Extreme weather and climate change: are they linked?

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Areas of the UK have suffered record flooding in 2012

Areas of the UK have suffered record flooding in 2012

An interview with Professor Sir Brian Hoskins, Director of the Grantham Institute, on the link between climate and weather.

The Earth has seemingly been under siege from extreme weather events in 2012, including record summer temperatures in the USA and Russia, 'superstorm' Sandy and a deluge of flooding in the UK.

The extent to which we can directly link individual extreme weather events and the number of them in any year to climate change is still unclear, but this has not stopped speculation from a range of public and political figures.

Professor Sir Brian Hoskins, Director of the Grantham Institute for Climate Change, discusses what we can say, if anything, in the week that delegates are meeting at UN Climate Change Conference COP18 in Doha, Qatar.

Irrefutable evidence of climate change or just another normal year?

It is too soon to say that there is irrefutable evidence that this collection of extreme events is associated with climate change, and this may remain the case until it is too late to do much about it. However, we can say that some of the events are more likely to occur because of the greenhouse gases added to the atmosphere by human activity. I know that some scientists, like high profile NASA climate expert James Hansen, already say there is a definitive link between the occurrence of the extreme events and increase of greenhouse gases in the atmosphere. This does a great job of keeping climate change in the news, but to me it goes beyond what we can say with confidence based on current scientific understanding and evidence.

So what can we say about all this extreme weather?

Many of these prolonged periods of extreme weather in our latitudes occur because of an atmospheric pattern called a blocking high.  Regions get stuck under the same weather system for entire seasons and this interrupts the region's normal weather patterns. Blocking highs led to the Russian heat wave in 2010, the very hot summers in Europe in 2003 and 2007, and the UK's recent remarkably cold winter months.  At the time of the cold winter in 2010, some people in the UK asked where global warming had gone, but on some days when it was below freezing in London, it was +11°C in Greenland! In this blocking high weather pattern Greenland was stuck under warm air and the UK was stuck under cold air.

All the events we’ve seen recently have happened before; the question is whether we have altered the climate to the extent that they’re occurring more often or with greater intensity. In the longer term, if you take a system like the earth’s climate and give it as large a kick as we’re giving it, we’re going to have to be incredibly lucky to not see severe climate changes at some time. The question is when.

In the above excerpt from the Imperial College Podcast, Jo Haigh, Professor of Amospheric Physics, talks about the weather and climate situations that led to superstorm Sandy.

What is the difference between climate and weather?

  • Professor Hoskins says: "I want to get away from the idea that there's a distinction between weather and climate. The atmospheric system knows no barriers on those time scales, it’s a continuum like a sliding scale, weather or climate for a given period of time is the collection of events on shorter timescales. On a one to two week timescale we ask questions like 'is it going to get generally warmer?', 'are we going to see more low pressure systems?’. As you move to the monthly or seasonal timescale we're trying to say 'are we likely to get more of one pattern or another?'. On a ten year timescale we start to look at predictions for the seasons, for example can we expect to experience colder or warmer winters?"

What research is the Grantham Institute doing into extreme weather?

One of my PhD students, Erica Thompson, has been looking into how extreme storms might change in the future but she has concluded that the models and records we currently have aren’t good enough to make a confident prediction.  You often hear in the media that we’re going to get more and stronger storms, but maybe they know more than I do about it! 

What does the research mean for future weather events?

There’s already good statistical evidence from around the world that heavy rainfall events are becoming more intense, even in areas of the world that are going to get drier on average. In regions that are already dry these heavier rains will cause more floods and make it more difficult to maintain reservoirs, and providing clean safe drinking water will be a major problem.

The last record temperatures were recorded in 2010, what are the chances that we'll break these in 2013?

I'll be surprised if we don’t get a record year soon. The multi-decadal trend of increasing global temperature is very clear; of the 10 hottest years on record, nine of them have occurred over the last 12 years. If we get another El Nino event in the Pacific 2013 has a high chance of breaking the record.  Globally every month since February 1985 has been above the 20th century average temperature, that’s 332 consecutive months. Since the 20th century average itself includes the warmer period at the end this makes it even more impressive. It is an amazing statistic!

And another record breaking year for melting Arctic sea ice?

This year the extent of Arctic sea ice was almost half the normal amount of sea ice you would expect in September at the end of the Arctic summer. Low atmospheric pressure over the Arctic caused very strong winds for about a week that broke up the sea ice. A big concern is that there may be a positive feedback in which heat given off by the warm ocean exposed by the missing ice causes the low pressure and the winds to be even stronger or more persistent. This is something we must look into because if it’s right then this would mean that summer sea ice decline could be even more dramatic in future.

Do you have a message for the UN climate negotiators at COP18 in Doha?

We need global agreement and action to reduce the impacts of climate change. There are no winners in this game, but without an agreement there will only be losers.

If you talk about 2°C or 4°C warming people say ‘oh we can adapt to that’, but beyond a certain point the entire climate system will change and we’re going to see massively different weather patterns. These thresholds are likely to have really large impacts and we don’t want to cross them. However, we don’t know what they are or when we might reach them.

Scientists contribute the necessary background research but it’s governments that decide what will happen. The Committee on Climate Change, of which I'm a part, has set UK targets based on reducing global CO2 emissions consistent with limiting the risk of a 2°C temperature rise to 50 per cent. It also means a negligible chance of 4°C temperature rise, as it is thought that damaging climate thresholds will have been passed before this point .

Professor Sir Brian Hoskins FRS has been Director of the Grantham Institute for Climate Change since 2008; he holds a position as Professor of Meteorology at Reading University and is currently a member of the UK government's Committee on Climate Change.  In November 2012, he was awarded the distinction of Fellow to the American Association for the Advancement of Science (AAAS).

The Grantham Institute for Climate Change recently published its Outlook for 2012, which showcases research and activities at the Grantham Institute over the last 12 months. You can view the publication online or request a printed version of the report using our contact form.


Simon Levey

Simon Levey
Communications Division

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Email: s.levey@imperial.ac.uk

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Emma Critchley

Emma Critchley
The Grantham Institute for Climate Change

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Email: press.office@imperial.ac.uk
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