A new study says global tourism accounts for 8% of carbon emissions, around three times greater than previous estimates.
The new assessment is bigger because it includes emissions from travel, plus the full life-cycle of carbon in tourists' food, hotels and shopping.
Driving the increase are visitors from affluent countries who travel to other wealthy destinations.
The US tops the rankings followed by China, Germany and India.
Tourism is a huge and booming global industry worth over $7 trillion, and employs one in ten workers around the world. It's growing at around 4% per annum.