400 and Other Numbers

May 31, 2013

This month, it finally happened: we reached 400 parts per million of CO2 in the atmosphere.

Though atmospheric CO2 levels inched over 400 ppm briefly last summer, this is the first time that NOAA, the National Oceanic and Atmospheric Administration, has witnessed a daily average at 400 ppm or above. To those familiar with the math of climate change, this number is far outside of our climate comfort zone, and is being regarded as a milestone in the process of climate change.

Other numbers have special significance, as well. James Hansen, former NASA Climatologist, has stated that if humanity “wishes to preserve a planet similar to that on which civilization developed and to which life on Earth is adapted,” we will need to reduce our atmospheric carbon dioxide levels to at least 350 ppm. Following this statement, 350 ppm has become a rallying point for the climate movement. 350.org, an organization founded by journalist and environmentalist Bill McKibben, aims to lower CO2 levels down to this “safe” range. 350.org explain their namesake in the following video:

Though our recent record has been given special significance in discussions of climate change, there is nothing significantly more distressing about 400 ppm than 399 ppm. Just like 350 ppm, the importance of the 400 ppm marker is mostly symbolic. Checkpoints like this become important to environmentalists, because the slow-building disaster of climate change takes place over long timescales and is, at most times and in most places, easy to ignore. Except, of course, when and where it isn’t.

If the number 400 does not speak to you, perhaps some other statistics from 2012, one of the most extreme years in terms of weather and climate, will make an impression:

5: The number of countries that set heat records in 2012.

144: The number killed in the flash floods that struck the Krasnodar region of Russia in July of 2012. Similar floods were experienced in Pakistan and China.

2300: The number of counties impacted by drought in the midwestern U.S. last summer.

13: The height in feet that Hurricane Sandy’s storm surge reached in some parts of New York City.

285: The total number of deaths attributed to the superstorm.

65,000,000,000: The cost of Hurricane Sandy, as estimated by London-based reinsurance firm Aon Benfield.

Looking to the future, Scientific American reports that, due to “a combination of local geography, vulnerable coastal development and already-happening sea-level rise as a result of climate change,” flooding like we experienced during Sandy will be commonplace, rather than unprecedented. The “frankenstorm” may soon become just a “storm.”

On a global scale, one extremely troubling number emerged from the 2012 weather and climate statistics:

18: The percentage that summer sea ice in the Arctic shrank below its previous low.

We will likely see 400 ppm again. Perhaps we will adjust to it; perhaps 400 will become the new normal, and 450 will become the new statistic of doom held out by environmentalists. But 400 is only one number among many, and it may not be the most important. From 350 on up, we have experienced the devastating effects of climate change, and we will continue to see this destruction play out in statistics and in stories. The most severe outcomes of unmitigated climate change may not hit us on a global scale at 400 ppm or at any number near to it, but for those who have been affected by floods and freak storms, or have lost their livelihoods to drought, this destruction is very real and very present. It is these numbers which make up the real statistical drama of climate change, and it is these numbers which may be most powerful in reversing our climate trajectory.


-Sharon Hartzell


Borenstein, Seth (2012). 2012 Extreme Weather Sets Records, Fits Climate Change Forecasts. Huffington Post Green. http://www.huffingtonpost.com/2012/12/21/2012-extreme-weather-climate-change_n_2348079.html

350.org (2013). http://400.350.org/

BBC News (2012). Russia Flash Floods: 144 Killed in Krasnodar Region. BBC News, http://www.bbc.co.uk/news/world-europe-18751198

Rice, Doyle (2013). Hurricane Sandy, drought cost U.S. $100 billion. USA Today, http://www.usatoday.com/story/weather/2013/01/24/global-disaster-report-sandy-drought/1862201/

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