Anthropogenic Global Warming (AGW) is a theory (hypothesis).

It is an unproven theory. What you do with theories is put them to the test with scientific observations. Let's see what data points we now have:

1) Average annual temperatures have not surpassed 1998 (NOAA)
(University of Alabama)

2) Average annual temperatures are now trending downward since 1998
(NOAA) (University of Alabama)

3) Ocean temperatures have not risen since 2000 when the 3000 Argo buoys
were launched. The buoys even show a slight decrease in ocean temperatures

4) The Arctic ice froze to February levels by December 07, there are 1mm
more sq km than before (previous was 13mm sq km)

5) The Arctic ice is 20cm thicker than "normal" (whatever that is)

6) All polar bear pods are stable or growing (NOAA/PBS)

7) Mount Kilimanjaro is not melting because of global warming, rather
"sublimation"

8) The Antarctic is not "melting", it is growing in most places, the
sloughing off at the edges is normal as the ice mass grows

9) The majority of the Antarctic is 8 degrees below "normal" (again,
whatever that is)

10) The coveted .7 degree rise in temperatures over the last 100 years
has been wiped out with last years below "normal" temperatures (NOAA
coolest winter since 2001)

11) Al Gore's film was just deemed "propaganda" in a court of law in the
UK as many points could not be substantiated by scientists

12) It was also just reveled that some of the footage in Als film was
CGI. The ice shelf collapse was from the movie The Day After Tomorrow (ABC)

13) One of the scientists that originally thought that CO2 preceded the
warming has now found with new data that the CO2 rise follows the
warming (Dr David Evans)

14) August 2008 was the first time since 1913 there were no sun spots.

15) The Medieval Warm Period was warmer than the 20th century (no SUVs)

16) Many scientists are now predicting 30 years of cooling.

17) The greenhouse effect is real, our small contribution to it cannot
even be measured

18) Several publications, including those that are warmist have recently
written that the natural cycles of the earth may mask AGW. Give me a break.

Or you can believe people like Al " I invented the Internet" Gore or Ted Turner who says we're all going to be eating each other and no crops will grow in 30 years.