Protecting the environment is one of the defining issues of the 21st century, with the United Nations estimating that the global community has just five years left to cut emissions enough to avoid catastrophic climate change.

While it’s easy for environmentally-minded individuals to feel cynical or hopeless about the prospect of preventing climate change, many scientists argue that it’s important to remember that humans do have the ability to improve our planet’s health.

“Optimism gives us hope and audacity to go out and make change,” chemist Dick Co told Yale Climate Connections in 2022. “I don’t feel it helps me to look back at the last 100 years and go, ‘Well, we shouldn’t have done that.’ But now we know better about the impacts of that on climate, so we can do better.”

Municipalities across the globe are increasingly investing in green initiatives to ensure that cities will have long term sustainability. A recent report from the IESE Business School included environmental sustainability as one of the nine metrics to determine the overall vibrancy of more than 180 cities in the world.

The IESE report defined environmental sustainability as “development that meets the needs of the present without compromising the ability of future generations to meet their needs.” Among the indicators used to assess sustainability were the amount of green space per capita, carbon dioxide emissions, the percentage of the population with access to water, and the cities’ vulnerability to climate change.

While American cities performed well in most of IESE’s other categories, the United States lagged behind its European counterparts in the study’s sustainability rankings. Five American cities appeared in the top 20 of IESE’s overall most vibrant cities — but no American city appeared in the top 50 most sustainable cities. The greenest American cities in the IESE rankings was Austin, Texas in 79th place. Los Angeles — the second largest city in the U.S. — came in 158th place.

One factor that could be compounding this issue is the lack of reliable public transit in much of the U.S., another component of the IESE rankings. While New York City came in third place for transportation, most other American cities performed poorly in this metric.

Northern European cities dominated the top of the IESE rankings, though Vancouver, Canada did place in the top 10. Click through to see the five most sustainable cities in the world.