Comment: It was 28C near the Arctic Ocean as carbon dioxide hit its highest recorded level

An Extinction Rebellion climate change protester in London last month. Photo / AP file

Last weekend, the climate system sounded simultaneous alarms.

Near the entrance to the Arctic Ocean in northwest Russia, the temperature surged to 28.8C.

The concentration of carbon dioxide in the atmosphere eclipsed 415 parts per million for the first time in human history.

By themselves, these are just data points. But taken together with so many indicators of an altered atmosphere and rising temperatures, they blend into the unmistakable portrait of human-induced climate change.

Sunday NZT's steamy 28.8C reading was posted in Arkhangelsk, Russia, where the average high temperature is around 12.2C this time of year. The city of 350,000 people sits next to the White Sea, which feeds into the Arctic Ocean's Barents Sea.

In Koynas, a rural area to the east of Arkhangelsk, it was even hotter on Sunday, soaring to 30.5C. Many locations in Russia, from the Kazakhstan border to the White Sea, set record-high temperatures over the weekend, some well above average. The warmth also bled west into Finland, which hit 25C, the country's warmest temperature of the season so far.

The abnormally warm conditions in this region stemmed from a bulging zone of high pressure over western Russia. This particular heatwave, while a manifestation of the arrangement of weather systems and fluctuations in the jet stream, fits into what has been an unusually warm year across the Arctic and most of the mid-latitudes.

In Greenland, for example, the ice sheet's melt season began about a month early. In Alaska, several rivers saw winter ice break up on their earliest dates on record.

Across the Arctic overall, the extent of sea ice has hovered near a record low for weeks.

Data from the Japan Meteorological Agency show April was the second warmest on record for the entire planet.

These changes all have occurred against the backdrop of unremitting increases in carbon dioxide, which has now crossed another symbolic threshold.

Sunday's carbon dioxide measurement of 415 parts per million at Hawaii's Mauna Loa Observatory is the highest in at least 800,000 years and probably over three million years. Carbon dioxide levels have risen by nearly 50 per cent since the Industrial Revolution.

The clip at which carbon dioxide has built up in the atmosphere has risen in recent years. Ralph Keeling, director of the programme that monitors the gas at the Scripps Institution of Oceanography, tweeted that its accumulation in the last year is "on the high end".

Carbon dioxide is a greenhouse gas that, along with the rise of several other such heat-trapping gases, is the primary cause of climate warming in recent decades, scientists have concluded.

Eighteen of the 19 warmest years on record for the planet have occurred since 2000, and we keep observing these highly unusual and often record-breaking high temperatures.

They won't stop soon, but cuts to greenhouse emissions would eventually slow them down.

- Jason Samenow is the Washington Post's weather editor and Capital Weather Gang's chief meteorologist.