What does the unusually hot summer say about climate change?

Climate change deniers have frequently pointed to regional weather patterns to provide irrefutable evidence against climate change. Back in January Gerald Warner of the Telegraph, for example, was quick to use his frosty windows to denounce the phenomenonon:

"You have to wrap up well against this global warming. Over the past 48 hours the temperature has fallen as low as -12C in Dorset, with the sea at Poole Harbour frozen up to 20 yards from shore, and parts of Britain colder than Greenland. Phew, what a scorcher! Might be a good idea to start up the car (if it will start) and pump some more CO2 into the atmosphere before we freeze to death. What did the media warn us about climate change?"

But now that we're in the throughs of a heat wave (here in London), George Monboit of the Guardian keenly points out that surely this provides irrefutably proof to the contrary, at least using Warner's logic:

"If a single cold snap in the UK persuades them that global warming isn't happening, then a single heat-wave in the same place must surely convince them that it is. Logic would dictate that the world must now be destined for a century of heating - until the next cold snap, whereupon it is obviously destined once more for a century of cooling."

He's got a pretty good point but logical consistency is not typically a strong point of climate change deniers so it may not have too much of an impact.

Perhaps more worryingly though,is that this talk about local weather and climate change more generally may muddle even the most astute climate advocates' logic.

The increasingly clear truth is that the effects of climate change on weather are uneven and inconsistent. When we talk about a 2-3 degree rise in temperature, we're talking about the earth's median temperature over time, which most likely will not reflect the actual temperature in any of the world's cities. Any generalization between the local and global can claim, at the most, that climate change affects local weather patterns, how much and in what direction is entirely ungereralizable!

If Warner or Monboit decide to consult the real scientific evidence on climate change effects in the UK, they will find out that local weather effects really vary. The except below is from BBC weather centre:

Regarding temperature:

- Annual average temperatures look set to rise by between 2C and 3.5C by the 2080's. The south and east of the UK will most likely see the largest rise in temperature, in contrast to the north and west which will see the least.

- Most of the warming will be in summer and autumn

- Summer rises in southern England and south Wales are expected to be the highest

- In contrast, winter rises in the winter in the northwest of Scotland are predicted to be between 1C ('low emissions') and 2C ('high emissions').

- Temperatures in the south east may rise by as much as 5C on average, by 2080's, according to the 'high emissions' scenario and over 4C with the 'medium-high emissions'.

Regarding precipitation:

- Precipitation in winter will increase in all areas of the country, in every one of the scenarios.

- The increase is predicted to range from between 10% and 20%, depending on the area of the country, for the 'low emissions' . For the 'high emissions' scenario, the range increases to between 15% and 35%.

- The summer will see less precipitation than we see now and will therefore be much drier.

- The 'low emissions' scenario predicts the country to become up to 35% drier. Whereas the 'high emissions' scenario forecasts 50% less rainfall than we experience now, by the 2080's.

- The largest changes are predicted for the southern and eastern part of England, the smallest changes are forecast to be in northwest Scotland.

- Less snow will fall throughout the UK - a decline of 60% in parts of Scotland and up to 90% elsewhere.

The difficult truth is that a little snow in the winter and a heatwave in the summer tell us little about climate change. At once the effects are highly visible yet impossible to pinpoint locally. In a previous blog, Ricki of Australia shared her very real experience of the effects of climate change, and I hope that you too will contribute your experiences here as well. For proof of climate change we can and should rely on your collective accounts.