Thus, the following alternative theory of global warming strikes me as somewhat credible. In short, the argument is that the recent warmer temperatures are due to the sun:
the sun drives climate changes more emphatically than greenhouse gases do. After becoming much more active during the 20th century, the sun now stands at a high but roughly level state of activity. Solar physicists warn of possible global cooling, should the sun revert to the lazier mood it was in during the Little Ice Age 300 years ago.
Not being a scientist, I can't really evaluate this theory in a meaningful way. (I haven't noticed the sun being more "active" recently, but then I usually try not to look directly at it). But I will keep an eye on news reports on the subject.