Nature 452, 503-504 (3 April 2008) | doi:10.1038/452503b; Published online 2 April 2008

Double vision


The need to transform the world's energy technology is even greater than many perceive.

How much energy, and of what sort, should we expect the world to be generating in the decades to come? This is a question of crucial importance to economics, development and the management of climate change. But as the Commentary on page 531 argues, it is not an easy question to answer (see also News on page 508).

In 2000, the Intergovernmental Panel on Climate Change introduced a range of 'emissions scenarios' that sought to estimate the amount of carbon emitted over the twenty-first century for a range of different assumptions. Climate modellers have since used a small subset of these scenarios as the basis for their analyses of possible climate change. But these scenarios are not without their controversies. One is their much-criticized approach to currency exchange rates, which some economists say overstates the impact of industrialization in developing countries. Another, it turns out, is not so much a problem with the scenarios themselves, but with the way some of them are seen as being 'business-as-usual' — in other words, what would happen if we do nothing differently.

That perception leads to an apparently straightforward measure of the climate-change problem for each scenario: take the anticipated carbon emissions and subtract an emissions profile designed to bring about a specific goal — say, a significant chance of keeping the increase in global average temperature at or below 2 °C. The result is the amount of carbon emissions that must be avoided to reach the goal. This figure, typically hundreds of billions of tonnes of carbon over the century, is then treated as the challenge that must be met by new energy technologies and efficiency drives.

But this approach brings with it a risk of double counting. The 'business-as-usual' scenarios actually assume that economies will somehow steadily increase their energy efficiency and decrease the amount of carbon they emit per unit of energy. The scenarios don't specify what technologies will be used to achieve these things, so unwary users could wrongly consider all reductions in either measure as progress over the status quo scenario. As a result, the amount of decarbonization required to achieve a stated goal is far larger than is often assumed.

The challenge is daunting enough without such misprision. An ever greater amount of world domestic product is coming from developing economies where the amount of energy used and carbon emitted per unit of economic activity is growing.

The history of the industrialized nations does suggest that there would, over time, be progress in energy technology and efficiency even without any threat of climate change. But global policy must now aim to increase this progress greatly, which means we have to accept that there are no meaningful 'business-as-usual' scenarios. The required progress requires new incentives, new research and, crucially, new costs imposed on the users of fossil fuels. It would also benefit from new economic models that, unlike the ones used with current scenarios, can show how the various policies aimed at replacing fossil fuels might work.

We also need to accept that the challenge of providing humanity with more energy in a minimally damaging way is even bigger than is usually thought. A simple calculation illustrates the point. If a growing population is to have access to the energy needed to drive development, then in 50 years the world's energy supply will need to at least double, even if energy use in tomorrow's great powers never rises to the per capita level seen in industrialized nations today, and if use in those nations is severely curtailed by efficiency improvements.

At the same time, if the world's climate is to be stabilized, carbon emissions from fossil fuels will have to be reduced dramatically in comparison with today's levels. To satisfy both those requirements, the amount of energy generated without the emission of fossil carbon needs to increase by something like a factor of ten.

That is the most daunting challenge humanity has ever sought to meet with a united front. The chances of success will be helped by models that allow different strategies to be compared. But no amount of scenario planning can replace the need for the will and leadership.