Procession of spring begins with a moderate March

Meteorologically March has been a relatively average month, certainly when compared to the record-breaking wet February the UK has just seen. The first month of meteorological Spring has delivered everything we expect in March from warm days to strong winds and snow.

Temperatures have been close to average for the month, with the UK as a whole just 0.1°C above the long-term average. England has been slightly warmer (0.2°C) and Northern Ireland slightly cooler (-0.3°C) than average.

2020_3_MeanTemp_Anomaly_1981-2010

In contrast to February, March was comparatively dry, with the UK receiving 82% (78mm) of its average rainfall. Most of the month’s rainfall fell during the first 18 days of March, continuing the unsettled spell from the past winter. The east of the country has been particularly dry, for example Aberdeenshire and Lincolnshire have had in the region of just 1/3 of their normal rainfall. Whilst some places in the west of the country have been much closer to or just above average. The Western Isles were the wettest compared to average, with 131% (189mm) of the normal rainfall total for the month.

2020_3_Rainfall_Anomaly_1981-2010

March has been a notably sunny month, with all regions seeing more than the average total of sunshine hours, especially in England and Wales. The sunniest county was Kent with 185.4 hours of sunshine. Some counties such as Essex, Kent and Rutland have recorded totals in the top 10 in their records.

2020_3_Sunshine_Anomaly_1981-2010

Although rather average on the usual statistical fields, March has still seen a new record set. Tim Legg from the National Climate Information Centre, said: “On Sunday 29 March, a new March record was set for the highest mean sea level pressure recorded in the UK, with 1051.2mb at South Uist in Scotland. The location in the Western Isles was one of the closest monitoring stations to the centre of the large area of high pressure out in the Atlantic which has been responsible for bringing the largely settled and sunny conditions to much of the UK over the final days of the month.”

With these fairly settled conditions, there have been a number of frosts, something the UK didn’t see a huge amount of over the winter months. Although it’s not unusual to get frosts in March, it is interesting that in Wales and northern England there have been more frosts in March than there were in any one of the winter months, showing just how mild it was through December, January and February.

Provisional March 2020 Mean temp (°C) Sunshine (hours) Rainfall (mm)
Actual  Diff from avg (°C) Actual % of avg Actual % of avg
UK 5.6 0.1 136.3 134 78.0 82
England 6.4 0.2 157.1 146 49.0 77
Wales 5.9 0.1 142.3 140 94.3 81
Scotland 4.1 -0.0 101.8 110 123.3 88
N Ireland 5.6 -0.3 126.2 128 68.6 72
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Climate change to bring heavier rainfall events

The rise of global temperature is the most easily understood metric of climate change. Its outwardly simple concept has instant appeal as it captures the key element of climate change – the warmer the planet becomes, the more the climate changes.

But aside from temperature, climate change will affect our atmosphere in other ways too. On World Met Day (23 March 2020) we highlight some recently published research exploring the subtle, but no less significant, relationship between climate change and atmospheric water vapour.

It’s long been realised that the warmer the atmosphere becomes, the more moisture in can contain. This is a well-known principle of meteorology and weather forecasting. A simple interpretation is that for every 1.0 °C rise in atmospheric temperature then water content can increase by around seven per cent. But recent research – led by Øivind Hodnebrog of CICERO (Center for International Climate Research), in Oslo, and supported by a range of organisations including the Met Office – has explored individual elements and has found that the relationship is more complex.

Dr Timothy Andrews is a climate scientist based at the Met Office. He said: “The amount of water in the atmosphere has direct consequences for all life on earth: too little for extended periods can lead to droughts; and too much can lead to floods. Given that we’re all dependent on atmospheric water every day of our lives, this is a vital area of research.

“To begin with let’s think of atmospheric water in the context of a reservoir. Evaporation from the sea and land, and water released from plants – a process known as transpiration – are like feeder streams helping to keep the reservoir topped up. Conversely, rainfall and other forms of precipitation are like outflows, draining the reservoir. We can extend the analogy further by saying that a warming atmosphere is like digging the reservoir deeper so that it can potentially hold more water.”

To understand more about the frequency and intensity of rainfall events and other precipitation, the Met Office contributed to a multi-national paper looking at the lifetime of water vapour in the atmosphere: water vapour lifetime (WVL).

