GLASGOW, Britain - World leaders on Monday called for concrete actions to tackle the challenges of climate change at the 26th United Nations Conference of Parties on Climate Change (COP26).

"This COP must be a moment of solidarity. The $100 billion a year climate finance commitment in support of developing countries must become a 100 billion dollars climate finance reality," UN Secretary-General Antonio Guterres said in his speech at the World Leaders Summit at COP26.

"This is critical to restoring trust and credibility," he said.

In 2009, developed countries, who built their wealth by burning fossil fuels and have contributed most to the climate crisis, pledged 100 billion dollars a year to help lower-income nations by 2020. However, they still have not made good on the pledge. Recent reports indicate that this goal could slip to 2023.

Guterres added that beyond the 100 billion dollars, developing countries need "far greater resources" to fight COVID-19, build resilience and pursue sustainable development.

"Visions will come true only when we act on them," Chinese President Xi Jinping said in a written statement.

Parties need to honor their commitments, set realistic targets and visions, and do their best according to national conditions to deliver their climate action measures, Xi said.

British Prime Minister Boris Johnson, whose country hosts the two-week climate gathering, said, "while COP26 will not be the end of climate change, it can and it must mark the beginning of the end."

Admitting that developed nations' support for developing countries is "still falling short," US President Joe Biden said, "there's no more time to hang back or sit on the fence or argue amongst ourselves."

"This is the challenge of our collective lifetimes; the existential threat to human existence as we know it. And every day we delay, the cost of inaction increases," he said.

Seychellois President Wavel Ramkalawan said he is "scared" of the impact climate change will have on his country as "the beautiful archipelago of 115 islands may be reduced to less than 50 islands as the coral islands disappear."

COP26, delayed by a year due to the COVID-19 pandemic, kicked off on Sunday in Glasgow, Scotland. It is the first conference after the five-year review cycle under the Paris Agreement inked in 2015.