The IPCC, in the AR4 working group one, stated what could be called the central claim of global warming, the estimate of the net radiative forcing.
“The understanding of anthropogenic warming and cooling influences on climate has improved since the TAR, leading to very high confidence that the effect of human activities since 1750 has been a net positive forcing of +1.6 [+0.6 to +2.4] W m–2.”
Remember a forcing is an imbalance that causes heating, like a hot plate heating a saucepan of water. While the forcing continues, the temperature of the water will continue to rise. Global warming is the theory that increases in anthropogenic CO2 in the atmosphere are producing a radiative imbalance, or forcing, causing the earth to warm dangerously.
The IPCC level of forcing equates to the stated estimates for doubling of CO2 from around 1.5 to 6C per doubling, and the central estimates of warming to the end of the century from increasing CO2 of about 3C.
The paper by Levitus et al. uses the array of ARGO floats, and other historic ocean measurements, to determine the change in the heat content of the ocean from 0 to 2000m, and so derive the actual net radiative forcing that has caused it to warm over the last 50 years.
“The heat content of the world ocean for the 0-2000 m layer increased by 24.0×1022 J corresponding to a rate of 0.39 Wm-2 (per unit area of the world ocean) and a volume mean warming of 0.09ºC. This warming rate corresponds to a rate of 0.27 Wm-2 per unit area of earth’s surface.”
To compare these figures, say the continuous top-of-atmosphere forcing is 1Wm-2, a figure given by Meehl and Hansen and consistent with the IPCC estimates. The forcing of the ocean from a TOA forcing of 1Wm-2 is a lower 0.6m-2 due to losses, estimated by Hansen.
The best, recent measurements of the forcing 0f 0.3Wm-2 are half these IPCC estimates. The anthropogenic component of the forcing is even less, as a large part of the 0.3Wm-2 in the last 60 years is due to increased solar insolation during the Grand Solar Maximum.
This mild forcing is right in the ballpark that skeptic scientists such as Lindzen, Spencer, Loehle and Idso (and myself) have been consistently saying is all that is justified by the evidence. It appears that Levitus et al. confirms the skeptics, and the IPCC has been falsified.
What commentary on Levitus do we hear from the alarmists? Skeptical Science ignores that the IPCC has been exaggerating the net forcing, and attempts to save face:
“Levitus et al. Find Global Warming Continues to Heat the Oceans”
Skeptical Science “Put this amount of heat into perspective”, in a vain attempt to sound an alarm by quoting a scenario that is almost insane, having a infinitesimally small probability of happening.
“We have estimated an increase of 24×1022 J representing a volume mean warming of 0.09°C of the 0-2000m layer of the World Ocean. If this heat were instantly transferred to the lower 10 km of the global atmosphere it would result in a volume mean warming of this atmospheric layer by approximately 36°C (65°F).”
To do this, heat would have to defy all known physics and move backwards, from the boiling water to the hot plate.
The ocean is a big place. The best evidence is that its heating very slowly, much slower than the IPCC projected, and just as the skeptics predicted. The ARGO floats are arguably the most important experiment in climate science. It is all about good science: directly measuring the phenomenon of interest with sufficient accuracy to resolve the questions.
UPDATE: data1981 explains.
It’s definitely a confusing issue. What we’re talking about here is basically the amount of unrealized warming, whereas the radiative forcing tells you the total net energy imbalance since your choice of start date (the IPCC uses 1750). So they’re not directly comparable figures.
The unrealized warming has been fairly constant over the past ~50 years whereas the radiative forcing increases the further back in time you choose your initial point. So if you look at the unrealized warming starting at any date from 1950 to 2010, it will be a fairly constant number. But the radiative forcing from 1950 to 2010 is larger than the forcing from 1990 to 2010, for example.
Hopefully I got that right.
No he didn’t.
UPDATE: Roger Pielke Sr has a post on this topic.