Just not in the way that you think. Anthony Watts (Watts Up With That) has a long, detailed post, and you should read every . . . single . . . word, but essentially, it is this: several temperature reporting stations have data that is missing something very important: a minus sign.
In other words, data that should be below zero degrees celsius is reported as above zero celsius. Of course, the error is regionally based (emphasis in original) . . .
You wouldn’t notice METAR coding errors at the equator, because the temperature never gets below 0°C. Nobody would have to code it. In middle latitudes, you might see it happen, but it is much more seasonal and the difference is not that great.
M05/M08 to 05/M08 brings the temp from -5°C to +5°C, but in a place like Boston, Chicago, Denver, etc a plus 5C temperature could easily happen in any winter month a -5C temperature occurred. So the error slips into the noise of “weather”, likely never to be noticed. But it does bump up the temperature average a little bit for the month if uncorrected.
But in the Arctic and Antarctic, a missing M on a M20/M25 METAR report makes a 40°C difference when it becomes +20°C. And it doesn’t seem likely that we’d see a winter month in Siberia or Antarctica that would normally hit 20°C, so it does not get lost in the “weather” noise, but becomes a strong signal if uncorrected.
Meanwhile, whaddya know! “Man-made global warming” is now being theorized to show up first in the polar regions.
Watts ends with a classic:
It has been said that “humans cause global warming”. I think a more accurate statement would be “human error causes global warming”.