Weather in a changing climate: Edward Jackson

Edward Jackson

August is here again and with it comes the release of two reports reflecting our latest knowledge of issues relating to weather and climate. the first is the Met office annual report on the uk’s weather, looking back at 2020. the data it contains form the basis for the descriptions of annual and seasonal weather patterns in our part of the east of england – the significant events and comparisons with past trends. the second is the far more wide-ranging and impactful publication by the international Panel on climate change, the title of which – ‘iPcc Working Group 1 report, Climate Change 2021: the Physical Science Basis’ – belies the fact that it contains some uncomfortable truths. More of these later, but let’s summarise the weather in 2020 for our part of the uk, as it’s important to keep placing these annual reviews on the record.

Significant Weather in 2020

Across the uk as a whole, 2020 was warmer than average compared with the annual temperatures recorded in the 30 years from 1981 to 2010. it also ranks as the third warmest year in the 136 years since 1884, exceeded only by 2008 and 2014. All the top ten warmest years since the mid-1800s have occurred since 2000. it was also the sixth wettest year since 1862 and the eighth sunniest since 1919, so is remarkable for being ranked in the top ten years for all these three key weather variables. 2020 was also a year of uk extremes. it saw the wettest february on record, the sunniest spring, a heatwave in the summer, a day in october breaking rainfall records and numerous incidences of flooding in the autumn and early winter. the mean annual temperature across england (the average between the daytime maxima and night-time minima) was 10.7°c, a full 1.0°c and, therefore, almost 10% above the 30-year average. Suffolk lies well within the zone of this temperature anomaly, so this outcome certainly applies here. rainfall across the uk was 114% of the 30-year average, but most of Suffolk was at or slightly below average, with the Shotley peninsula between the orwell and Stour being up to 15% drier. record sunshine levels in spring helped the uk be 109% sunnier than average, with Suffolk enjoying up to 120% of average sunshine over the full year, particularly in the south-west of the county.

As in previous reports, the following season by season summary uses the standard meteorological format of ‘Winter’ as December, January and february; ‘Spring’ as March, April and May; ‘Summer’ as June, July and August and ‘Autumn’ as September, october and November. the Met office combines monthly data from weather stations around Suffolk to create averages for the county and region as a whole, smoothing out the inevitable variations experienced at particular locations. unfortunately, the AccuWeather website used last year to give some more fine-grained detail to these summaries, by highlighting specific records from east Bergholt, Santon Downham and Lowestoft, no longer appears to have these data readily accessible. Where comparisons of average temperatures and rainfall are cited, they refer to the Met office 1981-2010 30-year long-term mean. Where the phrase ‘on record’ is used, data on the more extreme rainfall, temperature and other weather events are referenced to the baseline for uk weather recording established 160 years ago in 1862 – or in the case of sunshine records, which commenced later, to the 100-year baseline of 1919.

Winter: (December), January and February

Winter 2019/2020 was the fifth wettest on record, as well as the fifth mildest. A strong jet stream in the upper atmosphere was frequently directed towards the uk, allowing a succession of Atlantic low pressure systems to push their weather fronts across the country.

Named storms ciara, Dennis and Jorge brought significantly wet and windy weather towards the

end of the winter period, making this february the wettest on record. At 237% of the uk average, rainfall totals were well above normal virtually everywhere, with many places experiencing more than three times the expected average. february 2020 was also the fifth wettest of any calendar month on record. on the changing nature of our winters Dr Mark Mccarthy, head of the Met office’s National climate information centre, has observed: ‘We have seen a number of exceptionally wet winters in the last decade and due to climate change we expect UK winters to become wetter. Of the top 10 wettest winters, four have occurred since 2007 and seven since 1990, while there has been a 17% increase in the total rainfall from extremely wet days’. this unusually wet weather at the end of winter came as the breeding season for resident species was underway and is likely to have impacted on some early nesting attempts.

Spring: March, April and May

After this remarkably wet period there was a marked change to much drier and more settled weather patterns from mid-March onwards, with more records exceeded. Along with the whole of the uk, Suffolk experienced its sunniest spring since records began in 1919, recording over 135% more sunshine hours than the 30-year long-term average. there were more sunshine hours this spring than in most meteorological summers. remarkably, only the summers of 1976, 1995 and 1998 were sunnier than spring 2020. this spring was also warmer than average, mostly due to a very warm April when temperatures in the second week were almost 2.0°c higher than average, a trend which continued through into a warmer than average May. Spring temperatures across Suffolk were between 0.5°c and 1.0°c above the long-term average, although there was an east-west split, with the coastal areas slightly cooler than those inland.

With the warmth and sunshine came a significant reduction in spring rainfall. Along with most of the east of england, rainfall in Suffolk was only 30 to 50% of the 1981-2010 average, contributing to the uk’s fifth driest spring on record. this combination of factors was likely to favour breeding attempts for many resident and migrant species, although as ground conditions became drier it would be challenging for species relying on terrestrial invertebrates to feed their young.

