U.S. President Barack Obama said Sunday he was "optimistic" about sealing a global climate agreement at the upcoming two-week UN conference in Paris.

"What makes this gathering different is that more than 180 nations have already submitted plans to reduce the harmful emissions that help cause climate change," Obama said in a Facebook post as he traveled to the talks.

Negotiators in Paris, he said, will try to put in place "a long-term framework for further emissions reductions" that includes "targets set by each nation, but transparent enough to be verified by other nations."

The UN climate talks will officially start in Paris on Nov. 30, tasked with adopting a universal climate deal. More than 180 countries have submitted their action plans before the conference.

However, it is unclear whether these pledges are enough to prevent the temperature from rising above 2 degrees Celsius from the pre-industrial level.

Obama said the UN summit will also "work to mobilize support to help the most vulnerable countries expand clean energy and adapt to the effects of climate change we can no longer avoid."

Obama, who intends to cement his climate legacy, has acted mostly through executive power, including his push for emissions cuts from power plants.

Republicans, who controlled the U.S. Congress, however, denied the reality of climate change and claimed that Obama's climate policies may produce significant damage to the U.S. economy.

Such intense opposition surely sowed doubts on the world stage about whether the United States will honor its climate promises in the future.

Obama, who has just one year in office, rejected such claims.

"In fact, our businesses and workers have shown that it's possible to make progress towards a low-carbon future while creating new jobs and growing the economy," he wrote. "Our economic output is at all-time highs, but our greenhouse gas emissions are down towards 20-year lows."

Obama will only be attending on Nov. 30 and Dec. 1, the first and second day of the two-week events, during which he will have several bilateral meetings planned, including with Chinese President Xi Jinping and Indian Prime Minister Narendra Modi.

"I'm optimistic about what we can achieve -- because I've already seen America take incredible strides these past seven years," he said.

With the terror attacks on Paris two weeks ago, the U.S. president also said the UN climate summit is also an opportunity for the world to "stand as one and show that we will not be deterred from building a better future for our children."