What is the meaning of volcano?

  A volcano is an opening, or rupture, in a planet's surface or crust, which allows hot magma, volcanic ash and gases to escape from below the surface.
Volcanoes are generally found where tectonic plates are diverging or converging. A mid-oceanic ridge, for example the Mid-Atlantic Ridge, has examples of volcanoes caused by divergent tectonic plates pulling apart; the Pacific Ring of Fire has examples of volcanoes caused by convergent tectonic plates coming together. By contrast, volcanoes are usually not created where two tectonic plates slide past one another. Volcanoes can also form where there is stretching and thinning of the Earth's crust in the interiors of plates, e.g., in the East African Rift, the Wells Gray-Clearwater volcanic field and the Rio Grande Rift in North America. This type of volcanism falls under the umbrella of "Plate hypothesis" volcanism.^[1] Volcanism away from plate boundaries has also been explained as mantle plumes. These so-called "hotspots", for example Hawaii, are postulated to arise from upwelling diapirs with magma from the core–mantle boundary, 3,000 km deep in the Earth.
Erupting volcanoes can pose many hazards, not only in the immediate vicinity of the eruption. Volcanic ash can be a threat to aircraft, in particular those with jet engines where ash particles can be melted by the high operating temperature. Large eruptions can affect temperature as ash and droplets of sulfuric acid obscure the sun and cool the Earth's lower atmosphere or troposphere; however, they also absorb heat radiated up from the Earth, thereby warming the stratosphere. Historically, so-called volcanic winters have caused catastrophic famines.

Global Warning Effect

This planet is Warming, from North pole to South pole, and everywhere between. Globally, teh mercury is alredy up more than 1 degree Fahrenheit(0.8 degree Celcius), and even more in sensitive polar regions. And effect of rising temperatures aren’t waiting for some far-flung future. They are happening rigth now. Sings are appearing all ove, and soem of them are surprising. The heat is not only melting glaciers and sea ice, it’s also shifting precipitation patterns and setting animal on the move.
Some impact from Some impacts from increasing temperatures are already happening.

•     Ice is melting worldwide, especially at the Earth’s poles. This includes mountain glaciers, ice sheets covering West Antarctica and Greenland, and Arctic sea ice.

•     Researcher Bill Fraser has tracked the decline of the Adélie penguins on Antarctica, where their numbers have fallen from 32,000 breeding pairs to 11,000 in 30 years.

•     Sea level rise became faster over the last century.

Some butterflies, foxes, and alpine plants have      moved farther north or to higher, cooler areas.

•     Precipitation (rain and snowfall) has increased across the globe, on average.

•     Spruce bark beetles have boomed in Alaska thanks to 20 years of warm summers. The insects have chewed up 4 million acres of spruce trees.

Other effects could happen later this century, if warming continues.

•     Sea levels are expected to rise between 7 and 23 inches (18 and 59 centimeters) by the end of the century, and continued melting at the poles could add between 4 and 8 inches (10 to 20 centimeters).
•     Hurricanes and other storms are likely to become stronger.
•     Species that depend on one another may become out of sync. For example, plants could bloom earlier than their pollinating insects become active.
•     Floods and droughts will become more common. Rainfall in Ethiopia, where droughts are already common, could decline by 10 percent over the next 50 years.
•     Less fresh water will be available. If the Quelccaya ice cap in Peru continues to melt at its current rate, it will be gone by 2100, leaving thousands of people who rely on it for drinking water and electricity without a source of either.
•     Some diseases will spread, such as malaria carried by mosquitoes.
•     Ecosystems will change—some species will move farther north or become more successful; others won’t be able to move and could become extinct. Wildlife research scientist Martyn Obbard has found that since the mid-1980s, with less ice on which to live and fish for food, polar bears have gotten considerably skinnier.  Polar bear biologist Ian Stirling has found a similar pattern in Hudson Bay.  He fears that if sea ice disappears, the polar bears will as well.

Source for climate information: IPCC, 2007