Californian city Long Beach decided this week to study the feasibility whether to sell credits to polluters as a way to maintain its 393,000 trees in parks and public spaces, writes The Press-Telegram.

Planting and maintaining forests in urban areas is one of four ways emitters can offset their greenhouse gas output, according to California's cap-and-trade regulations. Thus, the trees may one day be a source of income for the city.

The proposal was presented by Long Beach Councilwoman Gerrie Schipske who told Reuters Point Carbon that she wants the city to be an early player in California's burgeoning carbon offset market, and to take advantage of the revenue it can earn - especially in light of tight economic conditions.

Long Beach would follow in the footsteps of the beachfront city of Santa Monica in western Los Angeles if it registers its urban forest as a carbon offset project.

Santa Monica has listed a project in the Climate Action Reserve (CAR) - an offset registry that will become an accredited registry for California cap-and-trade program - that aims to add 1,000 trees to its urban forest.

Gary Gero, president of the CAR, said the registry has reached out to Long Beach officials to encourage it to convert its forest into an offset project. He said the credits could help fill "anticipated supply shortages in California cap-and-trade, especially in second phase."

"Tree planting programs have a wide range of benefits and offsets are just one part of that," Gero said, noting that they will help combat heat and air pollution, among other benefits.

"These are trees that are going to generate credits over their life so the payback is long term," he said.

Gero said other cities, in states such as Rhode Island and Maine, have expressed interest in registering urban forest offset projects under the CAR.