The Atmosphere Doesn't Lie

The United States, along with just about every other country on earth, has committed to the objective of stabilizing the amount of heat-trapping pollution in the atmosphere in order to prevent dangerous changes in our climate (see article 3 of the climate convention). How’s it going?

Not well.

The National Oceanic and Atmospheric Administration (NOAA) monitors the concentration of heat-trapping gases in the atmosphere more-or-less continuously and compiles an annual summary of the combined effect on the earth’s energy balance. NOAA released the results from 2010 last week. As you can see from the key figure reproduced here, the atmosphere doesn’t seem to have noticed the climate convention. In fact, the heating effect of atmospheric pollution has increased by 29 percent since 1990, the year international climate negotiations were initiated.

Method

NOAA provides an explanation of its measurements and analysis here, but despite having developed the “Annual Greenhouse Gas Index” to provide a “normalized standard that can be easily understood and followed” its explanation is rather technical (Note to NOAA: If you are trying to write something that is easily understood, try saying “increase in heat trapping” rather than “perturbation to direct climate forcing (also termed “radiative forcing”).”

Nonetheless, the basic approach is pretty straightforward. Since 1979 NOAA has been monitoring the concentrations of carbon dioxide, methane, nitrous oxide, CFCs and other gases that absorb heat energy coming from the earth’s surface (infrared radiation). The heating effect of these gases is calculated by comparing their measured concentrations to natural background levels, which are taken to be IPCC’s estimates of what they were in 1750 (CFCs didn’t exist in 1750 and concentrations of the other gases are estimated by analyzing old air trapped in ice sheets on Greenland and Antarctica). The AGGI for any year is defined as the combined heating effect of the “long-lived” gases relative to what it was in 1990 (just as the consumer price index is the combined cost of a given market basket of goods relative to the cost in a specified base year).

By “long-lived” NOAA means gases that stay in the atmosphere for at least several years so that their concentration is similar throughout the lower atmosphere. They do not include ozone or aerosols, which also influence climate, but only last a few weeks and vary drastically in concentration from place to place.

Individual Gases

The results for individual gases include some good news and a mystery that may be bad news. While the concentrations of carbon dioxide and nitrous oxide have been rising quite steadily, that isn’t the case for methane or CFCs. In fact, the concentrations of CFC-11 and CFC-12 are actually falling, having peaked around 1993 and 2002, respectively. This is the good news result of the Montreal Protocol to protect the stratospheric ozone layer. Had CFCs not been regulated the AGGI would have increased by even more, and might have increased by 43 percent from 1990 to 2010, rather than 29 percent.  

Methane provides the mystery. Its concentration grew quite steadily until 1999, when it leveled off for seven years before starting to increase again in 2007. The reasons for this pattern are unclear, but there is some evidence that climate change itself may be one reason for the renewed growth in methane concentrations over the last few years. Warmer temperatures in the arctic enhance methane emissions, creating a bad news feedback loop that amplifies climate change.

Bottom Line

As negotiators and non-governmental organizations from around the world prepare to converge on Durban, South Africa for the 17th Conference of Parties to the climate convention, let’s hope they keep the original objective of the convention in mind. Unless their efforts ultimate show up as a stabilization of the amount of heat-trapping pollution in the atmosphere they have not succeeded.

Thanks to NOAA, we can all keep our eyes on the bottom line.

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