NASA Study: Ocean Abyss Has Not Warmed

submitter bigwheel sends this excerpt from a NASA news release: The cold waters of Earth's deep ocean have not warmed measurably since 2005, according to a new NASA study, leaving unsolved the mystery of why global warming appears to have slowed in recent years. Scientists at NASA's Jet Propulsion Laboratory (JPL) in Pasadena, California, analyzed satellite and direct ocean temperature data from 2005 to 2013 and found the ocean abyss below 1.24 miles (1,995 meters) has not warmed measurably. Study coauthor Josh Willis of JPL said these findings do not throw suspicion on climate change itself. "The sea level is still rising," Willis noted. "We're just trying to understand the nitty-gritty details."

Comments

Re:Thermal capacity of rock?

[radtea]

Allow my naivete to shine: What's the temperature of all of the rock that water is in contact with, and what's its thermal capacity relative to the water? Could it be that it's slow to warm as you need to warm all the rock it's in contact with?

You are correct to label your question naive :-)

The average ocean depth is about 4000 m, so the depth being looked at here (just under 2000 m) isn't typically in contact with rock at all. That is, if you demarcated the 2000 m depth line it would intersect very little ocean floor, and that just off the edges of continental shelves. These are pretty much the "mid-depths" we are talking about.

Furthermore, rock is both a) insulating (compared to water) and b) of relatively low heat capacity (compared to water).

Water has a heat capacity of about 4 kJ/kg*K, which is to day it takes 4 kJ to raise 1 kg of water 1 K in temperature. A typical rock (granite, say, although most others are similar) has a heat capacity of 0.8 kJ/kg*K, so rock is both less able to transport heat and less able to absorb heat than water.

Oceans are far more important to the heat balance of the Earth than the air is. Consider the scales. Earth has 5E18 kg of air, and 1.4E21 kg water, and water has 4 times the heat capacity of air, so the thermal mass of the oceans is about 1000 times greater than that of the air (I'm actually surprised it's not more than that, but I've confirmed the numbers from a couple of different sources.)

Given that AGW is adding about 1.6 W/m**2 to the Earth's heat budget, consider a typical square metre of ocean surface, below which is a water column 4000 m deep with a mass of 4E6 kg. That 1.6E-3 kJ/s*m**2 has the capacity to raise the temperature of that water column by 1.6E-3/4*4E6 = 1E-9 K/s. Which doesn't sound like much until you realize there are 3.14E7 s/year, so ocean warming, all else being equal, could be as much as 0.03 K/year, or 0.3 K/decade, or 3 K/century.

These are pretty appreciable numbers, and give a sense of the utility of precise ocean measurements as a way of getting at AGW, because we should be able to see a characteristic depth profile of temperature developing over time that would allow us to infer the additional radiative forcing very directly.