Atmospheric levels of the greenhouse gas carbon dioxide have reached another record high, a new report has revealed.

The last time the Earth experienced a comparable concentration of CO2 was between three million and five million years ago, according to experts from the World Meteorological Organisation.

Scientists claim this enduring trend towards greater levels of carbon dioxide in the atmosphere will lead to more severe climate change — from rising temperatures to extreme weather.

The globally-averaged carbon dioxide concentration reached 407.8 parts per million in 2018, up from the 405.5 parts per million in 2017.

This rise was similar in extent to the one observed from 2016–2017, and slightly above the average of the increases seen across the last decade.

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Atmospheric levels of the greenhouse gas carbon dioxide have reached another record high, experts from the World Meteorological Organisation are warning (stock image)

The alarming findings were published in the World Meteorological Organisation (WMO)'s Greenhouse Gas Bulletin.

'There is no sign of a slowdown, let alone a decline, in greenhouse gases concentration in the atmosphere despite all the commitments under the Paris Agreement on Climate Change,' said WMO Secretary-General Petteri Taalas.

'We need to translate the commitments into action and increase the level of ambition for the sake of the future welfare of the mankind.

'It is worth recalling that the last time the Earth experienced a comparable concentration of CO2 was 3–5 million years ago.

'Back then, the temperature was 2–3°C warmer, sea level was 10–20 meters (33–66 feet) higher than now.'

Experts predict that the rate of global greenhouse gas emissions will not reach a peak by 2030, let alone in the next decade, if current climate policies remain unchanged.

In September of this year, the UN's 'United in Science' report — authored by various major partner organisations who undertaken climate research — also indicated that greenhouse gas emissions had continued to rise across 2018.

These findings, scientists warn, are highlighting the considerable and growing gap between agreed climate targets and the actual real-world scenario we are facing.

This enduring trend towards great levels of carbon dioxide in the atmosphere will lead to more severe climate change — from rising temperatures to extreme weather (stock image)

Experts also found that the concentrations of fellow greenhouse gases methane and nitrous oxide also swelled from 2017–2018, rising at a higher rate than seen at any other time during the past decade.

The observations that led to these conclusions were collected by the so-called 'Global Atmosphere Watch Network', which has stations in such diverse settings as tropical islands, mountain chains and the remote Arctic.

Alongside this, the report highlights how the burning of fossil fuel is the main contributor to the rising levels of atmospheric carbon dioxide.

There are various indicators to support this conclusion — notably that the radio of radiocarbon-free carbon dioxide in the atmosphere is increasing.

This fingers fossil fuels as the source, as they were formed from plant matter millions of years ago and consequently do not contain radiocarbon.

According to the US National Oceanic and Atmospheric Administration, there has been a 43 per cent increase in the warming effect of atmospheric greenhouse gases since 1990 — with carbon dioxide accounting for 80 per cent of this effect.

Once emitted into the atmosphere, carbon dioxide remains there for centuries. In the oceans, it can persist for even longer.

A complementary 'Emissions Gap Report' will be released by the United Nations on 26 November, examining the latest research into current a estimated future greenhouse gas emissions.

It will compare these with the minimum emissions levels required to achieve the goals of the Paris Agreement — this divide between where we are likely to end up and where we need to be is referred to by experts as the emissions gap.

According to UN Secretary-General Antonio Guterres, the UN's Climate Action Summit in September — during which the United in Science report was published —had delivered 'a boost in momentum, cooperation and ambition.'

The matter will be carried forward to the UN Climate Change Conference, which is to be held in Madrid, Spain, from 2–15 December 2019.

'But we have a long way to go,' Mr Guterres added.