Storm Warning – Bill Gething's Design for Climate Change research

The Design for Future Climate Adapting Buildings programme was the largest research programme yet focused on adaptation in the British building context. The programme integrated fifty research projects, and the conclusions were released in a series of reports, by the leading sustainability authority Bill Gething.  The last of these reports was published as a book, Design for a Climate Climate. This is an adapted version of the book's first two chapters.

Part 1
There is an overwhelming scientific consensus that the climate is changing, that these changes are likely due to increased global greenhouse-gas concentrations, which contain considerable momentum that will continue even if climate concentrations are stabilised, and there will be severe consequences for all life on the planet if we remain on our current path

Given the scale of observed change, considerable scientific effort has been made to understand the global climate system and the reasons behind the warming, and to predict how the climate might change in future. As a result of the first World Climate Conference in 1979, the Intergovernmental Panel on Climate Change (IPCC) was established in 1988 by the United Nations Environment Programme and the WMO to assess the risk of human induced climate change, its potential impacts and the options for adaptation and mitigation. From 1990, the IPCC has issued a series of reports based on peer-reviewed and published research, which have tended to grow in detail, evidence and confidence, the latest is the 2013 Fifth Assessment Report.

Project locations map click for link to interactive map of all Design for Climate projects -

1.1 - The report outlines the potential extent of global warming, providing three future scenarios for three greenhouse-gas emission scenarios through the 21st century, as well as a plot showing what would happen if greenhouse-gas concentrations were held at year-2000 values. The scenarios and the issue of uncertainty are described in more detail in part 2.

While the climate models vary in their predictions of the speed and magnitude of warming, there are no credible models that show global temperatures remaining steady or decreasing.

The report also sets out the  potential  impact  of  rising  temperatures  on  the  planet’s ecosystems, human settlements and way of life, summarised in the table overleaf from the UK Treasury’s 2006 Stern Review. There is a high level of confidence that a rise of more than 2°C would result in very significant impacts for all aspects of life, particularly coastal flooding and species extinction. Coastal flooding on this scale is not about the loss of a few distant islands or remote wetlands – their trading origins mean that most of the world’s great commercial centres are in coastal locations.

The potential impacts of climate change have set the agenda for successive United Nations Climate Change conferences, which have led to a general acceptance that warming must be limited to a 2°C rise if we are to avoid catastrophic impacts. This is the stark criterion on which ongoing attempts to reach international agreement to limit global emissions are based.

The issues are thus clear, urgent and interlinked. We need both to reduce the emissions that drive climate change (mitigation) and to deal with the physical effects of inevitable changes that are already under way (adaptation). The more successful we are at the former, the less will be the need for the latter.

For the construction industry, this means pursuing the now-familiar low-energy low-carbon design agenda that is increasingly embedded in legislation, but also recognising that we need to design differently in order to adapt to changes such as higher summer temperatures and to cope with more extreme events. In 2008, the Climate Change Act was passed, setting the world’s first long-term legally binding targets for emissions reduction (80% by 2050) and establishing the independent Committee on Climate Change. Its remit is to advise the government on setting and meeting carbon budgets and monitoring its progress, and also informing and monitoring progress on adaptation through the Adaptation Sub-Committee.

This table is taken from the Stern Review, produced by the UK Treasury (2006). Its shows a range of disastrious impacts if global temperature rise more than 2 degrees. Source: The Stern Review Report. Crown Copyright 2—6. The Economics of Climate Change: The Stern Review CUP 2007

The government’s National Adaptation Programme is led by the  Department  for Environment, Food and Rural Affairs (DEFRA). Its first step was to produce a UK Climate Change Risk Assessment (CCRA) in January 2012, to be updated every five years. The key risks identified for buildings were:

 •  damage due to flooding and coastal erosion

•  overheating

•  increasing impact from the urban heat island effect (see Chapter 2)

•  subsidence.

Other risks directly relevant to the built environment included:

•  water supply shortage

•  increased water demand for energy generation

•  higher energy demand for cooling

•  flood risk to energy infrastructure

•  heat damage/disruption to energy infrastructure.

Government departments have also been required to draw up Departmental Adaptation Plans, setting out key climate-change risks and priorities. These were published in March 2010, and updated in May 2011.

It is interesting to note an apparent disconnection between our mitigation policies and our approach to adaptation. The Committee on Climate Change has explored a number of ways of achieving our mitigation goal, set, as described above, in order to limit warming to below 2°C. To give an indication of the magnitude of the action required, a typical reduction pathway would be to cut emissions by 4% year-on-year, starting in 2016. This scenario is plotted overleaf, against the Low (B1), Medium (A1B) and High (A1FI) emissions scenarios used by the Met Office Hadley Centre for UK climate projections.

