(CNN) President Joe Biden wrapped up his multi-leg trip to Europe on Tuesday with a press conference after attending the United Nations climate summit in Glasgow, Scotland, telling reporters he's optimistic about the outcomes of the gathering even though "there's a reason for people to be worried."
"I'm worried if we don't continue to move forward and make the kind of progress we're now making, that ... we throw into jeopardy the prospect that we're going to be able to keep the temperature (from) rising above 1.5 degrees Celsius," the President said. "But I'm optimistic, because ... populations of each of our countries have a different perspective than they did at COP25."
"All of a sudden, people are seeing these things happening they never thought would happen," he added, also saying that he couldn't think of another two days that more had been accomplished in dealing with climate issues.
The President repeatedly dug into leaders who decided not to attend the summit, called COP26, in person. He said it "was a problem" for China, Russia and Saudi Arabia not to go, but added that the United States' attendance had "a profound impact on the way the rest of the world is looking at the United States and its leadership role."
"I think it's been a big mistake quite frankly for China," Biden said, adding, "The rest of the world is going to look to China and say, 'What value added are they providing?' And they've lost an ability to influence people around the world and all the people here at (COP26) -- the same way, I would argue, with regard to Russia."
He singled out China and Russia's absence at the summit, arguing that "it just is a gigantic issue. And they've walked away."
"How do you do that claim to be able to have any leadership now?" he asked.
"(T)he fact that China (is) trying to assert, understandably, a new role in the world as a world leader -- not showing up? Come on. The single most important thing has gotten the attention of the world is climate," Biden said.
Russian President Vladimir Putin "has serious, serious climate problems," Biden said. "And he is mum, on the willingness to do anything."
But when Biden was asked why members of Congress considering his climate priorities should get behind him, when countries such as China, Russia and India are not meeting their climate commitments or aren't even showing up, the President responded, "Because we want to be able to breathe and we want to be able to lead the world."
The President departs Scotland Tuesday evening and arrives back in Washington early Wednesday. He's spent five days in in Glasgow and Rome to attend the earlier Group of 20 meeting and the climate summit.
Biden spent much of his final day of his trip to Europe making the case for democracies to lead the way on fighting the climate crisis.
During a meeting on the margins of the summit regarding climate aspects of his Build Back Better World (B3W) initiative, the President argued that the collective effort by western nations to support infrastructure in the developing world is a chance to prove democracy can still deliver.
The B3W program was announced in June at the G7. It is meant to counter China's Belt and Road initiative.
"We offer a positive alternative to debt traps and corruption. We can hold entire countries back if we don't do that. Transparency is critically important. And by assisting and responding to the needs of developing countries, rather than dictating projects from afar, we can deliver the greatest impact for those who need it the most," Biden said. "We have to show -- and I think we will show -- that democracy is still the best way for delivering results."
Biden said there's an "urgent need for infrastructure development in countries ... that prioritizes the fight against climate change from the moment the spade goes into the ground and jumpstarts green, economic growth."
"By coming together to make a difference in the lives of people all around the world, you have to show -- and I think we will show -- that democracy is still the best way for delivering results," he added.
Earlier Tuesday, Biden launched a new plan to conserve forests worldwide that aims to bring together diplomatic, economic and policy tools to promote preservation of forests around the world.
The issue of keeping important ecosystems alive is an "indispensable piece of keeping our climate goals within reach," the President said.
Biden cited forests' ability to capture carbon and promote biodiversity as reasons to place attention on the issue, in addition to reducing emissions.
"We need to approach this issue with the same seriousness as decarbonizing our economies. That's what we're doing in the United States," Biden said.
The President also delivered brief remarks at an event to highlight the progress of the Global Methane Pledge and launched a new initiative to ratchet up methane reduction efforts, which he argued were the "most important things we can do" to keep global temperatures in check.
Around 100 countries have signed up to a global pledge to cut methane emissions by 30%, European Commission President Ursula von de Leyon announced on Tuesday.
Biden encouraged other countries to join the US in the efforts.
"This isn't just something we have to do to protect the environmental future. It's an enormous opportunity ... for all of us, all of our nations, to create jobs and make meaningful climate goals a core part of our global economic recovery as well," he said.
The Biden administration is proposing new rules from a number of federal agencies to slash methane emissions, which includes a regulation from the Environmental Protection Agency that would push oil and gas companies to more accurately detect, monitor and repair methane leaks from new and existing wells, pipelines and other equipment.
During a speech at an event aimed at "Accelerating Clean Technology Innovation and Deployment", the President announced the First Movers Coalition. Biden said the federal government will work with the coalition, which includes more than two dozen of the world's largest companies across eight different sectors "that comprise 30% of the global emissions we now are dealing with."
"These companies will be critical partners in pushing for commercially viable alternatives to decarbonize the industrial cities, industrial sectors and more. And while championing the US innovation of good paying jobs, at the same time, the US government is going to use our enormous market power, as the world's largest buyer of goods and services ... to do the same," he said.
The goal of the coalition is to spur better products into the market, new companies and new projects.
He said the US was also launching a new partnership with the United Arab Emirates called the Agricultural Innovation Mission for Climate. Along with 75 partners, the mission aims to "catalyze public and private investment in climate-supported agriculture and food system innovation."
On Tuesday afternoon, Biden spoke briefly with Japanese Prime Minister Fumio Kishida. Biden "reinforced the (importance) of the U.S.-Japan alliance and discussed regional and global issues," the White House said. The President also met with Prince Charles to discuss "the importance of global cooperation in tackling climate change."
"They underlined the need for ambitious commitments and concrete actions among partners worldwide and discussed Prince Charles' initiatives to engage the private sector on sustainability," a senior administration official said.