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State of the UK Climate 2022

2023; Wiley; Volume: 43; Issue: S1 Linguagem: Inglês

10.1002/joc.8167

1097-0088

Mike Kendon, Mark McCarthy, Svetlana Jevrejeva, Andrew Matthews, Joanne Williams, Tim H. Sparks, Fritha West,

Geophysics and Gravity Measurements

This report provides a summary of the UK's weather and climate through the calendar year 2022, alongside the historical context for a number of essential climate variables. This is the ninth in a series of annual 'State of the UK Climate' publications and an update to the 2021 report (Kendon et al., 2022). It provides an accessible, authoritative and up-to-date assessment of UK climate trends, variations and extremes based on the most up-to-date observational datasets of climate quality. Futile it were to heave the fretful sigh When facile mirth is free to such as I: Should cheerless rain from high Olympus fall, I choose wet weather, and record it all. A poem in the preface to British Rainfall, 1916 (British Rainfall Organization, 1917) This report provides a summary of the UK's weather and climate through the calendar year 2022, alongside the historical context for a number of essential climate variables. This is the ninth in a series of annual 'State of the UK Climate' publications and an update to the 2021 report (Kendon et al., 2022). It provides an accessible, authoritative and up-to-date assessment of UK climate trends, variations and extremes based on the most up-to-date observational datasets of climate quality. The majority of this report is based on observations of temperature, precipitation, sunshine and wind speed from the UK land weather station network as managed by the Met Office and a number of key partners and co-operating volunteers. The observations are carefully managed so that they conform to current best-practice observational standards as defined by the World Meteorological Organization (WMO). The observations also pass through a range of quality assurance procedures at the Met Office before application for climate monitoring. Time series of near-coast sea-surface temperature (SST) and sea-level are also presented, and in addition there is a short section on phenology which provides dates of 'first leaf' and 'bare tree' indicators for four common shrub or tree species plus several other indicators. The reliance of this report on these observations highlights the ongoing need to adequately maintain the observation networks, in particular the UK land weather station network, into the future, to ensure that this UK climate monitoring capability is continued. National and regional statistics in this report are from the HadUK-Grid dataset which is the principal source of data (Hollis et al., 2019). Temperature and rainfall series from this dataset extend back to 1884 and 1836 respectively. Details of the datasets used throughout this report and how the various series which are presented are derived are provided in the appendices. This version of the dataset includes two significant additions compared to last year: firstly, an updated version of the digitized historical monthly rainfall data between 1836 and 1960, further improving the geographical representation of rainfall through this period (Hawkins et al., 2022); secondly, the addition of digitized historical monthly sunshine data from Met Office Monthly Weather Reports (MWRs) before 1919, allowing for the extension of the national sunshine series back to 1910. The report presents summary statistics for the most recent year 2022 and the most recent decade 2013–2022 against the 30-year standard climate normal period 1991–2020 and the baseline period 1961–1990, following WMO climatological best practice (WMO, 2017). These two 30-year reference periods do not overlap. The baseline reference period 1961–1990 provides a consistent reference period used throughout the series of State of UK Climate reports and more widely for historical comparison, climate change monitoring and climate modelling. The full series provides longer-term context, while a comparison is also made to centennial averages for the Central England temperature (CET) series. The decade 2013–2022 provides a 10-year 'snapshot' of the most recent experience of the UK's climate and how that compares to historical records. Differences between 2013–2022 and the 30-year reference periods may reflect shorter-term decadal variations as well as long-term trends. For this annual publication, the most recent decade (currently 2013–2022) changes every year, while the most recent 30-year reference period (currently 1991–2020) changes every decade. Throughout the report's text the terms 'above normal' and 'above average' etc. refer to the 1991–2020 reference period unless otherwise stated. The majority of maps in this report show the year 2022 relative to 1991–2020 – that is, they are anomaly maps which show the spatial variation in this difference from average. Some anomaly maps relative to 1961–1990 are also included, and the