Weather in a changing climate: Edward Jackson

Edward Jackson

It’s the first week of August and I shouldn’t keep the Editor waiting much longer for this promised annual piece! I’m prompted by the forecast that an extended period of summer heat, well over 30°C, is predicted for the week ahead and also, as if on cue, I’ve seen the Met Office has just released its own UK Weather Report for 2019. So, it feels the time is right to don the research goggles once again, summarise Suffolk’s weather story for the year just past and also to give some meteorological and also climatological context for all the records that follow these pages.

How does Weather relate to Climate?

Despite the oft-quoted British obsession, let’s start by being clear about the difference between weather and climate. The term weather is used to describe the state of the atmosphere at a location at any given moment. Looking outside right now at 14:30hr on August 6th 2020, here in Brantham the sky is virtually overcast with what I judge to be stratocumulus cloud (7/8 cloud cover to use the formal description); there’s no rain or other form of precipitation; the outside thermometer in the shade registers 27°C and in terms of wind, a light breeze (Force 2) is blowing from the west.

There were longer periods of sunshine earlier today, but I don’t have the more sophisticated equipment needed to record the actual hours of sunshine in a day, or to measure air pressure and humidity. However, the basic variables of cloud cover and type; precipitation (rain, drizzle, sleet, snow and hail); temperature (daytime maximum and night time minimum) and wind (reflecting the speed and direction of movement of an air mass due to differences in atmospheric pressure) are simple enough for us all to observe. Our experiences of these changing characteristics are easily woven into everyday conversation.

The Met Office (based in Bracknell until 2003 and now in Exeter) maintains a network of 435 observation stations across the UK. Around 265 of these are known as ‘Synoptic Stations’ and automatically report hourly readings of key variables using digital equipment. The remaining 170 or so are the ‘Climate Stations’ and rely on people rather quaintly called ‘Co-operating Observers’, who take daily readings of temperature, rainfall and other variables at 09:00hr GMT (10:00hr BST in summer), using equipment supplied by the Met Office. These data used to be transcribed from the daily weather logbook onto large format monthly return sheets and sent off in the post, but they are now reported online much more efficiently.

Suffolk hosts five automated Synoptic Stations: Santon Downham on the north-west border with Norfolk; Brooms Barn Experimental Station west of Bury St Edmunds; Cavendish on the upper Stour; Wattisham north of Hadleigh and Charsfield north-east of Ipswich. The only Climate Station is on the lower Stour and officially named East Bergholt, though it is actually in the grounds on the Field Study Centre at Flatford Mill. Successive generations of Field Centre staff - myself included - have ensured its continuous operation since the Centre opened in 1946.

When atmospheric variables are subject to regular and systematic observations, whether manually or automatically, the data collected create a time series. Hourly and daily changes can then be analysed and averaged out over the longer timescales of months, years and decades. Although I have 30 years’ experience of changing weather patterns and therefore a sense of the climate of my home area in south Suffolk, the concept of climate is more usually applied to areas larger than this, at the scale of counties (Suffolk), regions (East of England) and countries (England and then the UK).

As the size of the area under consideration increases, the changes in the atmosphere that generate weather conditions and the averaged sequences we call climate are progressively influenced by external geographic variables. The most important have traditionally been latitude

(position on the globe in relation to the poles and equator); relief (the shape of the land surface and altitude above sea level) and also proximity to other land masses and large water bodies such as seas and oceans. Vegetation type and the extent of cover can also exert an effect. The average weather or climate of Suffolk has therefore largely been determined by the fact that it’s a county with relatively low relief situated on the eastern side of the UK, which in turn faces the Atlantic Ocean to the west and the North Sea and the vast Eurasian land mass to the east.

The averaging of weather data allows us to appreciate and, more importantly, to quantify the concept of the climate of a particular area, including the range of variations that can be expected away from the mean. At the outer edges of this climatic range, in effect bracketing either side of a ‘typical’ climate, are the extremes of rainfall intensity and duration and the opposite of extended periods of drought; exceptionally high and low temperatures; high wind speeds and so on. The frequencies with which these phenomena are expected to occur are usually expressed as time probabilities, such as a 1 in ten-year or 1 in a 100-year event. When it becomes evident and statistically significant that either the average values for key atmospheric variables are shifting away from their long-term means or that the frequencies of extreme weather events are increasing - or that both are happening at the same time, - then we can say with a high degree of confidence that ‘climate change’ is occurring.

