Danish physicist Neils Bohr, who knew a lot about uncertainty, said: "Prediction is very difficult, especially about the future." But to take the timely action needed to give the UK a clean, secure and sustainable energy system and avert the worst impacts of climate change, that's exactly what you have to do.
Chris Huhne, the energy and climate change secretary, on Thursday made two big predictions. First, that gas prices will not fall over the next decade or so and, second, that a government guarantee can persuade millions of homeowners to open our doors to workers and refit our appallingly inefficient homes.
The two are connected but let's look first at energy prices: their soaring trajectory has made all politicians sweat. Nothing in the complex interaction of energy, climate and the economy hits voters harder or more obviously than their gas and electricity bills.
Huhne says when you balance the cost of all the government's energy and environmental policies against the savings some deliver, the average bill will be 7% lower (£94) in 2020, than if nothing was done and homeowners took their chances on international fossil fuel prices.
That is based on Decc's "central" forecast for 2020, with wholesale gas at 68p/therm and oil at $118 a barrel. Today, the prices are about 65p/therm and $107 a barrel. In a world with a fast-growing population and increasing pollution taxes on carbon, what do you think will happen to the price of the limited amounts of gas and oil? Most think people they are going up, and I agree.
Shale gas, I hear some of you cry. Take a look at the International Energy Agency's most recent report: it predicts only 20% of all gas will come from fracking by 2035. Handy, but it's no gamechanger.
Huhne set out the costs and benefits of the government's policy in detail and it shows just how ludicrously misinformed the debate on energy costs has been.
The cost of all support for renewable energy passed on the energy customers is currently £20 and (1.5%) will be £54 (4%) in 2020. Not hundreds, not thousands, but £54. The sum of all the fuel poverty and environmental measures in 2020 will be £280, Decc predicts, but the savings will be £373.
About £53 of that saving is ascribed to the Green deal, the government's scheme to increase the energy efficiency of the nation's ageing and leaky homes, for which full details were released today. It is ambitious and absolutely necessary, and solves the problem of people not having the cash available to invest in efficiency measures. It does this by creating loans for which the repayments are smaller than the savings the measures deliver on energy bills.
But the crux is take-up. Scheme after scheme has shown before that often you literally can't give insulation away. Decc reckons that is because people are worried about letting cowboy builders into their homes and will therefore accredit Green deal providers. That fear is a real one, but will a government stamp on a scheme run through widely mistrusted energy companies solve the problem?
Huhne seems to have ruled out an advertising campaign, with the consultation document lamely stating: "Advertising campaigns have struggled to raise awareness effectively." But the decision is more to do with government spending cuts than anything else.
Another obvious factor in driving take-up is incentives but there's just one on offer so far: up to £150 cash back at the start, which is then dumped on your loan. Other incentives will be be crucial, such as cuts in council tax, stamp duty or other related taxes. Those lie in the gift of the Chancellor George Osborne, which is a worry.
There are other concerns over the Green deal, including the lack of any target for the policy, its ability to help the one in six people living in fuel poverty and whether the interest rates charged will be too high.
The Decc minister Greg Barker has often stated the "ambition" to treat 14m homes by 2020, though that has slipped to recent weeks to the "early 2020s". The government dismisses "top down" targets as a discredited legacy of Labour, but without them how do you ensure energy bills and carbon emissions are kept in check?
On fuel poverty, about a quarter of a new £1.3bn-a-year levy dubbed Eco will be devoted to helping fuel poor homes. But that less than was being spent before, and fuel poverty is rising. The rest of the Eco will supplement Green deal loans for those homes that are more expensive to upgrade - mainly those needing solid-wall insulation. But there is nothing in place to prevent that money, paid by all customers, being concentrated on the homes of the rich, which has led to accusations of regressiveness.
On interest rates, the pooling of Green deal loans, as proposed by those behind the Green Deal Finance Company idea, would lower rates and make the loans more attractive. But where's the seed money for the GDFC going to come from? Not Decc.
So much for the details. The big picture is a positive one. In the face of uncertainty, Huhne has weighed the risks and taken decisions, as he was elected to do. On the future cost of energy, his core decision to get the UK off the fossil fuel hook is the only smart one.
I am less convinced that a goverment guarantee is the missing spark that will ignite the much-needed transformation in the UK's energy efficiency and relying on Osborne to sweeten the Green deal makes me sweat.
But the potential prize for taking on the uncertainty and acting is great: warm homes, stable utility bills, greater energy security and tackling global warming. Doing nothing, leading to volatile bills, erratic energy supply and chaotic climate, is by far the more uncertain option.