Greenhouse Effect | National Geographic Society (2023)

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 five to six 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 three to five degrees Celsius (five to nine 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 s

oil

. 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: