They debate the cause and effect of the observation. The earth is warming relatively rapidly.
At least the outer layer.
You're actually not going to find many people who disagree with that. The disagreement comes in other forms such as:
1. Did man really cause it or are CO2 emissions just
coincidentally happening during one of the Earth's many warming cycles that have happened, some of which man was not even on the planet?
2. Do we really have an honest hope of reversing the trend? I mean, if we did everything the left wanted us to do would we be saved from ourselves or would we just slow down the process and delay the inevitable until a later date?
3. Who is we? The left often imply that if the US and several other countries did everything the left asked, would it actually make a difference if the world's biggest polluters such as China and a few others, kept on merrily polluting more and more? The left claim that we can reverse or at least stop this if we do our part but if China and others keep on polluting, what
WE do won't probably make a difference in a hill of beans.
Part of the left's problem is they demonize the other side as science deniers and people who believe in hoaxes, instead of having an honest debate on the points I just made. They seem to think that well, if we at least do our part, then we can feel better about ourselves, even though the world is doomed anyway because others won't be doing their part, such as China. Also, if man just being here contributes to the problem, and the world's population grows, exponentially, then we will never fix the root cause of man made global warming - man. If we're really serious about tackling the problem then we need to start talking about culling billions of people. Since the left won't get serious about that real problem, we will be forever doomed to have rising temperatures because no matter how much we address the problem, there will always be a constant supply of ever increasing people.