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.

Future Changes

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:

Greenhouse Effect
The lonely polar bear—the unofficial mascot of global warming.

Shell Shock
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.

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.

Disappearing Penguins
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.

abnormal
Adjective

unusual.

adapt
Verb

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.

ancient
Adjective

very old.

Noun

layers of gases surrounding a planet or other celestial body.

biofuel
Noun

energy source derived directly from organic matter, such as plants.

buffer
Noun

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.

century
Noun

100 years.

chlorofluorocarbon (CFC)
Noun

chemical compound mostly used in refrigerants and flame-retardants. Some CFCs have destructive effects on the ozone layer.

climate
Noun

all weather conditions for a given location over a period of time.

Noun

gradual changes in all the interconnected weather elements on our planet.

Noun

person forced to leave his or her home and community because of climate change.

climatologist
Noun

person who studies long-term patterns in weather.

Noun

dark, solid fossil fuel mined from the earth.

Noun

edge of land along the sea or other large body of water.

committee
Noun

group of people elected or appointed to perform a task.

Noun

management of a natural resource to prevent exploitation, destruction, or neglect.

consistent
Adjective

maintaining a steady, reliable quality.

cope
Verb

to handle or deal with problems.

Noun

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.

critical
Adjective

very important.

cyclone
Noun

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.

decade
Noun

10 years.

decay
Verb

to rot or decompose.

desalination
Noun

process of converting seawater to fresh water by removing salt and minerals.

devastate
Verb

to destroy.

diminish
Verb

to become smaller or less important.

dissolve
Verb

to break up or disintegrate.

diverse
Adjective

varied or having many different types.

Noun

period of greatly reduced precipitation.

electricity
Noun

set of physical phenomena associated with the presence and flow of electric charge.

emission
Noun

discharge or release.

encore
Noun

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.

Noun

act in which earth is worn away, often by water, wind, or ice.

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.

evaluate
Verb

to decide something's worth.

farming
Noun

the art, science, and business of cultivating the land for growing crops.

fertilizer
Noun

nutrient-rich chemical substance (natural or manmade) applied to soil to encourage plant growth.

flee
Verb

to run away.

fluorinate
Verb

to add or combine with the element fluorine (F).

forest
Noun

ecosystem filled with trees and underbrush.

Noun

remnant, impression, or trace of an ancient organism.

fossil fuel
Noun

coal, oil, or natural gas. Fossil fuels formed from the remains of ancient plants and animals.

freeze
Noun

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.

geographer
Noun

person who studies places and the relationships between people and their environments.

Noun

mass of ice that moves slowly over land.

Noun

increase in the average temperature of the Earth's air and oceans.

Great Plains
Noun

grassland region of North America, between the Rocky Mountains and the Mississippi River.

greenhouse
Noun

building, often made of glass or other clear material, used to help plants grow.

Noun

phenomenon where gases allow sunlight to enter Earth's atmosphere but make it difficult for heat to escape.

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.

hydrochlorofluorocarbon
Noun

greenhouse gas often used as an industrial cooling material.

hydroelectric power
Noun

usable energy generated by moving water converted to electricity.

hygiene
Noun

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.

Noun

area of fewer than 50,000 square kilometers (19,000 square miles) covered by ice.

Noun

thick layer of glacial ice that covers a large area of land.

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.

infrastructure
Noun

structures and facilities necessary for the functioning of a society, such as roads.

insect
Noun

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.

Noun

watering land, usually for agriculture, by artificial means.

Kyoto Protocol
Noun

(1997) international agreement to reduce greenhouse gas emissions.

landfill
Noun

site where garbage is layered with dirt and other absorbing material to prevent contamination of the surrounding land or water.

landmass
Noun

large area of land.

Noun

distance north or south of the Equator, measured in degrees.

livestock
noun, plural noun

animals raised for sale and profit.

manure
Noun

animal excrement or waste used to fertilize soil.

Noun

wetland area usually covered by a shallow layer of seawater or freshwater.

meltwater
Noun

freshwater that comes from melting snow or ice.

meteorologist
Noun

person who studies patterns and changes in Earth's atmosphere.

methane
Noun

chemical compound that is the basic ingredient of natural gas.

Noun

movement of a group of people or animals from one place to another.

model
Noun

image or impression of an object used to represent the object or system.

multiple
Adjective

many.

Noun

type of fossil fuel made up mostly of the gas methane.

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.

oil
Noun

fossil fuel formed from the remains of marine plants and animals. Also known as petroleum or crude oil.

penguin
Noun

bird native to the Antarctic.

power plant
Noun

industrial facility for the generation of electric energy.

Noun

all forms in which water falls to Earth from the atmosphere.

protocol
Noun

series of rules.

rain catchment
Noun

system to collect and store rainwater.

ratify
Verb

to formally approve or confirm.

refrigerant
Noun

substance used to keep materials cool.

research
Noun

scientific observations and investigation into a subject, usually following the scientific method: observation, hypothesis, prediction, experimentation, analysis, and conclusion.

Noun

overflow of fluid from a farm or industrial factory.

Noun

base level for measuring elevations. Sea level is determined by measurements taken over a 19-year cycle.

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.

skyrocket
Verb

to increase rapidly.

slurry
Noun

liquid waste, such as that from the coal mining and cleaning process, also called sludge.

snow
Noun

precipitation made of ice crystals.

solar power
Noun

rate of producing, transferring, or using solar energy.

spruce
Noun

coniferous, or cone-bearing, tree.

storm
Noun

severe weather indicating a disturbed state of the atmosphere resulting from uplifted air.

Noun

abnormal rise in sea level accompanying a hurricane or other intense storm. Also called a storm tide.

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.

surveillance
Noun

observation of a person, community, or situation.

Noun

degree of hotness or coldness measured by a thermometer with a numerical scale.

tourism
Noun

the industry (including food, hotels, and entertainment) of traveling for pleasure.

tropical
Adjective

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.

unprecedented
Adjective

never before known or experienced.

vital
Adjective

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.

Noun

area of land covered by shallow water or saturated by water.

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.