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.
Previous estimates of the impact of all this travel on carbon suggested that tourism accounted for 2.5-3% of emissions.
However in what is claimed to be the most comprehensive assessment to date, this new study examines the global carbon flows between 160 countries between 2009 and 2013. It shows that the total is closer to 8% of the global figure.
As well as air travel, the authors say they have included an analysis of the energy needed to support the tourism system, including all the food, beverage, infrastructure construction and maintenance as well as the retail services that tourists enjoy.
"It definitely is eye opening," Dr Arunima Malik from the University of Sydney, who's the lead author of the study, told BBC News.
"We looked at really detailed information about tourism expenditure, including consumables such as food from eating out and souvenirs. We looked at the trade between different countries and also at greenhouse gas emissions data to come up with a comprehensive figure for the global carbon footprint for tourism."
The researchers also looked at the impacts in both the countries where tourists came from and where they travelled. They found that the most important element was relatively well off people from affluent countries travelling to other well to do destinations.
In the leading countries, US, China, Germany and India, much of the travel was domestic.
Travellers from Canada, Switzerland, the Netherlands and Denmark exert a much higher carbon footprint elsewhere than in their own countries.
When richer people travel they tend to spend more on higher carbon transportation, food and pursuits says Dr Malik.
"If you have visitors from high income countries then they typically spend heavily on air travel, on shopping and hospitality where they go to. But if the travellers are from low income countries then they spend more on public transport and unprocessed food, the spending patterns are different for the different economies they come from."
When measuring per capita emissions, small island destinations such as the Maldives, Cyprus and the Seychelles emerge as the leading lights. In these countries tourism is responsible for up to 80% of their annual emissions.
"The small island states are in a difficult position because we like travelling to these locations and those small island states very much rely on tourist income but they are also at the same time vulnerable to the effects of rising seas and climate change," said Dr Malik.
Demand for international tourism is also being seen in emerging countries like Brazil, India, China and Mexico, highlighting a fundamental problem - wealth.
The report underlines the fact that when people earn more than $40,000 per annum, their carbon footprint from tourism increase 13% for every 10% rise in income. The consumption of tourism does "not appear to satiate as incomes grow," the report says.
The World Travel and Tourism Council (WTTC) has welcomed the research but doesn't accept that the industry's efforts to cut carbon have been a flop.
"It would be unfair to say that the industry is not doing anything," said Rochelle Turner, director of research at WTTC.
"We've seen a growing number of hotels, airports and tour operators that have all become carbon neutral so there is a momentum."
Experts say that offsetting, where tourists spend money on planting trees to mitigate their carbon footprint will have to increase, despite reservations about its effectiveness.
Awareness is also the key. The WTTC say that the recent water crisis in Cape Town has also helped people recognise that changes in climate can impact resources like water.
"There is a real need for people to recognise what their impact is in a destination," said Rochelle Turner, "and how much water, waste and energy you should be using compared to the local population."
"All of this will empower tourists to make better decisions and only through those better decisions that we'll be able to tackle the issue of climate change."
The study is published in the journal Nature Climate Change.