Generals must give us their exit strategy for climate change

It's not unreasonable for us to ask how today's sacrifices will meet tomorrow's climate change goals, says Myles Allen

Myles Allen
guardian.co.uk, Wednesday 29 April 2009 18.02 BST

Like many of us in these cash-strapped times, I lead a double life, fitting the job of a climate physics lecturer around the implacable 3pm primary school pick-up time. I get a range of reactions at the school gates when other parents find out that I work on climate change. Some mention how much effort they put into recycling or ask whether it really is as bad as the papers make out. Others quietly change the subject when it looks as if our work on flood risk might affect house prices.
Like all scientists, most of what I do is arcane and technical and of very little interest to outsiders. For once, however, I'm involved in a couple of studies (published today in Nature), that my fellow parents might just find interesting. The headline result of both papers is that the risk of dangerous climate change is primarily determined by the total amount of carbon dioxide that we, the human race, release into the atmosphere over all time, not by emissions in any particular year.
For example, releasing a total of a trillion tonnes of carbon causes a most likely warming of around 2C, which many scientists and governments regard as a threshold above which the risks rise steeply. A most likely warming of 2C means, of course, a substantial risk of warming higher still. Keeping the risk of warming over 2C to odds of less than one in four makes the job even harder. It cuts the total "cumulative budget" that we can get away with releasing to under three-quarters of a trillion tonnes.
Given that we have released over half a trillion tonnes already since 1750, we are left with a budget in the region of half-as-much-again to the-same-again. On current trends we'll use that up in only 20-40 years. Emissions are clearly going to have to start going down soon.
So is this just another climate doom-story to make the parents at the school gate feel even more worried and guilty? Worry and guilt comes naturally to green-minded parents. Listening to environmentalists, it's easy to get the feeling that climate change is primarily their fault, and that it's up to them to solve it.
It is they who are left struggling to find the right size of low-energy lightbulbs in Homebase; turning down the central heating; finding an electricity supplier who is 30% renewable; nagging the kids about turning the television off at the wall. And now, to cap it all, they have to worry sending the kids to school on the bus is exposing them to swine flu.
As the cannon fodder in the forthcoming battle to curb climate change, my fellow parents are entitled to know their generals' strategy. Heroic efforts to reduce your family's carbon footprint will reduce your contribution to the current rate of emission of carbon dioxide. But what our research papers coming out today show is that emitting carbon dioxide slower will not prevent dangerous climate change unless it is a means to an end of phasing out carbon dioxide emissions altogether.
So the question I'd like to see posed to our politicians, speaking now not as a scientist but from the primary school gates, is: "What do you plan to do with trillionth tonne?" (And, of course, every tonne thereafter.)
There are only three options: we release it into the atmosphere, in which case we are committing, most likely, to dangerous climate change greater than 2C; we set up an emission control regime so stringent that no one, anywhere in the world, will dream of digging it up and burning it; or we accept it is going to get burnt and prevent it getting into the atmosphere. None are palatable options.
There are promising signs though. The UK Committee on Climate Change acknowledged the need for a cumulative budget in their report last year, and politicians of all stripes are talking about carbon capture and storage. But the proposals are for pilot plants, "capture ready" plants (which seems to mean as much as HD-ready television), deployment over the next 20 years and so on.But we won't find out until try.
So, as your local environmental group urges you over the top to capture the next ridge in the fight against climate change, it is neither defeatist nor disloyal to ask, "what is the exit strategy?" How will the sacrifices we will have to make today achieve what must at the very minimum be our long-term goal – to save the trillionth tonne?
Dr Myles Allen is generally known as Colette, John and Jim's Dad. He is also a university lecturer in the department of physics, University of Oxford