If scientists are right and global warming is going to continue at the pace that they predict, then efforts to reduce it are worth the economic costs. The reason for this is that there will also be economic costs if we do not reduce global warming. These will include the costs of having to try to protect or even to relocate cities that are near the ocean - and whole island populations - if sea levels rise dramatically. They will include having to deal with people whose livelihoods are disrupted because changes in climate make agriculture in their regions less possible.
Sadly, it seems not to be in our nature to do painful things today in hopes of preventing worse pain in the future. We focus on trying to have what we want today and we try to forget about the potential future costs.