Climate change projections Benefits
- They assign probabilities to different future climate outcomes
The biggest difference between the UKCP09 climate change projections and previous UKCIP climate projections for the UK (e.g. UKCIP02, UKCIP98) is the inclusion of probabilities. All UKCP09 climate change projections are assigned probabilities, based on the modelling and statistical framework used in their preparation. This permits an assessment of the relative likelihood of future climate outcomes in the context of risk-based decision making. For more information see Chapter 2 and Chapter 3 of the Climate change projections report.
- They reflect uncertainties within the Met Office Hadley Centre's global climate model, including the most important known climate feedback processes
Unlike in previous climate change projections for the UK (e.g. UKCIP02), modelling uncertainties associated with the Met Office Hadley Centre's global climate model have been explored and quantified in the UKCP09 projections of climate change, by using a perturbed physics ensemble (PPE) approach. As part of this PPE approach, UKCP09 includes more feedbacks than previous UK climate change scenarios, and explores uncertainties associated with them in a systematic way. UKCP09 includes consideration of feedbacks associated with the carbon cycle and the sulphur cycle, as well as some ocean transport processes. Despite this, some feedbacks are not included in the UKCP09 projections of climate change either because their effect is assumed to be small or because they are as yet poorly understood (e.g. climate-methane cycle feedbacks).
Feedbacks are explained in more detail in Box 2.1 of the UKCP09 climate projections report, and more information about the method is given in Chapter 2 and Chapter 3 of the UKCP09 probabilistic climate projections report.
- They include information from other global climate models
Unlike in previous climate change projections for the UK (e.g. UKCIP02), the UKCP09 probabilistic climate projections use projections from other global climate models to give a more comprehensive range of uncertainties than could be provided from the Met Office Hadley Centre model alone. Twelve of the global climate models used in the IPCC's Fourth Assessment Report have been incorporated in the UKCP09 projections of climate change, and this forms the mulit-model ensemble, and thus allows the incorporation of structural error in the projections.
The IPCC Fourth Assessment Report is available from the IPCC website.
- The output can be used in different ways
The UKCP09 probabilistic climate change projections offer flexibility in terms of how the outputs are presented. The UKCP09 User Interface allows the probabilistic projections of climate change to be visualised and interrogated in a variety of ways. Users can obtain images (e.g. maps and graphs) or download the data behind the images as numerical outputs. Users can also produce output for several variables and temporal-average periods. Downloaded data can be used to feed into impact models.
See the UKCP09 User Interface .
- They are available for 25 km grid squares and for pre-defined aggregated areas
The UKCP09 probabilistic climate change projections are calculated for every 25 km grid square over land areas of the UK, which should be more closely aligned to the level at which decisions need to be made, than the projections in UKCIP02 were. However, the probabilistic nature of the climate change projections mean that the projections for a number of adjacent 25 km grid squares cannot be aggregated or averaged together by the end-user. Instead, certain aggregated areas have been pre-defined for which projections have been calculated by the Met Office Hadley Centre and which can be visualised through the UKCP09 User Interface.
Probabilistic projections over the oceans around the UK are provided for a number of marine regions.
- They use the longest set of RCM runs ever produced for the UK to date
Downscaling GCM projections (300 km) to 25 km resolution involves a lot of uncertainty in the way that regional physical processes affect fine scale detail. To capture some of this uncertainty, 11 different simulations of the RCM were run where the physical processes were varied in the same way as in the driving GCM. This gives greater confidence in the statistical relationships that have been developed between the GCM and RCM outputs (downscaling), and also allows us to include the downscaling uncertainty in the probabilistic projections. UKCP09 therefore captures more of the uncertainty involved in the downscaling process, which should lead to greater confidence being placed in the method that was used to produce the climate change projections.
See Section 3.2.11 of the Climate change projections report for more information on the downscaling method used in UKCP09.