1) They make no mention of taking into account major positive feedback mechanisms we're just now starting to notice, primarily methane release from a warming Arctic. The amount of GHG trapped in the permafrost and hydrates is enough to devastate the climate, and there are signs they've already entered feedback status.
2) They say this:
The U.S.—the world's largest emitter of greenhouse gases per person, among major countries—has continued a transition to less CO2-intensive energy use that started in the early 20th century. Natural gas—which emits 40 percent less CO2 than coal when burned—now dominates new power plants (nearly 188 gigawatts added since 2000) along with wind (roughly 28 gigawatts added), a trend broadly similar to other developed nations such as Japan or Germany.
The switch to natural gas in the US hasn't actually translated into a reduction in GHG's, because:
http://www.scientificamerican.com/article.cfm?id=us-methane-emissions-prove-higher
The study also focuses attention on Texas and nearby states as a source of nearly a quarter of the country's human-related methane emissions. "We've learned that methane emissions from the south-central United States are probably a lot higher than existing estimates," Miller explained.
Miller's research finds that, in 2007 and 2008, U.S. emissions of methane from human-related sources were 33.4 teragrams of carbon equivalent per year. That number is significantly higher than EPA's methane budget, which puts U.S. emissions for 2008 at 22.1 teragrams of carbon equivalent per year.
"The results show that the emissions ... are about 1½ times the EPA estimate," said Steven Wofsy, a professor of atmospheric and environmental chemistry at Harvard and a co-author of the study.
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