Global warming is an increase in the average temperature of Earth’s surface. Since the late 1800’s, the global average temperature has increased about 0.7 to 1.4 degrees F (0.4 to 0.8 degrees C). Many experts estimate that the average temperature will rise an additional 2.5 to 10.4 degrees F (1.4 to 5.8 degrees C) by 2100. That rate of increase would be much larger than most past rates of increase.
Scientists worry that human societies and natural ecosystems might not adapt to rapid climate changes. An ecosystem consists of the living organisms and physical environment in a particular area. Global warming could cause much harm, so countries throughout the world drafted an agreement called the Kyoto Protocol to help limit it.
Causes of global warming
Climatologists (scientists who study climate) have analyzed the global warming that has occurred since the late 1800’s. A majority of climatologists have concluded that human activities are responsible for most of the warming. Human activities contribute to global warming by enhancing Earth’s natural greenhouse effect. The greenhouse effect warms Earth’s surface through a complex process involving sunlight, gases, and particles in the atmosphere. Gases that trap heat in the atmosphere are known as greenhouse gases.
The main human activities that contribute to global warming are the burning of fossil fuels (coal, oil, and natural gas) and the clearing of land. Most of the burning occurs in automobiles, in factories, and in electric power plants that provide energy for houses and office buildings. The burning of fossil fuels creates carbon dioxide, whose chemical formula is CO2. CO2 is a greenhouse gas that slows the escape of heat into space. Trees and other plants remove CO2 from the air during photosynthesis, the process they use to produce food. The clearing of land contributes to the buildup of CO2 by reducing the rate at which the gas is removed from the atmosphere or by the decomposition of dead vegetation.
A small number of scientists argue that the increase in greenhouse gases has not made a measurable difference in the temperature. They say that natural processes could have caused global warming. Those processes include increases in the energy emitted (given off) by the sun. But the vast majority of climatologists believe that increases in the sun’s energy have contributed only slightly to recent warming.
The impact of global warming
|Thousands of icebergs float off the coast of the Antarctic Peninsula after 1,250 square miles (3,240 square kilometers) of the Larsen B ice shelf disintegrated in 2002. The area of the ice was larger than the state of Rhode Island or the nation of Luxembourg. Antarctic ice shelves have been shrinking since the early 1970’s because of climate warming in the region. Image credit: NASA/Earth Observatory|
Continued global warming could have many damaging effects. It might harm plants and animals that live in the sea. It could also force animals and plants on land to move to new habitats. Weather patterns could change, causing flooding, drought, and an increase in damaging storms. Global warming could melt enough polar ice to raise the sea level. In certain parts of the world, human disease could spread, and crop yields could decline.
Harm to ocean life
Through global warming, the surface waters of the oceans could become warmer, increasing the stress on ocean ecosystems, such as coral reefs. High water temperatures can cause a damaging process called coral bleaching. When corals bleach, they expel the algae that give them their color and nourishment. The corals turn white and, unless the water temperature cools, they die. Added warmth also helps spread diseases that affect sea creatures.
Changes of habitat
Widespread shifts might occur in the natural habitats of animals and plants. Many species would have difficulty surviving in the regions they now inhabit. For example, many flowering plants will not bloom without a sufficient period of winter cold. And human occupation has altered the landscape in ways that would make new habitats hard to reach or unavailable altogether.
Extreme weather conditions might become more frequent and therefore more damaging. Changes in rainfall patterns could increase both flooding and drought in some areas. More hurricanes and other tropical storms might occur, and they could become more powerful.
Rising sea level
Continued global warming might, over centuries, melt large amounts of ice from a vast sheet that covers most of West Antarctica. As a result, the sea level would rise throughout the world. Many coastal areas would experience flooding, erosion, a loss of wetlands, and an entry of seawater into freshwater areas. High sea levels would submerge some coastal cities, small island nations, and other inhabited regions.
Threats to human health
Tropical diseases, such as malaria and dengue, might spread to larger regions. Longer-lasting and more intense heat waves could cause more deaths and illnesses. Floods and droughts could increase hunger and malnutrition.
Changes in crop yields
Canada and parts of Russia might benefit from an increase in crop yields. But any increases in yields could be more than offset by decreases caused by drought and higher temperatures — particularly if the amount of warming were more than a few degrees Celsius. Yields in the tropics might fall disastrously because temperatures there are already almost as high as many crop plants can tolerate.
Limited global warming
Climatologists are studying ways to limit global warming. Two key methods would be (1) limiting CO2 emissions and (2) carbon sequestration — either preventing carbon dioxide from entering the atmosphere or removing CO2 already there.
Limiting CO2 emissions
Two effective techniques for limiting CO2 emissions would be (1) to replace fossil fuels with energy sources that do not emit CO2, and (2) to use fossil fuels more efficiently.
Alternative energy sources that do not emit CO2 include the wind, sunlight, nuclear energy, and underground steam. Devices known as wind turbines can convert wind energy to electric energy. Solar cells can convert sunlight to electric energy, and various devices can convert solar energy to useful heat. Geothermal power plants convert energy in underground steam to electric energy.
