The global average temperature actually showed a small, but nearly constant diminution, from 1000 to 1900, save for a slight warming period around 1100 when a 0.2°C rise was experienced and one little ice age in circa 1600 when the temperature dropped about 0.6°C. But the planet operates in geologic time, and there is a direct correlation between high CO2 concentrations and warmer climates.
There was a warm period 120,000 years ago when CO2 rose from 190 parts per million by volume (ppmv) to 290 ppmv, at a time when the sea level was about 20 feet higher (Woods Hole Oceanographic Institution, http://www.whoi.edu/institutes/occe). The same condition occurred 220,000 years, 310,000 years and 400,000 years ago. But all this might have been induced by an astronomical rhythm, the wobble of the Earth, which occurs at approximately 100,000 year cycles. But, could the carbon dioxide/methane hyperactivity have actually caused the gyration, which deviated the orbital path of the planet? Global temperatures during this half a million year cycle almost coincided with equivalent changes in carbon dioxide and methane. Which gas was really the problem? Maybe it was methane.
Today, the CO2 concentration is in the range of 380 ppmv, under continuous monitoring since 1958 on Mauna Loa, Big Island of Hawaii. South Pole records show similar data. Early correlations are obtained from chemical information collected from shells of organisms preserved in the deep sea. It’s frightening to confirm that our present level of carbon dioxide in the atmosphere is the highest in the past 650,000 years…six hundred and fifty thousand years…way before Homo Sapiens came into being. We began as a species all of 100,000 to 250,000 years ago.
To gain a sense of proportion, our atmosphere is 78.08% nitrogen, 20.9% oxygen, 0.93% argon, 0.038% (380 parts per million) carbon dioxide and smaller amounts of other gases. The pre-1750 concentration of CO2 was 280 ppm. However, methane was 0.7 ppm then and is now about 1.8 ppm. That is, methane has more than doubled, while carbon dioxide has “only” increased by about a third. Mars and Venus have carbon dioxide concentrations slightly greater than 95%. The Moon has zero percent carbon dioxide because it has no atmosphere. While there have been straight line increases of CO2 and nitrous oxide since 1960, over the past decade or two, chlorofluorocarbons have not only leveled off, but are showing signs of dropping, and the rate change of methane increase has decreased, which is somewhat bewildering, considering that 80% of methane comes biogenically (living things, like us, but, really, from anaerobic bacteria, the germs that don’t need much oxygen, like in our bowels and through agricultural practices) and we are increasing, but, growing and decaying plants might well be the greater factor, and something might be affecting that source.
Another way of looking at all this is to consider the existing carbon content:
o Oceans -----------------------40,000 gigatons
o Mineral soils -----------------1,500 GT
o Atmosphere-------------------- 730 GT
o Growing vegetation----------- 650 GT
o Burning fossil fuel/year------- 6.5 GT
Then, this part is controversial, but the authors who reported on the above figures state that the permafrost/tundra house something on the order of 900 GT. They don’t quite say what percent of this is carbon gas is methane, but they do state that the whole system is thawing, and it is ten to thirty times more concentrated in these greenhouse gases than mineral soils. A particularly scary determination is from John Atcheson, who reported in 2004 that that there are 3000 times more methane in these Arctic clathrates (hydrates) than currently exist in the atmosphere. Further, there is a lot more methane as hydrates in the ocean. If you were concerned about your gas guzzler emitting too much carbon dioxide, wait until you get to the section on methane, something you best know as natural gas.
Scientists have continued to model and refine their models. James Hanson and his colleagues in “Earth’s Energy Imbalance: Confirmation and Implication” from Science, the most prestigious of journals, report that their climate model calculates that our Earth is now absorbing 0.85 watts per square meter more energy from the Sun than it is emitting to space, and mostly from anthropogenic (man-made) greenhouse gases and aerosols. All texts show that 341 watts/square meter of insolation impact Earth, with 235 w/m2 being emitted as longwave radiation and 107 w/m2 as reflected solar radiation. Thus, 0.85 w/m2 is very serious stuff. James Hanson, who brought this issue to the forefront through his 1988 congressional testimony, and his co-researchers, are convinced something bad is happening and that society is responsible for this change, and actually go on to provide an exact figure for how much heat is being retained. His team reported that the average temperature in 2005 was 58.3°F, the hottest year on record, and the last time this happened was something on the order of 10,000 years ago.
Thus, the consensus of climate change scientists is that the carbon dioxide produced when fossil fuels are burned is warming the Earth through something called the Greenhouse Effect. The effect might be exacerbated when forests are cleared, because the carbon dioxide taken up by all flora is reduced. These Green House Gases (GHG), especially carbon dioxide, methane, nitrogen oxides and chlorofluorocarbons, act like the glass in a standard greenhouse that allows sunlight to enter the greenhouse, but, after the light is absorbed by the plants and ground, some of it is converted to heat, which cannot escape the house. An automobile on a hot day is a good example of a greenhouse.
How serious is this warming? During the past century, the atmosphere has increased by one Fahrenheit degree. The eight warmest years have occurred over the past decade.
The top ten hottest years have occurred during the past fifteen years. There is, thus, evidence of accelerated warming. The worst case scenario from the National Center for Atmospheric Research is that during the next century the temperature could increase by 6.3°F (3.5°C) and the sea could rise by 12 inches (30 centimeters). But this is an extreme proposition, from a generally realistic NCAR. There are more radical prognostications, from others.
There is one more matter that deserves some attention—global dimming. In 1985, Atsumu Ohmura at the Swiss Federal Institute of Technology suggested that the solar radiation level on the surface of our planet had declined 10% in 30 years. This was just about the time when scientists were beginning to worry about global climate warming, so Ohmura’s contention was ignored, partly because less sunlight should have meant global cooling. Recent records now show that over the past 5 decades the drop has been about 15%. Gerry Stanhill, an English scientist working in Israel, compared sunlight records from the 1950’s with today and found a 22% drop of insolation. Other researchers were noting that evaporation was also declining, in about the same rate as the dimming. PBS aired the NOVA documentary “Dimming the Sun” on April 18, 2006, showing that air pollution not only reflects sunlight back into space, but the particulates also make clouds more reflective, and that the next few decades will see a drop in particulates but an increase in carbon dioxide. Thus, the masking effect of global dimming needs to be factored into global climate models. Other scientists contend that they have, indeed, included aerosols in their prediction, but that the overall effects are very complex. In any case, a 5°C (9°F) temperature increase could well now be possible by 2050, not 2100.
So in summary, a one degree temperature change over decades and centuries does not sound like much, but it is in the exponential impact, the cascade effect, in specific situations, that life and the environment can be affected. Tellingly, the number of scientific papers recording changes in the ecosystem from global warming increased from 14 to more than a thousand in five years.