The discussion of rising levels of carbon dioxide in the atmosphere has centered on the predicted and -- to a certain extent -- experienced rise in the average temperature around the globe. That's one of the results, but there are three others. The four predicted changes are:
- Global Warming,
- Weather changes,
- Shifts in disease vectors,
- Oceanic acidification.
The descriptions after the jump
- Global warming is the first consequence, and one should realize that scientists' "warming" goes beyond a shift in temperature. When you bring a glass of water and ice cubes into a warm room, it absorbs the heat; its temperature doesn't change, however, until all the ice has melted. Now, that is a simple system while the global climate system is much more complicated. One principle remains the same; heat which goes into melting ice doesn't raise the temperature. People speak of the melting of the polar caps as a result of rising temperatures, and so they are; but they are also an alternative to rising temperatures. Some of the heat retained by current levels of carbon dioxide will increase temperatures; some will melt ice; some will evaporate water.
Which means, among other things, that current CO2 levels would increase northern-hemisphere temperatures more rapidly if the ice were not on the arctic sea to melt. There are predictions that it will be gone during summers fairly soon. What will happen to northern-hemisphere temperatures then?
- Weather changes are mostly a direct result of how CO2 modifies the heat transfer within the atmosphere. (The increasing likelihood of more serious hurricanes seems to be a result of the warming itself..)
When high-energy light from the sun warms the ground and the water, much of that heat is radiated back as lower-energy infrared light. Carbon dioxide absorbs more of that wavelength That heats the CO2 in the atmosphere, which then radiates that heat as infrared light in all directions.-- half of it going upward and half going downward towards the ground again. Just as a blanket which does not produce heat and which is colder than you keeps you warm at night by absorbing heat radiated from your body and radiating half of it back towards you, this reradiation keeps the earth warmer than it would otherwise be.
Some of the heat goes to evaporate water, even some of the heat falling on "dry" ground does. That water vapor enters teh atmosphere, is shifted around, and -- finally -- condenses back to liquid water. That liquid water is called rain, and when it condenses in the atmosphere, it releases as much heat as it absorbed in evaporating. Thus, an important factor in transferring heat from one point on the surface to another is the weather. This is unpredictable at the best of times. When the general conditions of heat exchange are stable from one year to the next, however, the probabilities of weather patterns are fairly consistent from one year to the next. When the atmosphere absorbs slightly more heat from the ground each year than it did in the previous year, those probabilities are much less reliable. And the differences of weather pattern in the previous year means that there is a different amount of ground water to evaporate in many regions.
One should be clear that "unusual weather" in any region means that it is unusual for that region. The rainfall that might be a drought in Oregon might cause floods in Arizona. What the earth experiences as rain falling in different places, particular localities experience as floods and droughts.
- Shifts in disease vectors. are a consequence of weather changes, but also of global -- or, at least, local -- warming. Diseases that affect humans are carried by insects and other animals. When the hosts can't cross natural boundaries because they are too cold (or too hot, or too dry, or too wet), then the disease doesn't cross those boundaries either. Slight changes in local weather can turn an impervious boundary into a quite easily crossed one. When that happens the disease can affect a different host animal with which the original host animal hadn't been in contact when the boundary was effective. That can spread the disease to an entirely new habitat. That habitat may be full of animals, including humans, who have no resistance to the disease.
The spread of such diseases as "West Nile Virus" are already being blamed on this factor.
- Oceanic acidification is the consequence of rising levels of atmospheric CO2 which is least related to Global Warming. It is, in fact, almost an alternative to it. Rising levels of CO2 in the atmosphere result in rising levels of CO2 in the surface levels of the ocean. That is the few meters where most life exists. Now, there is continual exchange between the surface waters and the atmosphere. I have never read even a denialist who claims that there is not. The concentrations in each are distinct, but they are positively related.
And higher concentrations of CO2 in water mean that the water is more acid or -- in the case of seawater -- less basic. (The CO2 dissolved in the ocean surface water is, however, removed from the atmosphere. It no longer participates in Global Warming.)
Paradoxically, while some sea animals use dissolved CO2 to form their shells, they find the amount available to them is diminished in more acidic water. The more CO2 dissolved in the water, the less CO2 removed by shellfish. Acidification has other negative consequences to marine life, as well.