The graph shows all too clearly that the three scenarios used as the basis for adaptation take a more pessimistic, or perhaps realistic, view of future emissions reduction. Even the Low emissions scenario represents a failure of our global mitigation goal and, by implication, of our attempt to avert catastrophic change.

One possible scenario for avoiding catastrophic climate change is for global emissions to peak in 2016 and continue to decline by 4% each year after that. This graph shows how this compares to the high, medium and low emissions used to inform climate change adaptation strategies.

It is all too easy for the challenge of adaptation to become an intriguing academic puzzle – for designers to become mesmerised by the interaction between projection data and theoretical building models without stepping back to consider the implications for the social and economic context within which their buildings will exist. The teams involved in the Design for Future Climate programme can be forgiven for not attempting to address this wider context, but policy makers must think more broadly. The construction industry may be able to deliver buildings that would in theory perform beautifully in temperatures even 4°C above current levels – but what will the world around them be like? What will be the human and economic consequences of this level of change in locations that are not blessed with our benign climate? And how will this affect “normal” life in the UK?


Trends observed in the UK reflect global patterns. The Central England Temperature (CET) record – the oldest-established instrumental record of temperature in the world – shows that after a period of relative stability for most of the 20th century, our annual average temperature has risen by about 1°C since the 1970s.
Observed trends are projected to continue and can be summarised as follows:

•  warmer, wetter winters

•  hotter, drier summers

•  rising sea levels

•  increased extreme weather events.

Weather events that are currently regarded as extreme are useful illustrations of what is projected to be normal in future. For example, the exceptionally hot summer of 2003 is likely to become the norm by the second half of this century.

The Design Agenda

Sheffield University's Engineering Graduate School designed by Bond Bryan Architects
The impact of climate change is particularly pertinent to the construction industry, simply because buildings last a long time. Our existing built environment, and every aspect of how we live our lives, has evolved in response to a particular climate. Now that climate is changing, and may soon be significantly different. We face a real challenge in converting and upgrading our urban fabric to function in a climate for which it was not designed.

Design for Climate Change follows the same structure as the Design for Future Climate report, published in 2010 to provide the background to inform teams embarking on their projects, in which climate change impacts for the built environment were split into three broad categories:

•  comfort and energy performance – warmer winters may reduce the need for heating, but it will be difficult to keep cool in summer without increasing energy use and carbon emissions

•  construction  –  resistance  to  extreme  conditions,  detailing  and  the  behaviour  of materials

•  managing  water  –  both  too  much  (flooding)  and  too  little  (shortages  and  soil movement).

Over recent years, the construction industry has responded to the mitigation agenda but it has not yet got to grips with adaptation. There must now be a recognition that some changes to our climate cannot be avoided, and that these changes will have a significant impact on how our buildings perform, where they should be built and how they are constructed. It should also be remembered that change is likely to be ongoing – the rate and extent being dependent on the success of global mitigation strategies – resulting in more significant change in the second half of the century. We need to rethink the way we design, construct, upgrade and occupy buildings to accommodate this, developing approaches that are based not on past experience but on calculated projections of future climate.


Climate change is a “moving target”, and the challenges will differ according to location and building type.  There are no universal  solutions.  Adaptation strategies must be thoroughly grounded in a building’s context, which means not only projected changes in the climate but changes to geography, urban fabric, energy, construction and society too.


The regional variations in climate that already exist across the UK (and which are sometimes ignored by building legislation and policy) are projected to increase somewhat. This could potentially exaggerate the differences between appropriate climatic design responses across the country, so evident in our vernacular tradition.

Achieving comfortable internal temperatures in the future climate in the north of the country will be easier than in the warmer urban south-east, for example. The same may be true of water resources. In more exposed areas, however, the challenge of building sufficiently robustly to deal with extreme weather events may be paramount, with materials that may have performed satisfactorily in the past being pushed beyond their capabilities.

Flooding from rivers or the sea will be an absolute focus in some locations and irrelevant in others, although all regions will need to consider the impact of extreme rainfall on roof and surface-water drainage.

Low-carbon imperative

As discussed above, the mitigation agenda is paramount, while the age of cheap fossil fuels is also drawing to a close. There is no guarantee that we will be able to replace these with similarly cheap, sufficiently large and reliable sources of low-carbon or renewable energy. Warmer winters may reduce the need for and cost of heating, but, in summer, the cost of running buildings that rely on energy-intensive mechanical cooling rather than intelligent passive design, which minimises or avoids cooling-energy consumption, is likely to be an unwelcome burden for their occupants in a future low-carbon world.

