The average annual temperature in De Bilt rose by 1.7 °C in the period 1952-2017. This trend has been adjusted for exceptionally severe winters or hot summers. The last few years have been by far the hottest since the start of the measurement series in De Bilt. In 2017, the average global temperature exceeded the average temperature in the years 1961-1990 by around 0.9 °C. This warming is statistically significant.
The pattern of rising temperatures is also reflected in the average temperature per season. The pace of warming is not the same in every season, however. Warming is most severe in summer and least severe in winter. Furthermore, the variability of temperatures around the long-term trend is by far the largest in winter. Cold winters may therefore still occur in the current Dutch climate. Warming is not equally severe in each part of the Netherlands: the highest temperature increase is seen in the province of Zeeland, the lowest in Drenthe and Groningen. These differences are due to a smaller solar influence and a lower impact of the North Sea in the northeastern provinces. Furthermore, the year-to-year variations are greater than these differences across the Netherlands (Bosatlas van het Klimaat, 2011 - page 23).
Over the past 65 years, the global average has increased by approximately 1 °C. The three decades 1980-1989, 1990-1999 and 2000-2009 were increasingly warm. All three were warmer than all previous decades. The pace of global warming is not constant but is subject to fluctuations. After an acceleration at the end of the last century, global warming slowed down again in the period 1998-2014. Such changes in the observed temperature pattern are not unique and can easily be explained by natural fluctuations (PBL / KNMI, 2015 - chapter 1). A sharp temperature rise was also seen in the years 2015 and 2016.