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Name: Mark
Status: other
Grade: 9-12
Location: 9-12
Country: N/A
Date: 5/31/2005


Question:
In all the discussions of global warming and pollution in general, I don't believe I have ever seen any information on background, natural sources for the green house gases and the various other pollutants. How do the man made sources of pollution and green house gases compare with the natural sources?


Replies:
Based upon what I remember having read in the Wall Street Journal (which has published several op-ed articles by experts) man made greenhouse gases are a very small fraction of the total. For example, water vapor is a greenhouse gas. "Google" on "natural greenhouse gas".

Mike Loop


There is a lot of literature on "natural" vs. "anthroprogenic" climate change and pollution. Once you tap into it you will find a lot of disagreement with extremists on both fringes abandoning science and data for posturing and dogma. For a start the report "Understanding Climate Change Feedbacks" published by the National Research Council in 2003 will give you some understanding of the complexity of the conflicting issues with a fairly balanced point of view. The book "The Skeptical Environmentalist" by Bjorn Lomborg provides a perspective tending toward skepticism of the conventional wisdom of environmentalists. There are any number of books that argue the conventional environmentalist perspective.

Both sides tend to commit logical fallacies to support their position -- in lieu of actual data, which is amazingly scarce. Two contrary examples suffice to illustrate my point. Global warming implies an increase in a "global temperature", but what does that mean? Where I live the temperature can range +/- 20 C. in less than a day, and changes by an even larger amount with altitude, so what does a "global temperature" mean, and how is it measured, and does it mean anything? On the other side some antagonists argue that increasing agricultural productivity with chemicals improves the environment by "freeing up" land for forests, wetlands etc. What is ignored is that the "freed-up" land often goes to "suburban sprawl" and not returned to pristine conditions.

If you do a literature review on the two journals "Nature" and "Science" for the past 1-10 years you will find a wealth of data surrounding the issues you wish to address. Both are prestigious, peer-reviewed journals so they are about as close to a non-biased position as you are likely to find on some very contentious issues.

Vince Calder


There is actually a great deal of naturally produced greenhouse gases in the atmosphere. And that is a good thing, because without our protective blanket of gases, we would fry during the day and freeze at night. There is a difference between the greenhouse effect (good) and global warming (faster than normal temperature change). Also, if you look at the records of climate change over geologic time, we have obviously had very many changes in our climate.

There is a cycle of ice ages that last approximately 100,000 years followed by a 10,000 year interglacial period. During the current interglacial period, humans have been evolving and developing culture and agriculture. So it has been only relatively recently that humans have had a chance to alter the global climate pattern. It has been 11,000 years since the last ice age so we are due for one. Scientific American had an article a few months ago that hypothesized that humans have prevented a new ice age through their agricultural practices. So, to answer your question. The atmosphere does contain a high concentration of carbon dioxide. But if you look at the trends in the atmosphere through the geologic record you will see that the atmosphere used to contain a lot more, in fact it was one of the most prevalent gases in the early atmosphere. Once life began and organisms started taking in carbon the amounts began to fall rapidly. Now the level of carbon dioxide is about 0.4% of the atmosphere. However, before humans began adding more by burning fossil fuels, the level was 0.2%. So, since humans have been around, the level has doubled. Is that enough to push global climate change to the levels we see now? Is it natural? Or is it a combination of both? Time will tell.

Van Hoeck


You bring up a very difficult and contentious issue: "natural" vs. "anthroprogenic (caused by humans)" greenhouse gases. The answer is no one really knows. The entire issue of global warming is hotly debated with both sides often basing all sorts of consequences without the aid of adequate data or climate models. If you can find the journals "Science" and/or "Nature" in your school or public library you will find numerous articles published every week. Everyone (almost) agrees that the level of CO2 in the atmosphere has been increasing over the last century. However, not everyone agrees that this is due to human activity, that it is necessarily bad, or that it is significant. Some question that "global temperature" is even a meaningful or useful term. That is: given the large variations in temperature with longitude, latitude, altitude, geography, etc. can a single "temperature" accurately measure what it is claimed to measure.

Global warming is often "measured" by "proxy" effects. These include effects like the pattern of tree rings, various isotope ratios in ice borings, and many others. However, the relation of these proxy measurements and climate depends upon some sort of model relating what is observed with global thermal effects. There is a lot of disagreement over the reliability of these models. There are a number of feedback mechanisms that determine both weather (short term) and climate (long term). Some are the CO2 cycle, the H2O cycle, particle and aerosol cycles, solar irradiance -- and those are just a few of maybe a dozen. All of these cycles interact with one another. In the recent past, some authors had predicted global disaster by the year 2000. It never occurred. That is not to say that the issues raised are not valid, but the models were not able to take into account developments, both in nature and in technology. The "green revolution" increased the efficiency of agriculture. That was not envisioned in the 1960's. Fiber optics greatly reduced the demand for copper. The invention of semiconductors made computation far easier and faster than anyone even dreamed of 50 years ago. I do not mean to belittle concern for the environment. The point is that if we try to predict the future based on the past, the basis for prediction is very uncertain, and one needs to be careful not to be too dogmatic about what the future holds.

Your question is very good, but the answer is very uncertain.

Vince Calder



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