Adaptation and mitigation measures can complement each other, but there can also be direct conflicts. For example, incorporating large areas of glazing in an attempt to reduce lighting-energy use can lead to overheating in summer, and even mid-season in highly insulated buildings, unless solar gain is carefully controlled.

The existing building stock

As with the mitigation agenda, the existing stock is the real challenge: adaptation is a conversion, not a new-build, challenge. Many older buildings, traditionally constructed in heavy materials, with small windows and good ventilation (both controlled and uncontrolled), have performed well during recent heatwaves. But many late-20th-century examples – characterised by lightweight, poorly insulated construction, large expanses of unshaded glazing and poor ventilation – already perform badly in summer and will become either unbearable or, if they rely on air conditioning, prohibitively expensive to run.

When upgrading existing buildings to improve their winter thermal performance by increasing airtightness and insulation, we need to take care that they do not then overheat in summer. Adapting external spaces  presents  a  parallel  challenge  to  building  design.  Generally speaking, our wider urban fabric has also evolved to take advantage of limited sunshine, rather than to provide shade and protection from it.


We expect our buildings to perform reliably with little if any maintenance. But familiar materials may behave differently under future conditions, and they may need to be substituted or fixed differently. Adaptation strategies that rely on new materials, components or approaches to construction will also need to demonstrate their long-term capabilities, and that they can be easily maintained.

Given that climate change is a moving target, even new buildings may need to be further adapted over time. There must be both an ongoing strategy for incorporating additional measures, and the physical provision to enable those adaptations to be carried out to the standard of the original build.


Sjolander da Cruz’s visualisation of their Franche Primary School,
where shading doubles as an external classroom.
A changing climate poses intriguing challenges for design and construction, and it is tempting to assume that every aspect must be addressed by ingenious or innovative design, comprehensively and immediately. Designers are often involved at the inception of a building project, advising their client on feasibility, helping to set the brief and, with an emerging agenda like adaptation, making their client aware of wider issues that they may not have taken into account. Designers should keep an open mind on alternative ways of approaching the challenge, which may offer better value for money than tackling them head-on in the confines of a building’s design.


Some problems can be circumvented simply by altering our behaviour rather than incorporating new design features or devices. Some of these are in the control of an individual client, such as not building in a potential flood zone or relaxing dress codes to compensate for higher temperatures. It might even be possible for an individual business to alter working hours to avoid those times of the day when internal conditions are most stressed, but, realistically, a wider coordinated response would be required for such measures to be effective.

Given that the existing stock presents the overwhelming adaptation challenge, much of which will be least able to cope with climate change, it seems likely that these approaches will be explored, particularly under extreme conditions. Perhaps the best example of this “soft” approach is the “Cool Biz” campaign introduced by the Japanese government in summer 2005 to reduce electricity consumption by air conditioning. The set-point temperature for government offices was raised to 28ºC and staff were encouraged to forgo jackets and ties and to wear short-sleeved shirts. The campaign was re-launched as “Super Cool Biz” in 2011 after the Tohoku earthquake and tsunami forced the closure of many of the country’s nuclear power plants, resulting in extreme shortages of electricity. Clearly, a designer will not be able to rely on such radical communal measures under most circumstances, but they should certainly be considered by policy makers.  


NW Bicester Eco-District, currently under construction, one of the fifty research projects
Climate change is a gradual and ongoing process, subject to multiple layers of uncertainty. Some aspects of a building must be designed for its whole life, such as the foundations or principal structure. But others, such as glazing systems and services, have shorter life expectancies and will require replacement or maintenance at regular intervals. While it is sensible to develop a comprehensive long-term adaptation strategy for the changing climate, it also makes sense to hedge one’s bets as far as possible, with a set of interventions that can be implemented as part of a refurbishment cycle when the evidence for their need becomes clearer. However, care needs to be taken not to design-in blind alleys, whereby a strategy will require very disruptive interventions, or even demolition, to make further adaptation possible.


Not all of the impacts of climate change must be resolved at the level of a single building. As a society, we need to be careful that the responsibility and costs of adaptation are sensibly allocated. For example, small-scale water-treatment plants or rainwater-harvesting systems may not be the most economic or carbon-efficient way of dealing with water shortage. Individual flood defence measures are similarly likely to be less reliable and more expensive than a comprehensive approach.

Competition, consensus and regulation

The market drivers for the adaptation of buildings are not yet clear. The key issues are the layers of uncertainty associated with climate change, and the fact that the benefits of a successful strategy may be reaped only in a time-frame considerably longer than conventional financial planning. Benefits may also not be easily valued in financial terms, with dependent costs that are highly uncertain given the time-frame. Neither may benefits accrue to those financing the capital cost of the project, or indeed to any individual or organisation, but only to wider society.

