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Sunday, September 16, 2012

What is the Average Global Temperature?

The Berkeley Earth Surface Temperature project redid the already done global mean surface temperature.  Unlike the other surface temperature compilers, BEST has a chart of the global temperatures with a number in real degrees not anomalies.

They even have one for the Northern hemisphere,

And the Southern Hemisphere
According to BEST, the global land surface average temperature is about 10 C degrees, the Northern hemisphere land surface average temperature is about 11.25C degrees and the Southern Hemisphere land surface average is about 7.8 C degrees.

The land in the southern hemisphere only amounts to about 31.8% of the total global land area and the northern hemisphere land is about 68.2% of the global land area which totals 145,547,000 of the 510,072,000 kilometers squared of the Earth's total surface area, or 28.5% earth on Earth. Wikipedia has a little more land at 29.2% and most folks just round off to 30/70 as the land to ocean ratio.

If 30% of the surface has an average temperature of about 10 C degrees, the other 70% should have an average temperature also.  That number is generally give to be 16C degrees or 289K degrees.  It used to be 288K degrees, but someone had to change that number a touch.

Now most of the "experts" on the fora say that the average temperature of the oceans in 17 C degrees.  If I remember basic ratios, 0.3*(10) + 0.7*(17) = 14.9 degrees which is the original estimates by the "experts" prior to the warming which started in the 1950s.  According to the AQUA satellite, the average temperature of the oceans is about 21.1 C degrees.  0.3*(10) + 0.7*(21.1) = 17.8 C degrees which is about 1.8 C degrees more than the average temperature estimated by some of the "experts".

When I used the 21.1 C degrees as the average temperature of the oceans, the "experts" said I was wrong, the average was only 16 to 17 C in their "expert" opinion.  Wikipedia also lists the average surface temperature of the Earth as 14 C degrees which would put the oceans at 16C degrees on average.  So the average surface temperature of the Earth is between 14 and 17.8 C and the average temperature of the oceans is between 16 and 21.1 C degrees.

I also mentioned to the "experts" than land typically is higher than sea level or it would not be called land.  Since land is higher than sea level, thanks to physics, the temperature decreases as the altitude increases, so the measured temperature at some altitude greater than sea level would have to be adjusted higher if that were to be compared with temperatures at sea level.  The temperature decrease with altitude because the air cannot hold as much energy due to lower thermal capacity cause by the reduced density.  If the average altitude of the land surface measurements is 1000meters, the temperature would have to be adjusted upwards by about 6.5 C depending on if they used the moist or dry lapse rate.  0.3*6.5= ~2 degrees, so there is up to two degrees that would represent temperature but not thermal capacity using temperature as a proxy for energy at the surface.

BEST also provides a northern hemisphere T minimum and

Southern hemisphere T minimum.  .31*3.1 + .69*5.4 = ~3 C degrees which would be the temperature most likely impacted by greenhouse gases retaining more heat.  So if we use T minimum and the ~17C for the oceans, .3*3 + .7*17 = 12.8 C degrees.  12.8C degrees would equal ~286 K degrees which is 2 to 3 degrees cooler than the estimated average surface temperature used to determine how much the Earth has warmed.  That 286K would have an effective radiant energy of ~379.5 Wm-2 which is 16.6 Wm-2 less than the 396Wm-2 currently estimated as the average radiant energy of the surface of the Earth which would be impacted by the addition of greenhouse gases.

Because of all the different possibilities, I, not an "expert", decided to use the measured AQUA sea surface temperature of 21.1 C degrees and focus only on the surface temperature and energy to avoid all the confusion of adjusting this or that to meet the need of having some "average" number than no one really knows what is or what if it matters.

Using that 21.1 C degrees and an equally simple model, I determined that the average range of temperatures that is allowed based on the estimated solar energy available and the limit imposed by the freezing temperature of water, salt and fresh, to be about +/- 1 degree on average for the global oceans.

If you consider that all the areas of the oceans included in these paleo climate reconstructions, the not the "expert" came pretty damn close.  So the next time you get into a rousing Climate Change discussion at your local tavern just remember to say, "natural variability if about two degrees" and look for a less liberal chick to chat up.

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