Berkeley Earth Absolute Temperature and the Remarkable Closeness of TMAX Lows and TMIN Highs

Bob Tisdale recently did a series of posts exploring the differences between using absolute temperature and temperature anomaly to understand the recent temperature evolution of our planet. Bob was interested in the extracted TMAX highs and TMIN lows, and showed that the TMIN lows have warmed about twice as fast as the TMAX highs.

We had never seen an analysis like this, and what struck us was the how close the lowest seasonal maximum temperatures were to the highest seasonal minimum temperatures. The closeness of these values in absolute terms suggests a conserved quantity or thermostatic mechanism.

Above it can be seen that while the seasonal fluctuations in average maximum and minimum temperatures are on the order of 15C, the difference between the lowest highs and the highest lows averages only .25C.

As the earth rotates, each day the sun warms every location on earth, creating each location’s daily high temperature or TMAX. Locations then rotate into darkness, creating the daily low temperature or TMIN. The graphic above is averaging these lows and highs, essentially treating the entire planet as a single location.

The simple explanation for the closeness of the TMAX lows and the TMIN highs would be that the temperature is “handed off” from the top of the low to the bottom of the high. This is not the case because the TMAX lows vary between November and February, and the TMIN highs are nearly always in July.

Above we got rid of the seasonal amplitude to focus on the difference between the high lows and the low highs. It can be seen that as the planet has warmed, the difference has diminished. This reduction in the difference is a clue, but it is not really surprising since we know that the planet has warmed more at the poles, and more in TMIN than TMAX. Essentially, the planet is warming more at the cold extremes.

We thought it would be interesting to compare Berkeley absolute TMAX with CERES net flux. It can be seen in the unsurprising result above that the highest temperatures correspond to periods of negative net flux to space; and the reverse. The TMAX highs typically lag the net flux lows by a month. It can also be seen that the TMAX warming over the CERES period was not caused by a reduction in radiation to space. Radiation to space actually increased slightly over the period.

The apparent thermostatic control that limits the TMAX lows and the TMIN highs to such a narrow range is probably the elastic nature of the specific heat of the ocean. The capacity of water to store energy increases as the water warms, and decreases as the water cools. It works like a rubber band.


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