1. The official 20th century temperature data that we have all been warned about so vociferously is probably not detecting true warming, but simply the results of urbanization, building around the thermometers, etc. To the extent that they have been aware of these issues, the climate pro's have probably found ways of selecting warming thermometers, and ignoring non-warming ones.
2. The central argument, that a certain increase in CO2 will cause a certain temperature increase, does not work mathematically.
Keven Trenberth , in the Times article referred to in #1, shows a willingness to move on: let's talk about sea level, Arctic ice, and snow cover in the northern hemisphere.
“It’s not just temperature rises that tell us the world is warming,” he said. “We also have physical changes like the fact that sea levels have risen around five inches since 1972, the Arctic icecap has declined by 40% and snow cover in the northern hemisphere has declined.”
Instead of a scientist with actual data about temperatures, proxies, and long-term trends, he's become a blowhard in a bar: how come Arctic ice is melting, if you're so smart? I don't know Kevin, I'm not an expert on this any more than you are, but I believe Arctic ice is always changeable, and no one has really established a long-term trend.
Sea level: Wikipedia has a piece on sea level and climate change, presumably written by the warmists, saying a recent increase is definitely caused by climate change, and may be as much as 3.5 mm per year over a recent decade:
"more recently at rates estimated near 2.8 ± 0.4 to 3.1 ± 0.7 mm per year (1993-2003). Current sea level rise is due significantly to global warming, which will increase sea level over the coming century and longer periods.[7"
The article on sea level itself says: "For at least the last 100 years, sea level has been rising at an average rate of about 1.8 mm per year. The majority of this rise can be attributed to the increase in temperature of the sea and the resulting thermal expansion of sea water. Additional contributions come from water sources on land such as melting snow and glaciers (see global warming)."
Sea level has been going up since the last ice age, roughly 20,000 years ago, the vast majority of the increase occurred in the first 10,000 years, and: "Note that over most of geologic history, long-term average sea level has been significantly higher than today."
All of this prompted Anthony Watts to spell out what a 3 mm per year increase (Trenberth has 5 inches in 30 years = less than one fifth of an inch per year) would actually look like.
Trenberth was agonizing to his friends in October 2009, in e-mails that he thought would remain private, that they really didn't know much of anything about why climate was the way it was in a particular period such as the 20th century.