We know that air travel is not the most eco-friendly way to get around. But a new study published in “Nature Climate Change” found that it’s even worse than scientists had known.

The study has found that global tourism is causing four times more greenhouse emissions than previously thought. It quantified tourism-related global carbon flows between 160 countries, and the results are startling.

“Between 2009 and 2013, tourism’s global carbon footprint has increased from 3.9 to 4.5 GtCO2e, four times more than previously estimated, accounting for about 8 percent of global greenhouse gas emissions,” the abstract of the study noted.

The disparity lies in previous estimates having not considered direct or indirect emissions to global tourism. Earther points out that, “Co-author Ya-Yen Sun of the University of Queensland told Earther via email, those estimates didn’t consider direct or indirect emissions from the supply chains that support tourism.”

Meaning, not just the means of travel itself, but the trinkets you’re buying, the meals you’re eating and the activities you’re doing all while on vacation. And U.S. travelers are by far the biggest perpetrators, having produced nearly a billion tons of CO2 in 2013, which is the largest contribution of a single country.

According to Pacific Standard, global tourism is a $1.2 trillion dollar industry — and not slowing down anytime soon. Which means tourism’s contribution to climate change will only keep growing along with it.

“The rapid increase in tourism demand is effectively outstripping the decarbonization of tourism-related technology,” the study states. “We project that, due to its high carbon intensity and continuing growth, tourism will constitute a growing part of the world’s greenhouse gas emissions.”

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