The global carbon footprint of tourism is almost four times larger than previously thought — accounting for 8 percent of the world’s greenhouse gas emissions, according to a new analysis of data from 160 countries published in the journal Nature Climate Change. The industry’s biggest emissions contributors are transport, shopping, and food.

From 2009 to 2013, global tourism-related emissions increased from 3.9 to 4.5 billion tons of CO2 annually. The United States topped the list for travel emissions, largely due to domestic flights, followed by China, Germany, and India. In small island nations like the Maldives, Mauritius, Cyprus, and the Seychelles, tourism accounted for 30 to 80 percent of national annual emissions.

“Our analysis is a world-first look at the true cost of tourism – including consumables such as food from eating out and souvenirs – it’s a complete life-cycle assessment of global tourism, ensuring we don’t miss any impacts,” Arunima Malik, an environmental economist and co-author of the study, said in a statement.

Malik and her colleagues argue that the findings suggest tourism should be included or considered in international climate commitments, such as the Paris Agreement. They also suggest that nations looking to expand tourism to boost economic development need to consider the industry’s impact on their national emissions and climate targets.

“A pursuit of economic growth comes with a significant carbon burden, as tourism is significantly more carbon-intensive than other potential areas of economic development,” the study says. “This finding should be considered in future deliberations on national development strategies and policies.”