For designers, the lack of an obvious financial case for adaptation measures may limit the marketing potential for adaptation design services. Given the current lack of consensus on which data to use for analysis, and the range of options that may therefore need to be explored, the additional design time and cost may be significant – and unattractive to clients who are, after all, under no obligation to consider the longer term. As a result, designers themselves may be reluctant to invest in research and training to develop these services.

More research is needed on a range of costs – of adaptation measures themselves, of the associated design time, and of the financial and other benefits – in order to strengthen the commercial case. The government also has a clear role in developing consensus on the range of “reasonable” parameters that should be considered, to enable adaptation to be embraced as a mainstream design issue. There may also be a role for regulation to address any shortcomings in the market in the interest of the common good.

Consideration of the impacts of future climate is new territory for both clients and the construction industry. It has the potential to radically alter the way we design, construct, use and adapt our buildings. As such, it could be a rich source of design inspiration as we develop elegant approaches to produce buildings that will be resilient in a future that is both certain (change is inevitable) and uncertain (the rate and magnitude of change is unclear), as well as meeting the challenging mitigation targets necessary to avoid catastrophic change.



There is a difference between climate and weather. Weather is what we experience from day to day, described using metrics such as temperature, precipitation, humidity, wind speed and direction, sunshine and cloud cover. Climate is the average weather experienced over a long period, typically 30 years. The averaging process means that climate data is less chaotic than weather data, and it is possible to identify trends that are difficult to discern amid the natural variability of weather patterns. However, buildings do need to be able to deal with that natural variability and, within reasonable limits of cost and likelihood, to withstand extreme conditions. In a changing climate, we cannot just rely on historical records to make design decisions but must also take account of the likely pattern, timescale and magnitude of potential change.

Climate projections for the UK have been produced since the 1990s by the Met Office Hadley Centre. The latest set was released in 2009, and is known as UKCP09 (UK Climate Projections 2009), replacing the previous set published in 2002 (UKCIP02). This is the key source of climate information on which government departments, research organisations, insurers, and regulation and standards-setting bodies are basing their responses to climate change.

The UK Climate Impacts Programme (UKCIP) (set up by the government in 1997) has been run since 2011 by the Environment Agency, but the range of tools and guidance developed by UKCIP for assessing the risks of climate change and developing adaptation strategies, some of which are described below, is still available on its website.

Emissions scenarios explained

Projections for future climate are made using increasingly sophisticated computer models, based on the interaction between greenhouse-gas emissions and the climate system. The IPCC’s Special Report on Emissions Scenarios (SRES 2000) presented 40 emissions scenarios reflecting a range of demographic, social, economic and technological factors, of which three were selected for UKCP09.

The UKCP09 briefing report stresses that because emissions will be governed by human choices, relative likelihoods cannot be assigned to different scenarios. However, it is salutary to note that global emissions have continued to rise in line with the upper range of the selected scenarios, checked only slightly by the effects of recession.

Introduction to UKCP09

The headline trends identified by earlier projections are unchanged – warmer, wetter winters; hotter, drier summers; rising sea levels; more extreme events. However, the approach taken by UKCP09 better reflects inherent uncertainties. Whereas the previous projections were based on the outputs of the Hadley Centre’s climate model alone, UKCP09 takes a broader view, using the outputs from a range of plausible climate models. These are weighted according to how closely they correspond with measured data when used to backcast past climate, and the resulting projections are presented as a probabilistic range rather than as single values. This new approach is statistically more robust but adds complexity. It also has the disadvantage that where there is insufficient agreement between the outputs of the models, a statistically robust, correlated projection cannot be made, resulting in a gap in the data. For example, wind data was not initially included in the probabilistic projections. Projections for wind have now been produced as a separate batch and so cannot be used in Weather Generator projections.

UKCP09 provides projections up to 2099 for 26 atmospheric variables using a 25km² grid. Customisable data is also available for any location in the UK via the UKCP09 User Interface. It includes both changes relative to the baseline period 1961–90 and absolute values, which designers need for definitive analysis.

The projections do not include any explicit representation of urban areas other than that reflected by the underlying base climate data at the resolution of a 25km² grid.

This table shows the assumptions underpinning the low, medium and high scenarios used in the UKCP09 climate projections, as well as those for the medium-low and Medium-high scenarios used in the earlier 2002 projections. Source IPCC, SRES, CIBSE, TM48

UKCP09 also includes information on sea-level change for the same three emissions scenarios, and for an additional extreme scenario, H++. This has been developed specifically to investigate sea-level rise and storm surges, and is regarded as high risk and low probability.

It aims to reflect the effect of melting ice, which presents a major source of uncertainty in projecting sea-level rise but is not well represented in current global climate models.

