Pretty much everyone working on climate change wants certainty - they want certain science, and they want certainty around what the impacts are going to look like and how they are going to be experienced.

Unfortunately, at this stage, science can't provide the information and the answers planners want. We need, therefore, to work with scientific uncertainty for the foreseeable future.

The question that's rarely asked is: do we really need scientific certainty about climate change in order to respond to the threat? We already know enough to take concerted action to reduce greenhouse gas emissions dramatically, yet few people are changing their behaviour in a way that will avoid dangerous climate change.

We also know that people living in vulnerable situations will be affected first and worst by climate change. But does that fact have any real effect on the behaviour of those with the power to address the threat? Not really.

I doubt whether scientific certainty will ever make us alter our resource-consuming behaviour or the values that underpin the global economy. Unless the political and economic system of the world changes markedly, the economy will always be valued above the environment, and no science will change the equation.

Looking for scientific certainty around climate change is, in truth, a bit of a smoke-screen since it's often used as a most effective stalling mechanism.

Politicians love uncertainty because it means they need never take concerted action. The argument is we should wait for certainty before responding in a way that might damage their hallowed economy.

And, dare I say it, scientists also benefit from continued uncertainty. It means they have plenty of research to get on with and can apply for money to do it.

In short, uncertainty makes the world go round.

TO PLAN OR NOT TO PLAN

But we in the humanitarian sector don't like uncertainty. It means we can't plan effectively, and that can cost lives. We want to know where the next big calamity is going to occur so we can act efficiently, effectively and appropriately.

The problem is we live in an extremely uncertain world, and the only certainty we have is that we don't know what the future holds. For us, climate change adds yet another level of complexity.

I've started to think that perhaps we should give up trying to plan for the future and just let it unfold. It may sound rather Buddhist, but there's an argument for responding to crises as and when they occur rather than putting resources into planning which might mean we're less able to respond to the unexpected because we've already allocated our resources based on our view of an uncertain future.

Unfortunately, my view of dealing with crises is sometimes construed as laziness! My line manager isn't convinced by my argument that we should simply watch the world go by and respond if and when necessary.

So, I do need to plan, but how can I plan when I'm faced with such immense uncertainty around the impacts of climate change?

I first grappled with this issue when I was researching the links between climate change and security in the island states of the Southwest Pacific. I was trying to use the scenarios of the Intergovernmental Panel on Climate Change (IPCC) and link these to specific security outcomes.

The task proved impossible and I got in a complete mess! I couldn't use the scenarios in a meaningful way, because they contained too much uncertainty to make such an assessment worthwhile.

MILITARY APPROACH

So what to do? I decided to shut myself away in a small hut on an island in Fiji with lots of gin and some food, and resolved not to come out until I had found a solution to the problem of scientific uncertainty and climate change.

Just as I was running out of gin, I had an epiphany of sorts. I realised that one group of people deals with uncertainty day in day out, and copes with frightening efficacy: the military.

So I started to investigate uncertainty in the context of military planning. I filled in my inter-library loan requests and was bombarded with information on everything from air-borne weapon systems to guerrilla warfare - fascinating reading which actually got me in trouble with the Fijian and Australian authorities, but that's another story!

Imagine you were a military planner just about to go into battle. Would it be prudent planning to assume your enemy was armed only with sticks and stones? No, a good military planner would start from the point that the enemy had weapons of mass destruction and, importantly, the intent to deploy them.

Unless a military planner assumes the worst, they are likely to lose the battle.

I concluded that, to deal with climate change, you only have to use one scenario for all planning, and that's the worst-case scenario. If the worst occurs, you're prepared and if it doesn't, then great. It's what's known as win-win.

Although I wasn't the first to come up with this approach (Gwyn Prins suggested the use of worst-case analysis for climate change planning in his book "Top Guns and Toxic Whales"), I think it's a great way to deal with scientific uncertainty.

After all, with climate science, there's nearly always a worst-case scenario. And usually it's easy to understand because it's cataclysmic.

Of course, there will be those (especially the economists) who say it's too costly to plan for the worst. But my answer to them is that it'll be even more costly if we don't. If you're not convinced, you need only glance through the Stern Review on the Economics of Climate Change.

So I would argue we no longer need to worry about uncertain science when it comes to climate change. We should simply start from the worst-case scenario and take action accordingly - easy!

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