By SAM KEMMIS of NerdWallet

Travelers encountered many weather surprises this summer, from wildfires in Europe to knee-deep mud at Burning Man. Indeed, it was the hottest summer on record around the globe, according to the European Union's Copernicus Climate Change Service.

"The dog days of summer are not just barking, they are biting," said U.N. Secretary-General António Guterres in a prepared statement published Sept. 6. "Our planet has just endured a season of simmering __ the hottest summer on record. Climate breakdown has begun."

Shifting weather patterns are raising questions about where, when, how and whether tourists will travel.

For example, does it still make sense to visit Italy in July, despite high temperatures, large crowds and minimal air conditioning? Or should "peak" travel season move to the more hospitable autumn or spring months?

Tourism destinations are starting to take note __ and get worried __ about the toll climate change could take on this enormous industry.

HOT DESTINATIONS

Escaping to the Spanish coast for the summer used to sound like a dream. This year it turned into more of a nightmare for Mediterranean travelers. The coastal city of Valencia, Spain, saw temperatures reach 116 degrees Fahrenheit in August, a record high. That came amid Spain's limits on air conditioning use in public spaces, leaving tourists to sweat it out.

These trends are only likely to get worse, driving travelers away from hot beachside destinations in Europe, according to a July report from the European Commission's Joint Research Centre. Southern coastal regions such as Greece, Italy and Spain are expected to see a drop in tourism if temperatures continue to increase.

On the other hand, colder destinations in Northern Europe could actually see more vacationers. Denmark, France and the United Kingdom could receive more tourists because of higher temperatures, according to the report. Greenland, which is mostly covered with ice, is expecting to see far more tourists in the coming decades, with a new airport set to open in 2024.

Closer to home, many popular destinations have already been affected by rising temperatures. The namesake glaciers of Glacier National Park have lost an average of 40% of their size between 1966 and 2015, according to the National Park Service. Florida's coral reefs were bleaching and dying under the stress of record ocean temperatures this summer.

PEAK TRAVEL SEASONS

Summers are for vacations __ that's a truth so universally acknowledged as to be almost self-evident. Families travel while kids are out of school, and office workers flee to vacation in ideal weather.

Yet, as summers continue to warm, these vacations could give way to "shoulder season" alternatives in spring and autumn months. In other words, tourists could change when (rather than where) they visit.