocline rises to near the surface as does the deep, cool water. The paper El Niño and the end of the global warming hiatus by Hu and Fedorov indicates that weak El Niño activity from 1998 until 2013 was the cause of the slowing of the rate of surface temperature increase, which like hurricane cooling of the surface is and was a temporary phenomenon. The years 2014–2016 were marked by El Niño conditions showing a rapid rise in the temperature of the atmosphere due to the release of the sub-surface that had accumulated during the hiatus. And 2017 was a case of minimal atmospheric cooling and significant ocean warming, possibly due to hurricane activity.
And finally, the surface is cooled by the addition of brine from freezing sea ice, which increases the density of the water that in turn sinks to the bottom as shown in Figures 3 and 4 and the overturning circulation that moves heat from the surface to the deep and back again as shown in Figure 4.
The bottom line is, a warm surface and a cool deep is the recipe for the global heat engine that produces the Thermohaline circulation, as well as the blueprint for the many smaller heat engines that can effectively convert the stratified heat potential of the oceans into productive energy.