There's little chance you haven't heard it before: Traveling is sex with elderly woman videoone of the worst things that you can do for the environment.

You've perhaps also heard of carbon offsets -- modern-day indulgences that can ease your guilt and the strain of your travel on the environment.

Carbon offsets are programs that allow people to "offset" the carbon emissions they've created through some activity by paying money to reduce carbon output in another place or context. You, the polluter in this example, pay to "either pull carbon out of the atmosphere or prevent the release of carbon that would have otherwise gone into the atmosphere," said Ted Martens, vice president of marketing and sustainability at Natural Habitat Adventures, a carbon-neutral travel company.

"A carbon offset is equal to one tonne of greenhouse gas emissions reduced from a project or somewhere in the world," said Marisa de Belloy, CEO of Cool Effect, a nonprofit that aims to reduce carbon emissions.

While they all seek to reduce greenhouse gas emissions, there's no one-size-fits-all carbon offset. Martens explained that they do typically tend to fit into a few major categories: forestry, renewable energy, and energy efficiency projects.

Forestry projects plant trees, which absorb carbon dioxide to make oxygen. Renewable energy projects can be anything from putting solar panels on rooftops to converting waste into methane gas to be used for fuel.

Energy-efficiency projects cover a broader scope. An example is giving new cookstoves that don't use coal to people in developing countries, one of de Belloy's favorite ways to offset travels. Projects like these offer benefits beyond carbon emission reduction: Efficient cookstoves help families save money on fuel and provide health benefits since they don't fill the air with smoke.

If you're going to fly somewhere, carbon offsets are one of the few tools available to combat the carbon emissions that accompany air travel. "Carbon offsets are best and really should only be used for emissions that you really cannot avoid any other way," said de Belloy.

They're most effective if you think of them as a supplement to other ways that you try to reduce your carbon footprint. "Everybody should strive to reduce their carbon imprint in the first place," said Martens. This includes everyday changes like taking public transportation when you can, eating less meat, and carrying a reusable water bottle.

But if you need to fly across the country to visit your family, if you're getting sent on a business trip around the world, or if you just want to finally take that trip you've been planning since you were 15 years old, carbon offsets are an option to consider.

Still, they're not perfect. "There are a lot of criticisms of carbon offsetting in terms of, 'oh you’re just sort of paying to emit. You’re purchasing the right to go ahead and emit what you want,'" said Martens. Martens and de Belloy both warned that carbon offsets shouldn't be used as a band-aid, or an excuse to take as many flights as you want and disregard the consequences.

It's also important to do your research. "The biggest con to carbon offsets is that there is a crazy market out there for people who are selling them in an unscrupulous way and even some people who are running projects in an unscrupulous way," said Martens.

De Belloy explained that it's best to find a carbon offset that is truly "additional," meaning that the project is something that wouldn't have been completed otherwise. For example, she said, "if someone’s running a profitable business managing a forest, and they say 'oh, I’d like to get some extra revenue, maybe I’ll sell carbon offsets,' that’s not additional because they’re doing what they’re doing anyway."

Nonprofits like Cool Effect and companies like Natural Habitat Adventures carefully vet the carbon offsets that they offer so that you don't have to worry about buying offsets from a potentially shady source. Natural Habitat Adventures offsets any trip that you book with them, while at Cool Effect, you can calculate the carbon your trip is emitting and buy an equivalent offset.

At Cool Effect, you can choose to donate across all projects or donate to specific projects that hit close to home for you through their project page. These projects include preserving bird sanctuaries, community tree building, and protecting grasslands.

If you book a trip through Natural Habitat Adventures, they will automatically offset the carbon footprint of your trip across their three projects: wind power, forest protection, and efficient cook stoves.

"I feel very strongly that the benefits that come from broadening our minds, from cross cultural understanding—the positive impacts of that are so much greater than the carbon impacts that come from the travel to and from," said Martens. "My goal is not to get people to travel less. Carbon offsetting allows us to have a tool that we can use to mitigate those unavoidable impacts."