One of those scientists is Dr. David Evans, a former consultant to the Australian Greenhouse Office. For six years he worked collecting and analyzing data and generating computer climate models for the Australian government. The more data he reviewed, the more convinced he was that CO2 was not the driving force behind climate change. As he put it, “As Lord Keynes famously said, 'When the facts change, I change my mind. What do you do, sir?'”
There were four basic facts that convinced Dr. Evans the theory of AGW was wrong.
1. The greenhouse signature is missing. We have been looking and measuring for years, and cannot find it.
Each possible cause of global warming has a different pattern of where in the planet the warming occurs first and the most. The signature of an increased greenhouse effect is a hot spot about 10km up in the atmosphere over the tropics. We have been measuring the atmosphere for decades using radiosondes: weather balloons with thermometers that radio back the temperature as the balloon ascends through the atmosphere. They show no hot spot. Whatsoever.
2. There is no evidence to support the idea that carbon emissions cause significant global warming. None. There is plenty of evidence that global warming has occurred, and theory suggests that carbon emissions should raise temperatures (though by how much is hotly disputed) but there are no observations by anyone that implicate carbon emissions as a significant cause of the recent global warming.
3. The satellites that measure the world's temperature all say that the warming trend ended in 2001, and that the temperature has dropped about 0.6C in the past year (to the temperature of 1980). Land-based temperature readings are corrupted by the "urban heat island" effect: urban areas encroaching on thermometer stations warm the micro-climate around the thermometer, due to vegetation changes, concrete, cars, houses. Satellite data is the only temperature data we can trust, but it only goes back to 1979. NASA reports only land-based data, and reports a modest warming trend and recent cooling. The other three global temperature records use a mix of satellite and land measurements, or satellite only, and they all show no warming since 2001 and a recent cooling.
4. The new ice cores show that in the past six global warmings over the past half a million years, the temperature rises occurred on average 800 years before the accompanying rise in atmospheric carbon. Which says something important about which was cause and which was effect.
So data being quoted by some to support the idea of AGW either have no connection with CO2 or are slanted in such a way to as to make it appear so.
Data that challenges AGW is being ignored or explained away as an anomaly, even though there's plenty of anomalous data being used to support the AGW theory. One of those 'anomalous' data sets shows global temperatures have been dropping since 1998, but the AGW faithful ignore it, trying to explain it away as merely a pause in the inexorable rise in temperatures. Yet solar astronomers point to a lengthy delay in the start of Sunspot Cycle 24, a signal the Sun's output has declined and may be entering a period of relative quiet after over a century of increasing sunspot activity. Earth's climate has a tendency to track sunspot activity, with long quiet periods of sunspot activity, called minimums, heralding equally long period of colder temperatures. Are we entering one of those minimums as some solar astronomers suspect?
Regardless, it would be prudent to examine all of the data available, making sure to take into account all factors that can affect the accuracy of the collected data, as mentioned by Dr. Evans. Otherwise the theory of AGW can never be adequately debated or tested.