Monday, December 14, 2009

The Primacy of CO2

In a recent article in the journal EOS, three different ideas were floated about the role people play in changing environmental systems such as long-term climate trends. These are scientists speaking before the so-called “climategate” controversy on the origins of climate change, the main forcing mechanisms driving it, and what we can do to help mitigate the situation. This is important because unless we know what is causing climate change, we cannot effectively figure out ways to stop it. The effectiveness of mitigation policies such as those being debated right now in Copenhagen is contingent on the science being right. In summarizing the situation, they laid out the possible positions one could take on the issue.

Hypothesis 1:
“Human influence on climate variability is of minimal importance and will continue to be significantly less important than natural causes of climatic variation.”

Hypothesis 2a:
“Human influences on climate variability are significant and involve a number of causes (first order climate forcings) including but not limited to human emissions of CO2. These human influences will continue to generate changes in the coming decades.”

Hypothesis 2b:
“Human influences on climatic variability are significant and are dominated by the release of additional greenhouse gases to the atmosphere, the most important of which is CO2. The impact of these additional gases constitute the primary climate issue in the coming decades.”

The authors grouped the last two together (Hypotheses 2a and 2b) because in many ways, they are oppositional views to the first. They quickly conclude that based on the scientific literature, overwhelming evidence exists showing a significant human role in changing climate conditions worldwide. So we can cross off Hypothesis 1 from the list of reasonable answers.

As for the others, a great deal of evidence indicates that while CO2 is a critical factor in the warming of the atmosphere, it is not the sole way in which people have been effecting change to climate. The other factors they mention include the effects aerosols have on clouds and precipitation, soot changing reflectance and absorptive qualities, and changes in land use/land cover in influencing atmospheric and oceanic circulation. This would seem to tilt the scale in favor of Hypothesis 2a.

This should serve as a significant reminder as we wait for decisions to be finalized in Copenhagen that while emissions may be important, any agreement should not be only focused on reducing CO2. While the social and economic implications of reducing CO2 emissions have been well documented in the popular media, the social conditions driving these other forcing mechanisms (such as population growth, urbanization, land management, agricultural clearing, insect and disease vectors, etc) may not be as widely understood.

Many of the drivers of climate variability and their impacts will play out on a local or regional scale (more on this later). Any type of mitigation strategy should look to include elements beyond CO2 emissions. Any assessment of local vulnerability and risk should also acknowledge the uncertainty inherent in these interdependent forcing mechanisms.

In a way, looking beyond CO2 makes any proposed international agreement on climate change far more complicated. On the other hand, if negotiations on CO2 emission caps stalls during negotiations we should be heartened by the fact that there is still progress that could be made on topics not as inherently politicized.

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