Tuesday, November 17, 2015

More Big Gains in Ocean Heat Content Just Posted

NOAA just released the 3Q15 numbers for ocean heat content*, and they are again huge.

In the last 12 months, the 0-700 m region of the ocean has gained 1.5 W/m2 of heat**, and the 0-2000 m region 1.7 W/m2.

That's a gain of 25 ZJ (zettajoules) for the 0-700 m region, and 28 ZJ for the 0-2000 m region. (By way of contrast, "...mankind generates 0.5 zetajoules of energy every year in its power stations.")

Or, if you prefer, 780 trillion Watts and 870 trillion Watts, respectively.


The graph above shows that the heat gain (a very good approximate to global warming) is obviously accelerationg; calculated from a 2nd-order polynomial fit to the top half of the ocean***, the acceleration remains at 0.10 W/m2/yr for the 0-2000 m region****.



An acceleration of 0.10 W/m2/yr sounds large to me -- what forcings are, in total, increasing at that rate? -- but that's what the data says.

Footnotes:
* NOAA ocean heat content data: 0-700 m, 0-2000 m.

** The area used here is that of the entire Earth, since about 93% of the GHG-trapped heat goes into the ocean.

*** Yes, heat may be increasing, or decreasing, below 2000 meters. I'm aware of this paper, which finds a small increase of 0.05 W/m2 for the region below 3000 m for the 1990s and 2000s. If you know of additional studies on the deep ocean, I'd appreciate if you left them in a comment.

**** The basic statistical error bar here (two-sigma) is ±0.03 W/m2/yr. I don't know how to include autocorrelation in a 2nd-order polynomial fit. If you can help me out with that, let me know. Thanks.

3 comments:

Paul Skeoch said...

what forcings are, in total, increasing at that rate?

Very unlikely to have much to do with forcing change over such a short period. I think the apparent acceleration can mostly be explained by geographical coverage bias in observations. Von Schuckmann et al. 2014 (pdf) showed that masking altimeter sea level by ARGO coverage for 2005 to 2012 resulted in a 20% reduction in trend, indicating a bias. If we assume a mass component of roughly half total SLR, with little relevant spatial variance, that suggests ARGO coverage bias caused an underestimate of steric contribution by about 40% over 2005-2012.

Since 2012 Pacific variability seems to have flipped, so the bias has likely been operating in the opposite direction. Accounting for these probable biases reveals a much more linear trend.

Lack of Arctic coverage may also play a small role. Arctic sea ice data suggest increased heat transport into the Arctic over 2005-2012, but not so much since 2013 and that variability North of 60N wouldn't be picked up by the ARGO network. This is independent of the coverage issue mentioned above because altimeter SLR data is also absent in the Arctic.

Finally, Brown et al. 2014 found that TOA energy imbalance tended to be reduced compared to forced response in CMIP models during periods of cooling internal variability influence, e.g. "The Hiatus".

David Appell said...

Paul Skeoch wrote:
"Very unlikely to have much to do with forcing change over such a short period. I think the apparent acceleration can mostly be explained by geographical coverage bias in observations. Von Schuckmann et al. 2014 (pdf) showed that masking altimeter sea level by ARGO coverage for 2005 to 2012 resulted in a 20% reduction in trend, indicating a bias."

This is a paper about sea level, not ocean heat content (which is only one component of sea level rise).

Paul Skeoch said...

The paper uses sea level as a means to assess possible biases in ARGO data, ocean heat content and salinity. Its focus is on the ability of the current ARGO network to accurately capture the true global signal in these data.

It says 'Our findings show that the area around the Tropical Asian Archipelago (TAA) is important to closing the global sea level budget on interannual to decadal timescales, pointing out that the steric estimate from Argo is biased low, as the current mapping methods are insufficient to recover the steric signal in the TAA region.' In other words, ARGO biases trends low over 2005-2012.

I can show this somewhat more directly by plotting what ocean heat content data is available around the TAA region. The global average for 2000m is included for scale reference.