The Greenhouse Effect [Text]

The Greenhouse Effect

If 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.  See the video (2 minutes)  to learn more about it

What's in a Name? The “Greenhouse Effect”

A greenhouse is a building made of glass that allows sunlight to enter but traps heat inside, so the building stays warm even when it's cold outside. Because gases in the Earth's atmosphere also let in light but trap heat, many people call this phenomenon the “greenhouse effect.” The greenhouse effect works somewhat differently from an actual greenhouse, but the name stuck, so that's how we still refer to it today.

The action of a greenhouse is to allow solar radiation to come in (glass being transparent to sunlight), but prevent heat from escaping by convective currents (glass acting as a physical barrier to rising warm air). The 'greenhouse' warming in the atmosphere works by blocking the long-wave (terrestrial) radiation from escaping the earth-atmospheric system (greenhouse gases like carbon dioxide acting as a radiative barrier). 

Greenhouse Gases

Greenhouse gases trap heat in the atmosphere, which makes the Earth warmer. People are adding several types of greenhouse gases to the atmosphere, and each gas's effect on climate change depends on three main factors:

1.      How much?  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.

2.      How long?  Some greenhouse gases stay in the atmosphere for only a short time, but others can stay in the atmosphere and affect the climate for thousands of years.

3.      How powerful? Not all greenhouse gases are equal as some trap more heat than others. This is represented using Global Warming potential (GWP), a measure of how much heat a substance can trap in the atmosphere over a specific time period relative to carbon di-oxide. GWP can be used to compare the effects of different greenhouse gases. For example, methane has a GWP of 34 over a period of 100 years, which means 1 kg of methane will trap 34 times more heat than 1 kg of carbon dioxide.

Carbon dioxide is the most important greenhouse gas emitted by humans, but several other gases contribute to climate change, too.

Figure : 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. Source: Intergovernmental Panel on Climate Change, Fifth Assessment Report (2014)

More about the "Warm family " of green house gases 

Is  water vapour a green house  gas?

Water can take form of water vapour, which is naturally present in atmosphere and has a strong effect on weather and climate. As planet gets warmer, more water evaporates from the earth’s surface and becomes vapour in the atmosphere. Water vapour is a green house gas, so more water in the atmosphere leads to even more warming. This is an example of positive looping where warming leads to even more warming.

Greenhouse gases come from all sorts of everyday activities, such as using electricity, heating our homes, and driving around town.

Figure : This pie chart shows the different activities that lead to greenhouse gas emissions. The largest pieces represent electricity production and transportation. Source: EPA's Inventory of U.S. Greenhouse Gas Emissions and Sinks (2016).

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.

Figure : This graph shows how the total amount of greenhouse gas emissions has been increasing around the world since 1990. Source: EPA's Climate Change Indicators (2016).

More about Carbon dioxide (CO₂)

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.