(AFP) - 2021 must be the year of action for protecting people against the "disastrous" effects of climate change, the United Nations said on Monday ahead of a crucial US-convened summit.

Time is fast running out to tackle the climate crisis, the UN warned, with the Covid-19 pandemic having failed to put the brakes on "relentless" climate change.

The call comes alongside a major report ahead of US President Joe Biden's climate summit beginning Thursday.

Forty world leaders have been invited to attend Biden's virtual talks aimed at galvanising efforts by the major economies to tackle the climate crisis.

"We are on the verge of the abyss," UN Secretary-General Antonio Guterres told a press conference as he unveiled the State of the Global Climate 2020 report by the UN's World Meteorological Organization (WMO).

"This is truly a pivotal year for humanity's future. And this report shows we have no time to waste, climate disruption is here," Guterres said, as he urged countries to "end our war on nature."

The report described 2020 as one of the hottest years on record, while greenhouse gas concentrations increased despite the pandemic-related economic slowdown.

Last year featured "extreme weather and climate disruption, fuelled by anthropogenic climate change, affecting lives, destroying livelihoods and forcing many millions from their homes," Guterres said.

"This is the year for action. Countries need to commit to net zero emissions by 2050," the UN chief said. "They need to act now to protect people against the disastrous effects of climate change."

- Stabilising the temperature -

The 2015 Paris Agreement on climate change calls for capping global warming at well below two degrees Celsius above the pre-industrial level, while countries will pursue efforts to limit the increase to 1.5 C.

The WMO believes there is at least a one in five chance of the average global temperature temporarily exceeding the 1.5 C mark by 2024.

The Paris goals will figure prominently at Biden's summit, which young Swedish environmental activist Greta Thunberg sees as an opportunity to help "change our mindsets" to get more serious about climate change.

"As long as we are not actually treating the crisis like a crisis, of course we won't be able to achieve any major changes," Thunberg told a World Health Organization event.

The WMO's 56-page annual report documents indicators of the climate system, including increasing land and ocean temperatures, sea level rise, melting ice and extreme weather.

It also highlights impacts on socio-economic development, migration and displacement and food security.

WMO chief Petteri Taalas said: "All key climate indicators and impact information provided in this report show relentless, continuing climate change, an increasing occurrence and intensification of high-impact events and severe losses and damages affecting people, societies and economies."

Stabilising global mean temperature at 1.5 to 2 Celsius above pre-industrial levels by the end of this century "will require an ambitious reduction of greenhouse gas emissions, which must begin to occur during this decade."

Falling short is not an option, Taalas warned: "If we fail with climate mitigation, we will see dramatic impacts which would last for centuries."

- Hottest years -

The report said concentrations of the major greenhouse gases -- carbon dioxide, methane and nitrous oxide -- continued to increase despite the temporary reduction in emissions in 2020 related to the Covid-19 pandemic, which shredded economies.

Statistics showed that 2020 was one of the three warmest years on record. The past six years, including 2020, have been the six warmest on record.

Temperatures reached 38 C at Verkhoyansk in Russia on June 20, the highest recorded temperature north of the Arctic Circle.

The report said sea-level rise was accelerating, while ocean heat storage and acidification is increasing, diminishing the ocean's capacity to moderate climate change.

During 2020, the unprecedented number of 30 named Atlantic storms led to at least 400 fatalities and cost $41 billion in damages.

Extreme heatwaves, severe droughts and wildfires also led to tens of billions of dollars in economic losses and many deaths.

Some 9.8 million displacements, largely due to hydrometeorological hazards and disasters, were recorded during the first half of 2020.

"This year is pivotal. At the United Nations climate conference, COP26, in November, we need to demonstrate that we are taking and planning bold action on mitigation and adaptation," said Guterres.

But the 71-year-old UN chief stressed that reaching bold emissions reduction targets would mean "radical changes" in financing as well as prioritizing efforts to help emerging regions like Africa and South Asia.

© Agence France-Presse