What is it?

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 Fahrenheit. 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, or exacerbated, by human activity. The Environmental Protection Agency has a page that explains this effect visually for the textually challenged.

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 of the earth) 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). The disagreement often hinges around whether this is just climatic variation. Yes, climates change, obviously if we were in a glacial period about 14,000 years ago.

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? The Bush/Cheney Adminstration clearly said that the U.S. wouldn’t self-impose CO2 emission limits if it hurt the economy, going so far as to restrict its own scientists from speaking publicly. Obama has been more open to policy changes, but there is great resistance and even he has been using the term ‘clean coal’ since before the election in 2008 (meaning he thinks that burning coal is okay, as long as it’s ‘clean’). Others say that addressing global warming would actually create many jobs –they just 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. The Bush Administration said that the science was ‘inconclusive,’ and that the effect on the economy would be disastrous. On the other side, on a warming planet with more extreme weather events (Hurrican Katrina or more recently Hurricane Sandy, for instance), the costs of dealing with just one weather-related disaster can be in the billions. One of the problems is, however, that by the time the science is indisputable, it may be too late to modify changed climatic patterns (most scientists think we’re already beyond reversing the trend).

So back to the greenhouse. If you’ve ever walked in one, you know how warm it can be. The sun’s rays hit the glass, and penetrate, some of that energy being taken up by plants, some bouncing around the greenhouse, some trying to re-radiate back out. But the rays aren’t able to re-radiate–they have longer wavelengths that make penetrating the glass (or the atmosphere) more difficult.

Now, imagine adding 10 or 12 space heaters to the greenhouse. How will you power them? Electricity, you say? From a plug? Powered by fossil fuels?

Then what?