Global warming describes the current rise in the average temperature of Earth’s air and oceans. Global warming is often described as the most recent example of climate change.
Earth’s climate has changed many times. Our planet has gone through multiple ice ages, in which ice sheets and glaciers covered large portions of the Earth. It has also gone through warm periods when temperatures were higher than they are today.
Past changes in Earth’s temperature happened very slowly, over hundreds of thousands of years. However, the recent warming trend is happening much faster than it ever has. Natural cycles of warming and cooling are not enough to explain the amount of warming we have experienced in such a short time—only human activities can account for it. Scientists worry that the climate is changing faster than some living things can adapt to it.
In 1988, the World Meteorological Organization and the United Nations Environment Programme established a committee of climatologists, meteorologists, geographers, and other scientists from around the world. This Intergovernmental Panel on Climate Change (IPCC) includes thousands of scientists who review the most up-to-date research available related to global warming and climate change. The IPCC evaluates the risk of climate change caused by human activities.
According to the IPCC’s most recent report (in 2007), Earth’s average surface temperatures have risen about 0.74 degrees Celsius (1.33 degrees Fahrenheit) during the past 100 years. The increase is greater in northern latitudes. The IPCC also found that land regions are warming faster than oceans. The IPCC states that most of the temperature increase since the mid-20th century is likely due to human activities.
The Greenhouse Effect
Human activities contribute to global warming by increasing the greenhouse effect. The greenhouse effect happens when certain gases—known as greenhouse gases—collect in Earth’s atmosphere. These gases, which occur naturally in the atmosphere, include carbon dioxide, methane, nitrogen oxide, and fluorinated gases sometimes known as chlorofluorocarbons (CFCs).
Greenhouse gases let the sun’s light shine onto the Earth’s surface, but they trap the heat that reflects back up into the atmosphere. In this way, they act like the insulating glass walls of a greenhouse. The greenhouse effect keeps Earth’s climate comfortable. Without it, surface temperatures would be cooler by about 33 degrees Celsius (60 degrees Fahrenheit), and many life forms would freeze.
Since the Industrial Revolution in the late 1700s and early 1800s, people have been releasing large quantities of greenhouse gases into the atmosphere. That amount has skyrocketed in the past century. Greenhouse gas emissions increased 70 percent between 1970 and 2004. Emissions of carbon dioxide, the most important greenhouse gas, rose by about 80 percent during that time. The amount of carbon dioxide in the atmosphere today far exceeds the natural range seen over the last 650,000 years.
Most of the carbon dioxide that people put into the atmosphere comes from burning fossil fuels such as oil, coal, and natural gas. Cars, trucks, trains, and planes all burn fossil fuels. Many electric power plants also burn fossil fuels.
Another way people release carbon dioxide into the atmosphere is by cutting down forests. This happens for two reasons. Decaying plant material, including trees, releases tons of carbon dioxide into the atmosphere. Living trees absorb carbon dioxide. By diminishing the number of trees to absorb carbon dioxide, the gas remains in the atmosphere.
Most methane in the atmosphere comes from livestock farming, landfills, and fossil fuel production such as coal mining and natural gas processing. Nitrous oxide comes from agricultural technology and fossil fuel burning.
Fluorinated gases include chlorofluorocarbons, hydrochlorofluorocarbons, and hydrofluorocarbons. These greenhouse gases are used in aerosol cans and refrigeration.
All of these human activities add greenhouse gases to the atmosphere, trapping more heat than usual and contributing to global warming.
Effects of Global Warming
Even slight rises in average global temperatures can have huge effects. Perhaps the biggest, most obvious effect is that glaciers and ice caps melt faster than usual. The meltwater drains into the oceans, causing sea levels to rise and oceans to become less salty.
