Met Office report spells out climate change link to UK storms and flooding
- 10 Feb 2014, 16:00
- Roz Pidcock
As flood waters continue to engulf parts of the UK this weekend,
the Met Office released a report looking at whether climate change
is playing a part in the exceptional weather.
Chief scientist Julia Slingo summarised
the Met Office's position by saying "all the available evidence
suggests there is a link to climate change" - though the full
report makes clear just how difficult it is to unravel the
special weather we get here in the UK.
Official Met Office
figures show this winter brought with it one of the most
exceptional periods of rainfall in England and Wales in at least
248 years, when records began. When the two months are combined, it
was the wettest December and January in the UK as a whole since
The rainfall has hit the south fastest. In January, parts of the
southern England received more than 200 per cent of the average
rainfall for the month - shown in dark blue in the maps below.
Total rainfall (mm) for January in southern England
from records going back to 1910 (top panel), and the
number of days with rain (>1mm) in southern England from records
going back to 1961 (bottom panel). You can see January 2014 on the
far right. (Met Office)
What's behind all the rainfall? A sequence of low pressure
weather systems coming across the Atlantic - with the UK sitting
right in their path, according to the Met Office report.
The Met Office explains it's unusual to see so many severe
storms in a short space of time - with major storms hitting the UK
on 4th December, again on 5th January and continuing into the first
week of February. The report says:
"Although no individual storm can be
regarded as exceptional, the clustering and persistence of the
storms is highly unusual … It is this continued run of storms that
has created the exceptional flooding conditions experienced in the
Somerset Levels, for example."
Why so stormy?
Storms usually follow a certain pathway across land and ocean,
known as a storm track. The position of the storm tracks is largely
determined by the jet stream - a thin, fast flowing ribbon of air
high up in the atmosphere that acts to steer weather systems
towards the UK.
The jet stream was unusually strong in December and January,
creating perfect conditions for a sequence of strong storms to
weave their way across the Atlantic to the UK, the report
A different jet stream extending across North Africa and the
North West Pacific has also showed some unusual movements, which
scientists think is contributing to recent storminess in the
A snapshot of a storm approaching the UK on the 5th January,
showing winds up to 60 metres per second (red). Met
The unusual run of weather in the UK isn't an isolated event,
says the Met Office. The new reports links weather systems on both
sides of the Atlantic, saying:
"The severe weather in the UK coincided
with exceptionally cold weather in Canada and the USA … There is a
strong association with the stormy weather experienced in the UK
during December and January and the upstream perturbations to the
jet stream over North America and the North Pacific."
So how much is climate change a factor in what we're seeing?
The new report says there are three things to consider in
assessing the role of climate change in past and future storm and
flood risk: the number and frequency of storms, the amount of
rainfall, and the extra impact of rising sea levels.
some evidence we're seeing more storms hit the UK over the last
century or so. The slope of the red lines in the graphs below
suggests the number of winter storms has increased in the North
Atlantic between the UK and Iceland - and that those storms are
Source: Wang et al., (
Over the UK, there's also growing evidence that heavy rainfall
events are getting more frequent. This fits in with
scientists' understanding of the fundamental physics of a
warming world - warmer air carries more moisture, which means that
rain falls in heavier bursts.
The Met Office report explains:
"What in the 1960s and 1970s might have
been a 1 in 125 day event is now more likely to be a 1 in 85 day
event. This supports other evidence that UK rainfall is increasing
What would have been a 1 in 125 year rainfall event in the
1960s is now more likely to be a 1 in 85 year event. Source: Met
On top of storminess and rainfall, coastal flood risk is
increasing as rising temperatures are causing sea levels to rise.
The report says:
"Sea level along the English
Channel has already risen during the 20th century due to ocean
warming and melting of glaciers. With the warming we are already
committed to over the next few decades, a further overall 11-16cm
of sea level rise is likely by 2030, relative to 1990, of which at
least two-thirds will be due to the effects of climate
Scientists can undertake research which lets them go a step
further than saying recent events fit their expectations of a
warming climate. By doing what's known as an 'attribution study',
it's possible to say more definitely whether we could have seen the
same scale of storms and rainfall in a world that wasn't
These sorts of analyses are very complicated, rely on
sophisticated computer modelling, and take a while. It's likely to
be some time before researchers can determine if climate change is
the reason for the unusual excursions of the jet stream - the
immediate cause of our recent run of weather.
The Met Office says:
"This is a critical question because
it raises the possibility that disruption of our usual weather
patterns may be how climate change manifests itself … As yet, there
is no definitive answer on the possible contribution of climate
change to the recent storminess, rainfall amounts and the
consequent flooding … It's only now that the climate models are
reaching a level of detail and skill that is necessary to address
the issues raised by recent events."
Preparing for the future
The bottom line from the Met Office is that the sequence of
severe storms we've seen recently is highly unusual, and may be
influenced by a warming climate changing atmospheric
The heavy rain those storms have been depositing also fits in
with what scientists broadly expect from climate change. Formal
attribution studies are yet to confirm exactly how much of what
we're seeing is down to human influence on the climate, but the
report makes it plain on many counts that we should be making
ourselves more resilient to flooding in the future.
Updated 11th February - The Met Office issued a correction
clarifying the projections for sea level rise in the channel by
2030 are relative to 1990 levels. We have updated the quote in the