"When cities try to figure out the amount of greenhouse gases they emit, they tend to undercount — and not just by a little.
The average error is nearly 20 percent, according to a study published Tuesday in the journal Nature Communications. The researchers suggested that if that error was consistent across all American cities, the resulting annual missed emissions would be nearly one-quarter higher than those of the entire state of California.
Nearly three-quarters of the carbon dioxide generated from fossil fuels comes from cities, the researchers said, and urban areas will continue to boom in coming years. Many cities around the world have set ambitious goals to lessen their burden to the planet, but there is not yet a consistent way for them to measure the amount of carbon dioxide or to gauge any reductions. The new research shows that voluntary efforts by cities to measure those emissions are inconsistent and flawed."