Ice sheets and glaciers advance and retreat naturally. As Earth’s temperature has changed, the ice sheets have grown and shrunk, and sea levels have fallen and risen. Ancient corals found on land in Florida, Bermuda, and the Bahamas show that the sea level must have been 5 to 6 meters (16-20 feet) higher 130,000 years ago than it is today. Earth doesn’t need to become oven-hot to melt the glaciers. Northern summers were just 3 to 5 degrees Celsius (5-9 degrees Fahrenheit) warmer during the time of those ancient fossils than they are today.
However, the speed at which global warming is taking place is unprecedented. The effects are unknown.
Glaciers and ice caps cover about 10 percent of the world’s landmass today. They hold about 75 percent of the world’s fresh water. If all of this ice melted, sea levels would rise by about 70 meters (230 feet). The IPCC reported that the global sea level rose about 1.8 millimeters (0.07 inches) per year from 1961 to 1993, and 3.1 millimeters (0.12 inches) per year since 1993.
Rising sea levels could flood coastal communities, displacing millions of people in areas such as Bangladesh, the Netherlands, and the U.S. state of Florida. Forced migration would impact not only those areas, but the regions to which the “climate refugees” flee. Millions more people in countries like Bolivia, Peru, and India depend on glacial meltwater for drinking, irrigation, and hydroelectric power. Rapid loss of these glaciers would devastate those countries.
Glacial melt has already raised the global sea level slightly. However, scientists are discovering ways the sea level could increase even faster. For example, the melting of the Chacaltaya Glacier in Bolivia has exposed dark rocks beneath it. The rocks absorb heat from the sun, speeding up the melting process.
Many scientists use the term “climate change” instead of “global warming.” This is because greenhouse gas emissions affect more than just temperature. Another effect involves changes in precipitation like rain and snow. Patterns in precipitation may change or become more extreme. Over the course of the 20th century, precipitation increased in eastern parts of North and South America, northern Europe, and northern and central Asia. However, it has decreased in parts of Africa, the Mediterranean, and parts of southern Asia.
Nobody can look into a crystal ball and predict the future with certainty. However, scientists can make estimates about future population growth, greenhouse gas emissions, and other factors that affect climate. They can enter those estimates into computer models to find out the most likely effects of global warming.
The IPCC predicts that greenhouse gas emissions will continue to increase over the next few decades. As a result, they predict the average global temperature will increase by about 0.2 degrees Celsius (0.36 degrees Fahrenheit) per decade. Even if we reduce greenhouse gas and aerosol emissions to their 2000 levels, we can still expect a warming of about 0.1 degree Celsius (0.18 degrees Fahrenheit) per decade.
The panel also predicts global warming will contribute to some serious changes in water supplies around the world. By the middle of the 21st century, the IPCC predicts, river runoff and water availability will most likely increase at high latitudes and in some tropical areas. However, many dry regions in the mid-latitudes and tropics will experience a decrease in water resources.
As a result, millions of people may be exposed to water shortages. Water shortages decrease the amount of water available for drinking, electricity, and hygiene. Shortages also reduce water used for irrigation. Agricultural output would slow and food prices would climb. Consistent years of drought in the Great Plains of the United States and Canada would have this effect.
IPCC data also suggest that the frequency of heat waves and extreme precipitation will increase. Weather patterns such as storms and tropical cyclones will become more intense. Storms themselves may be stronger, more frequent, and longer-lasting. They would be followed by stronger storm surges, the immediate rise in sea level following storms. Storm surges are particularly damaging to coastal areas because their effects (flooding, erosion, damage to buildings and crops) are lasting.
What We Can Do
Reducing our greenhouse gas emissions is a critical step in slowing the global warming trend. Many governments around the world are working toward this goal.
The biggest effort so far has been the Kyoto Protocol, which was adopted in 1997 and went into effect in 2005. By the end of 2009, 187 countries had signed and ratified the agreement. Under the protocol, 37 industrialized countries and the European Union have committed to reducing their greenhouse gas emissions.
