Do we understand the atmosphere enough to identify problems and solve them? Heck yes, we are two-for-two!

March 10, 2014 2:50 pm2 comments

Whenever I am asked the question of how well we understand the atmosphere that is being changed by the addition of carbon dioxide and other greenhouse gases, I often find it useful to look at the scientific history of two other recent atmospheric pollution challenges: acid rain and stratospheric ozone depletion.

In each case the scientific community identified the process that was causing changes to our atmosphere, and quantified the magnitude of the change. This knowledge led to suggested solutions that were approved, and steps were then taken to limit acid rain in the United States and reduce the rate of stratospheric ozone depletion globally. In both cases, not only were the mechanics understood, but the recommended solutions that were adopted have had a positive impact.

Acid Rain

Acid rain develops when compounds like sulfur dioxide and nitrogen oxides released into the atmosphere combine with water and oxygen to form acidic pollutants such as sulfuric acid (EPA, 2012). The 1990 Clean Air Act Amendments specifically targeted additional reductions of sulfur dioxide and nitrogen oxide emissions, using a cap and trade scheme. The success of this strategy has been monitored using the long term National Atmospheric Deposition Program (NADP), which measures atmospheric deposition and studies its effects on the environment. This network began in 1978 and expanded rapidly with funding from the National Acid Precipitation Assessment Program (NAPAP), established to improve understanding of the causes and effects of acidic precipitation. Recently a 2012 progress report by NAPAP noted the positive impacts that the Clean Air Act has had in reducing acid rain.

Between the 1989 to 1991 and 2009 to 2011 observation periods, wet deposition of sulfate (which causes acidification) decreased by more than 55 percent on average across the eastern United States.

The result is evident in the images below. The first two images are from the NAPAP report and show wet sulfate deposition in 1990 and 2010. The third image shows the level of acidity in precipitation at a single NADP site since 1978.


1990 wet sulfate deposition


2010 wet sulfate deposition


The acidity of rain at the University of Delaware long term monitoring station where acidity has dropped by 60%.

Stratospheric Ozone Depletion

The process of stratospheric ozone depletion begins when CFC’s and other ozone depleting chemicals (ODC) are emitted into the atmosphere (EPA, 2010). CFCs are extremely stable, and do not dissolve in rain. After a period of several years, ODC molecules reach the stratosphere. Strong ultraviolet light breaks apart the ODC molecule. The result is the release of chlorine atoms, and halons. It is these atoms that actually destroy ozone, not the intact ODC molecules. The process occurs most readily at temperatures below -77 C, at which point a polar stratospheric cloud can develop (UNEP image below). The Montreal Protocol was an international agreement that aimed to reduce the production and consumption of the ODC’s known, and was essentially a ban. It has been updated a number of times to include newly identified ODC’s. The Montreal Protocol has been noted by NOAA and UNEP to be successful at reducing emissions of ozone depleting substances, so successful that by 2008 the total tropospheric abundance of chlorine had declined to 3.4 parts per billion from a peak of 3.7 ppb. In terms of the springtime Antarctic total column ozone losses (ozone hole), the system has not recovered, but the rapid expansion of the pre-Montreal Protocol period has been reversed to modest declines. CFC’s were designed for their stability, which makes them a good vehicle to carry chlorine into the stratosphere. This is why scientists concluded that stratospheric ozone levels would not fully recover for quite sometime after the ban on production and consumption of CFC’s Montreal Protocol was reached in 1996.


UNEP image of stratospheric temperatures in polar regions



Will we heed the previous examples and pursue the solution to rising CO2?

Both of the aforementioned examples indicate that the science community correctly identified the processes involved and effective solutions. They do not indicate a complete understanding of the dynamics that would allow predictions quantifying the rate of recovery in either case. The impact of greenhouse gases is an even more basic science process than the aforementioned. If we as a nation choose to ignore the science community over greenhouse gasses, we would be ignoring a professional community that has served us well in recent atmospheric pollution issues. Bottom line, we have altered atmospheric CO2, the fourth most common element in the atmosphere, by 24% since 1958 (NOAA, 2013). How is this not going to have a profound effect? Once again the scientific community has identified the process, the rate of change of the causative elements, and recommended solutions. This is a third example of mother nature being impacted by our emissions. Will we heed the previous examples and pursue the solution before too much damage is done?

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Megan Pelto, Savannah College of Art and Design

Next time I want to look at Pine Island Glacier and why this was identified as the weak underbelly of the Antarctic Ice Sheet 30 years ago, and how that forecast has proved accurate also.


  • Important to look at these ‘past’ events indeed, and see what we can learn from them.

    Re stratospheric ozone depletion, an interesting article in that context is entitled “What would have happened to the ozone layer if chlorofluorocarbons (CFCs) had not been regulated?” (

    The societal inertia in dealing with environmental issues predicted by science led Nobel Laureate Sherwood Rowland to proclaim: “What’s the use of having developed a science well enough to make predictions if, in the end, all we’re willing to do is stand around and wait for them to come true?”

  • Paul Q: The point is not to compare the solution or the magnitude. It is to illustrate that we have understood both the causes and the needed solutions for two other atmospheric pollution issues. This is a strong indication that our understanding of the causes and solutions to GHG are on target.

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