Alternative sources of energy are more expensive to use than fossil fuels. However, increased research into their use would almost certainly reduce their cost.
Carbon sequestration could take two forms: (1) underground or underwater storage and (2) storage in living plants.
Underground or underwater storage would involve injecting industrial emissions of CO2 into underground geologic formations or the ocean. Suitable underground formations include natural reservoirs of oil and gas from which most of the oil or gas has been removed. Pumping CO2 into a reservoir would have the added benefit of making it easier to remove the remaining oil or gas. The value of that product could offset the cost of sequestration. Deep deposits of salt or coal could also be suitable.
The oceans could store much CO2. However, scientists have not yet determined the environmental impacts of using the ocean for carbon sequestration.
Storage in living plants
Green plants absorb CO2 from the atmosphere as they grow. They combine carbon from CO2 with hydrogen to make simple sugars, which they store in their tissues. After plants die, their bodies decay and release CO2. Ecosystems with abundant plant life, such as forests and even cropland, could tie up much carbon. However, future generations of people would have to keep the ecosystems intact. Otherwise, the sequestered carbon would re-enter the atmosphere as CO2.
Agreement on global warming
Delegates from more than 160 countries met in Kyoto, Japan, in 1997 to draft the agreement that became known as the Kyoto Protocol. That agreement calls for decreases in the emissions of greenhouse gases.
Thirty-eight industrialized nations would have to restrict their emissions of CO2 and five other greenhouse gases. The restrictions would occur from 2008 through 2012. Different countries would have different emissions targets. As a whole, the 38 countries would restrict their emissions to a yearly average of about 95 percent of their 1990 emissions. The agreement does not place restrictions on developing countries. But it encourages the industrialized nations to cooperate in helping developing countries limit emissions voluntarily.
Industrialized nations could also buy or sell emission reduction units. Suppose an industrialized nation cut its emissions more than was required by the agreement. That country could sell other industrialized nations emission reduction units allowing those nations to emit the amount equal to the excess it had cut.
Several other programs could also help an industrialized nation earn credit toward its target. For example, the nation might help a developing country reduce emissions by replacing fossil fuels in some applications.
Approving the agreement
The protocol would take effect as a treaty if (1) at least 55 countries ratified (formally approved) it, and (2) the industrialized countries ratifying the protocol had CO2 emissions in 1990 that equaled at least 55 percent of the emissions of all 38 industrialized countries in 1990.
In 2001, the United States rejected the Kyoto Protocol. President George W. Bush said that the agreement could harm the U.S. economy. But he declared that the United States would work with other countries to limit global warming. Other countries, most notably the members of the European Union, agreed to continue with the agreement without United States participation.
By 2004, more than 100 countries, including nearly all the countries classified as industrialized under the protocol, had ratified the agreement. However, the agreement required ratification by Russia or the United States to go into effect. Russia ratified the protocol in November 2004. The treaty was to come into force in February 2005.
Analyzing global warming
Scientists use information from several sources to analyze global warming that occurred before people began to use thermometers. Those sources include tree rings, cores (cylindrical samples) of ice drilled from Antarctica and Greenland, and cores drilled out of sediments in oceans. Information from these sources indicates that the temperature increase of the 1900’s was probably the largest in the last 1,000 years.
Computers help climatologists analyze past climate changes and predict future changes. First, a scientist programs a computer with a set of mathematical equations known as a climate model. The equations describe how various factors, such as the amount of CO2 in the atmosphere, affect the temperature of Earth’s surface. Next, the scientist enters data representing the values of those factors at a certain time. He or she then runs the program, and the computer describes how the temperature would vary. A computer’s representation of changing climatic conditions is known as a climate simulation.
In 2001, the Intergovernmental Panel on Climate Change (IPCC), a group sponsored by the United Nations (UN), published results of climate simulations in a report on global warming. Climatologists used three simulations to determine whether natural variations in climate produced the warming of the past 100 years. The first simulation took into account both natural processes and human activities that affect the climate. The second simulation took into account only the natural processes, and the third only the human activities.
The climatologists then compared the temperatures predicted by the three simulations with the actual temperatures recorded by thermometers. Only the first simulation, which took into account both natural processes and human activities, produced results that corresponded closely to the recorded temperatures.
The IPCC also published results of simulations that predicted temperatures until 2100. The different simulations took into account the same natural processes but different patterns of human activity. For example, scenarios differed in the amounts of CO2 that would enter the atmosphere due to human activities.
The simulations showed that there can be no “quick fix” to the problem of global warming. Even if all emissions of greenhouse gases were to cease immediately, the temperature would continue to increase after 2100 because of the greenhouse gases already in the atmosphere. Contributors: Michael D. Mastrandrea, B.S., Graduate Fellow, School of Earth Sciences, Geological and Environmental Sciences, Stanford University. Stephen H. Schneider, Ph.D., Professor of Biological Sciences, Stanford University.