I just read an article about light pollution in ‘Der Spiegel’. According to the interviewed scientist, global light pollution rises by 2% every year. They also posted a link to a very interactive light pollution map.
It is extremely detailed. You can zoom in an see exactly how much light pollution is in a certain area. This is a very helpful tool for finding good photo spots for night photography. The less light pollution an area has, the better the night sky will look in your photos.
One option that is unique to this map is that you can specify an area and look at the trend of light pollution over several years. For example, here is the area near the Paint Mines in Calhan, Colorado. You can see that the light pollution more than doubled since 2012.
It is interesting to check certain areas and see the localized increase of the light pollution. See for yourself on the light trends map.