All the individual species and populations of Suffolk’s birds reported in these pages have reacted to the timescales of typical seasonal changes in weather patterns. Increasing temperatures in spring trigger physiological changes in males and females in preparation for breeding. Rainfall or lack of it affects the availability of food supplies that determine fledging success and juvenile survival. Wind directions and wind speeds are among the factors that can influence when a migrant species starts its journeys from wintering to breeding area and back again several months later, with the weather on route also critical to their individual survival.

These situations apply all the time to the species we expect to see on a daily or seasonal basis; the regulars on the Suffolk list. The unexpected sightings, the accidental vagrants or wanderers that add spice to the birding year, often arrive as the result of more extreme weather events. Hurricanes tracking with speed across the North Atlantic carry with them North American waders and landbirds. Strong winds circulating around high latitude anticyclones over Eurasia drive migrants breeding in Siberia (such as Two-barred Greenish Warbler) westwards rather than into south and east Asia. For birds migrating from the high Arctic, a shift off course of just a few degrees of longitude near the pole can be amplified into tens of degrees by strong winds as they attempt to head south. Imagine an orange as the globe and you’ll see how easily this can happen in certain circumstances.

Birds are also responding over the longer time scales associated with a changing climate, as Suffolk and the UK generally become more (or less) favourable for meeting the survival requirements of individuals and populations. The colonisation of Suffolk and elsewhere of species such as Little Egret, described as a vagrant in my treasured 1967 edition of Peterson, Mountford and Hollom, is a natural range extension related to rising annual mean temperatures and particularly the component of warmer winters that makes survival more likely. Confirmed breeding by Cattle Egret, Purple Heron and others may not be far behind.

Significant Weather in 2019

Before summarising the significant weather events of 2019, let’s start by reviewing the bigger picture. If you look for trends behind the headline data for the UK as a whole, the Met Office report for 2019 and the science behind it may not make comfortable reading. Compared with the 1981-2010 long-term average, 2019 was a warmer than average year, as were both 2018 and 2017 before it. February, the final month of winter, was the second warmest in over 100 years, eclipsed only by 1998. On February 26th, a new UK winter daytime maximum temperature record of 21.2°C was set at Kew Gardens in west London.

The four months of March, April, July and December were all a degree or more warmer than

average overall. A new all-season UK daytime maximum record of 38.7°C was set at Cambridge Botanical Gardens on July 25th, while temperatures exceeded 30°C somewhere in the UK on 10 days during the summer. Combining daytime-maximum and night-time minimum temperatures, the provisional UK mean temperature for 2019 was 9.4°C, which is 0.6°C above the 1981-2010 average. This ranks as the eleventh warmest year in the longer historical UK series dating from 1910, when widespread standardised measurements of temperature officially began. Extending this series back another couple of decades, even allowing for a little more uncertainty, all the top ten warmest years since 1884 have occurred in the 20 years since the year 2000. In contrast, all the UK’s ten coldest years since 1884 occurred before 1964.

In reviewing Suffolk’s weather in 2019, the following season by season summary uses the Met Office 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 the Synoptic and Climate Stations to create averages for the county and region as a whole, smoothing out the variations experienced at particular locations. However, records from the East Bergholt Climate Station, Santon Downham Synoptic Station and from a third station in Lowestoft that appears to be outside the Met Office network have also been sourced on the AccuWeather website to highlight notable temperature and rainfall data on particular days. As noted above, comparisons of average temperatures and rainfall refer throughout to the Met Office 1981-2010 30-year long-term mean.

Winter: (December), January and February

Winter 2018-2019 was milder and drier than average, giving generally favourable conditions for resident and overwintering species. December temperatures across Suffolk were 1.5°C above the long-term average, placing them in the top ten warmest Decembers since 1910. Temperatures fell in the New Year, with the second half of January and first few days of February seeing some sharp frosts. However, these were offset by an exceptionally mild and sunny period lasting for most of the remaining winter period, with daytime maximum temperatures of 18°C recorded at East Bergholt on February 26th and 27th.

