It’s been a good month for climate-sceptics. Following the failure of the Copenhagen summit to deliver a global treaty, they have revelled in the discomfiture of the Intergovernmental Panel on Climate Change as it admitted it was wrong to say that the Himalayan glaciers could disappear by 2035.  Critics have seized on this admission, using it to call the entire credibility of the IPCC and the science of climate change into question. 

There is a lesson in this for those who think global warming is worth worrying about. And counter-intuitively perhaps, I would suggest that the lesson is not to try to prove global warming is a fact and simply show that it is a significant risk – because that should be cause enough for action.

Over the past decade, those who question climate change have cleverly made the issue one of proof. They have portrayed the case for action as if it were a complex mathematical equation requiring a clear ‘QED’, with the implication that if any part of the equation is flawed, then the whole construct falls apart. This is a classic political tactic. The easiest way to undermine an argument is to pick holes in it rather than challenge its overall direction.

The UK’s Daily Telegraph for example says “The case that global warming is man-made needs to be constantly tested” - as if something might come along at any moment that would utterly destroy that case. Once the debate is set up in this way, the case for action can be infected by a flaw in any part of it.

But this approach is a poor basis for public policy. If governments waited until a security threat was proven before investing in armed forces, for example, they would rightly be pilloried as irresponsible. In defence matters, as in protecting against pandemics, hackers and other threats, they take action on the basis of risk rather than proof.

Climate change should be no different. It should be an issue where we do not wait for proof but act on the basis of risk. We should be comfortable with the fact that certainty in science is rare. As the IPCC reports show, while the warming itself is ‘unequivocal’, most observations about climate change are not 100% certain and all projections of future impacts are risks rather than sure-fire bets. But for many of us they are big enough risks to worry about: the principle of risk-based decision-making being to examine both the scale of the risk – how bad will things be if the risk becomes reality - and the degree of likelihood that it will come to pass.

If someone tells you that the plane you’re about to fly in has a 99% chance of crashing, you won’t get on it. If you are then told that as a result of data errors the chance is in fact only 5%, do you get on board? I suspect you’ll still take the train – even if there is a 65% chance it will arrive 10 minutes late.  You weigh the scale and the odds.

A risk based approach is the right one for climate change and those who believe we have a real problem to confront therefore need to recast the debate as a balancing of risk rather than a quest for certainty.  That changes the terms of engagement. The big picture starts to matter more than this or that disputed statistic.
 
And the big picture starts with the fact that in the last 200 years – or the last one thousandth of human history -  the relationship between humanity and nature has changed irrevocably. The population has increased seven fold. Fossil fuels that took millions of years to form have been burned in massive quantities. Forests that took centuries to grow have been destroyed in a few decades. And carbon dioxide levels have reached the highest levels for half a billion years.

We then need to consider that eleven of the last 12 years have been the hottest on record; Arctic ice is melting at an unprecedented rate; villages are being flooded in Bangladesh; drought is afflicting east Africa; monsoons are failing in India.  And, by the way, glaciers are still melting at historically high rates, as the World Glacier Monitoring Service has just reported.   

Thousands of scientists say these two series of events are probably connected and if no action is taken then the impacts will worsen in the lifetimes of people alive today and become devastating in those of future generations. Call me naïve, but on that basis I am prepared to believe there is a prima facie case for doing something. You can see that as intellectually lazy; or you can see it as a commonsense response to a widely documented risk.

Framed this way, the debate also highlights the risk of inaction and challenges the climate sceptics. Instead of sitting back and rejoicing at ‘Glaciergate’, they need to put up their own peer-reviewed case to demonstrate global warming is not a risk. It’s not enough to chip away at it so it ceases to be a 100% bullet-proof certainty. Given its scale, they have to show that it isn’t even a 20% or 10% risk.  Do you happily play Russian roulette because you only have a 16.6% risk of blowing your brains out?

And what if the consensus turns out to be wrong? What if the scientific academies and governments of the leading economies have had the wool pulled over their eyes? What if climate change has all been cracked up in a mass conspiracy by researchers looking for grants?

Will it have been a waste of time to invest in using energy more efficiently? Will it have been a waste of effort to switch to renewable energy? These measures have an intrinsic logic to them beyond reducing emissions. Energy efficiency saves money and conserves resources while low-carbon energy provides the alternatives that will be needed when shrinking reserves of non-renewable fossil fuels become too expensive to extract.  We need to do this stuff anyway.

Post-Copenhagen, advocates of action on climate change need to set out the bigger picture and present climate change it for what it is – a massive global risk. The issue should cease to be one of proof, which is a pedant’s paradise, and become one of risk and judgement, in which wisdom prevails.

David Vigar authored Tomorrow’s Company’s report on global warming and business, Tomorrow’s Climate: Beyond Peak Carbon. It is available at forceforgood.com here.