{"id":6259,"date":"2025-05-02T14:48:11","date_gmt":"2025-05-02T14:48:11","guid":{"rendered":"https:\/\/timjoslin.org\/?p=6259"},"modified":"2025-05-06T10:33:52","modified_gmt":"2025-05-06T10:33:52","slug":"april-into-may-2025-yet-more-unseasonal-uk-warmth","status":"publish","type":"post","link":"https:\/\/timjoslin.org\/index.php\/2025\/05\/02\/april-into-may-2025-yet-more-unseasonal-uk-warmth\/","title":{"rendered":"April into May 2025: Yet More Unseasonal UK Warmth"},"content":{"rendered":"\n<p class=\"wp-block-paragraph\"><em>A close look at the data shows that the 29.3C recorded at Kew Gardens on 1st May 2025 is a notable (11 day) &#8220;date record&#8221; high temperature.  Whilst not in itself catastrophic, this event may help us better understand and quantify the heatwave risks we face in the global warming era.  Additionally, the &#8220;mini-heatwave&#8221; over the last few days of April (and into May) has (provisionally) made March-April 2025 the warmest over those 2 months in the entire Central England Temperature (CET) record.  This follows <a href=\"https:\/\/timjoslin.org\/index.php\/2023\/09\/12\/doughnut-summer-2023-still-on\/\">the &#8220;doughnut summer&#8221; of 2023<\/a>, when June and September were the hottest months and the similarly extremely unusual event in <a href=\"https:\/\/timjoslin.org\/index.php\/2024\/06\/10\/2024-in-the-cet-mild-warm-and-oh-june\/\" data-type=\"link\" data-id=\"https:\/\/timjoslin.org\/index.php\/2024\/06\/10\/2024-in-the-cet-mild-warm-and-oh-june\/\">2024 when May was warmer than June<\/a>.<\/em><\/p>\n\n\n\n<p class=\"wp-block-paragraph\"><strong>29.3C on 1st May 2025<\/strong><\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Being something of a <a href=\"https:\/\/en.wiktionary.org\/wiki\/thermophobe\" data-type=\"link\" data-id=\"https:\/\/en.wiktionary.org\/wiki\/thermophobe\">thermophobe<\/a>, it&#8217;s unfortunate that I happen to live not so far from Kew Gardens, where, once again, the UK&#8217;s highest temperature of 29.3C was recorded yesterday, 1st May 2025.  This was too warm for my liking, especially for the time of year.  And indeed it seems a notable temperature record was set: there is no reliable record of a temperature as high as 29.3C before 12th May.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">This makes 29.3C on 1st May 2025 not only a daily record &#8211; that is, the hottest 1st May on record &#8211; but much more notably a <em>date record<\/em>, <a href=\"https:\/\/timjoslin.org\/index.php\/2016\/09\/20\/how-not-to-report-a-weather-record-13th-september-2016\/\" data-type=\"link\" data-id=\"https:\/\/timjoslin.org\/index.php\/2016\/09\/20\/how-not-to-report-a-weather-record-13th-september-2016\/\">the terminology I&#8217;m using<\/a> for the hottest temperature either so early or so late in the year.  And quite a notable one at that, at 11 days (1st to 12th May).  (Sorry, I haven&#8217;t yet got round to a date record summary of the entire year, <a href=\"https:\/\/timjoslin.org\/index.php\/2017\/06\/23\/how-not-to-report-a-weather-record-21st-june-2017\/\" data-type=\"link\" data-id=\"https:\/\/timjoslin.org\/index.php\/2017\/06\/23\/how-not-to-report-a-weather-record-21st-june-2017\/\">as I once promised<\/a>).   <\/p>\n\n\n\n<p class=\"wp-block-paragraph\"><strong>The Unfortunate Case of Camden Square<\/strong><\/p>\n\n\n\n<p class=\"wp-block-paragraph\">But, I hear you cry, what about the 29.4C recorded on 16th April 1949, as widely reported in the media?  Well, let&#8217;s look at the data provided by an authoritative source on UK weather extremes, <a href=\"https:\/\/www.torro.org.uk\/about-us\" data-type=\"link\" data-id=\"https:\/\/www.torro.org.uk\/about-us\">the TORRO organisation<\/a>:<\/p>\n\n\n<div class=\"wp-block-image\">\n<figure class=\"aligncenter size-full is-resized\"><img decoding=\"async\" src=\"data:image\/gif;base64,R0lGODlhAQABAIAAAAAAAP\/\/\/yH5BAEAAAAALAAAAAABAAEAAAIBRAA7\" data-src=\"https:\/\/timjoslin.org\/wp-content\/uploads\/2025\/05\/image.png\" alt=\"\" class=\"wp-image-6261 lazyload\" style=\"width:618px;height:auto\"><noscript><img