A temperature of 20 degrees C in theUKwinter: a sign of the future?

The observational data show that in the context of the current climate, 20 degrees C in winter can only be produced by exceptional synoptic conditions such as occurred in late February 2019. The margin by which the record was broken may have been increased by human-induced climate change, but even without this it would still likely have been a record-breaking event. Model simulations for 1900-2018 and projections of the UK's future climate show that, should emissions remain high, by the late twenty-first century we may regularly see winters that have at least 1-2 days hotter than the historical record, with less rare synoptic conditions having the potential to produce temperatures as high as this. Correspondingly, daily maximum temperatures similar to 26 February 2019 when compared with a future climatology reference period might then be considered much less unusual. The shift in likely frequency of such extremes (from exceptional, to fairly routine) is therefore a stark reminder of how human-induced climate change is projected to affect the UK, and our perception of what is `normal', in the future.