Can we ‘prove’ climate change?

I-Hsien Porter

A view of flooding in Pakistan, taken from a helicopter near Ghazi, August 2010.

Referring to the ongoing heatwave in Russia and floods in Pakistan, a broadsheet newspaper recently printed an article with the headline “Disasters ‘prove that global warming is happening’.” The article was reproduced on the internet, with the more cautious title “global warming could be the cause.”

The Intergovernmental Panel on Climate Change (IPCC) agrees that extreme events like these are consistent with climate trends. However, global warming refers to long term climatic trends over periods of decades. Heatwaves and flooding, however extreme, are short term weather events. They do no more to ‘prove’ global warming than heavy snowfall across the UK in January ‘disproves’ it.

Extreme events have always happened. What we’re concerned about are long term trends in climate, which might make these sorts of events more common. But we can’t wait around for these trends to play out over decades before concluding that we have observed ‘proof’: by then it will be far too late to mitigate any damage already caused. So what constitutes scientific proof?

In a paper in Area, Greg O’Hare reviewed the uncertainties in climate science, ranging from measurement errors in data collection to simplifications introduced into computer models. The world’s climate system is complex and our knowledge and ability to measure it is incomplete. Scientists can only draw interpretations about climate change from the available evidence, albeit using increasingly sophisticated techniques such as computer models. Linking observations with the process of climate change is, therefore, an uncertain business.

Scientific research is inherently uncertain (if we were sure, there would be no point to research). While scientists can do their best to quantify and reduce uncertainty, the level of uncertainty that we are willing to accept when making decisions is a question for policy makers and wider society.

“Pakistan floods: Climate change experts say global warming could be the cause”, The Daily Telegraph, 10th August 2010.

O’Hare, G. (2000) “Reviewing the uncertainties in climate change science.” Area 32 (4): 357-368

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