State of the UK Climate 2021

This report provides a summary of the UK weather and climate through calendar year 2021, alongside historical context for number essential variables. is eighth in series annual “State Climate” publications an update to 2020 (Kendon et al., 2021). It accessible, authoritative up-to-date assessment trends, variations extremes based on most observational datasets quality. The majority this observations temperature, precipitation, sunshine wind speed from land station network as managed by Met Office key partners co-operating volunteers. are carefully such that they conform current best-practice standards defined World Meteorological Organization (WMO). also pass range quality assurance procedures at before application monitoring. Time near-coast sea-surface temperature sea level presented addition there short section phenology which dates “first leaf” “bare tree” indicators four common shrub or tree species. reliance these highlights ongoing need adequately maintain observation networks, particular network, into future, ensure monitoring capability continued. National regional statistics HadUK-Grid dataset principal source data (Hollis 2019). Temperature rainfall extend back 1884 1836, respectively. Details used throughout how various derived provided appendices. A recent development underpinning has been inclusion several million recently digitized monthly (Hawkins 2022). These significantly improve geographical representation 1960 allow extension national 1836. presents 2021 against decade 2012–2021, following (WMO) climatological 30-year standard normal period 1991–2020 baseline 1961–1990 (WMO, 2017). two reference periods do not overlap. full provide longer-term context, while comparison made centennial averages Central England series. 2012–2021 nonstandard period, but it 10-year “snapshot” experience UK's compares records. means differences between may reflect shorter-term decadal well long-term trends. For publication, (currently 2012–2021) changes every year, decade. year's report, we use first time, updated 1981 2010 last retained, consistent only State Climate reports more widely comparison, change modelling WMO best-practice. Throughout report's text terms “above normal,” average,” etc. refer unless otherwise stated. maps show relative is, anomaly spatial variation difference average. Maps actual values cases displayed because dominated underlying climatology, lesser interest than year-to-year variability. what happened years, necessarily expected happen changing climate. Values quoted tables rounded, where (e.g., comparing with 1991–2020), calculated original unrounded values. We would welcome suggestions recommendations future report. Please send any feedback [email protected]. was supported Hadley Centre Programme funded BEIS Defra. Figure 1 shows seasonal mean sea-level pressure anomalies seasons average, using ERA5 reanalysis (Hersbach 2020). indication atmospheric circulation patterns each season overall. Note scaled equally across all consistency; however, winter months typically tend have larger summer months. deep low-pressure centred southwest during winter, high-pressure Greenland, Iceland Scandinavia. Low-pressure systems December 2020, higher brought colder settled conditions few days year. January saw mixture types, cold often wintry weather, storm Christoph (January 18–20) some exceptionally wet weather. In early February, spell easterly winds freezing temperatures significant snow, second half month mild, windy days. Pressure spring March whereas April May were very contrasting character. Although high rule overall, disturbed mid-month persistent rain north week. influence continued April, air mass Arctic origin, leading lot dry sunny frosty. contrast, succession areas low bringing unsettled, shallow over northern June, extent August, near-normal July. Consequently spells June notably warm, after mid-July, unsettled thunderstorms torrential downpours—and included Evert late located west autumn. Much September fairly quiet. October, drier around mid-month. Frontal southern Scotland October. November again mild—particularly south, Arwen arrived month. Early Barra 7th 8th. High quiet Christmas generally north. New Year's Eve mild. 2 North Atlantic Oscillation (WNAO) index 1850 inclusive (Appendix details WNAO index). (Note here refers February fall.) measure large-scale surface gradient Azores Iceland, determines strength westerly Atlantic, mode variability region. When large, positive dominate stronger frequent storms. small, negative increased tendency blocked patterns, reducing systems. (−1.0), since (−3.1). be associated cold, dry, patterns. average (anomaly −0.6°C), although wetter 119%). However, western Scotland, area influenced frontal systems, colder, sunnier suggesting somewhat further south (Figures 5, 24 38). Overall, large mainly phase 1910s–1920s 1990s) phases 1960s). Hanna al. (2015) discusses NAO notes increase 1990. Since 2012 (Figure 2). 3 (SNAO) SNAO Similar index, gradient, northerly location smaller scale counterpart, reflecting track summer. positive. Summers lower rainfall, indeed warmer +0.7°C) 74%), this—with notable exception southeast England. Other summers include 2018 2013 too As its 1970s–1990s) 1880s–1890s), noting decrease 1990s, includes run 2007 2012. 