There are several ways that governments, industries, and individuals can reduce greenhouse gases. We can improve energy efficiency in homes and businesses. We can improve the fuel efficiency of cars and other vehicles. We can also support development of alternative energy sources, such as solar power and biofuels, that don’t involve burning fossil fuels.
Some scientists are working to capture carbon dioxide and store it underground, rather than let it go into the atmosphere. This process is called carbon sequestration.
Trees and other plants absorb carbon dioxide as they grow. Protecting existing forests and planting new ones can help balance greenhouse gases in the atmosphere.
Changes in farming practices could also reduce greenhouse gas emissions. For example, farms use large amounts of nitrogen-based fertilizers, which increase nitrogen oxide emissions from the soil. Reducing the use of these fertilizers would reduce the amount of this greenhouse gas in the atmosphere.
The way farmers handle animal manure can also have an effect on global warming. When manure is stored as liquid or slurry in ponds or tanks, it releases methane. When it dries as a solid, however, it does not.
Reducing greenhouse gas emissions is vitally important. However, the global temperature has already changed and will most likely continue to change for years to come. The IPCC suggests that people explore ways to adapt to global warming as well as try to slow or stop it. Some of the suggestions for adapting include:
- Expanding water supplies through rain catchment, conservation, reuse, and desalination.
- Adjusting crop locations, variety, and planting dates.
- Building seawalls and storm surge barriers and creating marshes and wetlands as buffers against rising sea levels.
- Creating heat-health action plans, boosting emergency medical services, and improving disease surveillance and control.
- Diversifying tourism attractions, because existing attractions like ski resorts and coral reefs may disappear.
- Planning for roads and rail lines to cope with warming and/or flooding.
- Strengthening energy infrastructure, improving energy efficiency, and reducing dependence on single sources of energy.
Emperor penguins made a showbiz splash in the 2005 film March of the Penguins. Sadly, their encore might include a disappearing act. In the 1970s, an abnormally long warm spell caused these Antarctic birds' population to drop by 50 percent. Some scientists worry that continued global warming will push the creatures to extinction by changing their habitat and food supply.
Barking Up the Wrong Tree
Spruce bark beetles in Alaska have had a population boom thanks to 20 years of warmer-than-average summers. The insects have managed to chew their way through 1.6 million hectares (4 million acres) of spruce trees.
A sudden increase in the amount of carbon dioxide in the atmosphere does more than change Earth's temperature. A lot of the carbon dioxide in the air dissolves into seawater. There, it forms carbonic acid in a process called ocean acidification. Ocean acidification is making it hard for some sea creatures to build shells and skeletal structures. This could alter the ecological balance in the oceans and cause problems for fishing and tourism industries.
Term Part of Speech Definition Encyclopedic Entry abnormal Adjective
to adjust to new surroundings or a new situation.
aerosol can Noun
container of liquid material under high pressure. When released through a small opening, the liquid becomes a spray or foam.
agricultural technology Noun
the art and science of complex machines used to perform tasks associated with farming and ranching.
layers of gases surrounding a planet or other celestial body.
Encyclopedic Entry: atmosphere biofuel Noun
energy source derived directly from organic matter, such as plants.
a cushion or shield.
carbon dioxide Noun
greenhouse gas produced by animals during respiration and used by plants during photosynthesis. Carbon dioxide is also the byproduct of burning fossil fuels.
carbonic acid Noun
chemical produced as carbon dioxide dissolves in water.
carbon sequestration Noun
process of capturing carbon emissions and storing them underground.
chlorofluorocarbon (CFC) Noun
chemical compound mostly used in refrigerants and flame-retardants. Some CFCs have destructive effects on the ozone layer.
all weather conditions for a given location over a period of time.
Encyclopedic Entry: climate climate change Noun
gradual changes in all the interconnected weather elements on our planet.
Encyclopedic Entry: Earth's Changing Climate climate refugee Noun
person forced to leave his or her home and community because of climate change.
