The annual report [PDF], which tracks progress in heading off global warming before it reaches the generally agreed-upon 2°C global temperature rise threshold, analyzes efforts to transition to clean energy in several key areas: cleaning up coal plants, growing nuclear power and renewables, improving fuel economy, and increasing the efficiency of buildings.
According to Plumer, "Right now, however, only renewables are pulling their weight. The IEA says the main problem is that most countries don't have stable, reliable policies to promote these clean-energy technologies. They recommend the usual batch of solutions - a price on fossil fuels, new standards for energy efficiency, and more money for research and development."
"All told, the IEA estimates, meeting that 2°C target would require $5 trillion in energy investments between now and 2020. That, in turn, would save $4 trillion in fossil fuel costs. And, over the next 40 years, the benefits from energy savings and reduced emissions would keep growing and eventually outweigh the costs."