Further information on the methodology and the projections themselves is available from the UKCP09 website, and a full description can be found in the UK Climate Projections: Briefing Report, sections 3 and 4.

A wide range of standard data tables, maps and graphs is available for climate variables for overlapping 30-year periods in a number of different forms. However, for those who simply need a broad understanding of the changes that we might need to deal with, UKCIP developed a series of maps specifically for the original design for Future Climate report.

Understanding and using probabilistic projections

UKCP09 uses the same set of terms as the IPCC reports to describe the probability of different outcomes for each climate variable. These terms have a precision, directly linked to statistical percentages, that is in marked contrast to the hyperbole of political and media coverage of climate change:
Virtually certain > 99% probability
Extremely likely > 95%
Very likely > 90%
Likely > 66%
More likely than not > 50%
As likely as not 50% (a central estimate)
About as likely as not 33–66%
Unlikely < 33%
Very unlikely < 10%
Extremely unlikely < 5%
Exceptionally unlikely < 1%

The three most widely used probability levels are 50% (the central estimate), and 10% and 90% (the lower and upper limits of the “likely” band of outcomes – ie it is “likely” that a variable will change by more than the 10% projection and “unlikely” that it will change by more than the 90% value).

Edge Lane Medical Centre, Liverpool by Medical Architecture
UKCP09 also features additional tools aimed at specialist users, which allow the generation and analysis of tailored data-sets: the Weather Generator and the Threshold detector. The Weather Generator can be used to produce synthetic, random but statistically plausible daily or hourly data at the resolution of a 5km grid. Though the spatial resolution is increased, the Weather Generator does not include any additional information on climate change. Instead, data from the baseline period is used to calculate the statistical relationship between weather variables, and the UKCP09 change factors are applied to produce future probabilistic outputs.

The Weather Generator should be run at least 100 times for the 30-year period in question, producing 3,000 years of data for statistical analysis. This requires specialist statistical skills and presents a heavy computational and data-handling burden, making it unsuitable as a tool for day-to-day project work. However, as discussed below, it has been used to make future weather files available in a form that can be readily used with standard building-simulation models. The Threshold detector tool (used on the Edge Lane TIME project,) allows further analysis of daily data produced by the Weather Generator to show how often a user-defined parameter is exceeded. The UKCP09 user interface provides three predefined outputs:

•  Heating Degree Days (HDD) – the number of days when the mean daily temperature is below 15.5°C, and heating would be required (it should be noted that this is different to the standard definition of Heating degree days normally used by engineers)

•  Cooling Degree Days (CDD) – the number of days when mean daily temperature exceeds 22°C

•  Heatwaves – when maximum daily temperature is greater than 30°C and minimum daily temperature is greater than 15°C for a minimum of three consecutive days.
It is also possible to define custom events.

At the Edge Lane project, Oxford Brookes University used the Threshold detector tool to show the changing demand for heating and cooling, and the incidence of heatwaves. The results are shown in the tables below.

The tables above produced by Oxford Brookes University for the Edge Lane Health Centre project in Liverpool, using the UKCP09 Threshold Detector

UKCIP also developed a number of tools to help organisations get to grips with their own vulnerabilities to climate change, including the Adaptation Wizard, a Risk Framework and Local Climate Impact Profiles.

LCLIP: Local Climate Impact Profile

This tool was developed to help local authorities understand their current vulnerability to weather and climate, as a starting point for preparing appropriate adaptation strategies. Organisations are prompted to gather information on the details and magnitude of the consequences of recent weather events for a given locality (initially using press reports as a source of information on past extreme events in the absence of more formal observed data), the agencies responsible for managing those consequences and their level of preparedness. Oxford Brookes University, advising both the Edge Lane and NW Bicester Eco Town projects, combined this technique with its own Local Environmental Factors (LEF) methodology to highlight local features that could either ameliorate or exacerbate the impact of climate change.



For an in-depth understanding of how climate change will affect a building design, the basic climate information needs to be “translated” into forms that designers are familiar with. This is particularly the case for the analysis of comfort and energy performance, where industry standard environmental modelling tools are typically used to test design proposals. Using these tools requires detailed future weather data-sets that are equivalent to current “standard” weather files – such as the CIBSE Test Reference Years (TRY) and Design Summer Years  (DSY)

When the design for Future Climate programme was initiated, the only available future weather files were produced by CIBSE with associated guidance (TM48: The use of climate change scenarios for building simulation),3 based on UKCIP02 projections. TRYs and DSYs were provided for three time “slices” (the 2020s, 2050s and 2080s) for each emissions scenario for 14 locations. They were produced using a “morphing” methodology, developed with Arup, which adjusted the standard CIBSE weather files in line with the projections, taking the monthly average changes set out in UKCIP02 to stretch and shift them.

