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Greta Thunberg, the 16-year-old Swedish climate activist, will cross the Atlantic Ocean in mid-August on an open-cockpit racing yacht to attend a United Nations summit meeting on global warming.

“Good news! I’ll be joining the U.N. Climate Action Summit in New York,” Ms. Thunberg said Monday on Twitter. “I’ve been offered a ride on the 60ft racing boat Malizia II .”

The trip to New York is expected to take two weeks. Ms. Thunberg, who is taking the year off from school to campaign against climate change, also plans to attend the annual United Nations Framework Convention on Climate Change talks, to be held in December in Santiago, Chile.

She has called the two conferences “pretty much where our future will be decided” because nations will be pushed to further reduce emissions of the planet-warming gasses that come from burning fossil fuels. “We still have a window of time when things are in our own hands. But that window is closing fast. That is why I have decided to make this trip now,” Ms. Thunberg said in a statement Monday.