Offsets are more complex than just paying for new trees to be planted after summer. For many eco-minded travelers, it's easy to check the "offset my flight" button when buying a ticket. Almost every airline offers such a program along with a calculator that shows how a passenger can compensate for their flight. In the midst of heat waves and massive flooding, why not spend a few extra dollars to help reduce greenhouse gas emissions? 

However, many of these carbon offset programs are not what they seem. According to one recent study published in Science , offset projects have not reduced deforestation, and projects that have seen some reductions are not as effective as claimed. Julia Jones, professor of conservation science at Bangor University, says the results are not good news because saving carbon-sequestering forests is critical to keeping warming below 2°C, or 3.6°F.

"It's really disturbing to find that these projects have been less effective than claimed," she said. "However, this does not mean that they were not an effective tool, that these projects did not achieve anything. It means that more carbon credits were sold than delivered.

Carbon offsets are a bit more complicated than just spending a few extra dollars per flight and then assuming that your money is helping to protect trees in the Amazon. Determining the amount of carbon you have personally emitted and determining the equivalent amount of offsets needed to potentially offset those emissions is complex.  billing process , which usually may not be accurate. And there's a chance that the compensation you bought to protect the trees in the forest went somewhere where  these trees would still be preserved , so your offset doesn't really add much to the carbon you put into the atmosphere. (Emily Driehaus)