At their annual summit last week, leaders of the Group of Eight (G8) industrialized nations pledged to try to keep the planet from warming by more than 2 °C above pre-industrial temperatures — an ambitious goal that has also been adopted by other countries including China, Brazil and South Africa (see page 313).

The absence of any commitment to reduce emissions before 2050 is less promising but — assuming that the G8 can be taken at its word — it shouldn't be a fatal defect. If warming is to stay within those two degrees, the global 'decarbonization' project must be tackled without delay anyway.

This will not be cheap or easy. When the two-degree ceiling is translated into a per-capita emissions limit, it is clear that the industrialized world, and particularly the United States, has already generated more than its fair share of greenhouse gases. By continuing to emit at these levels, these countries are taking up emissions allocations that developing nations need to use to grow. This creates a 'carbon debt' that must be repaid with technology and money, both of which will be necessary if poorer countries are to leapfrog the dirty development pioneered by the industrialized nations.

The only viable strategy is therefore a massive research-and-development drive for energy efficiency in the near term, coupled with a long-term move towards virtually carbon-free energy production by 2040 at the latest. Cap-and-trade regulations can play a part, but they are only the beginning. Smart urban planning, clean transport systems and lifestyle changes will also be important.

History teaches that great advances — such as agriculture, sanitation and mechanization — arrive in bursts. There is hope that, despite an agonizingly slow start, the energy revolution of the twenty-first century can still gain the required momentum. Avoiding long-term investment in high-emission technology will be more important than throwing around potentially unachievable emission-reduction numbers.

The G8 has set a point of reference for the UN climate-change conference in December. Global leaders must now put together a framework that allows — and requires — all nations to do their part.