The 2012 UK floods and climate change

Well, it’s been raining a lot in the UK recently. Even more than usual.

Lots of footage of overflowing rivers, flooded homes, people being rescued from their abandoned cars. Lots of interviews with flooded home owners, officials from the Environment Agency, and excited weather forecasters.

But one surprising omission in the coverage I’ve seen:
No mention of global warming.

No breathless activists blaming the floods on global warming, with or without any evidence for attribution. No contrarians or scientists saying ‘nothing to do with global warming’, or talking about ‘possibly some loaded dice but we can’t really tell yet and can’t attribute this particular event to GW’.

Nothing.

Just a few small undercurrents: on the BBC news last night there was footage of past floods from the 1950s and 60s implying that the recent floods are nothing exceptional, within the historical context. This may well be the case, but the ‘calm down, dear’ tone of the coverage seemed to be anticipating or answering those breathless activists making unsubstantiated claims about AGW. Given that those breathless activists hadn’t been given any airtime, though, the report seemed a little odd and/or superfluous.

I completely get that attributing these particular floods to global warming will be nigh-on impossible. I even get that the ‘loaded dice’ argument may not work, if there has not been any quantifiable increase in flood frequency in the observed record in the last fifty years or so (on a very quick look, the evidence here seems to be conflicting- but haven’t yet found any reviews more recent than the 2002 paper linked below). So we are left with models, like UKCP09, projecting forwards the likely impacts of AGW.

Essentially, they predict “warmer and wetter”. The regional modelling gets quite complex, but don’t worry— it’s all rooted in basic physics. In Noddy language: more CO2 means more ‘heat trapping’ in the atmosphere and higher global temperatures, as seen in the observed temperature record in recent years. More heat means more capacity for the atmosphere to hold water vapour. More water vapour equates to Potential Rain.

So, on the basis of modelling and Basic Physics (TM) more rain and floods are not unexpected with climate change. [There are some interesting caveats and complexities, though— when it comes to extreme weather it's the temperature change that's important— delta T rather than T— see blog discussion linked below].

We could well see a lot more of what we’re seeing now in future years. Yes it’s true: we can’t say these particular floods are related to climate change, or even that the observed record yet allows us to make any definite fractional attribution of these floods to climate change. But what we can say is that so far, the weather seems to be following the climate change script. This could be a taste of what’s to come.

OK, this lacks ‘the we’re all gonna die’ headline-grabbing punch of previous unsubstantiated extreme weather-induced climate assertions, but I’m a little surprised that nobody is making even this basic point— at least on the TV news/debate that I’ve seen in the last few days.

Wheater 2002 review article 

UKCIP

Blog discussion from Stoat and DA (Sandy-related but relevant, I think)

About these ads

4 Responses to “The 2012 UK floods and climate change”

  1. Chris Reynolds Says:

    Hello GeoDoctor,

    Since 2007 there’s been a drop in UK summer temperature (using Central England Temperature Index), and a tendency towards cool wet summers. This is because of what’s going on in the Arctic.

    The sea level anomaly pattern this year has been a classic example of the pattern that has persisted for June July August since 2007.
    http://farm9.staticflickr.com/8435/7948597742_cc32b1a063_o.png
    You’ll see from that graphic that the central high pressure over Greenland is surrounded by low pressure regions. The UK is on part of that ring. This pattern is unique since 1948, the year the NCEP/NCAR reanalysis records go back to.
    http://dosbat.blogspot.co.uk/2011/09/summer-daze.html

    It has now been noted in “The Recent Shift in Early Summer Arctic Atmospheric Circulation” Overland et al, Geophysical Research Letters, 2012. They find that the probability of an Arctic Dipole (part of the anomaly in the Arctic) over 5 years by pure chance is 1/1000. They also note that “an enhanced southward dip in the jet stream leeward of the increased ridging over Greenland has caused generally cool wet summers in the U.K. since 2007, with record rains and floods in 2007 and 2012 (e.g., Hanna et al., 2008b; UK Met Office, 2012).”

    BTW the early February cold snap mentioned in the C4 documentary last night was also due to the Arctic:
    http://dosbat.blogspot.co.uk/2012/03/cold-winters-from-theory-into-practice.html

    These are the best evidenced two patterns at present. IMO.

    Hope this interests you.

  2. Chris Reynolds Says:

    Sorry, I should have mentioned – search for Judah Cohen, he’s got some interesting ideas about cold winters and a link to Eurasian snowfall. This graphic is from one of his papers
    http://farm8.staticflickr.com/7020/6602153213_9000d61e12_o.jpg
    The paper is here:
    http://web.mit.edu/jlcohen/www/papers/Cohenetal_ERL12.pdf
    That graphic, read downwards, is a chain of connections that link reduced sea ice to colder NH winters.

    So that’s the 3 best evidenced patterns. ;)

  3. Matt Says:

    Thanks for the links Chris— good to see that clear trends seem to be emerging. TBH, the causal connections between loss of arctic sea ice and changes in atmospheric pressure patterns aren’t immediately clear to me, but I’ve only had a chance to have a quick look through (my lack of relevant educational background doesn’t help here).

    But certainly very interesting.

    • Matt Says:

      New Scientist 19 January 2013, p11:
      “It is the fourth year in a row that the northern hemisphere has seen large, intense waves of cold … there is growing evidence that retreating Arctic sea, which hit a record low in September, is to blame… Normally, winters in the northern hemisphere are dominated by westerly winds, driven by the temperature gradient between the warm equator and the cold North Pole. But as the Arctic sea ice retreats, the polar ocean warms faster and the westerlies are weakened. This allows cold air to spill out of the Arctic, and into Eurasia.”

      Having put this together with the Judah Cohen graphic Chris linked above, I think I can conceptualise what’s going on now: essentially it’s the greater relative warming in the Arctic compared to the equator. This causes more sea ice loss, evaporation and extra atmospheric moisture which incidentally contributes to greater winter snowfall where temperatures are already cold enough. In terms of cold UK winters though, it’s the weakening of the temperature gradient between equator and pole which weakens the Hadley and mid latitude convection cells. The pressure changes— weakening NAOs and AOs— follow on from this (the descending block of air in the Hadley cell corresponds to the Azores high). This in turn weakens the Atlantic Westerlies allow cold Arctic air to “spill out” onto Blighty as described above.

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s


Follow

Get every new post delivered to your Inbox.

%d bloggers like this: