Think of how a greenhouse works. The sun’s rays can penetrate the glass. But once inside, they’re pretty much stuck–they can’t re-radiate and escape through the glass, because the length of the rays has changed. The earth works in somewhat the same way. The atmosphere insulates us from the cold of space–without it, temperature here on earth would be around 0 degrees farenheit. The greenhouse gases play an important role in absorbing the heat that re-radiates from the earth, and keeping us warm. No one disputes the existence of the greenhouse effect. The dispute is over whether it is affecting our climate, and whether changes in global temperatures are being caused by human activity. The Environmental Protection Agency has a page that explains this effect in pictures (I struggle with stick figures).

So why do we care? Because we think that the greenhouse effect may warm average temperatures on the earth, causing changes in climate patterns. This doesn’t mean all climates will get warmer, but it does mean it may be more difficult to predict climates (that characterize regions) and weather (the hour-to-hour, day-to-day variations) in places, and that there may be more violent storms. And . . . likely more melting of the polar ice caps, as the oceans have great heat-holding capacity. Even a slight increase in average temperature could have dramatic effects on climate, and on the living organisms and their abilities to adapt.

One of the problems with showing that there is global climate is finding evidence of temperature changes. We’ve only been recording temperatures for 100 years or so. But there are records going back further –some in Europe (where people might have recorded when a certain flower blossomed, for instance, or when a lake began to thaw in the spring). Old trees of over 1,000 years can provide information in their growth rings. Polar ice cores show differences in sedimentation layers, suggesting when summers were warmer/longer. It’s also wise to remember that we’re in the middle of a glacial recession–this part of the world was once under ice–maybe 14,000 years ago, which isn’t really too long if you think like a geologist. The global warming skeptics often say that it is easy to find variation in temperature over the last 1,000 years or so. But scientists are looking for global averages–yes, some areas may get warmer and some colder–that’s why an average for the earth is important (and this requires painful data collection at many points on the globe). According to the video we saw (in Badgley 202), there is disagreement over whether this is just climatic variation. Yes, climates change, obviously if we were in a glacial period not too long ago (geologically).

However, it is indisputable that since the industrial revolution, humans have been putting a lot more of certain greenhouse gases into the atmosphere–mostly carbon dioxide. At the same time, we’ve deforested large areas of the tropics. This is a problem because trees are able to ‘fix’ the CO2, and release water and oxygen (part of the process of photosynthesis). Oceans can also absorb quite a lot of CO2. As the film said, since the 1940s, the amount of carbon dumped into the air has increased some seven fold. CO2 concentrations have increased 30% in the atmosphere since the beginning of the industrial revolution. There is pretty clear evidence that average global temperatures are increasing at unprecedented rates.

So . . . the evidence is compelling. What should be done, and who should do it? Some politicians believe that the U.S. shouldn’t self-impose CO2 emission limits if it hurts the economy. Others say that addressing global warming would actually create many jobs (but they wouldn’t be in the fossil fuel industry …). Of course, we’re talking in the short run . . . as economist John Maynard Keynes said, in the long run, we’ll all be dead (not trying to scare you, it just depends on how you define ‘long run’). The U.S. is the number one producer of greenhouse gases. Critics of making a transition from fossil fuels contend that the science is ‘inconclusive.’ The tobacco industry used the same argument for decades when confronted with evidence that smoking greatly increased chances of lung cancer. One of the problems is, however, that by the time the science is indisputable and the critics long gone from public office, it may be too late to modify changed climatic patterns. Current debates among leading scientists are beginning to broach whether in fact it may be too late to reverse some of the disturbing trends seen in the climate data.

Scientist James Lovelock referred to the atmosphere as an ‘organ of temperature regulation.’ What does he mean by that? The atmosphere is made up of gases: nitrogen (78%), oxygen (20.9%, and argon (.9%). 80% of these gases are in the lower portion of the atmosphere–the troposphere–which is warmest near the bottom, fortunately for humans. And the last .2%? That includes some very important ones, like ozone (O3) and carbon dioxide (CO2). Because of CO2’s heat-holding capacity, it turns out to be very important in terms of average global temperatures.

In the history of the earth there have been a few developments that have affected the warming and cooling trends. As Tim Flannery says in his book The Weather Makers, research suggests that cooling almost killed off the living species a couple of times–when ice reaches south as far as 30 degrees latitude, it creates a self-reinforcing cooling that can reach the equator. This is partly because of albedo, which means reflecting sunlight and heat off the earth’s surface–ice does this much better than water or forests, for instance (Check out where albedo is high, and not, in the image below). And though CO2 exists in such small amounts, it plays a crucial role in preventing excessive cooling. So some 540 million years ago the first living organisms with skeletons began to affect the carbon cycle–and remember, the more carbon in the atmosphere (and it comes from living organisms, usually long dead, and those ultimately from the sun’s energy), the more heat-holding capacity, the less carbon, the colder temperatures will be, the lower sea levels will be, and with more water will be locked up on the continent, meaning less water cycling through the planet (probably drier climates, in other words).

Source: NASA

Effects?

From scientist James Lovelock (speaking somewhat metaphorically):

There must be an intricate security system to ensure that exotic outlaw species do not evolve into rampantly criminal syndicates …

When a species … produces a poisonous substance, it may well kill itself. If, however, the poison is more deadly to its competitors it may manage to survive and in time both adapt to its own toxicity and produce even more lethal forms of pollutant.’