December rainfall totals were close to average, but January and February were both much drier giving a winter total around 80% of the long-term average. Snowfalls across most of the county were light and limited to January 24th and February 1st. The mild conditions were matched by sunshine totals that were at least 120% above average. These unseasonal warm, dry and sunny conditions in the second half of the 2018/19 winter generated headlines in some of the media, but with little reference to or analysis of the longer-term implications of these extremes.

Spring: March, April and May

Spring 2019 was slightly warmer than expected, with temperatures across the county up to 1.0°C higher than the long-term mean. Rainfall over the three months was around 80% below average, although sunshine was higher at 110%. All these conditions would have been generally favourable through the peak breeding season for most species. The first half of March was unsettled and dominated by winds from the west and northwest, with Storm Freya on 3rd and Storm Gareth on 12th/13th delivering 11 mm and 16 mm of rainfall respectively to Lowestoft and other coastal areas. The second half of the month was more settled, drier and warmer due to the influence of high pressure over the near continent.

April started cool and wet, became warmer for a few days until colder air was drawn across the country by 10th, giving six consecutive days of air and ground frosts around much of the county, just at the time when many summer migrants were expected to arrive. The second half of the month was much warmer and sunnier, with seven consecutive days around Easter of daytime maximum temperatures between 18°C and 23°C. Storm Hannah on 26th/27th brought unusually strong winds, but little significant rainfall. Early May was cool, especially by night, but there were warmer spells later in the month. The highest rainfall totals came on 8th, with variability across

the county shown by the 30.7 mm recorded at East Bergholt and 20.1 mm at Santon Downham, but only 17.5 mm on the coast at Lowestoft.

Summer: June, July and August

Across the UK as a whole, 2019 was the twelfth warmest and seventh wettest summer since 1910. However, Suffolk generally missed out on the experiences of locations further north and west, which in some places received 200% of their average rainfall and subsequent flooding as a result. Summer rainfall totals in the southern half of the county were up to 115% of the longterm average, but the northern half saw totals only around 80%. Sunshine totals were around 110% of the average.

Starting cool and unsettled, the latter part of June and most of July were more settled with some very warm periods. The June spell peaked on June 29th, with 30°C recorded at Santon Downham and 28°C at Lowestoft. Then on July 25th, as the new UK maximum temperature record of 38.7 °C was set in Cambridge, Santon Downham recorded 36°C, East Bergholt 34°C and, under the slightly cooler influence of the coast, Lowestoft reached 33°C.

In Suffolk, a heatwave is formally declared when daily maximum temperatures meet or exceed its calculated heatwave threshold of 27°C for at least three consecutive days. At East Bergholt and Santon Downham this July heatwave lasted for five days and at Lowestoft for three days. A second four-day heatwave lasted from August 22nd to 25th at the two inland locations, although Lowestoft was slightly cooler with just one day reaching 29°C. These persistent high temperatures and heatwave conditions will have increased the stresses on birds foraging for food, particularly inexperienced first-calendar-year individuals.

Autumn: September, October and November

There was a settled spell in mid-September with plenty of dry sunny weather, but the end of the month was very wet over most of the UK and this generally unsettled theme persisted for most of October and November. Driven by the planet’s rotation, the upper atmosphere midlatitude jet stream circulates west to east in the northern hemisphere and in turn influences the tracks of Atlantic weather systems below it. In autumn 2019, the jet shifted course and pushed these systems further south than usual, meaning that much of England and Wales was wetter than average for October and November.

Daytime maximum temperatures across the county reached 26°C in the first week of September, but as expected had dropped away to highs of 12°C by the last week of November, giving a seasonal mean close to the long-term average. Sunshine amounts also showed little variance from the mean. Suffolk escaped the severe rain and floods that affected many parts of Yorkshire in mid-autumn, but still experienced over 150% of average rainfall in the north of the county and 110% elsewhere.

Return to Winter: December

Despite nine nights of air frost recorded in December at Santon Downham and eight at East Bergholt, the 2019-2020 winter would end up being another notably mild ‘cold’ season. By the end of February, the daytime winter temperature across Suffolk would be 2°C above the longterm average. Heavy rainfall events of between 20 mm and 30 mm measured at the Met Office Stations on both December 6th and 20th also contributed to another wetter than average winter.

