The two attached pictures are schematic diagrams of the circulation of carbon on Earth (IPAA Report (2001) – the Carbon Cycle). If I Google “Carbon Cycle Diagram” in the image mode, I get close to a million entries. Most of these entries look like the second image – not the first. What is the difference? The second one doesn’t have numbers (photoshopping on my part).
The numbers in the arrows of the first image represent fluxes of carbon per year in units of billion tons of carbon. The numbers outside the arrows represent quantities in the same units of billion tons of carbon. The man-made (anthropogenic) contributions are shown by the dashed red arrows.
Scientifically, it is very difficult to argue with the second diagram. I have to make qualitative statements like, “I don’t believe that carbon is exchanging between the atmosphere and the oceans.” It is much easier to argue – scientifically – with the first diagram. If I have the background and tools, I can either try to follow the original measurements or to take the measurements myself. It doesn’t really matter if the job is too big; the fact that, in principle, I can do it, makes the first diagram science, while the second figure is obviously a good qualitative description but is not actually science.
Back to deniers and skeptics: I have been approached by friends (some of them with good science backgrounds) and students, who tell me (nicely) that since carbon dioxide is a “natural” product, it cannot be bad, so the EPA (Environmental Protection Agency) should not have to identify it as a pollutant. Sometimes the conversations have gone on to suggest that if I want to avoid global warming, I should simply stop breathing (since they know that we exhale carbon dioxide). They have asked me kindly to get off their backs and stay away from commenting upon their energy usage. In the cases where conversations got more heated and evolved to include other greenhouse gases, the suggestions went as far as, “Well, why don’t we regulate cows so they’ll stop farting.”
Well, here is where science comes in. When it comes to the carbon cycle, we can analyze the numbers. We can add up the amount of carbon that is going from the earth to the atmosphere, and subtract that which is doing the reverse – entering the earth from the atmosphere. (The carbon in theses fluxes mainly takes the form of carbon dioxide.)
The result? It shows that there are 3.1 billion tons of extra carbon being added to the atmosphere. Since carbon dioxide is a very stable compound, it will stay in the atmosphere for many years. If we assume that this same kind of flux will be more or less maintained from now until the end of the century (the “end of now” time-frame that I talk about in my book), the atmospheric concentrations of carbon will grow by close to 50%. This is a major difference that directly affects our energy balance with the sun.
3.1 billion tons is less than half of what we emit into the atmosphere (red broken arrows in the picture). The difference means that both the earth and its oceans have now become net “sequesters,” or absorbers of the excess carbon dioxide that we produce. Vegetation and soil, in the form of enhanced growth because of the carbon dioxide that fertilization contributes, and areas of the ocean that absorb carbon dioxide, contribute as well. As the temperature rises, the capacity of these methods of compensation is expected to decrease, until they reach the point where both the earth and our oceans no longer absorb the carbon dioxide, but instead reverse themselves to be net emitters. Some would call this a “tipping point.”
This makes us part of the physical system that we investigate, and negates, at least in my mind, the option of waiting with remedies until the consequences of these changes are absolutely certain. Science tells us that the danger exists, so the remedies should be approached as an insurance premium.
We are now busy searching for planets outside the solar system. We are particularly interested in finding planets in the habitable zone of stars- an area defined as a zone around a star, within which it is possible for a planet to maintain liquid water on its surface. We have, up to now, been able to identify more than 700 exoplanets; last December, NASA announced the its discovery of the first exoplanet in a habitable zone of another star. It is a narrow zone, but it offers the best chance so far to find life forms outside our own planet. We are doing well, but we have a long way yet to go in that quest. On a cosmological scale – destruction of a habitable zone is not very difficult – Venus can serve as a good example. The pace of the atmospheric changes that we are inducing, meanwhile, might lead to the first observable instance of the destruction of a habitable zone. For a far away civilization, it will be scientific observation. For us it will be a collective suicide.