Air pollution contributes to global warming because it releases excessive amounts of harmful gases into the atmosphere. Carbon dioxide, methane and chlorofluorocarbons are all considered greenhouse gases. While they occur in nature, in much smaller amounts, human activity has increased the output exponentially within the last 150 years.
People and animals all release carbon dioxide into the air when breathing. Plants pull carbon dioxide from the air into leaves and stems as part of photosynthesis. The chlorophyll, which makes plants green, uses the energy of the Sun to convert that carbon dioxide into oxygen and carbohydrates. The oxygen is released into the air. The carbohydrates are stored or used for food by the plants.
An excess of carbon dioxide in the air, put there by the use of fossil fuels and natural gas, overwhelms this system. Contributing to the problem is the gradual deforestation of the rain forests, meaning fewer plants to absorb the carbon dioxide. The warming of the oceans means fewer seaweeds. These water plants also help rid the atmosphere of greenhouse gases.
Greenhouse gases trap more of the Sun's energy, gradually warming the planet. Just like a gardener's greenhouse, the thicker atmosphere keeps the heat closer to the Earth's surface. Continually pumping polluted air into the atmosphere compounds the problem.