The 400 ppm CO2 Milestone

CO2 emissionsClimate scientists yesterday warned that the earth had crossed an important milestone. For the first time in 3 million years, the total amount of carbon dioxide (CO2) in the atmosphere exceeded 400 parts per million. The last time CO2 levels were this high was during the Pliocene era, when temperatures were 2 to 3 degrees Celsius higher and the earth was in a middle of a prolonged warm period.

It’s important to remember that the 400 ppm figure is a bit arbitrary. CO2 levels have been flirting with the 400 ppm level for several months. But the overall upward trend in CO2 levels does pose reason for concern. Scientists warn that failure to stabilize CO2 levels at less than 450 ppm could have catastrophic climate effects. But over the past fifty years, CO2 levels have been on a steady upward march (see graph below), and they show no signs of leveling off.


Carbon dioxide levels can be seen climbing steadily in Scripps data from the last 55 years.  Scripps Institution of Oceanography, UC San Diego
Carbon dioxide levels can be seen climbing steadily in Scripps data from the last 55 years.
Scripps Institution of Oceanography, UC San Diego

But reducing CO2 levels in the atmosphere presents a classic free rider dilemma. Collectively, we face dramatic consequences: increasingly erratic weather patterns, declining overall food productivity, rising sea levels, desertification, and so on. But any individual country’s actions are unlikely to have a significant impact on the overall trend. Thus it is in every country’s individual self-interest to continue business as usual, and rely on other countries to reduce their greenhouse gas emissions. In doing so, they capture all of the benefits of reducing greenhouse gas emissions while paying none of the costs. Every state behaving in a rational and self-interested way leads to the worst possible outcome—a classic example of the prisoners’ dilemma.

Yet we also know that there are several strategies to overcome the prisoners’ dilemma. Iteration (repeated plays) and communication (which leads to confidence building and trust) can overcome the otherwise nihilistic outcomes of the dilemma. The question, of course, is whether or not governments can work to overcome the dilemma in time to prevent the worst effects of climate change.

What do you think? Will governments be able to collectively address the challenges posed by climate change? Or are we locked into a nihilistic outcome, as the prisoners’ dilemma would suggest? Take the poll or leave a comment below and let us know what you think.


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