Last year, carbon dioxide crossed what may be an arbitrary threshold, 400 ppm (parts per million), in the middle of May, and stayed there for a few days.
Seasonal fluctuations in carbon dioxide concentration are typical, as the growth of plants in Spring, in the Northern Hemisphere, pulls carbon dioxide out of the air. As the plants die off in Winter, carbon dioxide concentrations increase once again. The overall trend, however, is ever=increasing concentrations of carbon dioxide, thanks to human activity.
This year, a full two months earlier, carbon dioxide concentrations have already breached 400 ppm, and it is expected to stay above 400 ppm for at least a month or two. Eventually, carbon dioxide levels will simply stay above 400 ppm, no matter what the season. Some may point out that 400 ppm is some arbitrary number, and they’d be right. On the other hand, taking a look at the trend over the last fifty years, it’s obvious that we’re having an impact.
Further still, the trend over the last million years, according to carbon dioxide readings taken from core samples in Antarctica, is even more striking. True, there are fluctuations to be noted, but these follow a familiar pattern, peaking, for example, around 250-300 ppm and dropping to around 150-200 ppm over about a 50,000-year period. The last major peak in the cycle was about 320,000 years ago, just over 300 ppm carbon dioxide.
Today’s carbon dioxide readings are a full 25% higher than even that peak, and climate change deniers dare to say that human activity has a negligible effect on the climate? When carbon dioxide concentrations peaked, 320,000 years ago, the oceans were 130 feet higher and temperatures were 11°F higher than today’s averages. So far, with today’s carbon dioxide concentrations peaking over 400 ppm, we’ve already seen eight inches of sea level rise due to the melting of the polar ice caps.
Image © NOAA