Coal is the dirtiest fossil fuel by far, producing more particulate air pollution and global warming gasses than any other, per unit of energy. But for some countries — even ones with the money and the motivation to go green — coal can be hard to quit.

Last month in Italy, members of the G7 — a consortium of industrialized democracies that includes Canada, France, Germany, Italy, Japan, the United Kingdom, the United States, and the European Union — agreed in a communiqué to “phase out existing unabated coal power generation” by 2035. Such a pledge, if followed through, is meaningful: The bloc is collectively responsible for one-fifth of global greenhouse gas emissions.

“This announcement is sending a very positive signal,” said Ryna Cui, research director for the Center for Global Sustainability at the University of Maryland. “Having a specific leadership signal from the G7 really can have an important influence.”

The word “unabated,” though, is doing some heavy lifting. It refers to carbon dioxide emissions that are not captured or somehow balanced out. Theoretically, a coal-fired power plant could continue running with a carbon capture and storage system in place or use an offsetting mechanism under this language, but the technology has yet to prove efficient and cost-effective at scale.

For some G7 countries, this is a light lift. In nations like Italy, Canada, and France, coal is clinging to single-digit percentage shares of their energy mixes. The UK’s last coal-fired power plant is scheduled to shut down this year. These countries will likely coast to zero coal well ahead of schedule.

For others, this is a massive burden. Japan’s 125 million residents get around 27 percent of their overall energy from coal, and the country depends on burning rocks for 31 percent of its electricity to power homes and businesses. Despite Japan’s high-tech reputation, its energy mix looks more like those of many middle- and lower-income countries. That’s why Japan’s journey away from coal offers a lesson (and a warning) for the rest of the world in the endeavor to limit climate change.

How Japan explains the bigger challenge of shifting the........

© Vox