Reducing the area occupied by an ecosystem reduces the number of species there. Perhaps two-thirds of species live in the tropics, with over half of land species in the rain forest. Over the coming 100 years, a still greater cause of loss is expected to be the burning of fossil fuels, which pollutes, increases CO2 in the atmosphere, and produces global climate change. Especially critical is climate change, which will occur faster than many ecosystems, especially those dependent on trees, can migrate a midrange estimate is that many will have to move 300 km over the next century. Global climate change will be an important contributor to destroying boreal, lake, and stream biomes.
Fossil fuels harm biodiversity in two other ways.
The increased CO 2 in the atmosphere that causes global climate change also changes the competitiveness of different plants. In the Southern hemisphere, competition between food crops and weeds is expected to intensify, and starvation to increase. Some exotics do not do well, but many prosper in ares with less competition and fewer enemies, supplanting native species. Biological predictions all have large uncertainties. Biologists don t know the actual number of species worldwide estimates range between 5 and 100 million or even on any single acre.