There are many myths about global warming running around, too many to address completely in a single node. Two selected myths - one general, and one highly specific, are addressed here.
The Impact of CO2
Carbon dioxide directly contributes a very small fraction of the greenhouse effect. Water contributes far far more. Of course, for global warming to arise from the greenhouse, there needs to be a change in the greenhouse effect. Does the added carbon dioxide contribute a significant amount of the change? Not directly. But indirectly, yes, it does. This is because of the water cycle.
Water evaporates, forms clouds, rains or snows down, and evaporates again in an endless cycle. In cold places, the balance of this cycle lies heavily in the solid state - ice. In warmer places, it favors the liquid and gas phases more, and in the hottest places, the capacity for water in the air is very high. This gas-phase water is what contributes to global warming. Not even so much clouds, as they increase albedo, but simple high humidity. Not relative humidity, but absolute humidity.
The water cycle is reasonably stable. If you just throw a bunch of water in the air, it will eventually condense out. The same applies to intermittent heating or cooling.
If, however, there is a steady change in the temperature - say, rising a little bit (from any source of climate forcing), more water gets into the air and stays there. Water, as noted above, is a greenhouse gas. So the additional water added to the air in turn warms things up, which in turn adds more water, and so on. How far does it go? If each kilo of water added to the air is directly responsible for adding r more kilos of water, then the 'generations' of this process form a geometric series. If r is less than 1, it doesn't run away completely, and the total change from an initial F forcing will be F/(1-r).
r can be very close to 1, however, without causing this runaway. If it is 0.99, then the total forcing will be 100F, and 99F of that will be from water. But without the 1F to start things off, the 99 F from water wouldn't be there. This is a classic case of amplification.
Now, the real climate is more complicated than that, but the general concept applies. A small forcing from carbon dioxide, or methane, or changes in solar input, or albedo changes, is amplified by the water cycle to much greater significance.
I'm not a climatologist, I'm a physicist. This isn't a statement of "this is how it is, in detail"; this is a statement of "here's an effect you have to be aware of if you're going to understand what's going on here". But this should be enough to alleviate the confusion of these small numbers producing these large effects.
The Notorious Climategate Email concerning "Diagram for WMO Statement"
The relevant portion of this email is: I've just completed Mike's Nature trick of adding in the real temps to each series for the last 20 years (ie from 1981 onwards) amd (sic) from 1961 for Keith's to hide the decline.
If one knows what the data set is, and what the decline is, then this statement presents no ethical issues at all.
The data is a bunch of tree ring specimens. Under certain specific conditions - principally on mountains - the growth of the trees is based on temperature reasonably tightly - enough that if you average a bunch of them it's a worthwhile measure of temperature.
Now, some but not all tree ring samples, after holding tightly to the thermometer-based record for a long time, suddenly diverged in a downward direction in the 1960's. Only certain tree samples were appropriate measures of temperature anyway, so it's understandable that these trees could have a new limiting factor on their growth arise, just like most other trees in the world. Contrary to some claims, the thermometers showed no such decline, it was just the tree rings. There are (as far as I am aware) no solid explanations for why these particular trees diverged at that particular time. A suspicion put forth by climatologists is a shift from temperature to water-limited growth (3). I would also suspect fallout from nuclear tests, and consider the possibility of some other artifact of human interference that only started at that time. Regardless of the cause of the decline, be it systematic or random, if you're drawing a smoothed trendline (as they were) it's a really bad thing if an endpoint is an outlier - it has an oversized effect on the trajectory of the curve.
Since we know what the actual temperatures were in that time period - we have had thermometers for a time span substantially exceeding 50 years - the proposal was, in a graph, to have one of the data sets for sourcing a trendline in a graph not be 'tree ring temperatures', but 'tree ring temperatures prior to 1960, thermometer measurements after 1960'. The resulting trendline is then cut off at 1960.
That was the 'trick' used in the paper mentioned, and when used in that paper, it was explained at the time so no one was under a false impression. After all, the author and recipient of this email both knew what the trick was, and attributed it to the one who devised it!
All in all, what was being hidden was misleading non-data, and the fact that this was being hidden was not going to be hidden.
~~ Resources ~~
- Use of tree ring samples as a gauge of temperature: Chapter 5 of Biotic Feedbacks in the Global Climatic System: Will the Warming Feed the Warming? Available free from books.google.com
- An early article about tree ring temperatures: http://www.agu.org/pubs/crossref/1995/95GB00321.shtml (not free)
- A more recent article, specifically addressing the decline, and freely accessible, is at http://www.clim-past-discuss.net/4/741/2008/cpd-4-741-2008.pdf
- The article which first used the trick: Nature 392, 779-787. At http://www.nature.com/nature/journal/v392/n6678/abs/392779a0.html (not free)