The fact is, there has been global warming, but the contribution of human-generated carbon dioxide is necessarily so minuscule as to be nearly undetectable. Here's why:
Carbon dioxide, considered the main vector for human-caused global warming, is some 0.038% of the atmosphere- a trace gas. Water vapor varies from 0% to 4%, and should easily average 1% or more near the Earth’s surface, where the greenhouse effect would be most important, and is about three times more effective a greenhouse gas than carbon dioxide. So water vapor is at least 25 times more prevalent and three times more effective; that makes it at least 75 times more important to the greenhouse effect than carbon dioxide. The TOTAL contribution of carbon dioxide to the greenhouse effect is therefore 0.013 or less. The total human contribution to atmospheric carbon dioxide since the start of the industrial revolution has been estimated at about 25%. So humans’ carbon dioxide greenhouse effect is a quarter of 0.013, works out to about 0.00325. Total warming of the Earth by the greenhouse effect is widely accepted as about 33 degrees Centigrade, raising average temperature to 59 degrees Fahrenheit. So the contribution of anthropogenic carbon dioxide is less than 0.2 degrees Fahrenheit, or under 0.1 degree Centigrade. Global warming over the last century is thought by many to be about 0.6 degrees Centigrade.
But that's only the beginning. We've had global warming for more than 10,000 years, since the end of the last Ice Age, and there is evidence temperatures were actually somewhat warmer 9,000 years ago and again 4,500 to 8,000 years ago than they are today. Whatever caused that, it was not human activity. It was not all those power plants and factories and SUVs being operated by Stone Age cavemen while chipping arrowheads out of bits of flint. Whatever the cause was, it melted the glaciers that in North America once extended south to Long Island and parts of New York City into virtually complete disappearance (except for a few mountain remnants). That's one big greenhouse effect! If we are still having global warming - and I suppose we could presume we are, given this 10,000 year history - it seems highly likely that it is still the overwhelmingly primary cause of continued warming, rather than our piddling 0.00325 contribution to the greenhouse effect.
Yet even that trend-continuation today needs to be proved. Evidence is that the Medieval Warm Period centered on the 1200s was somewhat warmer than we are now, and the climate was clearly colder in the Little Ice Age in the 1600s than it is now. So we are within the range of normal up-and-down fluctuations without human greenhouse contributions that could be significant, or even measurable.
The principal scientists arguing for human-caused global warming have been demonstrably disingenuous, and now you can see why. They have proved they should not be trusted.
The idea that we should be spending hundreds of billions of dollars and hamstringing the economy of the entire world to reduce carbon dioxide emissions is beyond ludicrous in light of the facts above; it is insane. Furthermore, it sucks attention and resources from seeking the other sources of warming and from coping with climate change and its effects in realistic ways. The true motivation underlying the global warming movement is almost certainly ideological and political in nature, and I predict that Anthropomorphic Global Warming, as currently presented, will go down as the greatest fraud of all time. It makes Ponzi and Madoff look like pikers by comparison.
 Fundamentals of Physical Geography, 2nd Edition
by Michael Pidwirny Concentration varies slightly with the growing season in the northern hemisphere. HYPERLINK "http://www.physicalgeography.net/fundamentals/7a.html" http://www.physicalgeography.net/fundamentals/7a.html
 HALOE v2.0 Upper Tropospheric Water Vapor Climatology Claudette Ojo, Hampton University; et al.. HYPERLINK "http://vsgc.odu.edu/src/Conf09/UnderGrad%20Papers/Ojo%20-%20Paper.pdf" http://vsgc.odu.edu/src/Conf09/UnderGrad%20Papers/Ojo%20-%20Paper.pdf. See p. 4.The 0 - 4% range is widely accepted among most sources. This source is listed for its good discussion of the phenomena determining that range. An examination of a globe will show that tropical oceans (near high end of range) are far more extensive than the sum of the earth’s arctic and antarctic regions and tropical-zone deserts (all near the low end). Temperate zone oceans are far more extensive than temperate-zone desert. This author’s guess of an average of 2% or more seems plausible. I have used “1% or more” in an effort to err on the side of understatement.
