Direct US government spending on climate change was $4.6 billion in 2003. It was $8.8 billion in 2010. That was 9.7% growth per year over this period. If present trends continue, by the year 2100 (typically the scale of climate projections), climate change spending will be $37 trillion, which would represent fully 2/3 of the expected federal budget at that time. This is clearly unsustainable.
And by the way, this is saying nothing about the billions spent each year for technology research, subsidies to green energy development, tax “loopholes” for favored companies, loan guarantees, and all of the “emergency” climate spending that will happen the next time we have a great recession.