decoding=\"async\" width=\"618\" height=\"561\" src=\"https:\/\/timjoslin.org\/wp-content\/uploads\/2025\/05\/image.png\" alt=\"\" class=\"wp-image-6261\" style=\"width:618px;height:auto\" srcset=\"https:\/\/timjoslin.org\/wp-content\/uploads\/2025\/05\/image.png 618w, https:\/\/timjoslin.org\/wp-content\/uploads\/2025\/05\/image-300x272.png 300w\" sizes=\"(max-width: 618px) 100vw, 618px\" \/><\/noscript><figcaption class=\"wp-element-caption\">Fig 1 Clip from <a href=\"https:\/\/www.torro.org.uk\/extremes\/date-records\/max-temp\">TORRO UK Maximum Temperature records<\/a> for April (as of 2\/5\/25)<\/figcaption><\/figure>\n<\/div>\n\n\n<p class=\"wp-block-paragraph\">Note the * by the record for 16th April.  TORRO explain:<\/p>\n\n\n\n<blockquote class=\"wp-block-quote is-layout-flow wp-block-quote-is-layout-flow\">\n<p class=\"wp-block-paragraph\">Note: Values qualified by an * are either (a) from rather sheltered sites or (b) more than 2\u00b0C above adjacent stations.<\/p>\n<\/blockquote>\n\n\n\n<p class=\"wp-block-paragraph\">and similarly qualify with an * several other records from the Camden Square site.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">The fact that the Camden Square temperature is so much &#8211; a full degree F or approx. 0.5C &#8211; higher than nearby locations is further grounds for suspicion.  Perhaps the data was recorded only to the nearest degree Fahrenheit, though then we have to ask, was it rounded up?<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">So I think &#8211; especially as the site is a serial offender &#8211; we need to disregard the Camden Square temperature of 29.4C on 16th April 1949 and consider 29.3C on 1st May 2025 to be a date record.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\"><strong>What is the Significance of the 2025 Record?<\/strong> <\/p>\n\n\n\n<p class=\"wp-block-paragraph\">I agree with <a href=\"https:\/\/x.com\/liamdutton\/status\/1917931116989714761\" data-type=\"link\" data-id=\"https:\/\/x.com\/liamdutton\/status\/1917931116989714761\">Liam Dutton&#8217;s comment<\/a> to the extent that a single hot day in London isn&#8217;t something to get too excited about (though 30th April 2025 with 26.7C at Wisley was also what I call a daily record), though I think all (of what I define as) date records are of note.  <\/p>\n\n\n\n<p class=\"wp-block-paragraph\">We now know that it can reach 29.3C in the UK as early in the year as 1st May, which we didn&#8217;t know (at least with certainty) before.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">But there are provisos. The CET record daily mean temperature baseline (i.e. for 1961-90) is (approx.) 5.7C for March, 7.8C for April, 11.1 for May and 14.0 for June. Mean CETs therefore clearly rise through Spring by over 2C a month. And peak (&#8220;heatwave&#8221;) temperatures likely increase faster than that (a glance at the data suggests that empirically they do). <\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Furthermore, with global warming we&#8217;d expect April temperatures to be higher in 2025 than in 1949.   The 21-year running mean (black line) in Fig 2 shows this to be the case, though &#8220;natural variability&#8221; seems to dominate in April over shorter timescales:<\/p>\n\n\n<div class=\"wp-block-image\">\n<figure class=\"aligncenter size-large\"><img decoding=\"async\" src=\"data:image\/gif;base64,R0lGODlhAQABAIAAAAAAAP\/\/\/yH5BAEAAAAALAAAAAABAAEAAAIBRAA7\" data-src=\"https:\/\/timjoslin.org\/wp-content\/uploads\/2025\/05\/image-4-1024x515.png\" alt=\"\" class=\"wp-image-6268 lazyload\"><noscript><img decoding=\"async\" width=\"1024\" height=\"515\" src=\"https:\/\/timjoslin.org\/wp-content\/uploads\/2025\/05\/image-4-1024x515.png\" alt=\"\" class=\"wp-image-6268\" srcset=\"https:\/\/timjoslin.org\/wp-content\/uploads\/2025\/05\/image-4-1024x515.png 1024w, https:\/\/timjoslin.org\/wp-content\/uploads\/2025\/05\/image-4-300x151.png 300w, https:\/\/timjoslin.org\/wp-content\/uploads\/2025\/05\/image-4-768x387.png 768w, https:\/\/timjoslin.org\/wp-content\/uploads\/2025\/05\/image-4.png 1071w\" sizes=\"(max-width: 1024px) 100vw, 1024px\" \/><\/noscript><figcaption class=\"wp-element-caption\">Fig 2 April CET mean