By Roberta Rampton

WASHINGTON (Reuters) - U.S. President Barack Obama on Wednesday embarked on a 10-day trip where he will stress the urgency of curbing climate change and try to achieve some final agreements with world leaders at a G20 meeting in China.

Obama, who is racing to cement his legacy on climate change before his presidency ends on Jan. 20, will showcase both progress and looming threats in stops at Lake Tahoe, Nevada; Honolulu; and an ocean refuge in the remote Midway Atoll.

On Saturday, he will discuss further steps on climate change with Chinese President Xi Jinping, who is hosting the G20 group of leading economies. The issue is part of the summit's agenda.

Obama and Xi worked together last year at a Paris conference to secure a global deal to cut carbon emissions and are expected to take the next steps soon to help bring the agreement into force.

At a Nevada summit on the health of Lake Tahoe, whose average surface temperature reached an all-time recorded high last year, Obama will talk about drought, wildfires and gains the United States has made in renewable energy. He will point to U.S. carbon emissions that are at their lowest level in almost two decades, the White House said.

"He has not backed off," Senate Democratic Leader Harry Reid of Nevada, who is hosting the summit, said in an interview. "He is somebody who has been unrelenting in recognizing that climate change is not a scientific hoax."

The administration set a goal to boost private and philanthropic investments for conservation to $10 billion per year. The number was about $230 million at the beginning of the Obama's first term and is estimated to hit at least $1 billion this year.

Green groups have cheered Obama but also are prodding him not to rest on his laurels. The Supreme Court put his plan to slash carbon emissions from power plants on hold earlier this year.

"We’re hoping that he will actually withdraw the Arctic from his five-year plan on offshore drilling, like he did with the Atlantic, because it’s an even worse place to drill," said marine biologist Jackie Savitz of the Oceana conservation group.

Later on Wednesday, Obama will speak with leaders of Pacific Island nations at risk from climate change, and a congress of conservation leaders in Honolulu.

Last week, he quadrupled the size of the Papahānaumokuākea Marine National Monument off the coast of Hawaii, banning commercial fishing and drilling from a huge area known for its coral reefs, sharks and seals.

He will venture deep into the monument on Thursday during a rare presidential stop at Midway Atoll, where climate advocates hope the pictures tell the story.

"Having the president standing in a place that could disappear would be a powerful message on climate change and ocean health," said Seth Horstmeyer, a director of Pew's Global Ocean Legacy project.

(Additional reporting by Timothy Gardner and David Morgan; Editing by Bill Trott and Lisa Von Ahn)