James Delingpole of Breitbart spotted it and explains:

The peer-reviewed study by two scientists and a veteran statistician looked at the global average temperature datasets (GAST) which are used by climate alarmists to argue that recent years have been "the hottest evah" and that the warming of the last 120 years has been dramatic and unprecedented.

What they found is that these readings are "totally inconsistent with published and credible U.S. and other temperature data."

That is, the adjusted data used by alarmist organizations like NASA, NOAA, and the UK Met Office differs so markedly from the original raw data that it cannot be trusted.

This chart gives you a good idea of the direction of the adjustments.

The blue bars show where the raw temperature data has been adjusted downwards to make it cooler; the red bars show where the raw temperature data has been adjusted upwards to make it warmer.

Note how most of the downward adjustments take place in the early twentieth century and most of the upward take place in the late twentieth century.