Summer: June, July and August

After the sunny and dry spring, the three summer months were mostly unsettled, although each did contain some hot weather, August appreciably so. June and August were warmer than average, but July was generally cooler, so temperatures across the uk in the summer season ended just slightly above average. However, the warmest uk regions were in the east and southeast and the temperature anomaly across most of Suffolk was 1.0°c to 1.5°c above the long-term average. in terms of a single day’s event July 31st was the third warmest day on record for the uk, with a temperature of 37.8°c verified at Heathrow. However, perhaps even more consequential was the significant heatwave across east and south-east england during early August as hot, humid air moved north from the near continent. Heatwaves are declared when a location experiences maximum daytime temperatures for at least three days above a calculated threshold based on the long-term average, which for Suffolk is 27°c. in this 2020 heatwave temperatures exceeded 34°c across parts of the east and south-east for six consecutive days. in addition, there were five ‘tropical nights’ over the six nights from August 8th to 13th, when overnight temperatures remained above 20°c. the heat and associated humidity generated thunderstorms, torrential downpours and flashflooding, making this one of the most significant heatwaves with subsequent rainfall events to affect southern england in the last 60 years. recent Met office research predicts that the chances of such extreme high temperatures in the uk are increasing. under a high co2 emissions

scenario, by the end of the century the uk could potentially be seeing 40°c days every three to four years on average.

Summer 2020 ended with two named storms: ellen on August 19th and francis on August 24th.

Having named storms in a summer month is not unprecedented, but it is unusual to have two so close in succession. Partly because of these storms, many areas across northern and western Britain experienced higher than average summer rainfall, but this did not extend across into the east and south-east. Suffolk was drier than usual, with rainfall anomalies of 70% to 90% below average extending up to 30km inland from the coast. the coastal strip also countered the uk overall trend of a dull and cloudy summer by experiencing sunshine totals around 110% of the long-term average.

Heatwaves and extreme rainfall events are likely to have their greatest impact on the survival of inexperienced juveniles, whose recruitment into the breeding population the following spring is a significant factor affecting population trends.

Autumn: September, October and November

Autumn produced fewer contrasts overall, but still managed to include another extreme rainfall event which broke national records. A relatively sunny and dry September was followed by a dull and wet october and then a near normal November, balancing out rainfall and sunshine totals across the season as a whole. temperatures across Suffolk and the east of england were generally up to 1.0°c higher than the long-term average. Night-time temperatures remained relatively mild, with fewer frosts than normal recorded throughout the autumn.

Storm Alex tracked across the uk from october 2nd to 4th. Although Suffolk escaped relatively lightly compared with areas further west and north, its associated rainfall made october 3rd the wettest day on record in the uk as a whole, with enough rain falling across the country – 7.5 km3 in total – to fill the 7.4 km3 capacity of Loch Ness to overflowing. So, the uk’s first and third wettest days on record, in october and february respectively, both occurred in 2020.

Seasonal weather patterns and longer-term climatic shifts are among the major factors affecting trends in bird populations. By mid-autumn in a normal year all the results from volunteers carrying out the twin visit Bto Breeding Bird Survey have usually been collated online. However, fieldwork for 2020 was severely compromised by the first covid-19 lockdown. coverage of survey squares was 40% down in england and 49% down for the uk as a whole. the number of ‘early’ visits carried out in england was 86% down on the 2019 season and although by the time of the second ‘Late’ visits this shortfall was reduced to 40%, the challenge for Bto statisticians to produce reliable population trends for many species has been considerable. further details of how the biases introduced by lockdown have been managed can be found on the Bto website.

Return to Winter: December

December was generally wet and mild, with some colder interludes. Normal December rainfall had already been exceeded in Suffolk by the middle of the month. then Storm Bella brought more heavy rain and strong winds on December 26th, despite snow the day before making for an official White christmas in some parts of the county. However, snow days when at least 50% of the ground is covered with snow at 09:00hr are becoming increasingly rare. only four christmas days in the last 50 years have recorded ‘widespread snow’, defined as snow lying at more than 40% of uk weather stations.

Suffolk’s weather in the wider context

the increasing incidence in these annual summaries for Suffolk of rising temperatures, extreme rainfall events and other weather phenomena are the personally experienced local expressions of the changes affecting human and natural communities globally. the intergovernmental Panel on climate change report published in August 2020, signed off by 195 governments worldwide

and headlined a ‘code red for Humanity’, provides evidence that climate change is ‘worldwide, rapid and intensifying’. it unequivocally attributes this to human activities releasing greenhouse gases – primarily carbon dioxide, methane and nitrous oxide. compared with the pre-industrial baseline of 280 parts per million in 1800, atmospheric co2 rose once again in 2020 to 413ppm. All these gases blanket incoming heat from the sun, preventing it from re-radiating back to space. As a consequence, the global ‘weather machine’ is being energised to an extent not seen for thousands of years, as it transfers this excess heat northwards and southwards towards the polar latitudes.

By the time you read this, we will know to what extent the meeting of international organisations, national governments, scientists and volunteer groups at the uN coP26 climate change conference in Glasgow – and also the first round of the parallel coP15 Biodiversity convention conference in china – have been successful in driving top-down responses to the climate and ecological emergencies. Whatever these outcomes are, they can be complemented and reinforced by any contributions we make by changing our own individual behaviours and lifestyles.

References

for national and regional weather summaries: www.metoffice.gov.uk/research/climate/maps-and-data/summaries/index accessed August 2020

for uk bird population trends: www.bto.org/our-science/projects/bbs/latest-results/bbs-trends-2020 accessed August 2020

for information on global climate change: www.ipcc.ch/2021/08/09/ar6-wg1-20210809-pr/ accessed August 2020