Teen climate activist Greta Thunberg arrived in New York this week after completing an emissions-free voyage by boat across the Atlantic. She traveled to take part in a United Nations climate summit, and to draw attention to the amount of carbon travelers emit when they hop on a plane. Estimates vary, but plane travel represents a significant portion of carbon emissions each year. So what do you do if you can’t set sail like Thunberg? One option is carbon offsets. “A carbon offset is really just a purchasable greenhouse gas emissions reduction,” said Maggie Lund, a manager with Center for Research Solutions Green-e certification program. “So as a consumer, you can go out and buy a carbon offset to negate your carbon emissions.” Lund said that could look like paying $5 to $7 to help block deforestation after a flight across the country. Your flight emitted a lot of carbon, but your offset saved trees that will continue to suck carbon from the air into perpetuity. “One of the core principals of carbon offsetting is that without the revenue from the carbon offset or the carbon credit, the emissions reduction would have never happened,” Lund said. “So your investment as a consumer into that carbon offset is driving the emissions reduction to happen in the first place.”