As the Warsaw negotiations continue, here at Sense & Sustainability we’ll continue the discussion of international climate change treaties. Building on Monday’s examination of some of the theoretical evidence suggesting that international climate change treaties could be successful, today we’ll look at one case in which an international agreement has been very successful in addressing climate change. While it wasn’t directly intended to deal with this issue, the 1989 Montreal Protocol has been very successful in slowing global temperature increases. So successful, in fact, it has provided fodder for climate change deniers.
Climate change deniers have latched onto the recent slow-down in global temperature change as evidence that climate change is a hoax, or at the very least, not driven by human activity. A new paper in the journal Nature Geoscience suggests, however, that at least part of this temperature stability is due to the reduced use of chlorofluorocarbons (CFCs): a direct result of the adoption of the Montreal Protocol.
The original intent of the Montreal Protocol was to eliminate the emission of CFCs responsible for the infamous ozone hole. But because these same CFCs are far more damaging to the global climate than CO2, their curtailment has resulted in a reduction of radiative forcing. In less scientific language, reducing CFC emissions means there are fewer heat absorbing gases in the atmosphere (and the ones that are there do not traps as much heat) so the earth is not warming as quickly. All of this has been achieved by the type of international treaty that optimists hope the COP process will eventually produce.
Indeed, not only has the Montreal Protocol succeeded in its initial goal of cutting CFC emissions, it has developed into a flexible tool that appears likely to allow signatories to target new categories of chemicals. First among these are hydroflourocarbons (HFCs), which replaced CFCs after the initial protocol, and whose curtailment may result in as much as a half a degree Celsius reduction in global warming by 2100. While it is too much to expect that the Protocol could ever be used to regulate CO2, it certainly provides a model for a comprehensive climate change treaty.
Because of the potential similar treaties may have in slowing the march of climate change, we should talk about what this paper demonstrates that the Montreal Protocol actually accomplished. The authors examine changes in the warming trend over the past century in order to provide evidence that humans are driving climate change without utilizing climate modelling. The primary method of doing this is through “optimal fingerprinting” which is the search for “spatial and/or temporal patterns consistent with the anthropogenic forcing signals that are common to observed and externally forced simulations of climate variables.” In other words, the authors identify an underlying non-linear trend in warming over the last century with breaks in the trend line that can be seen in the temperature record and whose timing is consistent with specific human events. This links human activity to shifts in the pattern of warming over the last century.
Using a number of different temperature data sets, the authors demonstrate with a Perron-Yabu testing process — at its heart a regression analysis of the temperature trend — to show breaks in the temperature trend consistent with the increase in the global rate of economic growth that followed WWII. It is at this point that temperature trends demonstrate a noticeable break and start on a sustained warming trend.
The authors also focus on explaining the two most notable cooling periods of the last 100 years. The first of these took place from 1940-1970. The authors attribute this to the decline in CO2 emissions resulting from the disruption caused by two World Wars and the Great Depression. They point out that there is no comparable reduction in CO2 emissions even if you look as far back as 1751.
The second cooling event they discuss, and the one that ties the paper to the Montreal Protocol, is the cooling period from the mid-1990s. Applying the same procedure for finding breaks as above, the authors found statistically significant evidence of a break in 1994. Further tests, this time examining emissions trends rather than temperature trends, reveal breaks in the emissions rates of major CFCs in 1991 and 1992. These breaks indicate a decline in emissions rates of over 90%. Allowing for a lagged effect, there is clear evidence that the reduction in emissions resulting from the implementation of the Protocol contributed to the cooling break in 1994. As the authors point out, their new results suggest that, ironically, “the recent decrease in warming, presented by global warming skeptics as proof that humankind cannot affect the climate system, . . . [has] a direct human origin.”
As the negotiations at Warsaw conclude this week it is unlikely that they will result in a groundbreaking new climate treaty. That failure should not be a reason to believe that international climate treaties hold no hope however. Both the theory of international negotiations, and the evidence presented in this recent Nature paper of the success of the Montreal Protocol in slowing warming, suggest that international treaties do have the potential to slow or stop global warming. It remains to be seen whether that potential will be realized or if climate change treaty negotiations will continue to be so much hot air.
Image Credit: By NASA