UK Again in Climate Crosshairs
December 10, 2015
More record flooding in the UK this week fits the profile of climate enhanced precipitation activity. I profiled the extraordinary storms of 2014 in the video above, which featured an interview of Glaciologist Alun Hubbard, whose house had just been hammered by hurricane force winds.
I’ll be chatting with Alun again in San Francisco next week. Meanwhile, here’s an update on current storms.
While scientists will not point to a single event and say it has been caused by global warming, they are clear that human influence on the climate is loading the dice in favour of these extreme events.
Greenhouse gas emissions from power generation, industry, transport, deforestation and agriculture are pushing up global temperatures.
Warmer temperatures mean the atmosphere can hold more water, with humidity increasing around 5% for every 1C rise, which in turn prompts more intense rainfall and storms.
Heavy rainfall can cause flash flooding, where rain falls too quickly to soak into the ground – especially if it is already saturated from previous storms, or baked hard by previously dry conditions as in the 2007 summer floods – and causes floods on road and land surfaces.
It can also cause river flooding, when rivers are overwhelmed with the amount of water that is flowing into them.
Increased storminess can batter coasts and cause storm surges which combine with rising sea levels – also caused by climate change – to lead to coastal flooding where defences fail.
One of the predicted consequences for the UK of climate change is an increase in very wet winters, such as the one seen in 2013/2014 – the wettest winter on record for England and Wales – extreme weather and flooding.
In the wake of the 2013/2014 winter, which saw widespread flooding and coastal damage, researchers from Oxford University found climate change was already making this kind of intensely wet winter 25% more likely, meaning that what would be a one-in-100-year event has became a one-in-80-year event.
Periods of intense rainfall could increase in frequency by a factor of five this century as global temperatures rise, the Government’s advisory Committee on Climate Change has warned.
The severity of Storm Desmond in the mountainous Cumbria region of the United Kingdom is consistent with observed regional climate change trends and projections, including increases in the heaviest rainfall events and the occurrence of persistent atmospheric rivers. It’s likely Desmond also gained strength from Atlantic sea surface temperatures that are 1.8°F (1°C) above average and global-scale warming that adds extra moisture to the air.
The UK Met published a study in November 2015 showing that, thanks to climate change, the odds of extreme rainfall increases by eight times during winters in the UK that have Desmond-like atmospheric river patterns. The study also finds that climate change increases the chance of extreme heavy rain over 10 consecutive days by seven times.
Storm Desmond—a 5,300-mile long atmospheric river storm, or relatively narrow, long stream of clouds and atmospheric water vapor—set new UK records for any 24- and 48-hour period on December 4–6. The new 24-hour record of 13.4 inches (341.1 millimeters) and 48-hour record of 15.9 inches (405 millimeters) beat the previous records set in November of 2009 also in Cumbria .
A 2015 study by Jamie Hannaford summarizes the science on climate-driven changes to UK water flows and finds “an increase in high flow magnitude and duration,” or the most extreme events, from the 1960s to the early 2000s. Hannaford also cites studies that find links between climate change in the UK and seasonal rainfall (e.g. Murphy et al., 2009), extreme rainfall (e.g. Fowler et al., 2005) and river flows (e.g. Arnell, 2011; Kay and Jones, 2012).
Studies have also demonstrated the importance of atmospheric rivers in causing winter flooding and extreme rainfall in the northern and western UK, and while there has been no analysis as to whether human-caused climate change has already made such storms more frequent, atmospheric rivers are expected to become more frequent in the future due to global warming.