Climate Sense

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The UK Climate Projections – Met Office

science and headline results

Vicky Pope, James Murphy, David Sexton, Geoff Jenkins, Daniel Williams, Julia Slingo, Met Office, United Kingdom

ur climate is changing faster than it has done for hundreds

of thousands of years, driven by the greenhouse gases

produced from human activities. Some changes have

already occurred and, because of the greenhouse gases already in

the atmosphere, we are guaranteed further changes in the coming

years and decades. This will have significant effects on the UK –

posing many potential threats and opportunities. It is essential to

understand these issues so that we can start adapting now for the

changes ahead.

The UK Climate Projections 2009 (UKCP09) – commissioned by

the UK Department of Environment, Food and Rural Affairs – are

a major step forward in addressing this need. UKCP09 involved the

Met Office Hadley Centre producing an ambitious and comprehensive

analysis of regional climate change. The projections provide proba-

bilistic information on how the UK’s climate will change in the 21st

century based on state of the art climate models, observations and

statistical analysis, combined with expert knowledge. The projections

are a key part of a programme of measures from the UK Government

to both encourage and support action to prepare for the impacts of

our changing climate. The UK Climate Impacts Programme (UKCIP)

provides the first point of contact to help stakeholders use UKCP09.

The projections are designed to inform planners and decision makers

about the risks associated with different levels of climate change in

their efforts to tackle future challenges.

How the projections were made

Scenarios of UK climate change were published in 1991,

1996, 1998 and 2002. These projections have formed

the basis for many climate adaptation schemes already in

progress. UKCP09 provides a step change in the informa-

tion available, by using the latest science and advanced

computing power to produce the most comprehensive

information to date.

The projections have been generated using the Met

Office Hadley Centre climate model – recognized as one

of the best in the world. This has been updated to take into

account improved understanding of the climate system –

such as recognition of how changes in the carbon cycle can

exacerbate climate change.

There are still inherent uncertainties in climatemodelling,

however. These focus around an incomplete understand-

ing of the complex processes of the atmosphere ocean and

land surface combinedwith natural varaibility. There is also

uncertainty as to how manmade greenhouse gas emissions

will change over the projection period.

UKCP09 tackles these uncertainties by using a range

of projections generated by running its model hundreds

of times using a range of different values for key param-

eters. This means many nuances in the understanding

of atmospheric science are taken into account. To

ensure an even wider spread of the possibilities is

considered, 12 of the world’s other leading models have

also been used to create projections. For the more local

projections (at 25 kilometres resolution), more detailed

climate models were run to include local factors that

are known to affect regional climate, such as mountains

and coastline.

The Met Office uses climate science, observations and

expert judgement to attach levels of confidence to each of

the projections. The level of probability given can be seen

as the relative degree to which each climate outcome is

supported by current evidence.

The probabilistic approach, used at a regional level for

the first time, allows UKCP09 users to get a clear picture of

the likelihood attached to each projection. This enables an

informed approach to risk–a highly important assessment

when making vital decisions on levels of adaptation.

The benefits of this approach are illustrated by compar-

ing results from UKCIP02 with those from UKCP09. The

UKCIP02 projections for changes in summer average

rainfall are shown to be very unlikely in the new UKCP09

bserving

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A schematic diagram showing the progression from UKCIP02 to

UKCP09, using temperature as an example

Source: Met Office UK