We have previously reported on a series of studies showing that the Arctic warmed after the end of the last ice age and spent thousands of years in the mid-Holocene at temperatures well above those observed today, despite low CO2 levels. Now comes evidence that the warming was not confined to the far North. The US Southwest was also much warmer, at the same time, for a long time. And these patterns correspond to what was happening in the Tropical Pacific. Just in case anyone wants to claim that the mid-Holocene warming in the Arctic was strictly local and didn’t occur anywhere else.

H/T NTZ it turns out that over the same interval (about 9,000 to 5,000 years ago) when the Arctic was warmer than today, the southwestern US was also much warmer, and was nearly a desert while Arctic sea ice was at its lowest extent of the Holocene. Temperature and aridity hit long-lasting highs which have never been seen since. Likewise wildfires were more common and trees grew much farther up mountain sides than today. In other words, there is no denying the world was much warmer. The new study we are referencing is itself a survey of dozens of scientific papers that have documented a long mid-Holocene interval of exceptional warmth even though CO2 levels were much lower than today’s.

How can that be? It’s only a mystery if you insist that the climate was static and unchanging prior to the invention of the steam engine, and that CO2 is the big control knob that determines everything. Once you toss those assumptions in the recycling bin where they belong, a lot begins to make sense.