WVL is the number of days that water vapour typically stays in the atmosphere before it is rained out. Climate change is causing the atmosphere to warm, which allows the air to hold more water, increasing WVL. Tim Andrews added: “This study investigates how different greenhouse gases and aerosols can cause WVL to change. We used the results from 11 global climate models where we explored the effects on water vapour lifetime by altering (perturbing) the concentrations of carbon dioxide, methane, solar irradiance, black carbon, and sulphate. For every degree of temperature increase, the air can hold roughly seven per cent more water, and global-mean precipitation increases by between one to three per cent. This results in an overall moistening trend. Tim Andrews added: “Computer models have supported weather observations showing a historical increase in WVL, causing a slowdown of the water cycle and leading to heavier rainfall events.

“Our study has shown that WVL has already increased by 4-5% since the pre-industrial period, and half of this was due to fast atmospheric processes. We also found that between 1986-2005 and 2081-2100 – under a scenario assuming high-emissions of greenhouse gases – WVL is projected to increase from eight days to ten, an increase of 25%. This is expected to result in heavier rainfall events in the future.”

The paper – Water vapour adjustments and responses differ between climate drivers – is published in the journal, Atmospheric Chemistry and Physics.

World Meteorological Day takes place every year on 23 March and commemorates the coming into force on 23 March 1950 of the Convention establishing the World Meteorological Organization. It showcases the essential contribution of National Meteorological and Hydrological Services to the safety and wellbeing of society and is celebrated with activities around the world.  The themes chosen for World Meteorological Day reflect topical weather, climate or water-related issues.

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Record-breaking rainfall

Those interested in the UK’s climate records have only had to wait two months of the new decade for a significant new rainfall record to be set.

February 2020 set a new UK record for February rainfall in a series stretching back to 1862. Storms Caira, Dennis and Jorge, brought 44% of the month’s rainfall, beating the previous record that was set in 1990.

Rainfall amount Winter 2020 UK

Three individual peaks stand out in the February 2020 daily rainfall record. These peaks from left to right are: Storm Ciara; Storm Dennis; and Storm Jorge.

Dr Mark McCarthy is head of the Met Office’s National Climate Information Centre. He said: “Of the top ten wettest winters, four have occurred since 2007 and seven since 1990. Associated with these changes we have also observed a 17% increase in the total rainfall from extremely wet days and a paper published in 2014 showed the 2010s contain more monthly to seasonal UK rainfall records than any other decade in the observational record.”

Dr Mark McCarthy – a guest on the Met Office’s Weather Studio Live – discusses rainfall variability in a changing climate. More content from Weather Studio Live is available here

This record-breaking February is consistent with a previous Met Office study in Nature Communications – published in 2017 – showing a high chance of one or more UK regions experiencing record monthly rainfall each winter in the current climate.  To understand the likelihood of new rainfall records, you need to understand that the rainfall record in the UK is subject to a very wide range of natural variation both within years and between years, as well as the effects of the climate change we have accrued so far.

February 2020 UK rainfall map

There was more rainfall recorded across the UK in February 2020 than has been recorded in any previous February in a series stretching back to 1862.

This latest rainfall record agrees with the Met Office’s estimates for the government’s National Flood Resilience review 2016 which took into account current climate change and the range of natural variability of climate.

Professor Adam Scaife is the Met Office’s head of long range forecasting. He said: “In that report and the subsequent science paper, we showed that there is a one-in-three chance of one or more UK regions experiencing record monthly rainfall each winter.”

The method – known as UNSEEN* – used thousands of simulations of UK winters run on the Met Office supercomputer to estimate the chances of record rainfall events.

Prof. Scaife said: “In recent times, we have seen events for which there was no observational precedent but using the UNSEEN method, large numbers of computer simulations of UK winters can tell us about the really extreme cases, like February 2020, that break the current record.

“The record February rainfall is in agreement with these estimates based on the latest science and we should expect similar events in coming years.”

* UNprecedented Simulated Extremes using ENsembles

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Space mission blasts off for the sun

Solar Orbiter blasted off from Cape Canaveral at 04:03 GMT this morning. Solar Orbiter is a European Space Agency (ESA) science mission, with support from NASA in the US, that will provide data to help improve our understanding of the Sun.

Solar Orbiter liftoff. Credit: ESA–S. Corvaja

Why is it important to understand the Sun?

The Sun, which is vital to sustaining life on our planet, is also the source of what we know as ‘Space Weather’. Explosive bursts of energy & matter from the Sun presents a risk to the technology that we rely upon on a day-to-day basis. Severe solar storms in 1989 and 2003, caused power blackouts in Quebec Province, Canada and Malmo, Sweden respectively and can disrupt space based services that we all rely on, whether it be communications, GPS signals to our Satnavs, or the industries that use these services such as aviation.

