Technological change can raise the efficiency of resource use, but it also tends to raise both per capita resource consumption and the scale of resource extraction, so that, absent policy effects, the increases in consumption often compensate for the increased efficiency of resource use.
Here's the little phrase that got me (I put it in bolded italics in the quote above): "absent policy effects."
What the article is saying is that technology will not prevent the collapse of civilization unless some sort of "policy effects" are put into play.
What does that mean?
What that means is that we can prevent the collapse of civilization, but we can only do so if we change our "policies."
"Politics" is how we change our "policies," and the policies we establish for ourselves can, in very rapid order, change the world.
Let's not let those "policy effects" go "absent," or we are the ones who are going to disappear.