A group of states on the East Coast has been operating a cap-and-trade system for carbon emissions for years. But the compact made headlines this fall as some states weighed whether to join the effort.

Maybe, but even the ones that want to be environmentally friendly face energy challenges.

The transportation sector accounts for a third of all greenhouse gas emissions. One port is trying to eliminate emissions entirely within the coming decade.

The building materials are a major source of greenhouse gases.

The Carbon Removal Standards Initiative just launched in the U.S. this week.

The funding aims to cut the cost of cleaner manufacturing in industries like food, paper and chemicals.

Emissions from transportation, on the other hand, were up.

Another example of how hard it can be to recycle polymers.

Microsoft is paying $200 million to a company using crushed rock to absorb carbon, and the Frontier consortium is backing emerging technology.

A growing number of scientists and economists see a novel kind of credit as an important tool to help reverse global declines in biodiversity.