On the Path to 400: Weekly CO2 Averages Above 398 PPM For First Time


Worldwide CO2 averages inched slightly higher last week topping 398.08 ppm.  This measure is 2.87 parts per million higher than for the same week last year and 21.21 parts per million higher than the value recorded for the same week in 2003.

To find sustained levels of CO2 comparable to those measured during the week of March 31, we have to go back more than 2 million years into Earth’s geological past. This change has at a  remarkable and increasing pace over the past 130 years. In that period, world CO2 levels have risen from about 275 parts per million to the extraordinarily high levels we see today. This jump of about 120 parts per million CO2 was caused by rampant burning of fossil fuels in the period of 1880 through 2013.

Long term temperature averages in a world of 400 ppm CO2, according to paleoclimate, are between 2-3 degrees Celsius warmer than 20th century averages. Sea levels are 15-75 feet higher and both weather and climates are radically different.

But it is important to note that the human addition of 120 parts per million CO2 is just an initial forcing to the world’s climate system. This large forcing, occurring at about 10 times more rapidly than any comparable forcing in the geological past, presents a high risk of resulting in feedbacks from the Earth’s environment that pump even more CO2 and other greenhouse gasses into the atmosphere. Loss of glaciers and reduced overall albedo will also result in the removal of a key cooling feature. These responses, at best, are likely to keep worldwide CO2 levels at or just below current high marks for hundreds or thousands of years even if all emissions immediately cease. The result is that a long-term trend of warming and somewhat harmful climate change is mostly locked in. At the worst case, we enter a period of amplifying feedbacks where the Earth contributes large volumes of CO2 and other greenhouse gasses comparable to the amount humans have already pumped into the atmosphere.

Both of these scenarios are probably survivable. But both involve substantial increased risk of damaging Earth changes, altered and erratic weather patterns, and increased instances of damaging, extreme events. So it must be emphasized that we are at the threshold of a period of increasing harm now and that continuing to pump CO2 into the atmosphere at increasing rates is simply a devastating regime of self-inflicted harm. In such a case, we risk runaway climate change of a kind that would be impossible for humans and civilizations to adapt to long-term.

The only wise, sane choice would be to draw down CO2 and greenhouse gas emission as rapidly as possible. Sadly, the rate of CO2 emission is increasing.

2013 or 2014 will likely see world CO2 levels cross the 400 ppm threshold. But at the current rate at which the world continues to burn fossil fuels this marker will only serve as a milepost on a road toward increasingly damaging and catastrophic harm.

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