UKCP Frequently Asked Questions

Commonly asked questions about using the latest UK Climate Projections datasets.

Questions

Answers

What data are available from UKCP?

A large range of data products are available from UKCP, including projections dervied using statistical methods, climate model outputs, derived and marine projections. Information on the available data and how to access them can be found at UKCP18 Guidance: Data availability, access and formats [PDF - 1.5 MB].

Are there observational datasets available?

Yes. You can find information about our observational datasets at HadUK-Grid.

The Met Office's National Climate Information Centre has produced these at 12 km, 25 km and 60 km on the Ordnance Survey's National Grid, i.e. the same as the UKCP Regional, Probabilistic, and Global products.

These datasets are currently only available on the CEDA Archive and can be access through the CEDA Catalogue.

Which data product(s) should I use?

The Probabilistic Projections for the UK is a useful starting point for atmospheric variables (e.g. precipitation and temperature). For coastal applications, start with the sea-level projections from the UKCP Marine projections.

The Probabilistic Projections assess the broadest range of future outcomes from the UKCP projections over land. It includes projections for five future emissions scenarios as well as monthly, seasonal or annual temporal averages. For information on daily timescales use UKCP Global, Regional and Local and for sub-daily use UKCP Local; however, these products are available for a limited set of emissions scenarios.

Information on using the projections over land are available here: UKCP18 Guidance: How to use the UKCP18 land projections [PDF - 1.8 MB].

What spatial resolutions are currently available?

The Probabilistic Projections are at 25 km spatial resolution. Data and graphical plots are also available for a high emission scenario (RCP8.5) that use the Global (60 km), Regional (12 km) and Local (2.2 km) products. The UKCP Marine Projections are available at 11 km resolution. Please note, climate model data at higher spatial and/or temporal resolution adds more detail but does not necessarily provide greater confidence. For further details see UKCP18 Guidance: Caveats and Limitations [PDF - 787 kB]. For details on the available data see UKCP Guidance: Data availability, access and formats [PDF - 1.5MB, updated July 2021].

What is a "Perturbed Parameter Ensemble"?

A perturbed parameter ensemble (PPE) is a group of simulations (i.e. an ensemble) created from a single model with each simulation slightly different to the other due to changing the model parameters (i.e. the model setup).

The climate models used in UKCP represent the real world by dividing it up into grid boxes. For UKCP Global, the entire globe is divided into ~60 km grid boxes. For UKCP Regional, Europe is divided into grid boxes of ~12 km and for UKCP Local, the British Isles are divided into ~2.2km grid boxes. However, a number of atmospheric processes occur on scales much smaller than 60 km, 12 km and even 2.2km, i.e. they aren't modelled explicitly. Instead we use "parameterisations" or representations of these smaller-than-grid-scale processes. These equations contain parameters that have a range of plausible values. A PPE explores the uncertainties in these parameters.

How are the UKCP Regional and Local products related to the Global products?

The results of UKCP Global are used as inputs into UKCP Regional models and in turn the results of UKCP Regional are used as input to UKCP Local models. You can find a diagram on this at UKCP18 How are the land projections connected [378 kb].

The UKCP products are generated using climate models at three spatial resolutions: UKCP Global at 60 km, UKCP Regional at 12 km and UKCP Local at 2.2 km. The reason for having multiple resolutions is that it would be computationally infeasible to produce an ensemble of climate model simulations for the whole globe at 2.2 km. Instead, the higher resolution climate models are run over a smaller area. This is referred to as a Limited Area Model (LAM). For UKCP Regional, this area covers the North Atlantic-Europe domain, while for UKCP Local this covers the British Isles.

The LAMs are “nested” within each other, meaning that they take information from the larger domain model as a starting point before running their simulation. This is referred to as “dynamical downscaling”. In UKCP, the regional LAM is nested within the global model and the Local LAM is nested within the regional LAM.

What sampling method should I select when using ‘data only’ outputs from the User Interface?

If you wish to get the full Sampled Data output that can be downloaded in data files (in CSV or NetCDF format), use the “Select All” option. This returns 3000 sets of data (samples), from which you can calculate percentiles as required. Alternatively, you can sub-sample this data by one of three methods:

Random: returns the number of samples the user requests (minimum of 100)
By ID: returns data for the sample numbers specified by the user
By Sample: a subset of the probabilities:

Random: If you choose to randomly sample the Sampled Data you can select the number of random samples required. The number of samples must be between 100 and 3,000 inclusive. The minimum of 100 is considered the smallest number of samples allowable to maintain the probabilistic nature of the data. The random selection algorithm considers each selection as an independent event. Because of this you can potentially get multiple samples that are in fact the same in the output data.

By ID: You may wish to identify certain sample IDs as being of particular interest or you may wish to use sample IDs supplied by another user. Sampling by ID allows them to re-use the same samples in different requests.

By Sample: Sampling by a subset of the probabilities enables you to sample a particular part of uncertainty space that might be representative of extremes that you’re interested in, and represents the most complex method of sampling the probabilistic projections data. Sampling by a primary and secondary variable at set percentiles hones in on a certain area in uncertainty space. Note that once you have collapsed the uncertainty in this way then it is invalid to make probabilistic statements about the results obtained without also saying that this is only relevant to the 10% (if sampling by 1 variable) or 1% (if sampling by 2 variables) of model variants that have been sub-sampled. Your selection may be scientifically valid for specific studies, looking at particular conditions, but is no longer a representation of the overall uncertainty. You should note that final sample is NOT the 10% (or 1%) extreme nor is it the 10% (or 1%) return period.

