The Mauna Loa Observatory in Hawaii reported that atmospheric carbon dioxide had reached 415 ppm on Friday:
In poetic punctuation to that point, Arkhangelsk, Russia, near the Arctic Ocean, recorded a temperature of 29°C Saturday:
In Koynas, a rural area to the east of Arkhangelsk, it was even hotter on Sunday, soaring to 87 degrees (31 Celsius). Many locations in Russia, from the Kazakhstan border to the White Sea, set record-high temperatures over the weekend, some 30 to 40 degrees (around 20 Celsius) above average. The warmth also bled west into Finland, which hit 77 degrees (25 Celsius) Saturday, the country’s warmest temperature of the season so far.
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.
Why is 415 ppm a "symbolic threshold?" Because for years, climate scientists have believed that at 415 ppm, we can't undo the damage; we can only slow it down a little. Even if we return to pre-industrial levels (280 ppm), we now have too much carbon in the atmosphere to stop radical climate change:
For the planet itself, 415 ppm is no BFD. Over the past 4 billion years or so, it’s been much, much higher. But for us humans, 415 is a very dangerous number. The last time CO2 levels were at 415 ppm, during the Pliocene period about 3 million years ago, there was plenty of life on Earth, but the Earth itself was a radically different place. Beech trees grew near the South Pole. There was no Greenland ice sheet, and probably not a West Antarctic ice sheet, either. Sea levels were 50 or 60 feet (or more) higher.
That’s the world we’re creating for ourselves by pushing carbon dioxide levels to 415 ppm. Right now, a lot of atmospheric warming is being absorbed in the oceans. But those oceans are like a big flywheel, and the heat will be radiated out. That means, among other things, goodbye ice sheets, hello condo diving in Miami.
One way to think about carbon dioxide levels in the atmosphere is as a thermostat for the planet. As you’ll remember from third-grade science class, carbon dioxide is exhaled by animals, including humans, and inhaled by plants. It is also released when plants and animals decay, volcanoes erupt, and, most importantly, when we burn fossil fuels. Last year, we dumped about 37 billion tons of carbon dioxide into the atmosphere by burning fossil fuels. The more coal, oil and gas we burn, the faster that number rises. Before the Industrial Revolution, the level of carbon dioxide in the atmosphere was 280 ppm. Sixty years ago, it was 315 ppm. For the past few years, it has been rising by about 2 or 3 ppm a year.
That might not sound like much. However, carbon dioxide molecules happen to be very good at trapping heat in the atmosphere. Scientists have understood this very well since the 19th century. Carbon dioxide molecules are like the prison guards of the Earth’s atmosphere — they let sunlight in, but they don’t let heat out. Scientists argue about exactly how efficient carbon dioxide is at warming the Earth, but there is basic agreement that a doubling of carbon dioxide levels from 280 ppm will warm the Earth’s atmosphere by 2 to 3 degrees Celsius.
We predicted this in time to slow it down or even stop it. Nice work, team.