2013, marked contrast sequence. (Tmean) 9.3°C, 0.1°C above 18th warmest 1884. Nevertheless, still one (1949) prior ranked 29th (CET) 1659. near slightly much UK, highest Northern Ireland (+0.4°C) 4 Table 1). daily maximum (daily hereafter referred Tmax) 13.0°C, 0.2°C Tmax many areas—particularly Ireland, below East Anglia minimum Tmin) 5.6°C, pattern similar Tmean—again, Figures 5 6 Tmean 2021. monthly, ranks countries CET 7 both compared 20th century 9). (December 2020–February 2021) 3.5°C, 0.6°C Temperatures half—particularly coldest 2011. +0.1°C) −0.1°C) near-normal, −1.7°C) 2013. run-up Year, airstream wake Bella pulled Maritime Air remaining place January. There widespread hard frosts, even far southwest, −3.3°C Culdrose, Cornwall 25th. milder incursions times contrasts; example, 28th, 13°C London 2°C Inverness. severe (for see 10.1); milder, increasing 10°C space 7.1°C, 1.0°C unremarkable unusually warm end On 30 31st, reached 20–22°C Wales. At Oxford Radcliffe Observatory, 22.6°C 30th day records began 1815. 24.5°C recorded Kew Gardens, Greater London—only third record 24°C—and equalled 12.7°C Kinloss (Moray). Cold fronts swept country 4th–5th, unseasonably temperatures, recovered half. overall −2.2°C), especially temperatures; Tmin 1922 frosty (see 10.2 details). Unusually, March. rather −1.5°C) 1996. frosts grass −7.5°C Larkhill (Wiltshire) 6th. warmer. 15.3°C, 0.7°C ninth fourth/equal-third record, areas, July reaching 30°C; issued extreme heat warning UK. had their 21st, new all-time set 10.3). Water experienced network. fine led crowded beaches, particularly along coast. sadly, fatalities open water swimming. cool absence warmth August. Most stations—even central England—failed reach 25°C point month's modest 27.2°C Tyndrum (Perthsire) week largely confined autumn 10.8°C, 1.1°C equal-third 1884; record. Ahead International COP26 Conference, Glasgow (the venue) summer, equal-warmest September, months: (+1.7°C), October (+1.2°C) (+0.5°C). 30°C 8th, mild snow 27th 28th November, daytime struggling rise northwest −0.3°C Shap, Cumbria). (+1.1°C). remarkable inversion month: Aonach Mor, Highland (1,130 masl) Cairnwell, Aberdeenshire (928 14.8 14.4°C, respectively; nearby valley locations making stations, Scotland's mountain summits mid-December, 16.8°C Colwyn Bay, Conwy 31st eve record—in start 8 time inclusive, 9 1970s 2000s (2012–2021) being 1991–2020. All top ten years occurred century; none 8). (2010) 22nd series; other falls seen 1961–1990, 1.2°C 0.9°C spring, 0.8°C series, interannual variability, 2000s. Warming greater decades 10) resulting small diurnal (DTR, Tmax–Tmin) levels those observed mid-20th century. uncertainty principally function distribution stations observing varies time. error less consequently simplicity presentation nearest 0.1°C. More information relating uncertainties estimated Appendix B. 11 highly correlated overlap (R2 value 0.98) root-mean-square comparable described could effectively considered proxy 1659, different produced ways, inevitable. cooler warmed period. evidence 21st so equivalent length previous three centuries 12). (2001–2021) averages, 0.5–1.0°C 1901–2000 0.5–1.5°C 1801–1900 1701–1800, (Table 13 plots global “best-estimate” HadCRUT5 (Morice Both plotted temperature. warming trend broadly with, than, globally, covers approximately 1/2000 Earth's surface, comprises combination sea, larger. experiences ground frost. frost ranges 100 10 parts Cornwall. 63 days, greatest numbers 14). frostiest 2013) record; details, 10.2), December. 104 15). grids 1961, decade, showing reduction 1980s 1990s. 21%/18% fewer per 5% Prior explains areal-series calculated. degree integration commonly relate impacts. sum degrees threshold fixed monitored heating, cooling growing requirement heating buildings comfortable suitable plant growth, indices useful metrics, only, users should aware relevant factors solar gain, length, will responses of, growth. thresholds (HDD), (CDD) (GDD) 15.5, 22 5.5°C, respectively, formulae A. 1960. HDD close England, Wales (95%) 16). Averaged 99% lowest 1999 17). Milder result HDD. 11% 2% demonstrate possible winters. requirements months, split July, quite and, unusually, September. suppressed August (Perthshire). CDD (15) (14); 18). Across peaks coincide heat-waves (including 1976, 1995, 2003, 2006 2018). rising trend. 25 14 1961–1990. lower, five 19). GDD 105–110% areas—especially 120% upland 20). 105% seventh 1995. 17% 1991–2020, (downward) (upward) date 21), coupled extended season. 1993 Phenology species 11. (SST) waters 11.7°C, equal SST 1870 22). SST, Nine 2002, 1989. Every fallen within Near-coast 0.83; B) 0.3°C. Some trends apparent, 1960s pre-1900. apparent shown 22, closely follows Uncertainties scales (such near-coast) can bias adjustments applied minimize effect instrumentation changes. total 1,104 mm, 95% precipitation 978 101% Wales, totals average; 85% widely. relatively Shetland 23). wettest Honister Pass (358 Lake District 3,964 106% frequently stations. driest Suffolk, Essex Cambridgeshire received 500 mm. 26 area-average totals. always case, course 412 119% Rainfall exceeded 150% eastern district east northeast (defined black boundary maps) 1877. De