It’s a fantastic time to be a space weather scientist or solar physicist with two missions Parker Solar Probe and Solar Orbiter operating at the same time and generating new data from which we can improve our understanding of the Sun.

Solar Orbiter will give us a glimpse of the Sun’s poles for the first time, which is expected to help us understand the 11-year solar cycle which drives the frequency of explosive solar events that are so important for space weather.

At a time when the importance of space, both as a growing economy and also the impact of a loss of space-enabled services, is increasingly being recognised by the UK Government, it is great to see UK organisations playing such key roles in the mission. Imperial College London, UCL Mullard Space Science Laboratory (UCL-MSSL) and the Science and Technology facilities Council’s RAL Space (STFC-RAL Space)  led international teams to develop and build three instruments while UCL are a major contributor to a fourth. Airbus in Stevenage have designed and built the spacecraft that will be required to withstand the exceptional heat from the Sun as the spacecraft gets as close as 26 million miles of the Sun’s ‘surface’ (the Earth is 93 million miles from the Sun!).

Although it will take many years, the knowledge gained from these two missions will generate new scientific understanding of the Sun which will ultimately improve space weather forecasts.

Artist’s impression of Solar Orbiter. Credit: ESA/ATG medialab

What’s next for space weather missions?

At the ESA Council of Minister’s Meeting last December, funding was approved to take forward a dedicated space weather mission to the Lagrange 5 (L5) location to provide a permanent side-on view of the Sun-Earth line to maintain, and improve, our ability to predict the arrival time of the most impactful type of space weather, coronal mass ejections (CMEs). CMEs give rise to geomagnetic storms at Earth which give us beautiful bright aurora (Northern & Southern lights) but also put power grids at risk, as evidenced in 1989 & 2003 events.

The ESA L5 mission is very much being led by the UK, with Airbus, STFC-RAL Space and UCL-MSSL leading the mission study, remote sensing instruments and in-situ instruments respectively with European partners. Here at the Met Office, we’re engaged in defining the user requirements for the mission to ensure it delivers the data required to improve space weather forecasts. This will be quite a different mission to Parker Solar Probe and Solar Orbiter as the mission is less about gaining new knowledge and more about providing the vital data we know we need for accurate space weather forecasts.

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Sixth warmest January in series since 1884

Across the UK, January 2020 was the sixth warmest January in a series starting in 1884, making it the warmest since 2007. With an average mean temperature for the month of 5.6 °C, it was 2.0 °C warmer than the average between 1981-2010. It was the fifth warmest January in Scotland with an average mean temperature of 4.8 °C, 2.1 °C above the 1981-2010 average.

The warmest January on record was 1916 with a mean temperature of 6.3 °C, which is a notably long-standing climate record.

2020_1_MeanTemp_Anomaly_1981-2010

In line with the theme of higher than average temperature, the number of days of air frost was considerably below average; where air frost is defined as a day in which the minimum temperature falls below freezing (0 °C).

Dr Mark McCarthy is the head of the Met Office’s National Climate Information Centre. He said: “January 2020 experienced only five days of widespread air frost the fewest recorded for January since 1990, and third lowest in a series from 1960.

“The weather station in Morpeth, in Northumberland, has broken a 135-year January record by not observing a temperature of 0.0 °C or below during the month.”

2020_1_AirFrost_Anomaly_1981-2010

Rainfall saw mixed fortunes, with Northern Ireland, eastern Scotland and north east England all recording a relatively dry January with Inverbervie, Aberdeenshire recording 15.6 mm, just 30% of its average January rainfall and the driest place in the country in January. In contrast, north-west Scotland was wetter than average, with 655mm of rain at Achnagart in Ross and Cromarty, which is 151 % of average and was the wettest place.

2020_1_Rainfall_Anomaly_1981-2010

An east-west contrast was also apparent for sunshine with the sunniest place in the country during January being Leconfield, Humberside with 145 % of average sunshine while Stornoway and Tiree recorded their dullest January on record with just 42% and 38% of average respectively.

2020_1_Sunshine_Anomaly_1981-2010

Provisional January 2020 Mean temp (°C) Sunshine (hours) Rainfall (mm)
Actual  Diff from avg (°C) Actual % of avg Actual % of avg
UK 5.6 2.0 44.5 94 121.7 100
England 6.2 2.1 56.3 104 71.1 86
Wales 5.8 1.7 45.2 93 142.5 91
Scotland 4.8 2.1 25.5 72 209.5 119
N Ireland 5.3 1.1 40.1 90 68.3 59
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Wet or dry? November mid-month statistics

As we pass through November’s mid-way point, the weather has never been far from many people’s minds with a notably cold and wet start to the month for some.

