Many scientists have determined that in order to avoid the risks brought about by climate change, steps must be taken to prevent the mean global temperature from rising by more than 2°C above pre-industrial levels. Current climate models indicate that achieving this goal will require limiting atmospheric carbon dioxide (CO₂) concentrations to less than 450 parts per million (ppm), a level that implies substantial reductions in emissions from burning fossil fuels.

The present atmospheric level of CO₂ is approximately 385 ppm, some 100 ppm above the pre-industrial level of about 280 ppm. It is expected to rise in future years.

"So far, efforts to curb emissions through regulation and international agreement haven't worked," Hoffert writes. "Emissions are rising faster than ever, and programs to scale up 'carbon neutral' energy sources are moving slowly at best."

Hoffert points to a pair of factors that show why current energy technologies are not sufficient to reduce carbon emissions to a level advocated by scientists.

One, alternative energy sources, such as solar and wind electricity, are not adequate to achieve "massive market penetration," which requires utility-scale systems that can store intermittent supplies of power until they are needed.

While Denmark and Norway have developed methods for this type of storage, these aren't "widely feasible in the United States, and other approaches to store power are expensive and need substantial research and testing," Hoffert contends.

Two, reliance on carbon-emitting fuels is once again growing.

"As natural gas and oil approach peak production, coal production rises, and new coal-fired power plants are being built in China, India, and the United States," writes Hoffert, a professor emeritus in NYU's Department of Physics.

Hoffert offers an array of approaches that would bring about new technologies while at the same time reducing the world's reliance on fossil fuels.

"Broad investment will be crucial to enabling basic research findings to develop into applied commercial technologies," he writes. "Carbon taxes and ramped-up government research budgets could help spur investments. But developing carbon-neutral technologies also requires, at the very least, reversing perverse incentives, such as existing global subsidies to fossil fuels that are estimated to be 12 times higher than those to renewable energy."

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• IPCC Report on Climate Change - 2007