The atmosphere is made up of a variety of gasses:
The greenhouse effect gets it name from glass (or plastic) greenhouses. Your car is an excellent example of a greenhouse. In a greenhouse, the suns rays come through the clear glass as visible light. Some of the light is absorbed by things (e.g. plants, dirt in a greenhouse, plastic, cloth in a car) and converted into heat. The heat does not escape easily back through the glass. Thus, the inside of the greenhouse is warmed!
The earth is one giant greenhouse. The three most important gases in the atmosphere which trap heat like glass does in a greenhouse are:
What would the earth be like if there were not greenhouse effect?
The answer is that the average temperature might be near zero degrees F instead of the nearly 50 degrees F it is today!!
Just how these various gases interact with other is quite complicated. For example, if the oceans are warmer, then more water is evaporated into the atmosphere which would trap more heat. But more water also makes more clouds which reflects sun light back into space - thus cloudy days are generally cooler than sunny ones. Scientific journals have many research papers on these questions.
It is important to know the difference!
Definition: Global Warming: the phenomena of the average climate on earth becoming warmer. Because this deals with average climate, and not day to day weather, not all places will be warmer and not all days will become warmer.
In the 1970s, there was great alarm that we might be heading for a new ice age as the earth was getting colder. In more recent years, the fear has been that the earth is warming. As we read, the earth's climate has had significant changes from time to time. Such changes can be very uncomfortable to people and the environment which come to depend upon a certain climate.
Along with scientific debate of global warming has come a call for political action to "stop" global warming. The first proposed action was called "Kyoto" - named for a meeting in Kyoto, Japan.(See The Kyoto Accords) This accord would require various nations to lower the amount of man made CO2 production. The US never signed the accords. Kyoto would require us to use less gasoline, natural gas, and coal. The actual Kyoto accords are no longer central in the discussions, but the concept of reducing man-made CO2 by using various cap/trade arrangements is central. The most recent international meeting was in Copenhagen in late 2009. The meeting ended with no unified call for action. The meeting bogged down in discussions of how many billions of dollars the US and other Western nations would give to other nations to "help" them reduce emissions. Also, China (and India) were realistic in saying that it was impractical for them to lead reductions in emissions.
Most politicians are promoting various kinds of so-called cap and trade schemes to "solve" global warming. The hope is that global warming can be "solved" by reducing man-made CO2 using cap and trade schemes. While there are many variations both in practice (some European nations for instance) and proposed (US, Australia), the idea is this:
Some who accept that global warming is a problem propose that rather than try to cut CO2 emissions, we should find other solutions. The idea to try to "fix" global warming without destroying the world economy. Proposals have included:
These alternatives receive less press than "cap and trade", even though they may be more likely to actually affect climate.
The proposed political action is based upon the following logic sequence. This sequence allows us to see the importance of these questions:
It is very important to understand this sequence. Our whole study of global warming depends upon it!
The "party line" goes like this: We should take political action to reduce man-made CO2 emissions into the air because: 1. Use of fossil fuels produces CO2 which is the major cause of 2. The amount of CO2 in the atmosphere is increasing 3. The increased CO2 in the air is the major cause of 4. The average temperature of the earth is increasing. 5. The average temperature will continue to increase as man-made CO2 increases 6. This increase is a bad thing. 7. The political action (in this case, Kyoto/cap/trade) will reverse the "bad thing" (CO2 in the air and, if all the above are true, global warming). 8. The side effects of the political action are not worse the the problem(s) it solves.Each of these 8 steps is the subject of some scientific and/or economic debate and study. It is critical to understand that if any one of these eight steps is not true, then the connection between the political action of decreasing CO2 emissions and avoiding something "bad" is broken!
There is legitimate scientific debate about most of these logical steps.
Notice that news reports make much fanfare when there is new evidence that perhaps one of these eight steps is true. But remember that all eight must be true to justify the political action in cap/trade schemes.
We could rate the 8 steps in terms of how well accepted they are or are not as follows:
||Source of Knowledge
|1 Man causes CO2
||Widespread but not universal. Serious science has
been proposed to say that a change in climate causes the
rise in CO2.
|2 CO2 increasing
||Mauna Loa measurements
|3 Increase in CO2 causes
|Models / Speculation
||Heated dispute among scientists.
High acceptance among politicians
|4 Earth is warming
|Serious debate due to measurement
problems. Recent information suggests that scientists processing raw data have "fudged" the data.
|5 Earth will continue to warm due to man
||Models have known errors and limitations (1)
|6 This warming is bad
||Models / Speculation
||Vigorous debate, both scientific and economic
|7 Cap/trade will fix
||Accepted only by political proponents
Opponents note that details make it unlikely that Cap/trade will reduce CO2 significantly.
|8 Cap/trade side effects are tolerable.
||Near religious faith that "environmentally
friendly" energy is available.
proponents don't discuss harmful side effects.
MAJOR concern of opponents of Cap/trade. It is argued that it is not practical shift from fossil fuels to alternatives in the next decade or two which means the only way to significantly reduce CO2 is to dramatically lower energy use - equivalent to ceasing economic activity. See note 2.
(1) The question of whether the earth will continue to warm has several components:
(2) The concept of step 8 is expressed in the book The Black Swan by philosopher Nassim Taleb: "Not understanding that doing nothing can be much more preferable to doing something potentially harmful. (Mistake made by most people who are not grandmothers.)" (emphasis added) This is item #5 in his list of the main errors people make in understanding the message of this significant book.
Final Policy Question: This is a critical question which is seldom asked in public!! "Given the uncertainties of the science, should we devote resources to trying to change the climate or to adapting to the changes we predict?"
Scientists have proposed various causes of climate change. An increase in atmospheric CO2 is a recent suggestion. Others have proposed that variations in the sun's energy, measured to vary about .1% during the most recent 11 year annual cycle.
It is interesting to note that during the "little ice age", the very cold period in the last 1600's and early 1700's, there was a noticeable change in the sun with far fewer than normal sunspots. Some scientists have proposed that the cold climate was caused by the change in the sun.
In the final analysis, there are no convincing, widely accepted explanations for historical changes in climate.
We will conclude these notes with an interesting example of what one believes about global warming affects the way in which scientific observations are interpreted. First, let's look at the actual scientific observation:
At the December, 2004, meeting of the American Geophysical Union, Dr. Lonnie Thompson of Ohio State University described the discovery of a bed of plants high in the Andes mountains which are believed to have been hidden by glacial ice for 50,000 years. (See http://researchnews.osu.edu/archive/quelplant.htm.) The 50,000 year date is based on Carbon-14 dating and thus subject to all of the uncertainties of that method. Previous finds of plants revealed as glaciers have melted were dated to about 5000 years.
Now, what does this mean? Consider two interpretations.
Which interpretation do you suppose has been dominant in the popular press?