With statistics up to 17 November, the wet start to the month is very clear to see for some parts of the UK. Overall, the UK has already seen 68% of its average November rainfall. However the distribution of this rainfall has not been even across the UK.

England has been the wettest UK country compared to average seeing 90% of its monthly average already. Nottinghamshire has been the wettest county compared to the long-term 1981-2010 average with 189% of average rainfall (107.8mm). Conversely, western and northern Scotland has been significantly drier compared to its average, with just 17% (23.5mm) of November average rain falling in Shetland so far this month, and Lerwick being the driest location in the whole UK. The distribution of rainfall can be seen in the map below.

2019_11_Rainfall_Anomaly_1981-2010

Map showing rainfall compared to 1981-2010 average 1-17 November 2019

On a more local level, our weather station in Sheffield has already surpassed its autumn record, with 440.8 mm of rainfall this autumn so far. The previous record was set in 2000 with 425.2mm.

Aberdeenshire, Berwickshire, Buckinghamshire, Derbyshire, East Lothianshire, Fifeshire, Forfarshire, Gloucestershire, Herefordshire, Kincardineshire, Leicestershire, Lincolnshire, Northamptonshire, Oxfordshire, Radnorshire, Rutland, Shropshire, Staffordshire, Warwickshire and Worcestershire have all had more than their average monthly totals of rainfall by 17 November.

The cold start is also evident with the UK mean temperature (5.3°C) -0.9°C below the long term 1981-2010 average for November.

Scotland has been the coldest when compared to the long-term average, -1.6°C below average. Sutherland is the historic county with the lowest temperature compared to the 1981-2010 average where it has been -2.3°C below average through November so far. Central and eastern England are closest to average mean temperature.

2019_11_MeanTemp_Anomaly_1981-2010

Map showing mean temperature compared to 1981-2010 average 1-17 November 2019

As well as being dry compared to average, Shetland has also been notably sunny. Up to  17 November, Lerwick had already recorded 44.8 hours of sunshine, easily surpassing the average for the whole of November (33.8 hours). To compare this to a location in the south east, Manston in Kent has only recorded 47.2 hours. This is significant considering that Shetland has a little over one hour less daylight compared to Kent at this time of year.

2019_11_Sunshine_Anomaly_1981-2010

Map showing sunshine hours compared to 1981-2010 average 1-17 November 2019

Provisional 1-17 November  2019 Mean temp (°C) Sunshine (hours) Rainfall (mm)
Actual  Diff from avg (°C) Actual % of avg Actual % of avg
UK 5.3 -0.9 81.7 68 30.2 53
England 6.3 -0.6 79.5 90 30.2 47
Wales 5.9 -0.8 127.3 79 27.3 49
Scotland 3.4 -1.6 72.2 44 29.2 64
N Ireland 5.3 -1.2 88.1 79 39.5 74

 

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The jet stream casts its shadow over the UK during October

October was an unsettled month, with frequent low-pressure systems influencing the weather of the UK, especially the south.

Jet stream positions for October 2019 and October 2018

The above maps show the composite mean for the position of the jet stream during October 2019 (top) and October 2018 (bottom). Images provided by the NOAA-ESRL Physical Sciences Division, Boulder Colorado  http://www.esrl.noaa.gov/psd/

The most notable influence on the month’s weather was the more southerly track of the jet stream when compared with an average October. This more southerly position brought more rain to southern parts and drier conditions to northern parts.

Although there were some calmer spells towards the end of the month, there were days with notable heavy rainfall, with over 100mm falling in 36 hours in the wettest parts of South Wales on the 25th and 26th.

Dr Mark McCarthy is the head of the Met Office’s National Climate Information Centre. He said: “The position of the jet stream has a major influence on the UK’s weather patterns, especially in autumn.  This October, the jet took a more southerly track, steering low-pressure systems towards southern Britain, bringing heavy rainfall to some. By comparison the northern parts of the UK, especially northern Scotland and Northern Ireland, saw less rainfall, more sunshine, but they were also slightly colder on average, reflecting their position on the ‘cool’ side of the jet stream.”

The UK received 109% (138.8 mm) of its average October rainfall. Although it was wetter than average for the UK as a whole, the rainfall was not distributed evenly, with many northern regions and Northern Ireland receiving less than their average monthly totals.

