The science is pretty solid: the average temperature of the world is getting warmer, we know what it causing it, and there will be effects, some of which will be negative.
Meh. Blowing away mod points for this but statements like this is what keeps keeps the deniers in business.
No. We do NOT know what is causing it. If we did, we could model it accurately.
What we do know for certain is that CO2 keeps heat trapped in the atmosphere. We are adding LOTS of CO2 to the atmosphere. The atmosphere is part of a chaotic and finely balanced system. CO2 is adding heat to that system (so we do actually know some of what is causing the heating).
In summary: We know that we are altering a system and by how much. We are unsure of other factors, some are even still unknown (how does the ocean absorb heat, distribute it, and eventually release it). Regardless of the unknowns, the facts that we do know indicate that our current practices are affecting the heat status of the planet.
Is heating of the planet a problem? That is not for Science to say. Science deals with facts and theory, not judgements. My personal opinion in all of this is that we need to be concerned about our "waste" products to ensure that the planet (the only place we can currently live) remains a livable location.