Arnold Kling's take is nicely summarized:
Computer simulations give you exquisitely precise unreliable results. Those who run such simulations and call what they do “science” are deceiving themselves.
For more, see this.
A classic example of the problem involved The Club of Rome, which predicted the earth would run out of resources using models that didn't incorporate any price effects on either the demand or the supply side.
And for a Lomborg summary of global warming, see this. Lomborg is not a denier. Here is his summary (from Facebook):
My cover story for The Sunday Times (the biggest UK broadsheet with 1m copies).
Getting smarter with global warming:
"As I fly into a snow-bound Britain, I realise that you might be asking where global warming has gone as you shiver in the coldest March for 50 years and wonder what you will do if gas has to be rationed. I have been involved in the climate debate for more than a decade, but I am still amazed at how wrong we get it. Let us try to restart our thinking on global warming.
Yes, global warming is real and mostly man-made, but our policies have failed predictably and spectacularly.
I was one of the strongest critics of the Kyoto climate change treaty, back when it was considered gospel.
People were aghast when you criticised it then. Now Kyoto has no friends, and everyone remembers how they really did not believe in it.
If we want to avoid our current ambitions failing in the same way, if we want to get past Britain’s unworkable and inefficient Climate Change Act and the EU’s climate policies, we need to face up to some hard truths.
I am going to explain the things everyone ought to know about climate change. Then I will set out the ways in which our policies do not work and show you an approach that has a much better chance of fixing the climate."
The whole article is behind a paywall; however, you will recognize some of the figures from my testimony for Congress (http://lomborg.com/testimony).