Concentrations of major greenhouse gases in the atmosphere continued to increase last year and during the first half of this year, and the Covid-19 pandemic did not slow the relentless advance of climate change, the World Meteorological Organization has said.

The WMO has warned that record levels of greenhouse concentrations now in the atmosphere are committing the planet to dangerous future warming, with spiralling impacts on economies and societies.

The United in Science 2021 report, published by a range of UN agencies and scientific partners just weeks before the COP26 climate summit, said climate change and its impacts were accelerating.

It warns that the average global temperature over the past five years was among the highest on record, estimated at 1.06 degrees Celsius to 1.26C above pre-industrial levels.

The 2015 Paris Agreement on climate change, struck at the COP21 summit, called for capping global warming at well below 2C above the pre-industrial level, and ideally closer to 1.5C.

The report also says there is now a 40% chance that temperatures will temporarily breach the threshold of 1.5C within the next five years.

Such temperatures are fuelling devastating extreme weather throughout the world, and billions of work hours have been lost through heat alone, according to the report.

It says the scale of recent changes across the climate system as a whole are unprecedented over many centuries to many thousands of years.

The report says that even with ambitious action to slow greenhouse gas emissions, sea levels will continue to rise and threaten low-lying islands and coastal populations throughout the world.

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United Nations General Secretary Antonio Guterres said the situation is alarming.

"This is a critical year for climate action," Mr Guterres said, saying the results were an "alarming appraisal of just how far off course we are".

"This year has seen fossil fuel emissions bounce back, greenhouse gas concentrations continuing to rise and severe human-enhanced weather events that have affected health, lives and livelihoods on every continent," he said.

"Unless there are immediate, rapid and large-scale reductions in greenhouse gas emissions, limiting warming to 1.5C will be impossible, with catastrophic consequences for people and the planet on which we depend."

The United in Science 2021 report presents the latest scientific data and findings related to climate change.

"Throughout the pandemic we have heard that we must build back better to set humanity on a more sustainable path and to avoid the worst impacts of climate change on society and economies," said WMO Secretary-General Petteri Taalas.

"This report shows that so far in 2021 we are not going in the right direction," he said.