Lomborg says, yes, AGW will cause a temperature increase of something over 2 degrees Celsius by 2100. However, initiatives like the Kyoto agreement will have minimal effect on this, despite their cost. He explains that the contribution of global warming to problems such as malaria and hurricanes is much less that is thought, and that it would be much better to put the money towards dealing with these problems directly. In the longer term global warming will need to be dealt with, but his recommendation for this is to invest more money in developing alternative energy sources.
I found this a somewhat disturbing book. Lomborg is right in that it's too easy to see global warming as the problem, and to minimise others. While I don't necessarily agree with Lomborg's claims, it made me realise I would need to think a lot more deeply about things such as economic growth, the needs of developing countries, and the trade offs between different ways of spending money. Whatever your view on global warming, I think that you will find this a very thought provoking book.