Over the past few years carbon offsets have become a popular tool for combating global warming, but recently ethical travel advocates have begun to question the practice. One prominent organization, UK-based responsibletravel.com, recently decided to stop selling carbon offsets to its customers. Carbon offsets or credits are most commonly purchased by travelers to help counteract the harmful emissions generated by travel, especially flying. However, Justin Francis, cofounder of responsibletravel.com, believes that carbon offsets are actually perpetuating environmentally unfriendly travel practices, rather than contributing to a solution.

Francis told The Independent that “Carbon offsetting is an ingenious way to avoid genuinely reducing your carbon emissions. It’s a very attractive idea—that you can go on living exactly as you did before when there’s a magic pill or medieval pardon out there that allows people to continue polluting.”

In theory, carbon credits can be an excellent asset in the fight to reduce harmful greenhouse gases. Take the Swiss company Myclimate, which focuses on sustainable emission reduction projects around the world, specifically in developing countries, with additional attention to improving the quality of life in local communities as well. Myclimate’s offset program is highly ranked by the ENDS Carbon Offsets Guide and is recommended by the Tufts Climate Initiative for its transparency and strict project standards. Yet even Myclimate does not view offsets as a panacea for irresponsible behavior. The company’s website urges consumers to purchase credits only for unavoidable emission producing activities, and to avoid and reduce polluting behavior whenever possible.

The carbon offset market has quickly grown into a multimillion dollar business that is criticized for more than being equivalent to a medieval pardoning system. There is tremendous concern about the effectiveness of projects funded by carbon credit dollars. Many companies lack stringent regulation of projects. In one high-profile case, the 2007 Academy Awards were declared carbon neutral after purchasing offsets from carbon offset company Terrapass. BusinessWeek later found that those carbon offset funds were allocated to projects that would have been completed anyway, such as a methane gas collection system installed in an Arkansas landfill. One of Tufts’ key criteria for recommending carbon offset companies is that projects must be ones that lack the funds for completion without carbon offset sales.

In addition, it can be difficult to accurately determine the amount of emissions reduced. For example, although many carbon credits fund tree-planting projects, there are several variables that contribute to how much carbon the new trees actually absorb. In an opinion piece in the Washington Times, policy analyst H. Sterling Burnett points out that trees that don’t live to be at least 100 years old never mature into net carbon absorbers.

Ultimately, although carbon offsets can contribute to funding valuable projects, they are not the easy fix for global warming that they are often made out to be. For carbon-conscious travelers, Dr. Harold Goodwin of the International Centre for Responsible Tourism offers simple advice: fly less and choose the most carbon friendly flights available whenever you do fly. Travelers can follow the link below to calculate which flights are the greenest: travelpledge.org/holiday-tips/flysmart/.