Michael Chricton's book,
State Of Fear, discusses global warming. He does this in a slightly disparaging fashion, which is responed to by the
Union of Concerned Scientists(UCS). After reading this, and in response to repeated denials of global warming by my otherwise very intelligent partner, I have decided to review the wealth of materials on the internet. Armed with said wealth, I will present a basis for the existence of global warming. I'm going to try to keep this as simple as possible, but not so simple that there is no substance. So, bear with me. And let me know if I missed something or made any errors.
Be the dolphin...
1) The Evidence of Warming: From the UCS:
Is global warming already happening?
Yes. The IPCC concluded in its Third Assessment Report, "An increasing body of observations gives a collective picture of a warming world and other changes in the climate system." The kinds of changes already observed that create this consistent picture include the following:
Examples of observed climatic changes
* Increase in global average surface temperature of about 1°F in the 20th century
* Decrease of snow cover and sea ice extent and the retreat of mountain glaciers in the latter half of the 20th century
* Rise in global average sea level and the increase in ocean water temperatures
* Likely increase in average precipitation over the middle and high latitudes of the Northern Hemisphere, and over tropical land areas
* Increase in the frequency of extreme precipitation events in some regions of the world
Examples of observed physical and ecological changes
* Thawing of permafrost
* Lengthening of the growing season in middle and high latitudes
* Poleward and upward shift of plant and animal ranges
* Decline of some plant and animal species
* Earlier flowering of trees
* Earlier emergence of insects
* Earlier egg-laying in birds
IPCC Caption: "Global mean surface air temperature anomalies from 1,000-year control simulations with three different climate models, HadCM2, GFDL R15 and ECHAM3/LSG (labelled HAM3L), compared to the recent instrumental record (Stouffer et al., 2000). No model control simulation shows a trend in surface air temperature as large as the observed trend. If internal variability is correct in these models, the recent warming is likely not due to variability produced within the climate system alone."
And in more scientific terms from the actual IPCC (International Panel on Climate Change, 2001) report:
Global surface temperatures have increased between 0.4 and 0.8°C since the late 19th century, but most of this increase has occurred in two distinct periods, 1910 to 1945 and since 1976. The rate of temperature increase since 1976 has been over 0.15°C/decade. Our confidence in the rate of warming has increased since the SAR due to new analyses including: model simulations using observed SSTs with and without corrections for time-dependent biases, new studies of the effect of urbanisation on global land temperature trends, new evidence for mass ablation of glaciers, continued reductions in snow-cover extent, and a significant reduction in Arctic sea-ice extent in spring and summer, and in thickness. However, there is some disagreement between warming rates in the various land and ocean-based data sets in the 1990s, though all agree on appreciable warming.
New analyses of mean daily maximum and minimum temperatures continue to support a reduction in the diurnal temperature range with minimum temperatures increasing at about twice the rate of maximum temperatures over the second half of the 20th century. Seasonally, the greatest warming since 1976 over land has occurred during the Northern Hemisphere winter and spring, but significant warming has also occurred in the Northern Hemisphere summer. Southern Hemisphere warming has also been strongest during the winter over land, but little difference between the seasons is apparent when both land and oceans are considered. The largest rates of warming continue to be found in the mid- and high latitude continental regions of the Northern Hemisphere.
Analyses of overall temperature trends in the low to mid-troposphere and near the surface since 1958 are in good agreement, with a warming of about 0.1°C per decade. Since the beginning of the satellite record (1979), however, low to mid-troposphere temperatures have warmed in both satellite and weather balloon records at a global rate of only 0.04 and 0.03°C/decade respectively. This is about 0.12°C/decade less than the rate of temperature increase near the surface since 1979. About half of this difference in warming rate is very likely to be due to the combination of differences in spatial coverage and the real physical affects of volcanoes and ENSO (Santer et al., 2000), see also Chapter 12. The remaining difference remains unexplained, but is likely to be real. In the stratosphere, both satellites and weather balloons continue to show substantial cooling. The faster rate of recession of tropical mountain glaciers in the last twenty years than might have been expected from the MSU and radiosonde records remains unexplained, though some glaciers may still be responding to the warming indicated by radiosondes that occurred around 1976 to 1981.
