Electricity accounts for more than 40 % of global energy-related CO2 emissions. This issue is most pressing for developing countries where growth in power demand is particularly high, fueling the risk of irreversible investment in CO2-intensive capacity, the so-called “carbon lock-in”.

Sectoral Approaches in Electricity – Building Bridges to a Safe Climate shows how the international climate policy framework could effectively support a transition towards low-CO2 electricity systems in developing countries. Sectoral approaches are intended to address sectors that require urgent actions, without waiting for countries to take nation-wide commitments.

Construction crews last week prepared a concrete slab to serve as a staging area for the replacement of Limerick's six huge transformers, a $90 million job that will take about two years to complete.

The improvements to the transformers, which convert electricity for transmission on big power lines, are only one component of a complicated effort to "uprate" the plant's output, adding 170 megawatts of generating capacity to each unit. Along with earlier upgrades, the improvements will expand Limerick's total capacity to 2,600 megawatts - 23 percent more power than it produced when the two units were completed in 1989.

Many politicians are supportive, not least Barack Obama, the US president, who in October promised $3.4bn in grants to pay for smart grid equipment.

However, an investment on that scale does no more than lay the foundations: a full smart grid for the US will require an investment that is orders of magnitude greater. The commercial and regulatory framework to deliver that investment has not yet been developed.

It's no small matter. In fact, Chu says that turning all the world's roofs white would eliminate as much greenhouse gas emissions in 20 years as the whole world produces in a year. But some critics point out that in northern cities, the gain in summer could be outweighed by the loss in winter. The ideal situation, then, would be to get the advantage of white roofs when it's hot and black roofs when it's cold.

Now, there may be a way to have both. A team of recent MIT graduates has developed roof tiles that change color based on the temperature. The tiles become white when it's hot, allowing them to reflect away most of the sun's heat. When it's cold they turn black and absorb heat just when it's needed.