The last glacial period ended about 11,500 years ago and in the following 5000 years the Earth’s climate warmed up. Geologists have long believed that it then began cooling again and has been getting colder for the past 6000 years. This eventually led to a little ice age during medieval times from about 1300 to 1850 CE which only ended, it was thought, when the burning of wood and fossil fuels to drive steam engines increased the rise of greenhouse gases which we still observe today.
However a report published in Nature in 27 January 2021   suggests that the data showing cooling was from seasonal temperatures and that, when you average the temperatures on an annual basis, the global temperature has in fact been rising over the past 12,000 years.
Nevertheless, there is no question that the very cold winters of the little ice age happened and had significant effects on human society. The terrible harvests which led, in part, to the French Revolution of 1789 can be seen as one of these.
This new report makes no reference to these cold periods, which shows we do not yet have a clear picture of the causes of recent changes of our climate. But one thing is clear: the Earth is now at its warmest for at least 12,000 years and possibly for ten times as long, and it is on its way to becoming far warmer still, due in main to human emission of greenhouse gases.