200 years ago, in the beginning of the 21:st century, Stockholm was, like the whole of Sweden a place with much snow and cold winters.

The whole world was colder. The north and south pole was covered with ice and animals like polar bears was still alive, but so is it not today. The ices melted because of the greenhouse effect. The gas layer of CO2 around our earth was, and still is today, so thick that to little sunbeams can get out. That makes the earth warmer.

400 years ago the plants and animals cooperated perfect, but from when the humans invented oillamps and until 100 years ago, we, the humans were letting out too much carbon dioxid. The trees can´t "eat" all the CO2, so the CO2 formes a layer of gas around the earth.