Causes & Effects of Global Warming

Particularly in the United States, media coverage may sometimes create the impression that global warming's existence and causes are highly controversial. Climate scientists worldwide agree to a remarkable extent, however, that global warming is real, results from human activity, and already is altering the Earth's environment for the worse.

Human-Generated Greenhouse Gases

• The "greenhouse effect," the atmosphere's capacity to trap solar warmth, makes life on earth possible. However, since the mid-20th century, the atmosphere has trapped excessive solar radiation, leading to the phenomenon of global warming. A worldwide scientific consensus identifies human-generated greenhouse gases as its primary cause. The major culprits are carbon dioxide (CO2) from burning fossil fuels such as coal and petroleum, nitrous oxide from petroleum-based fertilizers, and methane from industrial-scale livestock raising. Because forests absorb CO2, accelerating deforestation in many parts of the world worsens the impact of this greenhouse gas.

Increasing Global Temperatures

• The Intergovernmental Panel on Climate Change, or IPCC, has found that global warming has already pushed up the global average temperature by 0.8 degree C., with even steeper rises in both polar regions. With current trends, global average temperature will rise between 1.4 and 5.8 degrees C. by 2100, the World Meteorological Organization predicts. While these changes may sound small, scientists believe they can be devastating to the global environment.

Ice Meltdown

• Arctic sea ice, Antarctic ice sheets and mountain glaciers worldwide are melting at unprecedented rates. Because so many of the world's freshwater river and lake systems are glacier-fed, long-established, dependable sources of clean drinking water and hydroelectricity may dry up.

Disturbed Weather Patterns

• The IPCC attributes certain disturbed weather patterns to global warming. For example, between 1900 and 2005, precipitation rose in some parts of northern Europe, North and South America, and central and northern Asia. However, since the 1970s, the drought area in Africa's Sahel region has enlarged. Adverse weather events such as heat waves, hurricanes, floods and droughts are becoming more severe and frequent. The IPCC notes, for example, that since 1970, the number of hurricanes and the proportion of major hurricanes have grown. These trends may overstress human resilience in the face of climatic extremes, and threaten agricultural production and food security.

Ocean Devastation

• Ocean water is expanding not only because of ice melt, but because it absorbs much of the excess global heat. The IPCC predicts that by 2100, sea levels will rise by 0.6 meters -- enough to displace the dense human populations of many coastal areas and river deltas. Excess atmospheric CO2 is acidifying the oceans, the National Oceanic and Atmospheric Administration reports. This CO2 also depletes the ocean's oxygen content, according to the Center for Ocean Solutions. Both effects overstress and kill organisms such as fish, coral and plankton, endangering entire food webs, including those on which humans and other land creatures depend.

Related Threats to Life

• Because it alters global and local environments too fast for many species to adapt, global warming worsens the already great problem of biodiversity loss. Surviving species may change their geographic ranges. One possible consequence is that microbes responsible for tropical diseases like malaria may appear in new areas. The IPCC expects human deaths from these diseases as well as water-borne illnesses like cholera and malnutrition to rise by the millions.

Solutions

• The IPCC has concluded that 50 percent to 80 percent reductions in greenhouse gases could avert or mitigate the harms of global warming. By mid-century, renewables such as wind and solar could feasibly meet 80 percent of humankind's energy needs, according to a May 2011 IPCC report. Although industries emit most greenhouse gases, individual persons can help counter global warming, for example by recycling and by using public transit and green power whenever possible.