WASHINGTON — A new study says global warming is likely slowing the main Atlantic Ocean circulation, which has plunged to record weak levels. And this is pushing the Gulf Stream closer to the U.S. coast.

The ocean circulation slowdown has been predicted by climate models, but it’s now showing up in observations based on northern water temperatures. Researchers say it could make for more extreme weather across the northern hemisphere, especially Europe. They say it also could increase sea level rise along the U.S. East Coast.

Study co-author Stefan Rahmstorf says a complete shutdown of the ocean circulation — a crucial part of Earth’s climate — is a dangerous tipping point.

But other scientists are skeptical. One says it’s conceivable, but unsupported by data.

The study is in Wednesday’s journal Nature.