Nature’s Climate Feedback blog points out that the post-World War II cooling is a mirage:
The 1945 temperature drop is nothing else than the result of the sudden but uncorrected change from warm US measurements to cooler UK measurement?
That?s a rather trivial explanation for a long-standing conundrum, so why has it taken so long to find out? Because identifying the glitch was less simple than it might appear, says David Thompson of the State University of Colorado in Boulder. The now digitized logbooks of neither US nor British ships contain any information on how the sea surface temperature measurements were taken, he says. Only when consulting maritime historians it occurred to him where to search for the source of the faintly suspected bias. ?
But it may not be the last uncorrected instrument bias in the record. The increasing number of measurements from automated buoys, which in the 1970s begun to replace ship-based measurements, has potentially led to an underestimation of recent sea surface temperature warming.
In other words, older temperature measurements had various biases, and correcting those biases shows that anthropogenic climate change was more intense in the 20th century than previously known. I expect that everyone who got worked up over a 0.15 degree Celsius change in US temperature estimates will be equally vocal about this one.