Local flooding and climate change

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Following the recent flooding in West Oxford and other parts of the UK, LCWO committee member Ruth Mayne, put a series of questions to Oxford University climate change expert, Professor Myles Allen.

Myles is Professor of Geosystem Science in the School of Geography and the Environment and the Department of Physics, University of Oxford. His research focuses on how human and natural influences on climate contribute to observed climate change and risks of extreme weather and in quantifying their implications for long-range climate forecasts.

Ruth:  David Cameron recently told MPs that he “suspected” that the recent spate of wet weather, which has caused widespread flooding was linked to climate change. Does the evidence support that view?

Myles: The prime minister is right that there is good reason to suspect a connection, and also right to be cautious. Unusually high rainfall can happen in the absence of global warming, as part of the natural variation of the weather, but there are simple physical reasons, supported by results from computer modelling, to believe that human influence on the climate is making high wintertime rainfall events like these more frequent. It will never be possible to say “but for global warming, this event would not have happened”, but with detailed modelling, we can say how much global warming might have contributed to the risk of an event occurring.

Ruth: The latest  United Nations Intergovernmental Panel on Climate Change showed that scientists are more convinced than ever that the planet is warming, sea levels are rising and that humans are responsible for the majority of it, especially over the past 50 years. Is it still possible to limit global warming, and how much do we need to reduce global emissions by to do so ?

Myles: The sobering conclusion of the latest IPCC report is that, because carbon dioxide accumulates in the climate system, the only way to stop global warming in the long term is to reduce fossil CO2 emissions to zero. To have a reasonable chance (say 2-in-3) of limiting the warming caused by carbon dioxide alone to 2oC, we would need to limit total emissions over the entire industrial epoch to one trillion tonnes of carbon, over half of which has already been emitted. That is possible, but it would require global emissions to fall, on average, by 2.5% per year from now on — and, of course, the longer emissions rise, the faster they have to fall to meet the same cumulative budget. Right now, emissions are increasing at around 2% per year, and since many developing countries insist their emissions must continue to rise to meet their needs, it follows that those that can afford to do so will have to cut emissions much faster than 2.5% per year.

Ruth: Why limit warming to less than 2 °C?

Myles:  A sustained warming of 2 °C or more would already be well outside the range of temperature fluctuations experienced since the last ice age, and many vulnerable ecosystems and societies are expected to suffer under this level of climate change. We are already seeing the impact of less than 1 °C of warming on some types of extreme weather events — even a 2 °C world would be very different from the one we have grown up in. The question people should be asking is whether that is a future we want, when there are perfectly viable alternatives to continuing business-as-usual emissions.

Ruth: What can West Oxford residents do?

Myles: Clearly reducing your personal and community carbon footprint helps. But it is also very important to make your government aware that you want it to take action to limit cumulative global carbon emissions. Right now, we have a lot of tactical measures to get emissions down in the short term, but what is the long-term “exit strategy”?

See http://trillionthtonne.org/