So, what is KNOWN about climate change?
1. CO2 levels are rising rather quickly, from about 280 back in the day to over 400 ppm and climbing. This is a fact.
2. The additional CO2 is almost all due to burning fossil fuels, also a fact, determined by isotopic analysis of the carbon.
3. CO2 is a greenhouse gas, if there were none in the atmosphere, the planet would be a lot colder.
Then one gets into models about how much the additional CO2 is warming the climate. I've tried to read a number of papers on this aspect and it gets really complex quickly. The models are based on some best guesses about influences, the CO2 influence ALONE is calculable and pretty minor. However, a slight increase in temperature changes things like ice coverage and albedo, and that generates other warming influences. Modelers take what is thought to be the temperature history of the planet since say 1880 and devise a model to explain what was already seen. This is why we have so many different models that arrive at basically the same prediction. There is no other way to do it.
There is a problem here that Judith Curry goes into at some length, but it's useful to start with what is KNOWN, items 1-3.
We'll no doubt see some proposed climate legislation and it will be fun to watch what the MIT climate group has to say about how much it would fix climate change over time. It won't be much, at all. They plug in the reduction in predicted CO2 generated into the models and calculate how much that will change projected temperatures decades out, the change will be very very minor.