Dr. Judith Curry is one of the leading realist voices in the climate science community, even though she has now moved on from what she considers a hopelessly politicized field. This 12-minute interview is a good introduction to some (by no means all) of the reasons why global warming alarmism is wrong, and why politics has badly compromised, if not completely ruined, a nascent scientific discipline. Again, this is an introduction, not a master class, but it is well worth your time:
On balance, I don’t see any particular dangers from greenhouse warming. [Humans do] influence climate to some extent, what we do with land-use changes and what we put into the atmosphere. But I don’t think it’s a large enough impact to dominate over natural climate variability.