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What Warming Pause?

What happened to the pause in global warming?

The measurements are in and 2014 is officially the warmest year (for global average temperature) ever (at least since thermometers were invented). So, what happened to the so called global warming pause (see figure below)? Although it stimulated tons of interesting research into obscure places where the excess heat might have been hiding, the answer is apparently much more mundane. It now seems that new instruments to measure ocean temperature read systematically lower than the old sensors. In other words, the models were right and the measured global temperature was wrong!

How could this happen? Well, actually, it happens all the time, albeit in much less publicly embarrassing ways. Sensors are becoming so good that they are better than the equipment used to calibrate them. This means that calibrating scientific instruments is a research effort all its own. For example, in seismology the transition from mechanical to electromagnetic seismographs around 1910 created a subtle change in earthquake catalogs. Many decades later, these were picked up by pattern recognition software searching for earthquake precursors (i.e., testing earthquake prediction).

In the case of ocean temperatures, the calibration problem is exacerbated by the very high heat capacity of water. That is, tiny changes in temperature reflect a huge amount of heat absorbed. In any case, now that the calibration problem has been addressed, scientists can get back to studying the intricacies of the climate system and improving their models while politicians continue to debate what to do.

Global Temperature

Global temperature models (1870-2014)

Global average temperature from 1870-2014 comparing various climate models (light lines), the average model prediction (heavy red line), and the measured temperature (heavy black line). The over-prediction over the last decade and a half is the so called "Global Warming Pause".