This article on "Think Progress" highlights an interesting and encouraging trend. Aspen, famous as a ski destination, is the third city (after Burlington, Vermont and Greensburg, Kansas) to be able to supply all its electricity needs from renewable sources: a mixture of wind, hydroelectric, solar and geothermal.

Admittedly, Aspen is small: its permanent population is only 7,000, although with many more during peak tourist times, but it is nevertheless good news that one more place has eliminated a major source of atmospheric carbon.I am sure, however, that the residents of Aspen are still driving their fossil-fuel-driven cars, pick-up trucks and SUVs, so there is still much to be done to save the planet.

Greensburg is even smaller than Aspen, but Burlington is larger, having a population of around 45,000. To make a real difference, however, the same trend needs to be repeated in larger cities, and in more countries.

As the article describes, the move to renewable energy was made possible be the dramatic reduction in the cost of renewable energy, a drop that seems set to continue.

Of course, what would actually make much more difference to US carbon emissions would be an increase in the prices of petrol (gasoline) and diesel to the levels that Europeans pay, and the widespread introduction of energy efficiency in homes and businesses (energy efficient household appliances and air-conditioning, plus insulation against both heat and cold). Currently the USA comes pretty high in the rankings of per capita carbon emissions by country, and one of the reasons is that fuel for vehicles is so cheap there.