temperatures, graph by the author from <a href=\"https:\/\/www.metoffice.gov.uk\/hadobs\/hadcet\/index.html\" data-type=\"link\" data-id=\"https:\/\/www.metoffice.gov.uk\/hadobs\/hadcet\/index.html\">Met Office data<\/a><\/figcaption><\/figure>\n<\/div>\n\n\n<p class=\"wp-block-paragraph\">And, <a href=\"https:\/\/timjoslin.org\/index.php\/2022\/06\/17\/heatwave-horror\/\" data-type=\"link\" data-id=\"https:\/\/timjoslin.org\/index.php\/2022\/06\/17\/heatwave-horror\/\">as I explained a while back<\/a> &#8211; indeed, the nub of the problem &#8211; <em>we should expect peak temperatures to increase even faster<\/em>. <\/p>\n\n\n\n<p class=\"wp-block-paragraph\">With all this in mind, is 29.3C on 1st May in 2025 a more significant extreme than the fairly reliably recorded 28.9C on 16th April 1949 (see Fig 1)?<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">I think not.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">In fact, I also don&#8217;t think 29.3C on 1st May 2025 is a more significant extreme than 29.1C on 19th April 2018, 12 days earlier in the year (see Fig 1).<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">But these data points do help us understand how big a heatwave problem we have.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">We don&#8217;t know if any particular extreme is &#8211; under the current globally warmed climate &#8211; a once a decade or once in a century event.  Especially given the similarly hot weather in 2018, I suspect this latest date record &#8211; although for a significant number of days &#8211; is more likely the former.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">This suggests that we could see much higher temperatures in late April if or when we experience a once in a century heatwave as perhaps occurred in 1949 or (evidently) 1893 (see Fig 3):<\/p>\n\n\n<div class=\"wp-block-image\">\n<figure class=\"aligncenter size-full\"><img decoding=\"async\" src=\"data:image\/gif;base64,R0lGODlhAQABAIAAAAAAAP\/\/\/yH5BAEAAAAALAAAAAABAAEAAAIBRAA7\" data-src=\"https:\/\/timjoslin.org\/wp-content\/uploads\/2025\/05\/image-1.png\" alt=\"\" class=\"wp-image-6264 lazyload\"><noscript><img decoding=\"async\" width=\"640\" height=\"507\" src=\"https:\/\/timjoslin.org\/wp-content\/uploads\/2025\/05\/image-1.png\" alt=\"\" class=\"wp-image-6264\" srcset=\"https:\/\/timjoslin.org\/wp-content\/uploads\/2025\/05\/image-1.png 640w, https:\/\/timjoslin.org\/wp-content\/uploads\/2025\/05\/image-1-300x238.png 300w\" sizes=\"(max-width: 640px) 100vw, 640px\" \/><\/noscript><figcaption class=\"wp-element-caption\">Fig 3 Clip from <a href=\"https:\/\/www.torro.org.uk\/extremes\/date-records\/max-temp\">TORRO UK Maximum Temperature records<\/a> for April (as of 2\/5\/25)<\/figcaption><\/figure>\n<\/div>\n\n\n<p class=\"wp-block-paragraph\">To conclude the discussion, I suggest the heat in late April though to early May this year and the record temperature on 1st May 2025 in particular, coupled with historic data, is evidence that more severe heatwaves are possible in the UK even this early in the year. This may be of interest to farmers and others concerned with climate risks. For example, would a few days of 30C be a problem for particular crops?<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Quantifying these risks would require much more sophisticated analysis (and\/or modelling) than I am in a position to undertake.  To put it in simplistic terms it&#8217;s necessary to determine how often conditions like the recent heatwave are likely to occur (let&#8217;s say once a decade) and then how much more severe more extreme conditions (let&#8217;s say once a century) are likely to be. <\/p>\n\n\n\n<p class=\"wp-block-paragraph\"><strong>A Record-Breaking April in 2025<\/strong><\/p>\n\n\n\n<p class=\"wp-block-paragraph\">As <a href=\"https:\/\/www.metoffice.gov.uk\/about-us\/news-and-media\/media-centre\/weather-and-climate-news\/2025\/provisional-april-statistics\" data-type=\"link\" data-id=\"https:\/\/www.metoffice.gov.uk\/about-us\/news-and-media\/media-centre\/weather-and-climate-news\/2025\/provisional-april-statistics\">the Met Office reported<\/a>, April 2025 was the sunniest since their records began 1910 and also the third warmest. As shown in Fig 2, this is also the case in the CET.