Encyclopedic Entry: environmental refugee climatologist Noun
person who studies long-term patterns in weather.
dark, solid fossil fuel mined from the earth.
edge of land along the sea or other large body of water.
Encyclopedic Entry: coast committee Noun
group of people elected or appointed to perform a task.
management of a natural resource to prevent exploitation, destruction, or neglect.
Encyclopedic Entry: conservation consistent Adjective
maintaining a steady, reliable quality.
to handle or deal with problems.
tiny ocean animal, some of which secrete calcium carbonate to form reefs.
coral reef Noun
rocky ocean features made up of millions of coral skeletons.
weather system that rotates around a center of low pressure and includes thunderstorms and rain. Usually, hurricanes refer to cyclones that form over the Atlantic Ocean.
data Plural Noun
(singular: datum) information collected during a scientific study.
to rot or decompose.
process of converting seawater to fresh water by removing salt and minerals.
to become smaller or less important.
to break up or disintegrate.
varied or having many different types.
period of greatly reduced precipitation.
Encyclopedic Entry: drought electricity Noun
set of physical phenomena associated with the presence and flow of electric charge.
discharge or release.
reappearance by a performer after the end of the performance.
energy efficiency Noun
use of a relatively small amount of energy for a given task, purpose, or service; achieving a specific output with less energy input.
act in which earth is worn away, often by water, wind, or ice.
Encyclopedic Entry: erosion establish Verb
to form or officially organize.
European Union Noun
association of European nations promoting free trade, ease of transportation, and cultural and political links.
to decide something's worth.
the art, science, and business of cultivating the land for growing crops.
nutrient-rich chemical substance (natural or manmade) applied to soil to encourage plant growth.
to run away.
to add or combine with the element fluorine (F).
ecosystem filled with trees and underbrush.
remnant, impression, or trace of an ancient organism.
Encyclopedic Entry: fossil fossil fuel Noun
coal, oil, or natural gas. Fossil fuels formed from the remains of ancient plants and animals.
weather pattern of temperatures below 0 degrees Celsius (32 degrees Fahrenheit).
fuel efficiency Noun
ability to produce as much power with as little fuel consumed as possible.
person who studies places and the relationships between people and their environments.
mass of ice that moves slowly over land.
Encyclopedic Entry: glacier global warming Noun
increase in the average temperature of the Earth's air and oceans.
Encyclopedic Entry: The Greenhouse Effect and our Planet Great Plains Noun
grassland region of North America, between the Rocky Mountains and the Mississippi River.
building, often made of glass or other clear material, used to help plants grow.
greenhouse effect Noun
phenomenon where gases allow sunlight to enter Earth's atmosphere but make it difficult for heat to escape.
Encyclopedic Entry: Greenhouse Effect greenhouse gas Noun
gas in the atmosphere, such as carbon dioxide, methane, water vapor, and ozone, that absorbs solar heat reflected by the surface of the Earth, warming the atmosphere.
heat-health action plan Noun
public system for preventing or reducing death and disease due to extreme heat waves.
heat wave Noun
period of unusually hot weather.
greenhouse gas often used as an industrial cooling material.
hydroelectric power Noun
usable energy generated by moving water converted to electricity.
science and methods of keeping clean and healthy.
ice age Noun
long period of cold climate where glaciers cover large parts of the Earth. The last ice age peaked about 20,000 years ago. Also called glacial age.
ice cap Noun
area of fewer than 50,000 square kilometers (19,000 square miles) covered by ice.
Encyclopedic Entry: ice cap ice sheet Noun
thick layer of glacial ice that covers a large area of land.
Encyclopedic Entry: ice sheet industrialization Noun
growth of machine production and factories.
Industrial Revolution Noun
change in economic and social activities, beginning in the 18th century, brought by the replacement of hand tools with machinery and mass production.
structures and facilities necessary for the functioning of a society, such as roads.
type of animal that breathes air and has a body divided into three segments, with six legs and usually wings.
