Why "catastrophic human-caused global warming" is bullshit--short version
1. The folks pushing the scare story claim increasing CO2 in the atmosphere will trigger a series of "positive feedbacks" that will make global temps "run away" to a dangerous level. But we know that at one time CO2 levels were roughly ten times higher than today, yet there's no evidence global temperature warmed to an unusual or dangerous extent. This suggests that the "runaway" theory is wrong.
2. Deep ice cores from Antarctica show that rather than CO2 causing temperature to increase, CO2 actually lags temperature change by roughly 200 years. A decade or so ago, researchers drilled a couple of 14,000-foot "ice cores" into antarctic ice, revealing about 800,000 years of climate records. A quick first analysis of these cores showed that there was a good correlation between atmospheric CO2 and temperature, which the warmies touted as proving that rising CO2 made temperature go up. This conclusion made lots of headlines. But then a more careful analysis of the cores showed that CO2 was actually rising *after* temperature rose, instead of before. Hard to claim causation when temperature rose after the CO2. Yet the pushers of the theory still claim CO2 causes global warming. As far as I know, none of the pushers has addressed the ice core data wrecking their claim that CO2 causes warming.
3. Every government agency has been changing the actual measured temperature data in a direction that makes it appear that global warming is occurring at a "scary" rate. Since changing measured data on a whim would be considered pretty unscientific, one would expect the agencies were changing the temps based on some computer algorithm (rather than "I think...") to decide which measurements "needed to be changed," and which direction, and by how much. But the agencies refuse to release any such algorithm. A logical reason would be that no such algorithms were used, and that the temp changes were just fabrications made to make the data appear to support their theory.
4. The main pushers of human-caused global warming (supposedly due to rising CO2 caused by fossil fuels) have been caught exchanging emails in which they explicitly discussed how to change the measured data to make previous warmer historical periods disappear. This is prima facie evidence of fraud. The emails also showed them discussing ways to prevent papers by AGW skeptics from being published. This suggests those pushing CAGW know their theories, data and methods couldn't withstand an honest challenge. Otherwise why try to block those who claim to have evidence that would refute the CAGW theory? If the CAGW theory is right, it should be able to withstand an honest challenge.
5. The 1930's was the hottest decade on record in the U.S. Of course this was before the huge boom in cars and fossil fuel consumption that occurred after WW2. This shows that CO2 didn't cause the record heat of the 1930's, and that Earth's climate naturally oscillates between cooler and warmer periods. If so, how can the pro-AGW people claim with any certainty that the very slow warming seen over the last century is caused by CO2 and not by any "natural" cause?
6. Similarly, for about 30 years in the early 1600's Europe experienced a period of record cold referred to as the "Little Ice Age." Obviously no one was measuring CO2 back then but nothing in the record suggests that CO2 levels dropped before this cold period. This clearly shows--again--that the climate has significant variability independent of CO2 level. Warmists have no explanation for why the Little Ice Age happened, but it certainly seems to indicate that CO2 isn't a significant temperature driver.
7. Similarly, historical records show that the climate warmed significantly around 1000 A.D.--an event now called the Medieval Warm Period. During this time Greenland warmed so much that settlers successfully grew grapes for decades, before the climate cooled so much that they were forced to abandon the settlements there. Again, shows natural climate variation having nothing to do with CO2. As a result the warmists have been frantically trying to make this record vanish.
8. Glaciers in many parts of the world have been "retreating"--shrinking. OMG! Proof of global warming! Except...they've been retreating for the last couple of centuries--long before humans started burning a significant amount of fossil fuel. Which--again--strongly suggests that GW is NOT caused by CO2. Ask the warmies how they rationalize this data.
Wait, wait, I know! Just as the agencies decided they should "adjust" actual measured temps from decades ago--presumably because no one back then could actually read a thermometer correctly--it's obvious to socialists and liberals that early explorers either didn't know how to read a map, or couldn't correctly identify a glacier.
Yeh, dat's da ticket: Those early guys drew glaciers that weren't really there! So we'll correct their observations. Cuz we government scientists know what was there better than the guys who were actually, you know, there.
9. Finally (for now, anyway), the folks pushing the CAGW theory claim the antarctic has been losing ice like mad for the last couple of decades. Like, gigatons of ice. But then in the last four years or so sea ice in antarctica has hit record levels. Since this didn't fit the fable, the warmies replied that sea ice simply didn't matter. What counted was land ice! And they claimed gravity measurements by satellites showed that the continent was losing, like, gigatons of land ice.
But then someone found that laser measurements--by satellites--of elevations over that continent showed elevations were either steady or increasing.
Uh...wait...how could that happen if the land ice was melting? So the warmies countered that the laser data was simply wrong and should be ignored in favor of the gravity data.
Starting to see a pattern here? Sure--every time a dataset is found that casts doubt on AGW, the warmies claim that dataset or study or measurement should be ignored, and that we should only accept their data. So ask 'em the scientific basis for their claim that the laser data is wrong but the gravity data is right.