The atmospheric carbon dioxide reading taken at the Mauna Loa observatory in Hawaii is expected to reach 400 parts-per-million this week. Andrew Freedman puts that number in its historical context:
The news that CO2 is near 400 ppm for the first time highlights a question that scientists have been investigating using a variety of methods: when was the last time that CO2 levels were this high, and what was the climate like back then? There is no single, agreed-upon answer to those questions as studies show a wide date range from between 800,000 to 15 million years ago. The most direct evidence comes from tiny bubbles of ancient air trapped in the vast ice sheets of Antarctica. By drilling for ice cores and analyzing the air bubbles, scientists have found that, at no point during at least the past 800,000 years have atmospheric CO2 levels been as high as they are now.
That means that in the entire history of human civilization, CO2 levels have never been this high.
This is a new era – in which humanity has the power to change the entire climate of the planet so that it is more clogged with carbon than at any time since homo sapiens took dominion. This is the mark of dystopian science fiction – except that it’s real, and apparently unstoppable. What right does one species have to change the world’s climate so structurally it will destroy countless other life-forms? Greg Laden reminds us nonetheless about the seasonal variations in CO2 levels:
There is a lot more land in the Northern Hemisphere that goes through a dramatic cycle in plant activity, with most plants playing (or even being) dead over the winter and springing to life in the Spring. The Southern Hemisphere has much less land. So a small amount of CO2 moves into the atmosphere over the Northern Hemisphere winter and into spring, and then moves back into newly grown plant tissue during the northern growing season.
So, right now, CO2 should be at a short term peak. The range of this variation is around 8 ppm, so if we hit, say, 401 ppm next week, expect that value to go back below 400 ppm in a few weeks. In other words, we can and should note that we are probably hitting the 400 ppm barrier, but then later when we drop slightly below, temporarily, 400ppm, the climate science denialists will be all over that claiming that there is no global warming. Cuz they’re morons. In a few years … certainly by the end of the present decade …. the low values will be over 400 ppm unless something dramatic happens.