Slide 1

The Global WarmingSummaryCausesThe Greenhouse effectDeforestationConsequences

CausesGlobal warming is primarily a problem of too much carbon dioxide (CO2) in the atmospherewhich acts as a blanket, trapping heat and warming the planet. As we burn fossil fuels like coal, oil and natural gas for energy or cut down and burn forests to create pastures and plantations, carbon accumulates and overloads our atmosphere. Certain waste management and agricultural practices aggravate the problem by releasing other potent global warming gases, such as methane and nitrous oxide. See the pie chart for a breakdown of heat-trapping global warming emissions by economic sector.

CausesScientists have spent decades figuring out what is causing global warming. They've looked at the natural cycles and events that are known to influence climate. But the amount and pattern of warming that's been measured can't be explained by these factors alone. The only way to explain the pattern is to include the effect of greenhouse gases (GHGs) emitted by humans.One of the first things scientists learned is that there are several greenhouse gases responsible for warming, and humans emit them in a variety of ways. Most come from the combustion of fossil fuels in cars, factories and electricity production. The gas responsible for the most warming is carbon dioxide, also called CO2. Other contributors include methane released from landfills and agriculture (especially from the digestive systems of grazing animals), nitrous oxide from fertilizers, gases used for refrigeration and industrial processes, and the loss of forests that would otherwise store CO2.CausesDifferent greenhouse gases have very different heat-trapping abilities. Some of them can even trap more heat than CO2. A molecule of methane produces more than 20 times the warming of a molecule of CO2. Nitrous oxide is 300 times more powerful than CO2. Other gases, such as chlorofluorocarbons (which have been banned in much of the world because they also degrade the ozone layer), have heat-trapping potential thousands of times greater than CO2. But because their concentrations are much lower than CO2, none of these gases adds as much warmth to the atmosphere as CO2 does.CausesIn order to understand the effects of all the gases together, scientists tend to talk about all greenhouse gases in terms of the equivalent amount of CO2. Since 1990, yearly emissions have gone up by about 6 billion metric tons of "carbon dioxide equivalent" worldwide, more than a 20 percent increase.

The Greenhouse EffectThegreenhouse effectis a process by whichthermal radiationfrom a planetary surface is absorbed by atmospheric greenhouse gases and is re-radiated in all directions. Since part of this re-radiation is back towards the surface and the lower atmosphere, it results in an elevation of the average surface temperature above what it would be in the absence of the gases.The Greenhouse Effect

The Greenhouse EffectSolar radiation at the frequencies ofvisible lightlargely passes through the atmosphere to warm the planetary surface, which then emits this energy at the lower frequencies ofinfraredthermal radiation. Infrared radiation is absorbed by greenhouse gases, which in turn re-radiate much of the energy to the surface and lower atmosphere. The mechanism is named after the effect of solar radiation passing through glass and warming agreenhouse, but the way it retains heat is fundamentally different as a greenhouse works by reducing airflow, isolating the warm air inside the structure so that heat is not lost by convection.The Greenhouse EffectThe climate system can respond to changes inexternal forcings.External forcings can "push" the climate in the direction of warming or cooling.Examples of external forcings include changes in atmospheric composition (e.g., increased concentrations ofgreenhouse gases),solar luminosity,volcaniceruptions, andvariations in Earth's orbitaround the Sun.Orbital cyclesvary slowly over tens of thousands of years, and at present are in an overall cooling trendwhich would be expected to lead towards aglacial periodwithin the currentice age, but the 20th centuryinstrumental temperature record shows a sudden rise in global temperaturesDeforestationDeforestation,clearanceorclearingis the removal of a forest or stand of trees where the land is thereafter converted to a non-forest use. Examples of deforestation include conversion of forestland to farms, ranches, or urban use.By most accounts, deforestation in tropical rainforests adds more carbon dioxide to the atmosphere than the sum total of cars and trucks on the worlds roads. According to the World Carfree Network (WCN), cars and trucks account for about 14 percent of global carbon emissions, while most analysts attribute upwards of 15 percent to deforestation.DeforestationThe reason that logging is so bad for the climate is that when trees are felled they release the carbon they are storing into the atmosphere, where it mingles with greenhouse gases from other sources and contributes to global warming accordingly. The upshot is that we should be doing as much to prevent deforestation as we are to increase fuel efficiency and reduce automobile usage.

DeforestationDeforestation is ongoing and is shapingclimateandgeography.Deforestation is a contributor to global warming, and is often cited as one of the major causes of the enhanced greenhouse effect. Tropical deforestation is responsible for approximately 20% of world greenhouse gas emissions. According to theIntergovernmental Panel on Climate Changedeforestation, mainly in tropical areas, could account for up to one-third of totalanthropogeniccarbon dioxideemissions.But recent calculations suggest that carbon dioxide emissions from deforestation and forest degradation contribute about 12% of total anthropogenic carbon dioxide emissions with a range from 6 to 17%.

Deforestation

DeforestationThe water cycle is also affected by deforestation. Trees extract groundwater through their roots and release it into the atmosphere. When part of a forest is removed, the trees no longer transpire this water, resulting in a much drier climate. Deforestation reduces the content of water in the soil and groundwater as well as atmospheric moisture. The dry soil leads to lower water intake for the trees to extract.Deforestation reduces soil cohesion, so thaterosion, flooding andlandslidesensue.ConsequencesOver the last century, global average temperature has increased by more than 1F (0.7C). The 2001-2010 decade is the warmest since 1880the earliest year for which comprehensive global temperature records were available. In fact, nine of the warmest years on record have occurred in just the last 10 years. This warming has been accompanied by a decrease in very cold days and nights and an increase in extremely hot days and warm nights. The continental United States, for example, has seen record daily highs twice as often as record daily lows from 2000 to 2009. While the record shows that some parts of the world are warming faster than others, the long-term global upward trend is unambiguous.ConsequencesThe planet is warming, from North Pole to South Pole, and everywhere in between. And the effects of rising temperatures arent waiting for some far-flung future. Theyre happening right now. Signs are appearing all over, and some of them are surprising. The heat is not only melting glaciers and sea ice, its also shifting precipitation patterns and setting animals on the move.ConsequencesSome impacts from increasing temperatures are already happening:Ice is melting worldwide, especially at the Earths 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 Adlie 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.

ConsequencesOther 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.

ConsequencesLess 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 changesome species will move farther north or become more successful; others wont 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.

The EndRealised by: Virva Alexandra Cimpean Paul Berciu AncaClass : X-BProf. : Moldovan Adriana