Archive for October, 2013

Oceanic Cloud Decrease since 1987 Explains 1/3 of Ocean Heating

Thursday, October 3rd, 2013

I consider what follows to be potentially very significantÖbut also very preliminary.

Background
Global warming (including the increase in ocean heat content) is supposedly explained by human greenhouse gas emissions (CO2) reducing the ability of the Earth to cool through infrared radiation to outer space, leading to the observed warming in the last 50 years or so.

My (admittedly minority) view is that some portion of this heating/warming is due to Mother Nature, probably from natural cycles in low cloud cover changing the amount of sunlight absorbed by the Earth. (Why? Well, take your pickÖENSO, PDO, NAO, cosmic rays, etc.).

So, which is it? Are humans keeping the Earth from cooling by reduced infrared energy loss, or is nature causing warming from extra solar energy gain? Or both? Iíve maintained itís a mixture of both, in unknown proportions.

The answer would be much more obvious if we had accurate measurements of global absorbed sunlight and emitted infrared radiation over a long period of time. But we don’t. What we have, and only since 2000, is reasonably precise measurements of the month-to-month variations in these energy flows (from the NASA CERES instruments)… the absolute accuracies are not good enough to measure the (presumed) anthropogenic heating effect of more CO2 in the atmosphere. The ERBE satellite measurements before that time are rather spotty and much more uncertain.

What we need, if possible, are other observation-based surrogates for global radiative energy flows.

SSM/I Oceanic Cloud Water: A Surrogate for Net Radiative Energy Fluxes Back to 1987
We now have over 25 years of SSM/I (and SSMIS) oceanic cloud water measurements, from Remote Sensing Systems. The monthly departures from average (in percent) through August, 2013 look like this:
SSMI-clw-1987-2013
Iíve compared these cloud water variations to CERES radiative flux variations (both over the global ice-free oceans, between March 2000 and June 2010), and there is a pretty good relationship:
SSMI-clw-1987-2013-vs-CERES-Net-flux
The correlation coefficient is 0.72, and the regression line shown is a 2-way fit.

If we take this regression relationship, and convert the SSM/I cloud water variations in the original plot to Net radiative flux variations, we get the following plot:
SSMI-clw-1987-2013-convert-to-CERES-Net
Now we can sum up these monthly average flux variations over time, and over the area of the global ice-free oceans (~341 million sq. km.), to get energy accumulation in 10**22 Joules, and compare it to one estimate of the increase in ocean heat content:
SSMI-clw-Net-flux-energy-accum-vs-Levitus-OHC

Taken at face value, this plot shows that about 1/3 of ocean heating over the 20-year period from 1990-2010 can be accounted for just based upon a change in oceanic cloud cover alone, probably a decrease in low clouds. (I say probably a decrease in low clouds because the SSM/I and SSMIS instruments only measure cloud water, not cloud ice which is transparent at the 19.35 and 37 GHz microwave frequencies. The CERES comparison I did vs. cloud water showed that most of the relationship was in the reflected shortwave [sunlight], not emitted longwave [infrared], which is consistent with a low-cloud effect rather than high-cloud.)

What Does All This Mean?
I think it is additional evidence that natural cloud variations cause multi-decadal time scale climate change.

But how do we know that this isnít just positive cloud feedback on human-caused warming? Well, first of all there has been virtually no surface warming over this period of time, and cloud feedback is (by definition) in response to surface temperature.

Secondly, since about 2010 we see there has been an abrupt reversal in the trend of ocean energy accumulation…basically wiping out the energy accumulation caused by the previous 20 years of reduced cloudiness. Did positive cloud feedback suddenly change to negative cloud feedback? Seems hard to believe.

The more logical explanation is that there are natural cycles in cloud cover which cause multi-decadal periods of global warming or global cooling.

It will be interesting to see if the SSM/I-inferred changes in Net radiative flux after 2010 are supported with more recent CERES data (my CERES dataset only extends through June 2010). I doubt that it will be, at least to this large an extent, but who knows?

So what does this portend for the future? Well, there are (as always) different possibilities. The first that comes to mind is (again taken at face value), since the supposed warming effects of increasing CO2 are still twice the size of these cloud effects, if clouds are switching from augmenting anthropogenic warming to mitigating it, then what we might be seeing is a new period of reduced heating of the global oceans, as well as a continued plateau in global surface temperatures. The timing roughly coincides with the recent switch of the Pacific Decadal Oscillation (PDO) to its negative phase. This is just one possibility, and I’m sure readers here can suggest others.

Anyway, this is all very new, and seldom in my work has the final analysis ended up as clear cut as the initial analysis suggested. I donít know when (or if) Iíll have time to do a careful evaluation of the results and submit them for publication. But I thought I would throw these results out there for discussion anyway.

