Hawaii’s Mauna Loa Observatory has reported that worldwide carbon dioxide levels reached a new record high in April, hitting 410.31 parts per million (ppm). This is the highest concentration of this greenhouse gas seen over the course of human history–and prehistory, for that matter–as the Earth’s atmosphere hasn’t seen CO2 levels this high in well over 800,000 years, and possibly as long as 20 million years.

Over the last 800 millennia, CO2 levels would vary between 180–210 ppm during ice ages, and increase to 280–300 ppm when the climate warmed up during interglacials; however, in all that time it never rose above 300 ppm, and had otherwise remained relatively stable over the past 10,000 years. All of that changed shortly after the start of the Industrial Revolution, when human activity started releasing ever increasing amounts of carbon into the atmosphere: today’s levels are now more than 46 percent higher than the 280 ppm seen during pre-industrial times.

"As a scientist, what concerns me the most is not that we have passed yet another round-number threshold but what this continued rise actually means: that we are continuing full speed ahead with an unprecedented experiment with our planet, the only home we have," laments geochemist Ralph F. Keeling, with the Scripps Institution of Oceanography at the University of California. Despite rapid growth in the renewable energy industry and planet-wide agreements to stem CO2 emissions, human-generated greenhouse gas continues to accumulate in the atmosphere, raising global temperatures and prompting rapid ice melt at the poles.

Over the month of April, Pakistan suffered a prolonged heat wave, culminating in a worldwide temperature record for the month of April being broken, with Nawabshah district recording a high of 50.2ºC (122.3ºF). Bear in mind that this is not just a new regional record, but a new high for the entire planet–and it isn’t even summer yet.