The greenhouse gases driving climate change have reached highs not seen in at least 3 million years, prompting UN scientists to warn the “window of opportunity” to tackle emissions is rapidly closing.

Carbon dioxide, nitrous oxide and methane are all still on the rise, the World Meteorological Organisation (WMO) has said, and there has been a resurgence in ozone-depleting CFCs.

“The last time the Earth experienced a comparable concentration of carbon dioxide was 3-5 million years ago, when the temperature was 2-3C warmer and sea level was 10-20 metres higher than now,” said WMO secretary general, Petteri Taalas.

In its annual bulletin on greenhouse gas…