A 1 percent change in overhead brightness is far more significant than it might seem, partly because well over half of Earth’s species are thought to be nocturnal.
A site with sky brightness just 1 percent above natural zenith probably has much more skyglow near the horizon, because it is probably in a situation where it lies within the light dome of something else hundreds of kilometers away.
This is where the model is powerful for predicting light pollution threats from distant cities now and in the future. As populations grow and spread, areas with no evidence of artificial light are going to get much harder to find.
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I like to tell people that the nice thing about outdoor lighting is its environmental impacts can be instantly removed. All you have to do is turn the lights off.