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Old 10-05-2019, 03:35 PM   #7291 (permalink)
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The way I look at it is, what is the normal temperature and CO2 level for the Earth? If you look at graphs of CO2 and temperature levels from the Cambrian era to the present, our current CO2 and temperatures are abnormally low. The only time that CO2 and temperature levels were comparable to current levels was at the end of the Carboniferous/ beginning of Permian era, but at that time the O2 level was much higher than current levels.

CO2 levels started out at around 6,000ppm during the Cambrian era, dropping down to as low as 180ppm during the most recent Ice Age. The overall trend for carbon dioxide levels has been downward as plants pull carbon out of the atmosphere and put it into the ground where some of it converts into coal/oil/gas and also as sea floor ooze. Corals and mollusks also bind carbon in the form of calcium carbonate which eventually gets converted into limestone. Plate tectonics then subducts part of this stored carbon into the Earth's interior, making it forever inaccessible to life. Extrapolating this trend out into future, CO2 levels should continue to drop as carbon continues to get pulled out of the atmosphere and deposited into the earth's interior.

If you look at plants,the optimum CO2 level for C3 plant photosynthesis is around 1400 ppm, which is the level that greenhouse growers try to maintain in their greenhouses by using CO2 generators. But the minimum CO2 level for plant growth is 150 PPM, so the CO2 levels (180ppm) during the most recent Ice Age came very close to the level where C3 plants would cease to grow. Our current CO2 level is 400ppm, which is a lot closer to the minimum level where plants will grow then it is to the to the optimum CO2 level for plant growth, so I wouldn't mind having a bit more of a cushion above that minimum level.

The forests of the Cretaceous era, when CO2 levels were about 1400 PPM, were about twice as productive as our modern forests and were also growing in the Arctic and Antarctic regions which at the time were ice-free. The Antarctic ice cap appeared about 8 million years ago, the Arctic ice cap about 4 million years ago, but for most of the earth's history between the Cambrian and the present the poles were ice free. The fall line along the southeast US is where the seashore left its mark since this was the level where it was located for most of the time since the Atlantic ocean first appeared. The flat sandy coastal plains was seafloor. Lateritic soils and rocks are formed under moist tropical conditions, so any location with laterite is either tropical or has had tropical conditions in the past. Laterite can be found as far north as Scotland and the Ural mountains.

Another indicator as to what is the normal climate for the earth is to look at plant genetics. For practically every species of temperate zone tree for which cultivars have been selected, there is at least one columnar cultivar. But there almost no columnar cultivars of tropical trees. The columnar shape is the optimum shape for collecting sunlight at high latitudes and is the shape you see for trees growing in the taiga forests. Our temperate trees were growing in the arctic regions as recently as 4 million years ago and evolved into their current broader shape as they were pushed south by the cooling climate. This makes it is easy to pick the ancient genetics out of their gene pool, since the columnar shape is the shape that they had for most of their existence.

The way I look at it, the CO2 and temperatures levels are simply returning to the levels where they have been for most of the past 500 million years. Some of our current ecosystems will get disturbed by a warming climate, but life as a whole will thrive, especially since the warming climate will make the polar regions more clement for life. All of this hyperbole about the earth not being able to support life if the temperature rises a degree or two is just propaganda by people trying to advance various social causes.