Inside science >> Pinning down the detail

Defra scientists on why it is important to be precise about how the global climate is changing

We have well-founded confidence in predicting the general direction in which the climate is changing – warmer temperatures, changing precipitation patterns, sea-level rise, and more extreme events. But we have less confidence in pinning down the detail of, say, how much hotter the hottest summer days could be, or by what percentage winter rainfall will change.

The latest science (such as the UK Climate Projections 2009 (UKCP09) puts explicit estimates on how much confidence we have in different degrees of change, but the range is still large. For example, UKCP09 suggests changes in summer precipitation for London under a medium emissions scenario of –43% to +16% for the 2050s.

Making the uncertainty more explicit requires decision-makers to be able to handle these large ranges, rather than use averages, which, although more convenient, could result in less robust decisions. While the 2050s are seemingly a long way off, many decisions we make now will have ramifications during this period.

The planned lifespan of a house is about 50 years, but of course many houses and major costly infrastructure last much longer. Building in adaptation measures to house design now is often cheaper than trying to retrofit in the future when the impacts of climate change actually occur. So understanding the long-term projected changes in climate is important.

Overly complex information or uncertainty can act as a barrier to making this happen: what future should we adapt to? How can we work this out when presented with 10,000 different estimates of change, all of different likelihoods?

Another barrier, suggested by a variety of social research and economic studies, is that relatively small up-front costs receive a much greater weight from people than the long-term payoff.

Of course, we deal with uncertainty in everything we do – hence the widespread take-up of insurance by householders. Although climate change uncertainty seems very different, the basic principles are the same. For example, those planning the build site for a coastal power plant would (and do) plan on the basis of protecting against a very high level of flooding.

The chance of this occurring may be very remote, but the potential costs and impacts of flooding are so enormous as to justify significant investment in managing even low probability risks.

This is in effect their insurance policy; they are willing to pay a lot now to avoid the risk of flooding later. Sometimes surprise events, such as the recent Japanese Tsunami, demonstrate how we can still be vulnerable to very infrequent catastrophes. Even a 1-in-1,000 risk is as likely to happen tomorrow as in 1,000 years’ time.