[4 NIST Chemistry Webbook, Please compare the IR absorption spectra of water and carbon dioxide. ] HYPERLINK "http://webbook.nist.gov/" http://webbook.nist.gov/
 Three quarters of the atmosphere and virtually all water vapor are in the troposphere. Including all the atmosphere would change the ratios to about 20 times more prevalent and 60 times more effective. However, the greenhouse effect of high-altitude carbon dioxide on lower-altitude weather and the earth’s surface seems likely to be small if not nil.
 National Oceanographic and Atmospheric Administration. HYPERLINK "http://www.ncdc.noaa.gov/oa/climate/gases.html" http://www.ncdc.noaa.gov/oa/climate/gases.html. The estimated 90ppm increase in carbon dioxide, 30% above the base of 280 ppm, to a recent reading of 370 ppm, equates to just under 25% of present concentration, the relevant factor in estimating present contribution to the greenhouse effect.
 Oak Ridge National Laboratory http://www.esd.ornl.gov/projects/qen/nerc130k.html
 New York Nature - The nature and natural history of the New York City region. Betsy McCully http://www.newyorknature.net/IceAge.html
 Global Warming: A Geological Perspective John P. Bluemle HYPERLINK "https://www.dmr.nd.gov/ndgs/Newsletter/NL99W/PDF/globlwrmw99.pdf" http://www.azgs.az.gov/arizona_geology/archived_issues/Winter_1999.pdf This article, published by the National Oceanographic and Atmospheric Agency, is drawn from a paper by the author in Environmental Geosciences, 1999, Volume 6, Number 2, pp. 63-75. Note particularly the chart on p.4.
 Wikileaks: Climatic Research Unit emails, data, models, 1996-2009 HYPERLINK "http://wikileaks.org/wiki/Climatic_Research_Unit_emails,_data,_models,_1996-2009" http://wikileaks.org/wiki/Climatic_Research_Unit_emails,_data,_models,_1996-2009.
See also HYPERLINK "http://www.dailymail.co.uk/news/article-1246661/New-scandal-Climate-Gate-scientists-accused-hiding-data-global-warming-sceptics.html" http://www.dailymail.co.uk/news/article-1246661/New-scandal-Climate-Gate-scientists-accused-hiding-data-global-warming-sceptics.html and
HYPERLINK "http://online.wsj.com/article/SB10001424052748704075604575356611173414140.html" http://online.wsj.com/article/SB10001424052748704075604575356611173414140.html and, more diplomatically: HYPERLINK "http://www.nytimes.com/2009/12/01/science/01tier.html" http://www.nytimes.com/2009/12/01/science/01tier.html. Et al.
What initially troubled me was the aberrant behavior of the climate research unit at East Anglia University, which has been the main data source for AGW arguments. They initially refused (!) to reveal their algorithms and data on the grounds that they were proprietary(!!). They responded to critics with ad hominem attacks and efforts to block their publication in scientific journals. Now, as I am sure you know, this is not how one does honest science, in which you PUBLISH your data and methodology and invite critical comment to ferret out error or oversights. It took the now-famous Wikileaks "Climategate" to pry loose the data and expose their machinations. Yet despite the devastating blow these revelations should have to their credibility, the AGW "cause" has taken on a life of its own.
Fundamentally, the argument seems to rest on a logical fallacy, post hoc ergo propter hoc - after this, therefore because of this. We see a rise in temperature and a rise in (principally) carbon dioxide, and therefore conclude one must have caused the other. It does not necessarily follow at all. There can be other causes entirely behind both phenomena, and as you see above, almost certainly there are. Beyond that, I have encountered numerous assertions of fact that cannot add up given the physical properties of water vapor and carbon dioxide that go unchallenged. One-sided arguments proliferate and people arguing the other side are frequently denounced as being employed by business interests rather than rebutted on the merits.
In sum, I have not come lightly to the conclusion that the AGW argument as it applies to carbon dioxide is largely untrue and certainly does not account for more than a very small, nearly negligible part of the phenomena we are seeing. The implications of widespread assertions of and belief in such an untruth are staggering, and potentially enormously destructive. It is unwise indeed to let oneself be stampeded in this matter, and stampede is clearly what many have been and are trying to induce.
I can understand politicians behaving this way; a carbon tax or carbon trading regime would allow enormous revenues to fall into their hands. I can understand "Progressive" ideologues; it logically leads to enormous expansion of government power over industry, the economy, and the daily life of individuals, which they regard as a good thing. I understand the environmentalists; they want to shrink the size and impact on the environment of modern civilization. But responsible citizens need to put aside such considerations.