In order to rigorously evaluate this change, a first step is to review what we have observed. Fortunately, here in the UK our long fascination with the weather provides us with a legacy of observational data stretching back to the 17th century.
The State of the UK Climate report published this week is the fourth in a series of annual reports we produce in the Met Office to provide an authoritative statement on what changes we have observed here in the UK. The report looks at the most recent year, 2017; decade, 2008-2017; and past climates.
So what do the historical observations tell us? The UK has warmed by 0.8C when comparing the most recent decade with our 1961-1990 baseline reference. Last year may not stick in the memory as having been a notably hot year; experiencing a rather wet summer and some early winter snow, but it is in fact the fifth warmest year for the UK in a series stretching back to 1910.
For Scotland, it was eighth warmest but it is telling that all the warmer years have occurred in the 21st century. In fact nine of the ten warmest years on record have occurred since 2002.
It is not just the air temperature that we monitor. Rainfall has increased, particularly across Scotland which is 11 per cent wetter than it used to be, and so has sunshine in winter and spring. Other indicators of change include increasing sea-surface temperatures and sea level rise around our coastline.
In isolation, some of these changes sound fairly modest: but they have real impacts.
For example, we also saw that in 2017 the number of ‘growing degree days’ (a metric associated with temperatures suitable for plant growth) was the joint fifth highest on record. The number of frost days has also been decreasing.
This report is just one small, but crucial, piece of evidence to document our changing climate in the UK including Scotland.
The weather and extremes of weather that affect our day-to-day lives are super-imposed on this background climate change.
This summer we have experienced an extended heatwave and dry spell, which is in stark contrast to last summer which saw the second wettest June on record for Scotland. Despite being unsettled, the summer of 2017 was still above average for temperature, so one consequence is that our cool summers may not be as cold as they used to be and the hot summers could get even hotter.
The State of UK Climate report is published as an open-access special issue of the Royal Meteorological Society International Journal of Climatology. Dr Mark McCarthy is head of the Met Office National Climate Information Centre.