Basically, all this boils down to a warming trend in the last century that is unprecedented in recorded history, and even as we go back through our ice cores. Surface temperature has risen, sea ice thickness has decreased, the mountain glaciers have been drastically reduced in size and snow cover has fallen. More symptoms of warming are observable, and Chapter 2 of the IPCC's Scientific Basis Report should be consulted for further details.
2) The Greenhouse Effect
There should be little doubt about the truth of the greenhouse effect. Without the greenhouse effect we would be little more than frozen proteins...if that. The greehouse effect keeps us warm (UCS Global Warming FAQ):
The "greenhouse effect" refers to the natural phenomenon that keeps the Earth in a temperature range that allows life to flourish. The sun's enormous energy warms the Earth's surface and its atmosphere. As this energy radiates back toward space as heat, a portion is absorbed by a delicate balance of heat-trapping gases in the atmosphere--among them carbon dioxide and methane--which creates an insulating layer. With the temperature control of the greenhouse effect, the Earth has an average surface temperature of 59°F (15°C). Without it, the average surface temperature would be 0°F (-18°C), a temperature so low that the Earth would be frozen and could not sustain life.
Even the deniers of global warming think the greenhouse effect is correct. However, this does not mean that they believe in global warming. The disagreement is in how the change in emissions of greenhouse gasses affects the temperature of the Earth.
3) The Carbon Cycle (and what it has to do with warming):
The main greenhouse gasses are carbon based, primarily carbon dioxide and methane. Carbon dioxide is particularly pernicious because it is so stable and lasts for so long.
Basically this figure shows the release of CO2, followed by the storing and use of this CO2 by the earth's oceans, forests, and even some animals. Small shell producing animals will use that CO2 in the creation of the shells. These shells are eventually pressed into limestone, and then back down to the magma level to be spewed out again in volcanoes.
We add about an extra 7 billion tons of carbon dioxide (see Bill Bryson's A Short History of Nearly Everything, p.268). This is really not much compared to the 200 billion tons that the earth naturally emits. However, it adds up fast because the earth is not prepared to deal with it. From ice cores we know that the baseline "natural" level of CO2 in the atmosphere is about 280 parts per million. In 1958, it was 315 parts per million, now over 360 parts per million. By 2100, it is expected to be about 560 parts per million. The question is when will this come back to haunt us. Some say it won't, most scientists say it will.
Here's a link with a more technically complete list of greenhouse gas precursors. There is so much information in the IPCC report, that I can't possibly do it justice. But in terms of the gasses, here is what we should be watching: "Currently, tropospheric ozone (O3) is the third most important greenhouse gas after carbon dioxide (CO2) and methane (CH4)." Ozone is that stinky stuff which hangs over cities, especially in the summer. Just ask those in LA, they can tell you all about it.
4) Why we think the gasses matter:
Now, this is why scientists explain this stuff, not me. It's really hard, involves a lot of math, and is otherwise quite scary. But ultimately it boils down to a concurrent rise in temperature (GLOBALLY) and in greenhouse gasses. The rise in temperature has been well explained by the computer models that account for this.
UCS Simplified reasons:
* The observed warming over the past 100 years is unlikely to be due to natural causes alone; it was unusual even in the context of the last 1,000 years.
* There are better techniques to detect climatic changes and attribute them to different causes.
* Simulations of the climate's response to natural causes (sun, volcanoes, etc.) over the latter half of the 20th century alone cannot explain the observed trends.
* Most simulation models that take into account greenhouse gas emissions and sulphate aerosols (which have a cooling effect) are consistent with observations over the last 50 years.
But as with other burgeoning scientific fields, learn about this. This is an important area which should be thoughtfully reviewed.