I think it should be pretty clear that researching the state of the atmosphere is a tall order- and some journal articles go REALLY in-depth when it comes to chemical reactions and composition and simulations (after a while, I found my eyes glazing over anytime I encountered more than 2 pages of graphs)- but I felt that I needed to start with some basics about the make-up of and recent trends for our atmosphere. And although I’m sure this is not a complete account, I do think that I have a sense of how things have changed with regard to greenhouses gases and how those changes seem likely to impact us. (I feel I should point out that some models have so many variables that the magnitude of impacts can be hard to gauge- however, everyone seemed to agree that change is in the air.)
Overlooking the busy streets and canals of Copenhagen
Which gases are scientists concerned about and how have levels changed? Some studies took a broader view than others, but the big players seem to be: Carbon dioxide, which we tend to hear the most about since we have been so good at producing it since the Industrial Revolution- a 1976 review of air pollution sources and emission rates found that CO₂ levels in the atmosphere had increased by 9% from 1860 to 1969 (Bach 1976). That level increase was supposed to be 15% by 1979 and 23% by 1989- in other words, not only are we putting extra carbon dioxide into the atmosphere, but we are putting it in faster and faster. In 2004, Hansen and Sato calculated that the rate at which CO₂ is increasing had doubled between 1950 and the 1970s and fossil-fuel emissions themselves had more than quadrupled in the previous 50 years. Why is this important? Carbon dioxide helps trap heat within Earth’s atmosphere and contributes to global warming. According to Hansen and Sato (2004), 9 years ago, we were already reaching a point where CO₂ emissions would put us past the 1° C warming mark.
Methane is another big concern. Although we produce less methane, this gas is getting a lot of attention for several reasons. Atmospheric methane levels increased 1-2% per year through the mid-1980s (Wang et al. 1986), and much of that came from human activity (the biggest sources of methane include ruminants, such as the cow used for your hamburger than can produce around 200 L of methane each day (Cicerone and Oremland 1988), rice paddies where water-logged conditions facilitate anaerobic decay, and burning of biomass, such as when forests are cleared). Why is methane important? Methane (CH₄) is a thicker gas than CO₂ so it heats the atmosphere more (Guthrie 1986). It also takes longer to remove methane from the atmosphere (Hansen and Sato 2004) which increases its heating potential more. In addition, some methane is currently held in solid form under permafrost and ocean sediments, especially in the Arctic region (Harvey and Huang 1995). Global temperatures are expected to experience the greatest rise at high latitudes (Schuur et al. 2008), and that methane could be released into the atmosphere where it would intensify heating effects. One of the big concerns here is positive feedback– temperatures get warmer, so more methane is released, so temperatures get even warmer; more CO₂ means higher temperatures and more plant growth, more plant material means more methane-producing decomposition, and more methane adds to the rise in temperatures.
A quick shower gives way to clearer skies over Edinburgh
Scientists are also keeping an eye on several other gases, such as nitrous oxide (N₂O) which has been increasing at about .25% per year (Wang et al. 1986) and comes largely from bacterial and combustion (here, read ‘coal’) processes, but may also be increasing as a result of positive feedback from global warming (Hansen and Sato 2004). Nitrogen oxides are also released through combustion and can increase solar absorption by the atmosphere where abundant, creating localized heating (Wang et al. 1986). Carbon monoxide, coming in part from our transportation options, is a concern because it can alter ozone concentrations.
Are there any bright spots? Yes, to a certain extent. Harvey and Huang (1995) felt that, even under a worst-case scenario of methane clathrate release, the impact wouldn’t be as intense as the difference between their low, middle, and high CO₂ scenarios. And thanks to international regulations and cooperation, atmospheric CFC levels started declining in 2003 (Hansen and Sato 2004). Hansen and Sato (2004) also felt that coordinated efforts to reduce methane emissions could help counteract global warming caused by CO₂.
But our options may be diminishing. While in 2004 Hansen and Huang were concerned with 1° C further rise in temperatures (creating a total of 1.5° C since 1900), in 2009, Meinshausen et al. assessed our options for limiting global temperature change to 2° C- this may be a moving target. I do believe that it is possible to limit our emissions and I also think that individuals, acting in concert, can make a big difference here, but we don’t always have the information needed to make the best choices. Over the past few years, many studies have concentrated on precisely where greenhouse gases are coming from, not just by industry, but by specific product and from start to finish. It seems to me that this is exactly the kind of information that would be useful to us, but it’s not always easy to find. For next week, I’ll be looking at greenhouse gas emissions by fuel type and for specific goods that we use in our daily lives, trying to decipher how what I do in the course of a day impacts the atmosphere.
In this case, information is power- and we may discover that we have more options than we thought for creating positive change.
Works cited:
Bach, W. 1976. Global air pollution and climatic change. Reviews of Geophysics and Space Physics 14 (3): 429-474.
Cicerone, R.J. and R.S. Oremland. 1988. Biochemical aspects of atmospheric methane. Global Biogeochemical Cycles 2: 299-327.
Guthrie, P.D. 1986. Biological methanogenesis and the CO₂ greenhouse effect. Journal of Geophysical Research 91: 10,847- 10,851.
Hansen, J. and M. Sato. 2004. Greenhouse gas growth rates. PNAS 101: 16109-16114.
Harvey, L.D.D. and Z. Huang. 1995. Evaluation of the potential impact of methane clathrate destabilization on future global warming. Journal of Geophysical Research 100: 2905-2926.
Meinshausen, M., Meinshausen, N., Hare, W., Raper, S.C.B., Frieler, K., Knutti, R., Frame, D.J., and M.R. Allen. 2009. Greenhouse-gas emission targets from limiting global warming to 2° C. Nature 458: 1158-1163.
Schuur, E.A.G., Bockheim, J., Canadell, J.G., Euskirchen, E., Field, C.B., Goryachkin, S.V., Hagemann, S., Kuhry, P., Lafleur, P.M., Lee, H., Mazhitova, G., Nelson, F.E., Rinke, A., Romanovsky, C.E., Shiklomanov, N., Tarnocai, C., Venevsky, S., Vogel, J.G., and S.A. Zimov. 2008. Vulnerability of permafrost carbon to climate change: implications for the global carbon cycle. BioScience 58: 701-714.
Wang, W-C., Wuebbles, D.J., Washington, W.M., Isaacs, R.G., and G. Molnar. 1986. Trace gases and other potential perturbations to global climate. Reviews of Geophysics 24: 110-140.