By the time the Design for Future Climate projects themselves were under way, alternative future weather files were starting to emerge from the ARCC research programme (Adaptation and Resilience in a Changing Climate), based on the newer UKCP09 probabilistic climate projections and using the Weather Generator as an alternative to the established morphing technique.

Different teams chose to use different data-sets, providing a useful “road test” of the available options.
Three teams elected to use the original CIBSE TM48 weather files for a variety of reasons:

•  a preference for using data-sets that were directly comparable with the standard TRYs and dSYs used on projects where design work had already started

•  a preference for using data-sets that were tried and tested, and which had the CIBSE industry stamp of approval, rather than acting as guinea pigs for data-sets that were only just emerging. It should be borne in mind that all of the projects were “live”, with all of the concerns over design liability that this entails

•  the attraction of a comparatively simple set of data, with a single projection for each emissions scenario and time slice, as opposed to the range of choice presented by the probabilistic approach.

Of the projects which used the newer files based on the results of the Weather Generator, the majority analysed in detail for this book chose those produced under the University of Exeter’s PROMETHEUS project, although two used Manchester University’s COPSE. PROMETHEUS TRYs and DSYs are available to download for 50 locations, three time periods and the 10th, 33rd, 50th, 66th and 90th percentiles for two emissions scenarios (Medium and High) from the project website. Additional sets can be produced for specific locations. The COPSE methodology produces a single future TRY and DSY for each emissions scenario for a given location. COPSE also produced design Reference Years (DRYs), a new concept. These are hourly weather series, which can be used to assess both heating and cooling. They consist of months of near-extreme hot, high-solar or high-humidity data and months of near-extreme cold, low-solar and low-humidity data. A TRY is first used to identify the weather variable and month that is of greatest concern for a building design, and then the relevant month from the DRY can either be incorporated into the TRY or used as a standalone data-set to test a particular vulnerability.

CIBSE is planning to release an updated set of its morphed future weather files, using the UKCP09 probabilistic projections. For each location, the new TRYs and DSYs will include three time periods (2020s, 2050s, 2080s), and the 10th, 50th and 90th percentiles for the three emissions scenarios. A beta version of these new weather files was used by Arup for the 100 City Road project.

CIBSE is also in the process of developing weather files for London that take account of the urban heat island effect.

Morphing versus the Weather Generator

The CIBSE future weather years are produced by morphing historic TRYs and DSYs to reflect climate projections. The PROMETHEUS and COPSE weather files, on the other hand, use the UKCP09 Weather Generator to produce multiple sets of artificial weather, from which TRYs and DSYs are produced. There are ongoing discussions among experts as to the strengths and weaknesses of both methods, some of which are summarised below.

•  As both are based on historic observations, past relationships between weather variables are carried forward to future projections. Therefore they cannot predict changes in those relationships.

•  The averaging and selection process inherent in both approaches means that extreme events are not well represented.

•  As the morphing process is applied to the baseline weather file, morphed files retain the basic “shape” of the original file, making comparisons between weather files through the century clearer.

•  Weather Generator-derived files are more random and, while they may show the same overall trends, direct comparison between files is less obvious.

•  The morphing methodology depends on having suitable base data for any given location. There are relatively few locations (14 at present) where sufficiently detailed historic records have been kept over a long enough period. The Weather Generator, on the other hand, is able to synthesise data for a much more detailed 5km grid, but is limited by the number of variables it includes.

•  The morphed files are subject to copyright charges whereas files produced using the Weather Generator are not.


Central St Martins Art School, London by StantonWilliams Architects
Designers are not generally accustomed to analysing raw climate data. It is perhaps unsurprising, therefore, that a number of teams turned to these weather files to paint a picture of general changes in external climate, even before the form of the proposed building had been developed.

For example, the Central Saint Martins team (using the earlier CIBSE future weather files) illustrated the likely increase in demand for cooling by comparing the amount of time that external temperatures would be above internal comfort thresholds for current and future London design Summer Years. In the current London DSY, temperatures are higher than 28°C for 3.4% of the hours when a building would be occupied. Under the High emissions scenario, this reaches 30% of occupied hours by the 2080s. As summer accounts for 25% of the year, this effectively represents the whole of the summer.

The team also used the concept of Cooling degree days, which combines the severity and duration of outdoor temperatures. This indicated that demand for cooling could increase by a factor of between two and three by the 2080s.

This graph was produced by the team working on the Central St Martins project to asses how the changing climate could make achieving internal comfort more difficult. It shows the percentage of hours annually that external temperatures will be higher than the recommended internal comfort threshold, using current and future CIBSE Design Summer Years.