Scotland and Northern Ireland were the only regions in the UK to record drier than average totals for October, with 87% (152.7 mm) and 84% (100.3 mm) respectively. Caithness was the driest historic county, with only 68% (80.9 mm) of its average October rainfall.

Rutland was the wettest compared to average with 177% (113.0 mm) of its monthly total. For the UK as a whole this marks the fifth consecutive wetter than average month.

Temperatures throughout the month were unremarkable, with the nationwide average 0.5°C below the 1981-2010 mean. Each region recorded slightly below average temperatures throughout the month. Only Kent and Sussex were above average in October, and that was only by 0.1°C.

Provisional October 2019 Mean temp (°C) Sunshine (hours) Rainfall (mm)
Actual  Diff from avg (°C) Actual % of avg Actual % of avg
UK 9.0 -0.5 87.9 95 138.8 109
England 10.0 -0.4 86.6 84 124.8 136
Wales 9.5 -0.4 78.1 84 198.5 117
Scotland 7.2 -0.8 89.5 118 152.7 87
N Ireland 8.7 -0.7 105.4 120 100.3 84

 

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Met Office climate projections helping to inform the future of Great Britain’s farming

Climate change is happening now. And increasingly it will affect every individual and every sector. Understanding the extent of climate change across the UK – helping to inform local communities to stay safe and thrive – is a key driver for the Met Office’s scientific programme.

Agriculture – which has always been subject to the vagaries of the British weather – is likely to be one of the most impacted sectors in a rapidly changing climate, according to new research.

Arable and livestock farming are essential to the UK

The future of British farming, both arable and livestock, is likely to be affected by future climate change according to climate projection information provided by the Met Office.

Dr Lizzie Kendon is a science manager at the Met Office. She said: “The Met Office carries out very high-resolution climate projections, which provide detailed information on how the UK’s climate is likely to change over the next century. Any farmer knows that agriculture and the climate are inextricably linked, and a changing climate may bring changes to the industry.”

A new study published today led by the University of Exeter – using climate projection data from the Met Office – is suggesting that unchecked climate change could create a significant impact on farming in Great Britain, helping to redraw the agricultural map: driving Britain’s arable farming north and west, and potentially leaving the east and south-east unable to support crop growing.

At present, arable farming predominates in the east and south-east, with livestock rearing tending to dominate in the remaining areas.

The new study looks at the effects of the 5.0 °C warming predicted by 2100 if the world’s carbon emissions continue to rise at the current rate (a scenario known as RCP 8.5).

The study shows as well as being significantly warmer, Britain would have a predicted 140mm less rainfall per growing season (April to September) with more acute drying than this in the south-east.

“Britain is relatively cool and damp, so a warmer and drier growing season is generally expected to increase arable production,” said Dr Paul Ritchie, of the University of Exeter.

“However, our research suggests that, by 2100, unmitigated climate change would see a decline in arable farming in the east and south east. Crops could still be grown with the aid of irrigation, but this would involve either storing large quantities of winter rainfall or transporting water from wetter parts of the country. The amount of water required would be vast, representing a major challenge for UK agriculture.”

Part of the impact of warmer, drier conditions could be offset by higher levels of carbon dioxide in the atmosphere, because this allows plants to use water more efficiently.

“Our findings suggest that unmitigated climate change would change the way we use our land in Britain,” said Professor Tim Lenton, director of Exeter’s Global Systems Institute.

“In this scenario summer droughts mean that without significant irrigation, large regions of the east and south east of England would become less productive land. Meanwhile livestock farmers further west and north may be able to switch to more profitable arable farming.”

Dr Lizzie Kendon concluded: “We’re delighted that our projections have been pivotal in determining the climate challenges for the future of British farming; one of our vital industries.

“The climate is changing and will continue to change but armed with the best climate projections, industries like farming will know what’s coming and will be able to adapt to the new climate we’ll all be facing”

The research team – including the Met Office, the University of Trento and Wageningen University – used state-of-the-art, kilometre-scale climate change scenarios to drive a land surface model (JULES; Joint UK Land Environment Simulator) and an ECOnometric AGricultural land use model (ECOAG).

The study was supported by the Natural Environment Research Council. The paper, published in Environmental Research Letters, is entitled: “Large changes in Great Britain’s vegetation and agricultural land-use predicted under unmitigated climate change.”

