July Temperature Update: Faustian Payment Comes Due, James Hansen and Makiko Sato

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August 13, 2021: July global temperature (+1.16°C relative to 1880-1920 mean) was within a hair (0.02°C) of being the warmest July in the era of instrumental measurements (Fig. 1, left).  That’s remarkable because we are still under the influence of a fairly strong La Nina (Fig. 1, right).  Global cooling associated with La Ninas peaks five months after the La Nina peak,[1] on average.

Something is going on in addition to greenhouse warming.  The 12-month running mean global temperature (blue curve in Fig. 2) has already reached its local minimum.  Barring a large volcano that fills the stratosphere with aerosols, the blue curve should rise over the next 12 months because Earth is now far out of energy balance – more energy coming in than going out.

How far is the recent global temperature above the 50-year warming trend? The best measure is probably the average deviation from the trend line of the two El Nino maxima and the two La Nina minima that followed. That average is 0.14°C. That’s a lot, and we know that it’s a forced change, driven by a growing planetary energy imbalance.

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