400 Parts Per Million

May 1st, 2013 | Simcha Weinstein | Comments Off on 400 Parts Per Million

fossilFuelsSometime in the very near future, the concentration of carbon dioxide in the atmosphere is expected to hit 400 ppm (parts per million). That would be higher than at any time in human history.

On Monday, the daily average level recorded by the Scripps Institution of Oceanography was 399.5 ppm and is expected to reach 400 ppm in May, which is the month where CO2 concentrations typically reach their highest levels.

Since the beginning of human civilization up until about 200 years ago, our atmosphere was at 275 parts per million of carbon dioxide. Parts per million is a way of measuring the concentration of different gases, and is the ratio of the number of carbon dioxide molecules to all of the molecules in the atmosphere. Keep in mind that we do need some CO2 in the atmosphere – without CO2 and other greenhouse gases heat would not be trapped in our atmosphere and our planet would be too cold for humans to inhabit. So we do need a certain level of CO2 for us to have a livable climate for human survival. But, we’re reaching a point where with carbon dioxide levels of 400 ppm in the atmosphere, this pushes climate change to a new a new level and the world into a new danger zone.

Climate scientists have argued that CO2 levels need to be kept below 350 ppm if the world is going to meet the international targets to keep average temperature increases below 2 degrees C. Most climate scientists believe that levels above 400 ppm put the planet on track for what would be considered “dangerous” by the international community focused on climate change and global warming.

Scientists estimate that the last time CO2 was as high as 400 ppm was the Pliocene epoch, around 3.2 million to 5 million years ago, when the Earth’s climate was much warmer than today. CO2 was around 280 ppm before the Industrial Revolution, when humans first began releasing large amounts of CO2 to the atmosphere by the burning of fossil fuels. There is no known period in geologic history when such high rates have been found and the rise is a direct consequence of our heavy reliance on fossil fuels for energy, according to climate scientists.

While moving from 399 ppm to 400 ppm is not practically very significant or dramatic – it’s a milestone that clearly sends a message and draws attention to the fact that climate change is happening at a much more accelerated rate than scientists previously thought, and this rise is bad news for anyone who cares about a livable climate.

On a hopeful note, all is not lost. By decreasing the use of fossil fuels, and improving agricultural and forestry practices around the world, scientists believe we could get back below 350 by mid-century. But the longer we remain in the danger zone—above 350—the more likely that we will see disastrous and irreversible climate impacts.