Best way to fight climate change? Plant a trillion trees

A study says the best way to fight global warming is to plant a trillion trees - maybe more.

Swiss scientists calculate that there's enough space to plant trees to cover 3.5 million square miles. That's roughly the size of the United States
The study says those new trees could suck up about as much carbon pollution as humans have spewed in the past 25 years.

Study author Thomas Crowther says this is the cheapest and best climate change solution. But trees are no substitute for cutting emission from burning oil, gas and coal.

The study is in Thursday's journal Science.