These temperature and rainfall trends, in particular the reduced frequency of extended periods of frost, snow and ice, increase the survival chances for resident species. When these conditions are also repeated on the near continent, it means visitors from Scandinavia and Eurasia are less likely to cross the North Sea to spend the whole of the winter on Suffolk’s coast, estuaries and inland waters.

The Elephant in the Room…

….or, to use the only birding metaphor I can think of, The Cardinal Problem. Both the short- and longer-term effects on Suffolk’s birds of more extreme weather events and a changing climate are likely to become much more significant with time. Mention was made earlier of the importance of large-scale geographic features influencing climate. While these characteristics of land and water can explain most regional variations, they assume that atmospheric characteristics remain broadly stable – but unfortunately this is no longer true. Summarising the drivers of modern climate change in a couple of paragraphs is a challenge, but here goes!

The physical effects of introducing carbon dioxide, methane and other gases into the atmosphere through human activities, especially the extraction and burning of fossil fuels, have been well understood for over a century. Natural levels of CO2 and other gases are important in keeping global temperatures at an equable level. However, the increasing blanket of CO2 added to the atmosphere since the start of the Industrial Revolution, around 1800, has reinforced this previously-beneficial greenhouse effect, preventing progressively more of the incoming solar energy from being re-radiated out to space as heat.

Levels of atmospheric CO2 expressed in ppm (parts per million) show inexorable year on year increases. Measurements made since 1958 at the summit of Mauna Loa in Hawaii, along with comparisons of ancient air trapped in ice cores from Greenland and Antarctica tell a compelling story, with CO2 levels higher now than they have been for at least 30000 years:

2020: 413 ppm (average for the first week of August) 2000: 369 ppm 1950: 311 ppm 1900: 296 ppm 1800: 280 ppm (the pre-industrial baseline)

In other words, the greenhouse blanket of CO2 is almost 50% denser now than in pre-industrial times and as a result global heating is intensifying (global warming is too soft a concept). 350 ppm is considered by climate scientists a ‘safe’ level of atmospheric CO2, around which regional climates could potentially re-stabilise and revert broadly to how they were, but at present we are far beyond that point. To redistribute the higher levels of heat trapped in equatorial regions towards the relatively cooler poles, the global ‘weather machine’ is becoming persistently more and more energised. This is causing an increase in global mean temperatures, as well as in the frequency and extremes of the weather events associated with these energy transfers and forcing climate change.

Concentrations of 450 ppm and above are predicted to lead to at least a 2°C rise of global temperatures above the pre-industrial norm, accompanied by catastrophic and irreversible weather and climate effects for human populations and the species with which we share the planet. As residents of a well-developed nation, we all share some responsibility for what is happening at the global scale and can therefore all have a part to play in the solutions, which despite the starkness of the present situation are achievable.

Learning more about the science and impacts of climate change may prompt us to make significant changes in lifestyle at home and work and maybe to become engaged politically – note the small ‘p’, as these issues transcend simple party politics. As members of the Suffolk birding community we can also make our activities as climate-friendly as possible, for example by increasing the proportion of time we spend watching our own patch – something the related Covid-19 emergency has unintentionally encouraged anyway. Wherever possible, contribute your records to Suffolk Birds and/or to BTO projects such as BirdTrack, Breeding Bird Survey, the ringing and nest recording schemes and other long-term surveys. These data are needed more than ever, to confirm the ways in which Suffolk’s bird species and communities are responding to

climate change and hopefully, maybe, to identify a point in the not too distant future when the damaging weather and climate trends are starting to go into reverse.

In August 2021, as well as summarising 2020’s weather, I hope to be writing in more detail about the ways Suffolk’s birds are responding to this changing climate. In the meantime, please feel free to contribute to this conversation by sharing your thoughts directly or through the pages of Suffolk Bird Group’s quarterly magazine The Harrier.

Email: edward.jackson@uwclub.net

References

Met Office national and regional weather summaries for 2019 at: www.metoffice.gov.uk/research/climate/maps-and-data/summaries/index accessed August 2020 Suffolk weather station summaries for 2019 at: www.accuweather.com accessed August 2020 Wildlife reports in British Wildlife: April 2019 - February 2020