I spent the evening comparing USHCN V1 and V2 graphs, and discovered a huge discrepancy between their V1 and V2 adjustments.
This is their current US graph. Note that there is a discontinuity at 1998, which doesn’t look right. Globally, temperatures plummeted in 1999-2000, but they didn’t in the US graph.
It doesn’t look right, because they made a huge change going from USHCN V1 to V2.
In V1 they adjusted recent temperatures upwards (thin line below) and made little adjustment to older temperatures.
But when they switched to V2, they started adjusting older temperatures downwards, and left post-2000 temperatures more or less intact. This created a huge jump (greater than one degree) downwards for all years prior to 2000. You can see what they did in the animation below.
Blue line is thermometer data. Thin red line is…
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