# 155 Summary of Human and Ecosystem

CO₂ and methane are greenhouse gases, trapping outgoing long wavelength radiation in the atmosphere and warming the Earth. Increased concentrations of these gases are causing global warming.

• SO₂ is produced when coal and other fossil fuels burn.

• SO₂ and nitrogen oxides dissolves and react in water droplets in the atmosphere, and fall to the ground as acid rain. This leaches aluminum ions from soils, and kills plants and aquatic organisms.

• Fall-out from accidents at nuclear reactions emits ionising radiation, which damages DNA and can cause mutations, cancer and radiation burns.

• Deforestation reduces the amount of CO₂ that is taken out of the atmosphere for photosynthesis, and so may increase global warming. Combustion of the felled trees releases CO₂ into the atmosphere. Deforestation also destroys habitats for animals, possibly leading to their extinction. It increases soil erosion and flooding.

• Water pollution by fertilisers or raw sewage can cause eutrophication, in which large populations of aerobic bacteria form, reducing the amount of dissolved O₂ in the water and making it impossible for most animals to live there. Other chemical wastes, such as heavy metals, can also cause water pollution.