Climate change over the the last 100 years

More than 100 years ago, people around the world started burning large amounts of coal, oil, and natural gas to power their homes, factories, and vehicles. Today, most of the world relies on these fossil fuels for their energy needs. Burning fossil fuels releases carbon dioxide, a heat-trapping gas, into the atmosphere, which is the main reason why the climate is changing.
Heat-trapping gases are also called greenhouse gases. They exist naturally in the atmosphere, where they help keep the Earth warm enough for plants and animals to live. But people are adding extra greenhouse gases to the atmosphere. These extra gases are causing the Earth to get warmer, setting off all sorts of other changes around the world—on land, in the oceans, and in the atmosphere. And these changes affect people, plants, and animals in many ways.
Learn more about carbon dioxide and other greenhouse gases and how they are changing the Earth's climate:

• The Greenhouse Effect
• Greenhouse Gases
• All About Carbon Dioxide

All about carbondioxide

Carbon is an element that's found all over the world and in every living thing. Oxygen is another element that's in the air we breathe. When carbon and oxygen bond together, they form a colorless, odorless gas called carbon dioxide, which is a heat-trapping greenhouse gas. Whenever we burn fossil fuels such as coal, oil, and natural gas—whether it's to drive our cars, use electricity, or make products—we are producing carbon dioxide.
The atmosphere isn't the only part of the Earth that has carbon. The oceans store large amounts of carbon, and so do plants, soil, and deposits of coal, oil, and natural gas deep underground. Carbon naturally moves from one part of the Earth to another through the carbon cycle. But right now, by burning fossil fuels, people are adding carbon to the atmosphere (in the form of carbon dioxide) faster than natural processes can remove it. That's why the amount of carbon dioxide in the atmosphere is increasing, which is causing global climate change.
Check out this video to learn more about the carbon cycle and how people are changing its natural balance.

People are adding carbon dioxide to the atmosphere faster than it can be removed.

Green House Gases

Greenhouse gases trap heat in the atmosphere, which makes the Earth warmer. People are adding several types of greenhouse gases to the atmosphere.

People produce larger amounts of some greenhouse gases than others. Carbon dioxide is the greenhouse gas you hear people talk about the most. That's because we produce more carbon dioxide than any other greenhouse gas, and it's responsible for most of the warming.

Carbon dioxide is the most important greenhouse gas emitted by humans, but several other gases contribute to climate change, too. Learn more about the major greenhouse gases by selecting pieces of the pie chart below.

The size of each piece of the pie represents the amount of warming that each gas is currently causing in the atmosphere as a result of emissions from people's activities.

Greenhouse gases come from all sorts of everyday activities, such as using electricity, heating our homes, and driving around town. The graph to the right shows which activities produce the most greenhouse gases in the United States.
These greenhouse gases don't just stay in one place after they're added to the atmosphere. As air moves around the world, greenhouse gases become globally mixed, which means the concentration of a greenhouse gas like carbon dioxide is roughly the same no matter where you measure it. Even though some countries produce more greenhouse gases than others, emissions from every country contribute to the problem. That's one reason why climate change requires global action. The graph below shows how the world's total greenhouse gas emissions are continuing to increase every year.

Water Vapor: It's a Gas!

Water can take the form of an invisible gas called water vapor. Water vapor is naturally present in the atmosphere and has a strong effect on weather and climate.
As the planet gets warmer, more water evaporates from the Earth's surface and becomes vapor in the atmosphere. Water vapor is a greenhouse gas, so more water vapor in the atmosphere leads to even more warming. This is an example of a positive feedback loop, which happens when warming causes changes that lead to even more warming.

Green house effect

If it were not for greenhouse gases trapping heat in the atmosphere, the Earth would be a very cold place. Greenhouse gases keep the Earth warm through a process called the greenhouse effect. Play the video to learn more>>>

The Earth gets energy from the sun in the form of sunlight. The Earth's surface absorbs some of this energy and heats up. That's why the surface of a road can feel hot even after the sun has gone down—because it has absorbed a lot of energy from the sun. The Earth cools down by giving off a different form of energy, called infrared radiation. But before all this radiation can escape to outer space, greenhouse gases in the atmosphere absorb some of it, which makes the atmosphere warmer. As the atmosphere gets warmer, it makes the Earth's surface warmer, too.
Learn more about radiation.
Learn where the term “greenhouse effect” comes from.
Greenhouse gases keep the Earth warm through a process called the greenhouse effect.

Rise in temperature over the last 100 years

Averaged over all land and ocean surfaces, temperatures have warmed roughly 1.33°F (0.74ºC) over the last century, according to the Intergovernmental Panel on Climate Change (see page 2 of the IPCC's Climate Change 2007: Synthesis Report Summary for Policymakers (PDF)). More than half of this warming—about 0.72°F (0.4°C)—has occurred since 1979. Because oceans tend to warm and cool more slowly than land areas, continents have warmed the most (about 1.26° F or 0.7º C since 1979), especially over the Northern Hemisphere.
The graph above clearly shows the variability of global temperature over various time intervals (such as year to year or between decades) as well as the long-term increase since 1880.
There are slight differences in global records between groups at NCDC, NASA, and the University of East Anglia. Each group calculates global temperature year by year, using slightly different techniques. However, analyses from all three groups point to the decade between 2000 and 2009 as the hottest since modern records began more than a century ago. Temperatures in the 2010s have been running slightly warmer still.

Climate Change

Climate change is a significant and lasting change in the statistical distribution of weather patterns over periods ranging from decades to millions of years. It may be a change in average weather conditions, or in the distribution of weather around the average conditions (i.e., more or fewer extreme weather events). Climate change is caused by factors that include oceanic processes (such as oceanic circulation), biotic processes, variations in solar radiation received by Earth, plate tectonics and volcanic eruptions, and human-induced alterations of the natural world; these latter effects are currently causing global warming, and "climate change" is often used to describe human-specific impacts.
Scientists actively work to understand past and future climate by using observations and theoretical models. Borehole temperature profiles, ice cores, floral and faunal records, glacial and periglacial processes, stable isotope and other sediment analyses, and sea level records serve to provide a climate record that spans the geologic past. More recent data are provided by the instrumental record. Physically based general circulation models are often used in theoretical approaches to match past climate data, make future projections, and link causes and effects in climate change.