From Toronto to Minneapolis, Chicago to Omaha many places in North America are seeing a surge in summer heat well into fall. But one of the drivers is a weather phenomenon occurring thousands of miles away, in the Pacific Ocean.

A marine heat wave, stretching from the coast of Japan to North America, is contributing to higher temperatures—and is expected to have a crucial impact on winter forecasts.

Here’s what to know.

What is a marine heat wave and does climate change impact it?

Marine heat waves occur when sea surface temperatures exceed 90% of typical regional temperatures, the equivalent of an increase of about one to three degrees Celsius. “That doesn't sound like a lot when you're over land, but when you're over water, it makes a big difference,” says Paul Pastelok, senior mete

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