May, unlike other month in the CET series, has shown very little in the way of warming in the last 360 years. The trend has been a warming of just 0.15°C per century. Having said that only three of the last twenty years has been colder than average. The coldest May on record occurred at the very start of the CET series back in 1698 when the mean temperature for the month was just 8.5°C. The warmest May on record, by quite a margin, also occurred a long time ago, 186 years ago to be precise in 1833, when the mean was a whopping 15.1°C.