report also contains a number of anomaly maps for the most recent decade 2013–2022 against both 1991–2020 and 1961–1990. Maps of actual values are in most cases not displayed because these are dominated by the underlying climatology, which for this report is of a lesser interest than the year-to-year variability. These data are presented to show what has happened in recent years, not necessarily what is expected to happen in a changing climate. However, two figures showing UK Climate Projections (UKCP) for annual mean temperature and rainfall are included to provide future context to 2100. Values quoted in tables throughout this report are rounded, but where the difference between two such values is quoted in the text (e.g. comparing the most recent decade with 1991–2020), this difference is calculated from the original unrounded values. We welcome any suggestions for future publications of this report. Please send any feedback to the Met Office at [email protected]. This State of the UK Climate report was supported by the Met Office Hadley Centre Climate Programme funded by DSIT. Figure 1 shows seasonal mean sea-level pressure anomalies for the four seasons of 2022 relative to the 1991–2020 average, using the ERA5 reanalysis (Hersbach et al., 2020). This provides an indication of atmospheric circulation patterns for each season overall. A high pressure anomaly extended from north of the Azores eastwards to the Bay of Biscay during the winter, with a low pressure anomaly across Russia and eastern Scandinavia, consistent with a fairly weak positive WNAO (Section 1.2). In December 2021 pressure was slightly below normal across the southern half of the UK. In January, a large high pressure anomaly dominated the UK with a dry, settled spell of weather for much of the month. In contrast, in February the UK was between a high pressure anomaly over the Azores and a deep low pressure anomaly to the north. The month was very westerly – mild and wet – with a succession of low pressure systems; around mid-month a powerful jet stream drove three named storms across the country. Pressure was higher than normal across the UK during spring, particularly in the east, with a large high pressure anomaly over the North Sea. In March this high pressure anomaly was centred over the Baltic, whereas in April it was to the north over Iceland. Both months saw significant spells of high pressure with dry, settled weather in the second half. May was rather more unsettled generally with pressure below normal in the north-west. A shallow high pressure anomaly was located across the UK during summer, and overall it was a warm, dry and sunny summer, especially in the south. Pressure was near normal in June across much of the UK, but slightly below normal in the north and the weather was mostly fairly quiet and uneventful. Pressure was much higher than normal in July, with plenty of fine, settled weather, including an exceptional heatwave. Pressure was also higher than normal in August, although to a lesser extent. High pressure dominated the weather for the first half of the month and included a further significant heatwave but after this the weather was more variable. A low pressure anomaly was located to the west of the UK for autumn overall. September and October saw a fairly typical mix of weather types, whereas this pattern was particularly pronounced in November with a deep low pressure anomaly dominating the north Atlantic and a high pressure anomaly across northern Scandinavia, resulting in a very mild and rather wet westerly month. In December, a low pressure anomaly was located near the Azores and high pressure to the north, with the jet stream displaced to the south of the UK. The first half of the month saw northerly then easterly winds across the UK, bringing cold and at times snowy conditions with Atlantic weather systems blocked. However, from mid-month the normal mild westerly influence resumed. In summary, the year saw significant spells of dry, settled weather associated with high pressure particularly in January, March, April, July, August and December and unsettled weather in February and November. Figure 2 shows the winter North Atlantic Oscillation (WNAO) index from 1850 to 2022 inclusive (Appendix A1 provides details of the WNAO index). (Note here and throughout the report winter refers to the year in which January and February fall.) This index is a measure of the large-scale surface pressure gradient in the North Atlantic between the Azores and Iceland, which determines the strength of westerly winds across the Atlantic, and is the principal mode of spatial variability of atmospheric patterns in this region. When the pressure difference is large, the WNAO is positive and westerly winds dominate with stronger and more frequent storms. When the pressure difference is small, the WNAO is negative with an increased tendency for blocked weather patterns, reducing the influence of Atlantic weather systems. The WNAO index for 2022 was positive (+0.9), similar to the