They are also where emissions are rising fastest.
Bleak as the picture is, he said: "The key thing is where emissions go.
Officials say much of the pollution comes from neighboring areas, where emissions standards are lower and environmental policies virtually nonexistent.
Grinding in the lowest gear is most of the rest of the world, where emissions are still rising.
These designs can also be used to mitigate impacts from other air pollution sources where emissions occur near ground-level.
Parties can also obtain offsets through the Clean Development Mechanism (CDM) for projects in developing countries, where emissions are not otherwise limited.
In California and New York, where emissions standards are high, some generators are only allowed to operate for about 200 hours a year.
The T&E report also found that motor manufacturers often sell less polluting models of the same cars in the US, where emissions rules are stricter.
Where emissions cannot be eliminated the company said it will invest in offsetting schemes as a last resort and would not pass this cost on to the passenger.
"The ecosystems are big players, but they're almost certainly not going to save the day and result in a situation where emissions cuts aren't necessary," Dr. Field said.
This knowledge gap has serious policy implications; until it becomes clear where emissions are going, it will remain difficult to have verifiable credits for sequestering carbon.