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">They also mention that:<\/p>\n\n\n\n<blockquote class=\"wp-block-quote is-layout-flow wp-block-quote-is-layout-flow\">\n<p class=\"wp-block-paragraph\">&#8230;the UK has had its warmest first two months of spring (March and April) since the series began in 1960&#8230; <\/p>\n<\/blockquote>\n\n\n\n<p class=\"wp-block-paragraph\">I thought it might be worth checking that nothing more notable in that regard had occurred in the 3 centuries before that, according to the CET record. I had to extrapolate the final CET figure for April 2025 (which is not yet published*), but with that proviso, March though April was the warmest on record this year, just edging out 2011 (Fig 4):<\/p>\n\n\n<div class=\"wp-block-image\">\n<figure class=\"aligncenter size-large\"><img decoding=\"async\" src=\"data:image\/gif;base64,R0lGODlhAQABAIAAAAAAAP\/\/\/yH5BAEAAAAALAAAAAABAAEAAAIBRAA7\" data-src=\"https:\/\/timjoslin.org\/wp-content\/uploads\/2025\/05\/image-5-1024x515.png\" alt=\"\" class=\"wp-image-6269 lazyload\"><noscript><img decoding=\"async\" width=\"1024\" height=\"515\" src=\"https:\/\/timjoslin.org\/wp-content\/uploads\/2025\/05\/image-5-1024x515.png\" alt=\"\" class=\"wp-image-6269\" srcset=\"https:\/\/timjoslin.org\/wp-content\/uploads\/2025\/05\/image-5-1024x515.png 1024w, https:\/\/timjoslin.org\/wp-content\/uploads\/2025\/05\/image-5-300x151.png 300w, https:\/\/timjoslin.org\/wp-content\/uploads\/2025\/05\/image-5-768x387.png 768w, https:\/\/timjoslin.org\/wp-content\/uploads\/2025\/05\/image-5.png 1071w\" sizes=\"(max-width: 1024px) 100vw, 1024px\" \/><\/noscript><figcaption class=\"wp-element-caption\">Fig 4 April CET mean temperatures, graph by the author from <a href=\"https:\/\/www.metoffice.gov.uk\/hadobs\/hadcet\/index.html\" data-type=\"link\" data-id=\"https:\/\/www.metoffice.gov.uk\/hadobs\/hadcet\/index.html\">Met Office data<\/a><\/figcaption><\/figure>\n<\/div>\n\n\n<p class=\"wp-block-paragraph\">I doubt older readers will be surprised to see how much warmer the first 2\/3rds of Spring has been this century than in their youth!<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">6\/5\/25: * &#8211; the figure I used for the April 2025 mean CET (10.9C) in Figs 2 and 4, has been confirmed.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\"><\/p>\n","protected":false},"excerpt":{"rendered":"<p>A close look at the data shows that the 29.3C recorded at Kew Gardens on 1st May 2025 is a<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[92,20,183,31,51,52,65,1],"tags":[205,187,185,213,186],"class_list":["post-6259","post","type-post","status-publish","format-standard","hentry","category-effects","category-global-warming","category-heatwaves","category-media","category-science","category-science-and-the-media","category-uk-climate-trends","category-uncategorized","tag-central-england-temperature-record","tag-global-warming","tag-heatwave","tag-liam-dutton","tag-weather-record"],"_links":{"self":[{"href":"https:\/\/timjoslin.org\/index.php\/wp-json\/wp\/v2\/posts\/6259","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/timjoslin.org\/index.php\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/timjoslin.org\/index.php\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/timjoslin.org\/index.php\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/timjoslin.org\/index.php\/wp-json\/wp\/v2\/comments?post=6259"}],"version-history":[{"count":14,"href":"https:\/\/timjoslin.org\/index.php\/wp-json\/wp\/v2\/posts\/6259\/revisions"}],"predecessor-version":[{"id":6280,"href":"https:\/\/timjoslin.org\/index.php\/wp-json\/wp\/v2\/posts\/6259\/revisions\/6280"}],"wp:attachment":[{"href":"https:\/\/timjoslin.org\/index.php\/wp-json\/wp\/v2\/media?parent=6259"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/timjoslin.org\/index.php\/wp-json\/wp\/v2\/categories?post=6259"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/timjoslin.org\/index.php\/wp-json\/wp\/v2\/tags?post=6259"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}