majority of winters for the most recent decade, and in contrast to the previous winter (−1.0). A WNAO positive winter would tend to be associated with a mild, wet, westerly winter. For the UK this was a mild winter (anomaly +1.1°C); dull in the west but sunny in the east, although the rainfall pattern overall was variable. February was particularly dominated by westerly conditions, being mild, very wet and exhibiting a strong dull (west) to sunny (east) sunshine contrast. However, in January the UK was much more under the influence of high pressure. The UK has experienced a run of mild, wet winters in the most recent decade, consistent with this current positive phase of the WNAO, including the very wet winters of 2014, 2016 and 2020 (Figure 33). Overall, the WNAO index shows a large annual variability but also decadal variability with periods of mainly positive phase (e.g. the 1910s to 1920s, 1990s and 2010s) and negative phase (e.g. the 1960s) which are also represented by the smoothed trend line in Figure 2. Hanna et al. (2015) discuss changes in the NAO index and note an increase in variability of WNAO since 1990. Figure 3 shows the summer North Atlantic Oscillation (SNAO) index from 1850 to 2022 inclusive (Appendix A1 provides details of the SNAO index). Similar to the WNAO index, this is a measure of large-scale climate variability in the North Atlantic based on the surface pressure gradient, but based on a more northerly location and smaller spatial scale than the winter counterpart, reflecting the more northerly location of the Atlantic storm track in summer. The 2022 SNAO index was positive (+0.6). Summers with a positive SNAO index tend to be associated with higher temperatures and lower rainfall, and for the UK overall, the summer was warm (anomaly 1.1°C) and drier than average (anomaly 64%). Other recent summers with a higher SNAO index include 2013, 2018 and 2021 and these too were warmer and drier than average (the latter excluding the south-east). As with its winter counterpart, the SNAO shows periods of mainly positive phase (e.g. the 1970s to 1990s) and negative phase (e.g. the 1880s and 1890s), with Hanna et al. (2015) noting a decrease in the SNAO since the 1990s, which includes the run of wet summers from 2007 to 2012. The large fluctuations in the SNAO in the most recent decade reflect some markedly contrasting summers – illustrating the UK's large annual variability in the weather and atmospheric circulation patterns across this relatively small spatial scale. The UK mean temperature (Tmean) for 2022 was 10.0°C, which is 0.9°C above the 1991–2020 long-term average. 2022 was the warmest year on record in the UK series from 1884 and also the first year with an annual mean temperature reaching 10°C (exceeding 9.9°C in 2014). The highest anomalies relative to 1991–2020 were across central and eastern England (+1.0°C) and lowest across Northern Ireland (+0.7°C). The UK mean temperature was 1.7°C above the 1961–1990 baseline long-term average (Figure 4). The most recent decade 2013–2022 has been 0.3°C warmer than 1991–2020 and 1.1°C warmer than 1961–1990, with slightly more warming across England and Wales and slightly less across Scotland and Northern Ireland (Figure 4). Five of the 10 years 2013–2022 have been within the top 10 warmest for the UK overall, and this is the warmest 10-year period in the UK series. The UK annual mean daily maximum temperature (Tmax) for 2022 was 13.9°C, 1.1°C above the 1991–2020 long-term average and the warmest year in the UK's Tmax series from 1884 by a considerable margin (next warmest 13.5°C in 2014). The warmest areas were across eastern England with anomalies particularly high across counties such as Cambridgeshire, Bedfordshire and Hertfordshire (+1.5°C). The UK annual mean daily minimum temperature (Tmin) for 2022 was 6.2°C, which is 0.6°C above average, with anomalies generally lowest in the south. In contrast to the Tmean and Tmax series, for Tmin this was not the UK's warmest year on record, with 2014 warmer (6.3°C) (Figure 5). Figures 6 and 7 show seasonal and monthly Tmean anomalies for the UK for 2022. Table 1 shows monthly, seasonal and annual actual and anomaly values and ranks for the UK and countries for 2022. A key feature of the year was the persistent warmth throughout. All months of the year except December were warmer than the 1991–2020 average. Anomalies were +1.0°C or higher in 7 months (February, March, May, July, August, October and November), with the highest anomalies in the latter 2 months, +1.8°C and +1.7°C respectively. Although no month was record-breaking for the UK overall (for Tmean), 6 of the 12 months of the year were in the top 10 warmest in series from 1884. August 2022 was the equal-third warmest August for Tmax, November 2022 the third warmest November for Tmean and Tmin, and May 2022 the warmest May on record for Tmin. For the UK overall, there have been only two calendar months warmer than August 2022 in the last 10 years (July 2018 and July 2013). In contrast, December