At 100 City Road, Arup created the graphs above to compare external temperatures, as shown by the historic and future London weather files, with CIBSE’s internal overheating criteria. By the 2080s, under the 90th-percentile High-emissions TRY, there are more than 600 hours when the external temperature is above the comfort limit of 28°C compared with fewer than 30 in the 2005 TRY.

These graphs were produced by Arup for the 100 City Road project to show the increasing proportion of time when
external temperatures will be higher than CIBSE benchmarks for internal comfort (26 degrees and 28 degrees)
using future CIBSE TRY and DSY files.

This would suggest a significant impact on the mixed-mode operation of the building – ie the use of both controlled and “free-running” modes (the latter denoting a building that does not rely on mechanical cooling systems to remain comfortable in summer).

For the University of Greenwich project, Hoare Lea used frequency distribution graphs to provide a richer level of analysis than simple bar charts, showing annual exceedance of a given value. This kind of technique is necessary to reveal trends when using weather data which is inherently variable (in this case, Manchester University’s COPSE data-set, produced using the Weather Generator). This variability may reflect the chaotic nature of weather, but it does mean that underlying trends can be somewhat obscured by the considerable overlap between datasets for different time slices though the century.

Frequency distribution curves for external dry-bulb temperature (above) and direct solar radiation (below) through the century, produced by Arup for the University of Sheffield Engineering Graduate School project using PROMETHEUS data.


This point was highlighted by Arup on the University of Sheffield Engineering Graduate School. Initial work on the project was based on the earlier, morphed, CIBSE TM48 weather files but the team switched to PROMETHEUS data when developing their alternative design. They noted that the latter files, derived using the Weather Generator, exhibit a more pronounced element of randomness than the morphed CIBSE files, although general trends were still evident when they applied data analysis techniques such as the frequency distribution curves below.

Weather file anomalies

The teams discovered a number of anomalies and quirks in the weather files.

Arup, testing a pre-release version of morphed weather files based on UKCP09 probabilistic projections, noted that these indicated that solar gains will reduce due to increased cloud cover, which in turn would cause a rise in night-time temperature and a shift in the diurnal temperature range. This differed from Weather Generator-derived files, which indicated that solar radiation would intensify.

The University of Greenwich team also noted an increase in summer radiation, but pointed out that these apparently anomalous results produced by the Weather Generator had been raised by Napier University (a partner in developing the COPSE weather data used on the project). The relevant Weather Generator algorithm was revised and reissued in February 2011, and now shows no significant rise.

The discovery of these anomalies demonstrates the value of research projects like this, which allow designers to interrogate new data and tools in depth so that they are more robust when taken up by the mainstream. It is important that these issues are resolved fully, because they raise uncertainties in a field where there is already considerable unavoidable uncertainty.

Where there are discrepancies in derived data, it is perhaps helpful to return to the source of the projections for general design direction. Based on the UKCP09 projection maps for the Medium and High scenarios, the central estimate is that cloud cover will decrease through the century for the majority of the country. This trend will be more pronounced in the south than the north, with a slight increase in cloud cover in the far north of Scotland. The full range of likely projections shows a similar general trend towards a reduction in cloud cover, although in the 90th-percentile projections there is a slight increase first.

Climate analogues

Gale & Snowdon Architects St Loyes Extra Care project rendering

Some teams found it helpful to use the current climate in other geographical locations as a shorthand to illustrate future characteristics of the UK climate, referred to as a “climate analogue”.

Gale & Snowdon Architects St Loyes Extra Care
For example, Gale & Snowden  compared the future climate of their Exeter site to that of Cologne today – a particularly useful analogy as this gave them added confidence in the use of built examples of Passivhaus design in Germany as precedents for their work.

To illustrate the most extreme projections of climate change – High emissions, 90th percentile, 2080 – Triangle Architects used Casablanca, Morocco, as an analogue for Leek, Staffordshire. Meanwhile, the Mill project team compared the projected climate for Cardiff in the 2050s to that of Porto, Portugal, today, and used Brisbane, Australia, as an analogue for the extreme scenario for the 2080s.

Analogues can be powerful in terms of illustrating potential change, but care should be taken to understand which aspects of the climate are comparable and which are not. While temperature and perhaps rainfall patterns may move closer to these distant examples, the angle of the sun and the length of day will of course remain unchanged. As a result, while some techniques for keeping cool might be applicable, shading solutions that depend on excluding the sun at particular times could not be transferred wholesale.