Intergovernmental Panel on Climate Change (IPCC) Noun
group of scientists who review the most up-to-date research available related to global warming and climate change.
watering land, usually for agriculture, by artificial means.
Encyclopedic Entry: irrigation Kyoto Protocol Noun
(1997) international agreement to reduce greenhouse gas emissions.
site where garbage is layered with dirt and other absorbing material to prevent contamination of the surrounding land or water.
large area of land.
distance north or south of the Equator, measured in degrees.
Encyclopedic Entry: latitude livestock noun, plural noun
animals raised for sale and profit.
animal excrement or waste used to fertilize soil.
wetland area usually covered by a shallow layer of seawater or freshwater.
Encyclopedic Entry: marsh meltwater Noun
freshwater that comes from melting snow or ice.
person who studies patterns and changes in Earth's atmosphere.
chemical compound that is the basic ingredient of natural gas.
movement of a group of people or animals from one place to another.
image or impression of an object used to represent the object or system.
natural gas Noun
type of fossil fuel made up mostly of the gas methane.
Encyclopedic Entry: natural gas nitrogen Noun
chemical element with the symbol N, whose gas form is 78% of the Earth's atmosphere.
nitrous oxide Noun
greenhouse gas used in medicine and the manufacture of rockets. Also known as laughing gas or happy gas.
fossil fuel formed from the remains of marine plants and animals. Also known as petroleum or crude oil.
bird native to the Antarctic.
power plant Noun
industrial facility for the generation of electric energy.
all forms in which water falls to Earth from the atmosphere.
Encyclopedic Entry: precipitation protocol Noun
series of rules.
rain catchment Noun
system to collect and store rainwater.
to formally approve or confirm.
substance used to keep materials cool.
scientific observations and investigation into a subject, usually following the scientific method: observation, hypothesis, prediction, experimentation, analysis, and conclusion.
overflow of fluid from a farm or industrial factory.
Encyclopedic Entry: runoff sea level Noun
base level for measuring elevations. Sea level is determined by measurements taken over a 19-year cycle.
Encyclopedic Entry: sea level seawall Noun
barrier built to protect a beach or shoreline from erosion. Also called a bulkhead.
ski resort Noun
facility where people can ski for recreation or sport.
to increase rapidly.
liquid waste, such as that from the coal mining and cleaning process, also called sludge.
precipitation made of ice crystals.
solar power Noun
rate of producing, transferring, or using solar energy.
coniferous, or cone-bearing, tree.
severe weather indicating a disturbed state of the atmosphere resulting from uplifted air.
storm surge Noun
abnormal rise in sea level accompanying a hurricane or other intense storm. Also called a storm tide.
Encyclopedic Entry: storm surge storm surge barrier Noun
walls or obstacles built to prevent ocean or river water from flowing into an area after a storm. Also called levee or floodgate.
observation of a person, community, or situation.
degree of hotness or coldness measured by a thermometer with a numerical scale.
Encyclopedic Entry: temperature tourism Noun
the industry (including food, hotels, and entertainment) of traveling for pleasure.
existing in the tropics, the latitudes between the Tropic of Cancer in the north and the Tropic of Capricorn in the south.
United Nations Environment Programme Noun
organization whose mission is to provide international leadership and encourage partnerships in caring for the environment.
never before known or experienced.
necessary or very important.
water shortage Noun
reduction in the amount of fresh water available for drinking, hygiene, and industrial and agricultural use.
water supply Noun
amount of available fresh water for drinking, hygiene, and industrial and agricultural use.
weather pattern Noun
repeating or predictable changes in the Earth's atmosphere, such as winds, precipitation, and temperatures.
area of land covered by shallow water or saturated by water.
Encyclopedic Entry: wetland World Meteorological Organization Noun
United Nations agency that studies the Earth's atmosphere, its interaction with the oceans, the climate, and the distribution of water resources.