Global warming is the observed increase in the average temperature of the Earth's atmosphere and oceans in recent decades.

Causes
The increased amounts of carbon dioxide (CO2) and other greenhouse gases (GHGs) are the primary causes of the human-induced component of warming.

They are released by the burning of fossil fuels, land clearing and agriculture, etc. and lead to an increase in the greenhouse effect. The first speculation that a greenhouse effect might occur was by the Swedish chemist Svante Arrhenius in 1897, although it did not become a topic of popular debate until some 90 years later.

An increase in global temperatures can in turn cause other changes, including a rising sea level and changes in the amount and pattern of precipitation. These changes may increase the frequency and intensity of extreme weather events, such as floods, droughts, heat waves, hurricanes, and tornados. Other consequences include higher or lower agricultural yields, glacial retreat, reduced summer stream flows, species extinctions and increases in the ranges of disease vectors. Warming is expected to affect the number and magnitude of these events; however, it is difficult to connect particular events to global warming.

Effects on ecosystems
Both primary and secondary effects of global warming — such as higher temperatures, lessened snow cover, rising sea levels and weather changes — may influence not only human activities but also ecosystems. Some species may be forced out of their habitats (possibly to extinction) because of changing conditions, while others may flourish. Similarly, changes in timing of life patterns, such as annual migration dates, may alter regional predator-prey balance. The effect of advanced spring arrival dates in Scandinavia of birds that over winter in sub-Saharan Africa has been ascribed to evolutionary adaptation of the species to climactic warming

Prevention of Global Warming
Here are some easy steps you can take:

Stand out and Say. We require new laws that will steer our nation toward the most important solutions to global warming -- cleaner cars and cleaner power plants. Send a message to our elected officials, letting them know that you will hold them accountable for what they do -- or fail to do -- about global warming.

Choose an efficient vehicle: A car that gets 20 miles per litter will emit about 30 tons of carbon dioxide over its lifetime. A car getting 40 mpl will emit half that much. When buying your next car, pick the least-polluting, most efficient vehicle that meets your needs. Maybe it's an innovative hybrid that combines a gasoline engine with electric motors (and never needs to be plugged in).

Drive smart. Get your engine tuned up and keep your tires inflated -- both help fuel efficiency. A tune-up could boost your miles per gallon anywhere from 4 to 40 percent; a new air filter could get you 10 percent more miles per gallon.

Buy energy-efficient appliances. Start buying energy-efficient appliances for your use. You may spend a little more up front, but you'll save a lot on electricity, and you'll reduce pollution produced by power plants. Look for the Energy Star label, which identifies the most efficient appliances. You can also use the Energy Guide labels to compare the efficiency of specific models. Remember that refrigerators consume the most electricity in the home. Today's refrigerators consume less than one-fourth the energy of models built 30 years ago, so an upgrade could mean huge energy savings for your household. Click here for more energy-saving tips.