Steering a path through the layers of complexity inherent in the probabilistic projections provided by UKCP09 has clearly been a significant challenge for the project teams, even with the assistance of climate specialists and academics. The work involved went far beyond what would be expected as part of a normal design service.
Some teams developed their own in-house frameworks on which to base an adaptation service to clients. For example, Arup’s climate change appraisal framework provides a systematic approach to assessing and visualising the risks for both mitigation and adaptation strategies.

The assessment is summarised graphically as a circular chart (divided between mitigation and adaptation), including eight primary indicators for adaptation, each divided into four sub-indicators.

The performance of the project is assessed against each sub-indicator, with colours towards the centre indicating that adaptation has been accounted for and those towards the edge showing areas for improvement. It also offers an opportunity to rate the likelihood of a problem arising and the severity of the potential impact.

Arup developed this graphical framework to summarise a range of risks associated with climate change – both mitigation and adaptation – for the school of Engineering at the University of Sheffield..

For design teams struggling with the choice of future weather data, a Knowledge Transfer Partnership project between CIBSE and UKCIP, jointly funded by CIBSE, the TSB and the Engineering and Physical Sciences Research Council  (EPSRC), could provide a solution. It offers a comparatively straightforward step-by-step methodology to help clients and design teams agree parameters on which to base their climate-change strategy, and to select appropriate weather files for use in building analysis. The project produced a set of Probabilistic Climate Profile, or ProCliP, graphs that illustrate, for a given climate variable in a given location, the “likely” range of values (between the 10th and the 90th percentiles), in the 2020s, 2050s and 2080s for the three emissions scenarios.

The central estimate and the “as likely as not” between the 33rd and the 67th percentiles range of values are also highlighted, as is the 1961–90 baseline for comparison.

An example of a ProCliP graph, showing the mean daily maximum summer temperature for London.

The ProCliP graph above shows the mean daily maximum summer temperature in London: an appropriate variable when considering overheating. It indicates very clearly that the choice of emissions scenario may in fact be less sensitive than the choice of percentile within any of the emissions scenarios. The latter choice should be directly related to a project’s vulnerability to changes in a specific weather variable. For example, the residents of an extra-care facility would be considered particularly vulnerable to high summer temperatures, given the susceptibility of older people to heat stress and the fact that they may rarely leave the building. This vulnerability would suggest that weather data should be selected from the upper end of the probabilistic range when considering thermal comfort. Other considerations would include the anticipated lifespan of the building, or budget constraints that would make a phased approach more suitable.

Different climate variables are associated with different risks, so it may be appropriate to use different weather data to assess the impacts of each. The key is to explore the sensitivity of a project to change. Is there a significant difference in the impact of a temperature rise of 0.5°C compared with a rise of 1°C, to the extent that an adaptation strategy is no longer valid? Are there particular thresholds at which a step-change in adaptation strategies is necessary, or is the transition smooth and gradual?


The design for Future Climate teams reached different conclusions as to the most appropriate data to use for assessing the risks to their particular scheme. The diagram below shows the range of climates that were explored across the first tranche of projects, overlaid on a ProCliP graph for summer mean daily maximum temperature. This is a useful way of indicating which weather files were used, and the spread of the scenarios they selected, with the probabilistic range investigated in each case.

This diagrams shows the weather files chosen by all of the Design for Future Climate project teams, overlaid on a ProCliP file to demonstrate the range of future climates explored by the teams.

This diagrams shows the weather files chosen by all of the Design for Future Climate project teams, overlaid on a ProCliP file to demonstrate the range of future climates explored by the teams.

The principle of the probabilistic climate projections is that users of the data can make informed decisions about which data to use based on the time-frame for their project and the risks to which it is most vulnerable. For the construction sector, this puts the onus on individual clients and their designers to weigh up uncertainties with which they are not familiar. Of course, it could be argued that the uncertainties associated with other design and financial decisions, routinely handled, are much greater. For example, the effect of universal IT and mobile technology on how offices are used has been more profound than anyone registered when the first PCs entered our homes and offices some 30 years ago – the time-span that we now might consider in terms of design for adaptation.

There will be many, perhaps more modest, projects where clients and designers will feel overwhelmed by the data and would be glad for the decision to be taken out of their hands, either by regulation or by guidance that narrows the choice to a manageable level.

The decisions made by the design for Future Climate projects may be useful in helping to build some consensus on what a “reasonable” approach should be, although this might then be tempered by the circumstances of an individual project.

This is an edited version of the first two chapter’s of Bill Gething’s Design for a Changing Climate published by RIBA Publishing and was the third in a series of project’s Gething wrote for the Technology Strategy Board.

Bill Gething is a sustainability consultant, teaches within the University of the West of England’s architecture department and was a founder partner of FCBStudios

With thanks to Bill Gething and RIBA Publishing for permission to republish the two chapters.