was colder than average (anomaly −1.3°C) and ranked in the coldest third of the series for the UK and across all four countries. It was the UK's coldest December since 2010, although that exceptional month was very much colder (anomaly −5.1°C). Even so, only four previous months in the most recent decade (from 2013 to 2022) have been colder than December 2022; February and March 2013, February 2018 and January 2021. As a result of the persistent warmth, for the UK all four seasons were in the top 10 warmest in series from 1884 (winter from 1885): winter (anomaly +1.1°C, ranked eighth warmest), spring (+0.8°C, ranked fifth warmest), summer (+1.1°C, ranked fourth warmest) and autumn (+1.3°C, ranked third warmest). England had its equal warmest summer on record, with 2018. Remarkably, there were no locations in the UK with the seasonal mean temperature below the 1991–2020 average for winter, spring, summer or autumn 2022. The year 2022 overall was the warmest year on record for the UK and across all four nations. Table 2 shows monthly, seasonal and annual Tmean anomaly values for the UK and countries for the most recent decade 2013–2022 against both 1961–1990 and 1991–2020. The most recent decade has been 0.3°C warmer than 1991–2020 and 1.1°C warmer than 1961–1990. Warming has been relatively consistent across all countries, months and seasons comparing the most recent decade 2013–2022 to 1961–1990, with UK decadal anomalies between +0.9°C (for March and October) to +1.5°C (for July) for the UK overall, and the greatest warming of +1.7°C in July for England. Comparing 2013–2022 to 1991–2020, decadal anomalies are largest for June, July, October and December (between +0.5°C and +0.9°C), with winter, summer and autumn having all warmed by +0.4°C but no change in spring. These statistics reflect some annual and decadal variability in the UK's climate in addition to the ongoing warming due to climate change. Figure 8 shows a time series of annual Tmean anomalies for the UK and countries from 1884 to 2022 inclusive, and shows that the main period of warming for the UK has been from the 1980s onward at a rate of approximately 0.25°C per decade (i.e. 1°C in the last 40 years). All top 10 warmest years in the UK Tmean series have occurred in the 21st century; none of the top 10 coldest years have occurred in this century. The coldest year this century (2010) is ranked 22nd coldest in the UK series; every other year this century falls in the top third warmest years in the series. Half of the years in the most recent decade 2013–2022 have been in the top 10 warmest, including the two warmest years in the series, 2014 and 2022. Figure 9 shows annual mean maximum and minimum temperatures for the UK from 1884 to 2022 as anomalies relative to 1991–2020. These series are highly correlated (R2 0.82). Warming is slightly higher for Tmax than Tmin with the most recent decade (2013–2022) warmer than 1961–1990 by 1.3°C for Tmax and 1.0°C for Tmin. The UK average diurnal temperature range (DTR, Tmax − Tmin) is approximately 7°C. There has been a small recent increase in the average DTR but to levels similar to those observed prior to the mid-20th century (Figure 10). Figure 11 shows UK seasonal mean temperature for all four seasons. As with the annual series, the seasonal series show large inter-annual variability and some decadal variability, with a marked increase in temperature across all four seasons from the 1970s or 1980s onward. The most recent decade 2013–2022 has seen 15 seasons out of 40 in the top 10 warmest in their corresponding seasonal series (more than one in three): five in winter (2014, 2016, 2019, 2020, 2022); four in spring (2014, 2017, 2020, 2022); three in summer (2018, 2021, 2022); three in autumn (2014, 2021, 2022) – whereas only one has fallen in the top 10 coldest (spring 2013). Nearly one in four of the constituent months in the most recent decade 2013–2022 have also been in the top 10 warmest in their corresponding monthly series. These statistics emphasize the fact that the UK's climate is changing; in a stationary climate, we might expect on average around three seasons in the top 10 warmest and three in the top 10 coldest within a 10-year period in a series of this length. The uncertainty in these statistics is principally a function of the number and distribution of stations in the observing network which varies through time. For monthly, seasonal and annual averages the standard error is less than 0.1°C and consequently the uncertainty is much smaller than the year-to-year variability. For simplicity of presentation all the temperature data are presented in the tables to the nearest 0.1°C. More information relating to the uncertainties and how they are estimated is provided in Appendix B. Figure 12 shows annual Tmean for the CET series from 1659 and for England from 1884 to 2022. Their close consistency indicates that the CET series confirms the temperature trends in the HadUK-Grid dataset shown in Figure 8. 