When world leaders gather for the annual United Nations General Assembly meetings in New York this week, they will do so amid myriad pressing challenges that range from climate change to the war clouds hovering over the Persian Gulf.

To overcome these challenges, the role of the UN must be strengthened, not weakened.

Take climate change for example. Global warming, sea level rise and carbon pollution have all worsened over the past few years, according to a science report released by the World Meteorological Organization on Sunday. Actually, the last five years have been the warmest on record, prompting UN Secretary-General Antonio Guterres to label climate change as "the defining issue of our time".

Yet despite this harsh reality, little, if any, progress has been made since 2009 when world leaders agreed in Copenhagen to limit the global temperature increase to well below 2 degrees Celsius above the preindustrial level, largely due to the lack of global coordination. The United States, the second-largest emitter of greenhouse gases in the world, still refuses to join the global efforts to fight climate change with its leader claiming it is a hoax.

US President Donald Trump, who has previously said the concept of global warming was created "to make US manufacturing noncompetitive", will reportedly skip the UN Climate Summit on Monday.

Thus it is not strange that the world is "losing the race" on climate change, as Guterres said.

Indeed, it is no exaggeration to say that the world is facing a now-or-never moment for action. The report by the World Meteorological Organization suggests global temperatures between 2015 and 2019 have already risen 1.1 C above preindustrial times, making the global warming target increasingly unattainable.

The UN General Assembly meetings offer a crucial platform and opportunity for the international community to discuss the major issues bearing on world peace and development. Hopefully, they will show that countries can set aside their differences to work together at such a critical juncture.

China on its part is committed to such a course. It firmly defends multilateralism and supports the United Nations, as Zhang Jun, China's ambassador to the UN, said. It is to be hoped that other countries will also step up to the plate and offer cause for optimism that the concerted action that is so imperative is forthcoming.

As the most representative and authoritative intergovernmental organization in the world, the UN must demonstrate it is what it was meant to be — a strong champion for peace and security, development and prosperity.