Online Briefing report 3 Why new projections now?
Scenarios of UK climate change were published by UKCIP in 1998 and 2002, and many assessments of impacts and vulnerability, and guidance for adaptation, have been based on them. Recent research has shown that most recent trends in observed climate fall broadly within the range of projections shown in these scenarios. Continuing improvements in our understanding of the climate system and in modelling allows us to periodically update projections, which also helps to meet increasingly sophisticated user requirements. One example of our better understanding is the growing recognition of how changes in the can act to exacerbate climate change; this factor is included in UKCP09 for the first time. A further example of scientific improvements concerns uncertainties; reports accompanying previous UKCIP scenarios have mentioned the lack of a credible approach to dealing with uncertainties.
The development of new techniques, together with increased computing power enabling them to be exploited, has allowed us to quantify the spread of future projections consistent with major known sources of uncertainty. As mentioned earlier, this is done in different ways for projections of changes in climate and for changes in the marine environment; for the remainder of this section we consider changes in climate. Uncertainty in this case is dealt with by presenting projections which are probabilistic in nature. This sort of presentation is more informative than the single projection (for a given emissions scenario) in UKCIP02, or even a range of different projections from different climate models (as in Figure 4), but is also necessarily more complex. It gives the user the relative probability of different outcomes, based on the strength of evidence, and more openly reflects the state of the science. This is why probabilistic projections were adopted by IPCC for the first time in their most recent science assessment. The UKCP09 projections respond to demands from a wide range of users for this level of detail.