"Predictions of global warming are based on computer climate modeling, a branch of science still in its infancy. The empirical evidence actual measurements of Earth's temperature shows no man-made warming trend. Indeed, over the past two decades, when CO2 levels have been at their highest, global average temperatures have actually cooled slightly."
It's true that the science of climate modeling is still somewhat young. But we cannot infer from this, as the quote wishes us to, that it is therefore not to be trusted. As I've mentioned before, scientists can test the accuracy of any given climate model by running it against past climate data. If the model doesn't match the observed changes during that time, it's scrapped.
And the claim that global average temperatures have cooled slightly is a complete fabrication. This becomes painfully obvious when you look at any temperature record of the past few decades. The climate has been warming exactly as predicted.
But even if we assume for a moment that there
has been a recent cooling trend in global mean temperatures, the quote is still very misleading. It implies that global warming theory assumes that CO2 is the only driver of climate. Which is again completely and utterly false. There are a great many things, anthropogenic and otherwise, that could result in a cooling trend. A rise in aerosol use and other particulate pollutants, as well as a rise in volcanic activity briefly overwhelmed the CO2 signal and was responsible for the slight cooling trend seen from the 1940's through the early 70's, for example.
"The current increase in carbon dioxide follows a 300-year warming trend: Surface and atmospheric temperatures have been recovering from an unusually cold period known as the Little Ice Age. The observed increases are of a magnitude that can, for example, be explained by oceans giving off gases naturally as temperatures rise. Indeed, recent carbon dioxide rises have shown a tendency to follow rather than lead global temperature increases."
If I'm getting this right, their argument (the part in bold) goes something like this:
What they said:"In the past, temperatures lead rises in CO2."
What we're meant to infer:"Therefore CO2 cannot drive climate."
The argument is simply faulty mathematical reasoning:
Set A intersects set B
Set B does not intersect set C
Therefore Set A cannot intersect set C.
That CO2 is a feedback does not negate it from also being a forcing in any way, in much the same way that the lack of intersection between set B and set C tell us nothing about the relationship between set A and set C.
The fact is that past changes were mostly caused by variations in Earth's orbit called Milankovitch Cycles. These variations cause changes in the total amount of radiation that reaches Earth's surface, and thus forces the climate. Obviously these cycles had nothing to do with carbon dioxide so we shouldn't
expect to see it lead temperatures.
We are also meant to infer that a rise in temperatures causes a rise in atmospheric CO2, which is true, but misleading. As the global temperature starts to increase (such as when Earth enters a Milankovitch Cycle) more and more CO2 is released from the world's oceans (a process which is mentioned in the article), because carbon dioxide is less soluble in warm water. This extra CO2 in the atmosphere increases the greenhouse effect and drives temperatures even higher.
This is completely different than what is happening today. This particular change has been driven almost entirely by changes in atmospheric carbon dioxide, which has most certainly not lagged behind temperatures.
"In the troposphere, greenhouse-gas-induced temperature changes are expected to be at least as large as at the surface...While tropospheric temperatures have trended downward during the past 19 years by about 0.05 ºC per decade, it has been reported that global surface temperatures trended upward by about 0.1 ºC per decade (21, 22). In contrast to tropospheric temperatures, however, surface temperatures are subject to large uncertainties for several reasons, including the urban heat island effect."
The urban heat island effect is well understand and factored in to every direct surface temperature measurement. The idea that scientists have somehow 'missed it' is absurd.
I don't know a great deal about this subject, so as opposed to saying something stupid and misrepresenting the science I'll just link you to a wonderful
article from the folks at RealClimate discussing the UHI effect.
Also, the discrepancy in the surface and troposphere temperature measurements was primarily due to arithmetic errors and have largely been reconciled. Here's a statement (taken from the
US CCSP report executive summary) from the scientist who made the claim mentioned in your article in the first place:
"Previously reported discrepancies between the amount of warming near the surface and higher in the atmosphere have been used to challenge the reliability of climate models and the reality of human induced global warming. Specifically, surface data showed substantial global-average warming, while early versions of satellite and radiosonde data showed little or no warming above the surface. This significant discrepancy no longer exists because errors in the satellite and radiosonde data have been identified and corrected. New data sets have also been developed that do not show such discrepancies."---------------
Proof why CO2 isn't all what scientisitst are porposing it could do:
http://www.oism.org/pproject/s33p36.htm
Ignoring for the moment the fact that it is nearly nine years old (which is well before the IPCC AR 3 and 4 were released), and based on old and faulty data, the Oregon Petition is mostly irrelevant. A sample of the scientists who signed it, taken by
Scientific American, found that out of the 26 subjects reviewed, "
11 said they still agreed with the petition, one was an active climate researcher, two others had relevant expertise, and eight signed based on an informal evaluation. Six said they would not sign the petition today, three did not remember any such petition, one had died, and five did not answer repeated messages." They also roughly calculated that, of the 17,000 who signed the report, less than 200 were climate scientists. According the American Geophysical Union, ("If you ain't a member of the AGU you ain't no damn climate scientist in the US!" -
Eli Rabett), there are approximately 20,000 climate scientists working worldwide, so the number in the OP represents a very small fraction of the climate science community.
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Finally, your claims that an increase in CO2 will increase plant production are false as well. The simple fact is that carbon dioxide is not the limiting factor to plant growth. There is more than enough of it in the air already. Adding more isn't going to do a bloody thing. Any small effect it might have would be completely eclipsed by other, more important, factors such as climate, geography, soil quality, etc.