Is it possible to select multiple locations / adjacent grid squares?

Yes. However, this function is available for the map-based output only. Under this option, for the selection of "Spatial Selection Type", please choose the "Bounding Box" option which will allow you to select the area you are interested in across multiple grid boxes.

How do I plot graphs against time?

Select a "plume plot" product from the UKCP User Interface. This generates a graph showing changes with time for a selected variable, emissions scenario and location. For the probabilistic projections, the graph shows the 5^_th, 10^_th, 25^_th, 50^_th, 75^_th, 90^_th and 95^_th percentiles.

Are the absolute values available for the 25 km probabilistic projections?

No. We only provide the Probabilistic Projections as changes compared to a baseline (i.e. an anomaly).

Which baseline should I use?

For consistency, we use a baseline of 1981-2000 across the UKCP science reports, factsheets and guidance as well as the UKCP User Interface. Depending on the dataset, 1961-1990 and 1981-2010 baselines are also available through the UKCP User Interface. For UKCP Local, only the 1981-2000 baseline is available. Note that a 1981-2010 baseline is a standard currently used by the WMO and the State of the UK Climate reports.

What date format is used in the UKCP Products?

The date formats used depends on the UKCP Product:

For the UKCP Global, Regional and Local, the Met Office members of the model ensemble (i.e. members 1-15) use a 360-day year, consisting of 12 months each containing 30 days.
For UKCP Global, the CMIP5 members (i.e. members 16-28), adopt the same calendar as the source data. This means that there are 3 different calendars:
- Members 16-19, 25 and 28 use a 365-day year with no leap years (i.e. there is never a 29^_th February).
- Members 20-23 and 26-27 use a Gregorian calendar (i.e. 365/366-day year depending on leap years).
- Member 24 uses the 360-day year as per the Met Office members.

Why are there two sets of sea-level projections?

The UKCP Marine Projections include sea-level projections from the present to 2100 and also a set of exploratory projections to 2300. The exploratory sea-level projections are available for those who need to understand future changes beyond 2100. They are based on a different subset of models to the sea-level projections to 2100 and make use of a simple climate model emulator. There is additional uncertainty (that is accounted for in the ensemble) to reflect the use of the simple climate model. As a result, you will find some differences between the two sets of projections during the overlapping period (i.e. from the present to 2100).

What is included in the sea-level anomaly plot?

The sea-level anomaly plot provides projections of regional time-mean sea-level. Sea levels are affected by not only changes in global mean sea level due to climate change but also regional effects including vertical land movements such as the effects of the last glacial age.

What is meant by "future extreme still water return levels" at UK tide gauge locations using standard method?

"Still water" excludes waves but does include tides. This is what you would expect to see in tide gauge data. The level is measured above a datum and extreme still water refers to extreme values.

How do I delete ‘jobs’ from ‘My Jobs’ on the User Interface?

Once you have logged in to the User Interface, select the "My Jobs" tab and then click the "Delete" button next to the job you wish to delete from your records.

How can I best use the UKCP User Interface map outputs?

These are available for all products for the UKCP Projections over Land.

We suggest "zooming out" from the target location to get the output in the context of a wider area.

How do I plot (or access data for) a baseline for a specific grid square?

The Global and Regional dataset baselines can be calculated from the raw data available on the CEDA Data Archive.

Due to the method used to derive the Probabilistic Projections, they are provided as changes compared to a baseline (i.e. anomalies) only.

Some users have found the observed baseline data useful in this context. These are available from the CEDA Data Archive.

How do I compare global mean temperatures with future changes at a specific UK location?

UK climate data for Global Warming Levels of 2°C and 4°C are available in the Derived Projections. These are available on both the UKCP User Interface and the CEDA Data Archive. Find out more in the Derived Projections factsheet.

How do I reframe UKCP in terms of 1.5°C/2°C/4°C world?

The data/information for Global Warming Levels of 2°C and 4°C are available as part of the Derived Projections and can be found on the CEDA Data Archive. Find out more in the Derived Projections factsheet.

What is meant by "precipitation rate anomaly (%)"?

This is the change in precipitation in mm per day. It is a percentage change because it is a relative change compared to the baseline period.

Where can I find more information about the Local Projections Update?

The Local Projections update occurred in July 2021, as the data and guidance were updated following the discovery of a graupel coding error. Further details can be found in the UKCP Local Projections Update Report. Many questions regarding the update to the UKCP Local (2.2km) Projections are covered in the FAQ document.

What data are being updated?

The new 2.2km data from CEDA are available for all variables described in the Data Availability document. The data are regridded onto a 5km OSGB grid, and this is available for daily radiation, wind speed, relative and specific humidity, sea level pressure, snowfall amount, lying snow amount, daily mean, maximum and minimum temperature, as well as hourly precipitation, via CEDA and the User Interface.

Some variables are being processed onto the 5km OSGB grid, which we anticipate will be available from CEDA and the User Interface in the early autumn. These are hourly temperature, hourly wind speed (note that original data were three-hourly), and daily lightning data.

How can I access the original data?

We recommend using the new data for all new applications. The original data will be available from CEDA for twelve months after the update, until 21st July 2022.