* UK Climate Projections (UKCP) provides the most up-to-date assessment of how the climate of the UK may change over the 21st century. To find out more about how different sectors may use the new set of UK climate projections, have a look at these six project leaflets – written by sector specialists for their sectors. The leaflets cover water resources management, flood risk, coastal erosion risk, forestry as well as buildings design. http://bit.ly/36br8DB

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Is Humberto on the way to the UK?

At its most powerful Humberto was measured as a Category 3 Hurricane, but after leaving Bermuda and heading in to the cooler waters of the North Atlantic its intensity has waned.

Media reports have suggested that Humberto will reach the UK, bringing strong winds and heavy rain early next week. Is the story as simple and straightforward as that? As you may have guessed: no, not really.

Now as an ex-tropical system- heading north-eastwards across the north Atlantic, the former hurricane has become heavily modified to a point where it is now become wrapped into a new low-pressure system which only owes some of its origins to Humberto. Its influence will still be felt early next week when the low-pressure system approaches the UK, helping to push the current area of high-pressure eastwards, signalling an end to this week’s pleasant conditions.

Hurricanes heavily influence the climate of the north Atlantic by drawing up moist air from the tropics. By the time they reach our shores, they often only provide a boost to home-grown low-pressure systems – they are actually an important mechanism for redistributing temperature. The waters of the North Atlantic are too cold to sustain the vast energy demands of a hurricane in full force, so by the time they reach our latitude they have lost their tropical ferocity and have frequently become heavily modified.

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Zooming in on climate forecasts: the launch of UKCP Local (2.2km)

User panel

Earlier this week, the Met Office, BEIS, Defra and the Environment Agency launched the latest component of the UKCP climate projections, 12 projections of how the future climate could evolve, using a climate model resolution of 2.2km. Press release here.

Professor Jason Lowe, who has been leading the project for the Met Office, said: “Across the UK, we have all become accustomed to seeing very spatially-detailed models for weather forecasting a few days ahead: this new set of projections applies similar – kilometre-scale detail – to climate projections, several decades into the future. It provides users of the data with the most detailed glimpse of the future, enabling them to make informed decisions about how to plan for what could be some of the most damaging impacts of climate change.”

At a packed event in London, invited guests – including representatives from the user groups who helped with the development of UKCP – heard a range of speakers examine the capability of the latest phase of UKCP data, known as UKCP local (2.2km).

Dr Lizzie Kendon, a climate scientist with the Met Office, explained some of the benefits of this higher resolution. She said: “By working at a finer scale, we’re more clearly able to model for certain geographical features, such as mountains, coastlines and built-up areas to see how these can influence weather at a local scale. The higher resolution also enables us to gain an insight into weather features like convective summer rainfall that happen at a scale smaller than the resolution of the coarser outputs, such as the 12km regional projections. This is particularly important with events like summer thunderstorms which can unleash huge volumes of rainfall such as the event which occurred in Boscastle, Cornwall, in 2004.”

At the heart of the development of the UKCP portfolio was the idea of a set of projections which could be used together, with each providing a slightly different view of the world. Professor Lowe said: “Within the UKCP suite of products there are a range of different tools to investigate the future. For instance, users interested in looking at the range of seasonal warming for different levels of greenhouse gas emissions might focus more on the probabilistic forecasts. Users interested in the large-scale drivers of a changing climate, including beyond the UK, might focus more on the global 60km resolution projections. Those most interested in extremes or sub-daily metrics can focus more on the 2.2km projections. Whichever strand of UKCP is the focus we typically recommend using several of the strands together to get the most complete picture of the future.”

Elements of UKCP use different views of how greenhouse gas emissions will change in the future, covering cases from big reductions in human-driven emissions to a case with large future increases in emissions. In other parts of UKCP – because the calculations are so computationally intensive – we have only been able to run one emission case. The UKCP local (2.2km) projections use the RCP8.5 emissions scenario, which relates to a change in global temperature of around 4.0 C by the 2070s, relative to the period 1981-2000.  Jason Lowe added: “This does not mean this emission future is the most likely – the choice of scenario is still open for the world to make, and the majority of nations have pledged to aim to limit warming to well below 2.0 °C.

“When choosing which scenario to adopt for UKCP local (2.2km), it was agreed to use the higher RCP8.5 case. This is partly because risk-averse decisions, such as how to protect people from potentially dangerous flooding, often take a precautionary approach. It is also because choosing a high-emission scenario also allows users to estimate the response for lower levels of future global warming – for instance by scaling the projections or focusing on results earlier in the century.”

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