overhead: some temperature plots versus time for two cities at the same latitude. The average temperature of the city at higher elevation was lower than the city at low elevation for every month of the year. This once again emphasizes that latitude is not the only factor that determines temperature.
Some concrete examples of the moderating effect of water:
definition: thermal equator is line around the globe that goes through the hottest points. It will differ from the real equator (0 degrees latitude) and typically will go over landmasses (since water has a moderating effect on climate and land does not).
Most climate-action will occur over continental landmasses (Siberia is a good example of extreme temperatures). Remember that the elevations at the poles are important causes of the difference in their temperatures. The North Pole is mostly water and relatively flat. The moderating effect of water and the low elevation contribute to its relative warmth compared to the South Pole. The South Pole has an elevation of 9300 ft and has a few mountain ranges. In addition, it has a high albedo and is covered in ice and snow. All these factors contribute to the South Pole being quite cold.
When we look at global climates over the past 65 million years, we see that temperature has been dropping, and the trend has been toward colder and drier climates. If we look on a smaller timescale, we see that temperatures have increased since the "Little Ice Age" (mentioned earlier in the term while discussing sunspots). In the 1970's, temperatures actually decreased. So the question we face when trying to analyze temperature changes is what scale do we examine them on? We need to consider a global timescale, not a geologic one. The data then shows that the general trend is toward increasing temperatures. The cause of this has been attributed to the greenhouse effect.
What is the greenhouse effect? It is the natural trapping and recycling of energy that originally came from the sun but has been re-radiated from the Earth back to the atmosphere and from the atmosphere back to the Earth. This effect makes our planet livable and makes the temperature 30 to 35 degrees C warmer than it would be without it.
So what is the big deal about carbon dioxide causing the greenhouse effect? Greenhouse gases act to accelerate the natural greenhouse effect and increase the recycling of energy back down into the ground. This increases temperatures.
Actually, many gases are greenhouse gases, but humans are putting a lot of CO2 into the air, especially the lower atmosphere. Furthermore, CO2 has a long residence time, meaning that once it is put in the air, it stays there for a long time. There is also a correlation: the % CO2 in the atmosphere is increasing measurably, and at the same time, average temperatures are warmer no matter where you go. Even though the percentage of CO2 emissions from North America has dropped, the CO2 emissions have increased from 1.6 x 106 tons in 1950 to 5.2 x 106 tons in 1980, and show no signs of getting better.
What will the effect be of ever-increasing CO2 levels in the atmosphere? You need models to try to predict what will happen. The early models made incorrect predictions, which overestimated the rise in temperature that would occur. They were off partly because the CO2 cycle is not completely known. A lot of CO2 is tied up in the atmosphere and oceans. More subtle effects are photosynthesis and seasonality of plant life. Then you have to take into account that adding more CO2 may cause a natural buffer to try to balance the CO2 excess (one possible example: leaves on trees might get larger overall to increase rates of photosynthesis and thereby help lower CO2 levels).
Not only were the first models too simplistic, as we just discussed, but the effect of aerosols and of burning fuels was not taken into account. The effect of aerosols is opposite of the greenhouse effect.
So why don't we just reduce our CO2 output? Besides economic reasons, the proof is not convincing enough to those in power. For instance, very hot summers have been followed by cool summers, which is not what you'd expect. This makes people think that global warming is nonsense. However, you can not just compare one summer to the next summer. You have to look at a trend over a longer period of time.
That's it for Friday's notes. Monday's notes have a lot of Greenhouse Effect information, if you missed any. I'd recommend looking at your notes for that 11:15 PM Thurs. 3 Oct.
Back to GS 201 homepage