Is Global Warming a religion?

If you define religion as in accepting a concept on blind faith, then no. A scientific theory such as AGW is based on observational evidence, proved physical constants and laws of nature as well as drawing on the vast backdrop of already well establish supportive sciences. However, as with any scientific theory it is subject to revision and even falsification should new evidence demonstrate the need. This represents a degree of uncertainty, which one must inevitably accept with any theory. To the degree accepting theory as likely correct means accommodating a level of uncertainty, then all scientific theory is somewhat "religious".