On October 18th, Harvard’s Environmental Action Committee will kick off its “Road to Copenhagen” with a convocation by climate activist Bill McKibbon at Memorial Church. Over the following five days, the organization will host a series of events that focus attention on the need to stabilize the atmosphere’s carbon concentration at 350 parts per million. The festivities will culminate on the 24th with the International Day of Climate Action. The brainchild of McKibbon, 350 intends to promote global community actions that can be recorded and presented to world leaders when they meet in December at Copenhagen to negotiate a new climate treaty. McKibben, along with many other environmental activists, hopes that these images will serve as evidence of global support for reducing carbon concentrations to 350 ppm.

All of this begs the question: What is so special about 350 ppm, and why should it be the target? The answer to the former can be found in a December 2007 paper by NASA scientist Jim Hansen (and others), which identifies 350 ppm as the concentration at which carbon levels would have to stabilize in order to minimize climate-change impacts. The paper cites potential “irreversible catastrophic effects” if we exceed the 350 ppm target for a long period. An article in Nature and the support of the head of the Intergovernmental Panel on Climate Change, Rajenda Pachauri, have since corroborated their findings. Generally, the evidence suggests that sustained concentrations above 350 ppm will lead to drastic increases in global temperature, the complete melting of polar ice, and dramatic loss of biodiversity.

It may seem obvious then why 350 should be our target. However, nothing in climate politics is simple or obvious. Scientifically, it may be clear that if we do not target 350 ppm we are asking for a disaster. But politics does not always pay attention to science. Rather, officials see that the first step to hit the 350 ppm mark is to eliminate all coal-fired power plants by 2030, which buys a lot of political opposition. Power companies, coal companies, coal states, coal workers, and anyone who likes cheap energy have a stake in seeing that 350 ppm does not become the target.

As a result, events like the 350 Day can play an important role in reaching this goal. If we hope to change the political atmosphere, we must start with vocal public support for reducing emissions. Otherwise, the negotiators at Copenhagen and in the U.S. Senate, among other places, will accomplish nothing of substance. Anyone who has an interest in seeing a meaningful treaty develop this December (read: everyone) should be taking action this coming week to make sure that policy makers know what is at stake—and that the world demands change.

If we continue to increase from our current 390 ppm, we will soon hit the point between 450 ppm (the IPCC’s current target) and 500 ppm, at which Earth will become completely ice-free. An ice-free world would lead to, among other things, higher sea levels and decreased fresh-water availability as glaciers that supply nearly one billion people with water disappear. Furthermore, while many climate naysayers point to relatively stable global temperatures in the last decade, they ignore that the decline in summer arctic ice that scientists had predicted would occur in the next 80 years now appears likely to occur in the next five. This is one of a number of climate-related phenomena—including expanded ranges for mosquitoes and changes in amphibian breeding cycles—that are occurring much sooner than anticipated. This suggests that the current target is simply too high.

Thus, to come back to our question, why 350 ppm? The cynical answer is that ,while political inertia will prevent us from reaching 350 ppm in any meaningful time frame, aiming for that level might be the only way we can reach 450 ppm and avoid some of the worst dangers of climate change. Achieving 350 ppm promises to be enormously expensive and, barring a climate catastrophe in the next few years, is not likely to happen in the near future. However, without grassroots mobilization and political pressure to reach 350 ppm from events like the 350 Day, it is highly unlikely that we will change business-as-usual emissions enough to stabilize below the highly-dangerous 500 ppm.

As a step in the right direction, join the EAC on the 24th it weatherizes homes around Cambridge to make them more energy-efficient. This is a simple way to reduce Cambridge’s own footprint while helping to build the grassroots support for 350 ppm that will be necessary to overcome political inertia. The coal industry has a strong political voice already—those in favor of climate policy now need to match it.

A. Patrick Behrer ’10 is an economics concentrator in Eliot House. His column appears on alternate Thursdays.