Supplementary Evidence on Cloud Feedback
Since my discussion of clouds as ‘forcing’ versus ‘feedback’ is admittedly not very convincing, here is a lag regression plot of SSM/I cloud water versus HadSST3 sea surface temperatures during July 1987 thru August 2013. What it suggests, at least for year-to-year variability, is that a decrease in clouds tends to contribute to ocean warming, then clouds increase in response to that warming, leading to surface cooling:
SSMI-clw-1987-2013-vs-HadSST3-lag-regression

UAH V5.6 Global Temperature Update for September, 2013: +0.37 deg. C

Thursday, October 3rd, 2013

The Version 5.6 global average lower tropospheric temperature (LT) anomaly for September, 2013 is +0.37 deg. C (click for larger version):
UAH_LT_1979_thru_September_2013_v5.6

The global, hemispheric, and tropical LT anomalies from the 30-year (1981-2010) average for the last 21 months are:

YR MON GLOBAL NH SH TROPICS
2012 1 -0.145 -0.088 -0.203 -0.245
2012 2 -0.140 -0.016 -0.263 -0.326
2012 3 +0.033 +0.064 +0.002 -0.238
2012 4 +0.230 +0.346 +0.114 -0.251
2012 5 +0.178 +0.338 +0.018 -0.102
2012 6 +0.244 +0.378 +0.111 -0.016
2012 7 +0.149 +0.263 +0.035 +0.146
2012 8 +0.210 +0.195 +0.225 +0.069
2012 9 +0.369 +0.376 +0.361 +0.174
2012 10 +0.367 +0.326 +0.409 +0.155
2012 11 +0.305 +0.319 +0.292 +0.209
2012 12 +0.229 +0.153 +0.305 +0.199
2013 1 +0.496 +0.512 +0.481 +0.387
2013 2 +0.203 +0.372 +0.033 +0.195
2013 3 +0.200 +0.333 +0.067 +0.243
2013 4 +0.114 +0.128 +0.101 +0.165
2013 5 +0.083 +0.180 -0.015 +0.112
2013 6 +0.295 +0.335 +0.255 +0.220
2013 7 +0.173 +0.134 +0.212 +0.074
2013 8 +0.158 +0.111 +0.206 +0.009
2013 9 +0.367 +0.342 +0.392 +0.192

The Effect of Convective Oscillations On Tropospheric Temperature
I sometimes get asked why the tropospheric temperature variations are so large on a month-to-month basis. As I have mentioned before, these are usually due to natural oscillations in convective heat transfer from the ocean surface to the atmosphere. Just how large are these variations? The global average rate of energy transfer by moist convection (precipitation systems) has been estimated to be around 100 Watts per sq. meter. Since satellite (SSM/I) measurements of global oceanic rainfall have a monthly standard deviation of 3%, this equates to ~3 W/m2 monthly variations in convective heating of the troposphere. A quick calculation using the heat capacity of air will show that 3 W/m2 of more (or less) heating will raise (or lower) the tropospheric temperature by about 0.2 deg. C (assuming no other energy exchanges are affected). This is indeed the approximate size of the month-to-month variations in tropospheric temperature that we observe.

Note: In the previous version (v5.5, still provided to NOAA due to contract with NCDC) the temps are slightly cooler, probably due to the uncorrected diurnal drift of NOAA-18. Recall that in v5.6, we include METOP-A and NOAA-19, and since June 2013 they are the only two satellites in the v5.6 dataset, whereas v5.5 does not include METOP-A and NOAA-19.

Popular monthly data files:

uahncdc_lt_5.6.txt (Lower Troposphere)
uahncdc_mt_5.6.txt (Mid-Troposphere)
uahncdc_ls_5.6.txt (Lower Stratosphere)

Low Information Reporters…and Even Lower Information Scientists

Wednesday, October 2nd, 2013

I’ve seen a couple reports of scientists diverting attention from global warming (which went on vacation about 15 years ago) to the increase in the ocean heat content instead. They mentioned how all of that heat which has been accumulating in the ocean, if released at once, would warm the atmosphere by hundreds of degrees.

While theoretically true from an energy conservation standpoint, such a thing could never happen, of course.

This is what I told a reporter today, who just posted a story on the dubious reporting by CBS among others. The Second Law of Thermodynamics would not allow moving energy from a heat reservoir that is 0.1 deg C warmer than “normal” (whatever that is) and create hundreds of degrees of atmospheric heat from it.

We could throw our hands up and blame reporters…except that the hundreds-of-degrees claim started with people who should know better. Marc Morano reminds us that Stephen Hawking made a claim in Leonadro DiCaprio’s box office bomb “The 11th Hour” that Earth could become like Venus, with a temperature of 250 deg. C (100 deg. C boils water). (BTW, I think DiCaprio is an awesome actor).

Now, I’ve heard this Hawking guy is pretty smart. But…Really? As I recall, Venus has around 230,000 times as much carbon dioxide as Earth’s atmosphere. In contrast, we are worrying about what might happen when we reach 2 times as much CO2 as we had before. The difference between 2 and 230,000 is pretty darn big. Maybe Professor Hawking should stick to theoretical physics.

I’m reminded of Al Gore’s claim on late night TV that the Earth has a temperature of millions of degrees only a couple kilometers down in the ground.

Now, when the masses hear such drivel from people they admire — people who should know better — is it any wonder that so many people are scared out of the minds over global warming? I once got an e-mail from someone in Europe who was positively despondent, almost suicidal, over the fate of the Earth.

I really worry about the fate of a society where people are no longer capable of thinking critically. And it’s only hump day!! Sigh.