2022 was the warmest year in the CET series with an annual Tmean of 11.1°C, 0.9°C warmer than the 1991–2020 average and 0.1°C higher than the next warmest year, 2014. It was the warmest year in the CET Tmax series from 1878 by a wide margin (15.3°C compared to 14.8°C in 2003 and 2014), but only the third-warmest year in the CET Tmin series (2006 and 2014 both being warmer). The CET series provides evidence that the 21st century so far has overall been warmer than any period of equivalent length in the previous three centuries, and that all seasons have also been warmer (Figure 13). When comparing the early 21st century (2001–2022) to previous centennial averages, the annual Tmean difference is +0.9°C compared to 1901–2000, +1.2°C compared to 1801–1900 and 1701–1800, and +1.7°C compared to 1659–1700 – with some seasonal variations (Table 3). The most recent decade (2013–2022) has been the warmest 10-year period in the CET series. The CET and England series are highly correlated (based on an R2 value of 0.98 for the period of overlap) and have a root-mean-square difference of 0.1°C which is comparable to the estimated series uncertainty as described in Appendix B. The CET series could effectively be considered a proxy for an England series from 1659, although because these are different datasets produced in different ways, some differences are inevitable. The England series has warmed slightly more than the CET series, which means that in Figure 12 the England series anomalies are slightly lower than the CET series before the 1991–2020 period. Figure 14 plots annual Tmean for the UK from 1884 to 2022 alongside global mean surface temperature based on the 'best estimate' time series from the HadCRUT5 dataset (Morice et al., 2021). This figure therefore compares UK and global observations. Both series are plotted as anomalies relative to the baseline reference period 1961–1990. The table provides anomaly values relative to 1961–1990. The annual variability in UK Tmean is very much larger than HadCRUT5 as the UK covers only a small fraction (approximately 1/2000) of the Earth's surface, and comprises land surface, rather than a combination of land and sea. The most recent decade 2013–2022 has been 1.1°C warmer than 1961–1990 for the UK, compared to 0.8°C for global mean surface temperature. Globally, warming is greater across high latitudes compared to the equator, and over land compared to the ocean (Blunden & Boyer, 2022). (Section 2.7 shows that the warming has been slightly greater over UK land than UK near-coastal waters). The UK's climate is also subject to natural multi-annual to multi-decadal modes of variability (the same being true for the global climate). This variability will super-impose on any longer term trend, so with these factors taken into consideration the underlying warming observed for the UK is broadly consistent with that observed globally. However, to some extent, the comparison also depends on the choice of 1961–1990 as the baseline. Figure 15 shows daily maximum and minimum temperature anomaly maps relative to the 1991–2020 monthly averages for each day of 2022. In the UK's climate, daily maximum and minimum temperature anomalies are typically within ±8°C of the monthly average (encompassing the full colour scale of these charts) with anomalies generally only exceeding these values on a few days of the year – often across only a relatively small area. Figure 16a,b shows the UK area-average daily maximum and minimum temperatures through the year. The consistent warmth of the year is clearly evident, with the number of days of above average temperature very much greater than the number of days below. Compared to the 1991–2020 UK daily average temperature for the time of year, 2022 comprised 254/111 days above/below for maximum and 224/141 days above/below for minimum temperature. There were several prolonged spells of above average temperature through the year, whereas the only lengthy spell below average occurred in the first half of December. The year began with unusually mild conditions on New Year's Day, with daily maximum temperatures reaching 16.3°C at St James's Park, London, and daily minima widely 10–12°C across England and Wales. Temperatures reached 20°C during a spell of fine, settled weather with high pressure in late March, but by contrast there was a cold plunge of Arctic Maritime air at the start of April bringing some hard frosts as far as the south coast (−4.7°C at Hurn, Dorset on 3 April). By far the most exceptional feature of the year was the unprecedented heatwave of 18–19 July, where 40°C was recorded in the UK for the first time (described in the events Section 9.2). Temperatures also reached 30°C on one day in June (17th) and from 10 to 14 August (34.9°C at Charlwood, Surrey on 13th). There was a prolonged spell of generally mild conditions through October and November, and, for daily minimum temperatures, 11 November was exceptionally mild for the time of year, setting new November daily minimum temperature records for Scotland (14.9°C at Banff