This is really a very hind layer if you think about it. In the book The End of Nature, author Bill Mimicking tells of walking three miles to from his cabin in the Adirondacks to buy food. Afterwards, he realized that on this short journey he had traveled a distance equal to that of the layer of the atmosphere where almost all the action of our climate is contained. In fact, if you were to view Earth from space, the principle part of the atmosphere would only be about as thick as the skin on an onion!
Realizing this makes it more plausible to suppose that human beings can change the climate. A look at the amount of greenhouse asses we are spewing into the atmosphere (see below), makes it even more plausible. What are the Greenhouse Gases? The most significant greenhouse gas is actually water vapor, not something produced directly by humankind in significant amounts. However, even slight increases in atmospheric levels of carbon dioxide (CO) can cause a substantial increase in temperature. Why is this?
There are two reasons: First, although the concentrations of these gases are not nearly as large as that of oxygen and nitrogen (the main constituents of the atmosphere), neither oxygen or nitrogen are greenhouse gases. This is because neither has more than two atoms per molecule (I. E. Their molecular forms are 02 and NO, respectively), and so they lack the internal vibration modes that molecules with more than two atoms have. Both Water and CO, for example, have these “internal vibration modes”, and these vibration modes can absorb and irradiate infrared radiation, which causes the greenhouse effect.
Secondly, CO tends to remain in the atmosphere for a very long time (time scales in the hundreds of years). Water vapor, on the other hand, can easily condense or evaporate, depending on local conditions. Water vapor levels therefore tend to adjust quickly to the prevailing conditions, such that the energy flows from the Sun and re-radiation from the Earth achieve a balance. CO tends to remain fairly constant and therefore behave as a controlling factor, rather than a reacting factor. More CO means that the balance occurs at higher temperatures and water vapor levels.
How much have we increased the Atmosphere’s CO Concentration? Human beings have increased the CO concentration in the atmosphere by about thirty percent, which is an extremely significant increase, even on inter;glacial timescales. It s believed that human beings are responsible for this because the increase is almost perfectly correlated with increases in fossil fuel combustion, and also due other evidence, such as changes in the ratios of different carbon isotopes in atmospheric CO that are consistent with “anthropogenic” (human caused) emissions.
The simple fact is, that under “business as usual” conditions, we’ll soon reach carbon dioxide concentrations that haven’t been seen on Earth in the last 50 million years. Combustion of Fossil Fuels, for electricity generation, transportation, and heating, and also the manufacture of cement, all result in he total worldwide emission of about 22 billion tons of carbon dioxide to the atmosphere each year. About a third of this comes from electricity generation, and another third from transportation, and a third from all other sources. This enormous input of CO is causing the atmospheric levels of CO to rise dramatically.
The following graph shows the CO levels over the past 160 thousand years (the upper curve, with units indicated on the right hand side of the graph). The current level, and projected increase over the next hundred years if we do not curb emissions, are also shown (the part of he curve which goes way up high, to the right of the current level, is the projected CO rise). The projected increase in CO is very’ startling and disturbing. Changes in the Earth’s average surface temperature are also shown (the lower curve, with units on the left). Note that it parallels the CO level curve very well.
Is the Temperature Really Changing? Yes! As everyone has heard from the media, recent years have consistently been the warmest in hundreds and possibly thousands of years. But that might be a temporary fluctuation, right? To see that it probably isn’t, the next rap shows the average temperature in the Northern Hemisphere as determined from many sources, carefully combined, such as tree rings, corals, human records, etc. These graphs show a very discernible warming trend, starting in about 1900. It might seem a bit surprising that warming started as early as 1900.
How is this possible? The reason is that the increase in carbon dioxide actually began in 1 800, following the deforestation of much of Northeastern American and other forested parts of the world. The sharp upswing in emissions during the industrial revolution further added to this, leading to a significantly increased arbor dioxide level even by 1900. Thus, we see that Global Warming is not something far off in the future – in fact it predates almost every living human being today. How do we know if the temperature increase is caused by anthropogenic emissions?