It's certainly easy enough to believe, because, well, tourists seem to be every-frickin'-where. And if people have been complaining about tourists practically since the French writer Stendahl coined the term in the early 19th century--in fact, I bet that the first time he uttered the word, he preceded it with "those damn . . ."--and if our complaints have only gotten more numerous and vociferous, then surely, surely that's because the industry has swallowed the world like no other. Right?
The claim also fits our collective perceptions of the modern, globalized world: borders are less meaningful, cultures blur into each other, the internet makes it easier than ever to learn about other countries (although much of this is probably limited to assorted YouTube videos) . . . and at any given moment, roughly half the population of the globe is in transit to visit the other half and gawk at their funny customs and bizarre ways of life.
But. Though it may seem entirely plausible, tourism is not, in fact, the world's largest industry, as Alan A. Lew, Professor of Geography & Planning at Northern Arizona University, explains on the blog Tourism Place:
Tourism actually ranks about 6th in international trade, after trade in fossil fuels, telecommunications and computer equipment, automotive products, and agriculture (based on World Trade Organization data). It is just slightly smaller than agriculture, and given the fuzziness of all numbers of this kind, tourism at best might be 5th, just ahead of agriculture.
Tourism is the world's largest Service Sector Industry, in terms of international trade, as all of the other industries listed above are merchandise product industries. . . .