Golf Club, Banffshire) and Northern Ireland (14.5°C at Magilligan, County Londonderry). After the mild autumn, the cold spell in early December was a dramatic transition to winter (described in the events Section 9.4). This was by far the most notable spell of wintry weather in 2022, with UK area-average daily maximum temperatures below 5°C and daily minimum temperatures below 0°C for 11 and 12 consecutive days respectively. The UK area-average daily maximum temperature then increased by over 10°C in only 3 days from 16 to 19 December, bringing this spell to an abrupt end. Figures 17 and 18 show time series of the UK daily area-average mean maximum and minimum temperature distributions for each year as percentiles from 1960 to 2022, including summary statistics below. These provide insight into how these temperature distributions have changed over this period, with the extremes of the distribution of particular interest. Upward spikes in the 90th, 95th and 99th percentiles for Tmax coincide with years where major summer heatwaves have occurred (e.g. 1976, 1995, 2003, 2006 and 2018), whereas downward spikes in the 1st, 5th and 10th percentiles for Tmin coincide with particularly cold winter spells – with 2010 notably prominent in the 21st century. The most recent decade 2013–2022 has shown warming across all percentiles for both Tmax and Tmin, but this is not consistent across the distribution. For Tmax, the 99th percentile warmest day (representing the warmest 3 or 4 days in the year) has warmed by 1.9°C relative to 1961–1990, much more than the 50th percentile (+1.1°C). The hottest day has warmed to an even greater extent (+2.8°C). In 2022, the UK area-average Tmax exceeded 30°C for the first time on both 18 and 19 July (for more details see the events Section 9.2). For Tmin, there is a similar difference at the lower end of the distribution with the 1st percentile day (representing the coldest 3 or 4 days in the year) warming by 1.7°C relative to 1961–1990 compared to +0.7°C for the 50th percentile and the coldest day by +2.2°C. These time series display annual and decadal variability in the UK's climate in addition to the warming trend, and indicate an increased variability in the daily extremes series compared to the mean because sample size is smaller in each year. Nevertheless, these series show that the extremes of these distributions have changed faster than the means. Figure 19a,b shows the UK's highest daily maximum and lowest daily minimum temperatures for each calendar day of year 2022 based on the HadUK-Grid dataset. These are point values – the location of which will vary on a daily basis depending where in the UK that daily extreme happens to be located – so differ from Figure 16a,b which are UK mean (i.e. area-average) daily maximum and minimum. The highest and lowest values therefore represent the absolute temperature ranges of point values across the UK through the calendar year from 1960 to 2022 – that is, defining the absolute envelope of UK climate observations – as they do not include spatial averaging. The dramatic spike in July 2022 shows the unprecedented July heatwave event in which UK temperatures exceeded 40°C for the first time. The UK's highest daily maximum exceeded 20°C in late March, 25°C in mid-May and 30°C in June, July and August, while the UK's lowest daily minimum fell below −15°C in early December. The UK experiences a very large spatial variation in the number of days of air and ground frost. The 1991–2020 annual average days of air frost ranges from more than 100 days across much of the high ground of Scotland to less than 10 days across parts of west Cornwall. The average number of days of air frost for the UK for 2022 was 44 days, 9 days below average. The largest anomalies were across Scotland (13 days below average) (Figure 20). The number of air frosts was well below average in February and November, but above average in April and December. April saw some hard frosts early in the month – with −6.5°C at St Harmon, Powys as late as the 10th. By contrast, in November many stations in England were frost-free for the entire month, not just on the coast but inland – for example, 2.7°C as a November lowest minimum at Pitsford, Northamptonshire. By contrast, December had a run of widespread frosts from 8th to 18th – many of these hard. This was the frostiest December since 2010, although the cold snap was offset to some extent by milder conditions in the latter half of the month. The average number of days of ground frost for the UK for 2022 was 89 days, twice the number of days of air frost and 13 days below average. The most recent decade 2013–2022 has had 4%/7% fewer days of air and ground frost per year compared to 1991–2020 and 15%/23% fewer than 1961–1990; these representing substantial changes in the UK's climate with the number of ground frosts across Wales, Scotland and Northern Ireland decreasing by a quarter or more (Figure 21). Appendix A8 explains how these areal series are calculated. Note that air fros