Most greenhouses look like a small glass house. Greenhouses are used to grow plants, especially in the winter. Greenhouses work by trapping heat from the sun. The glass panels of the greenhouse let in light but keep heat from escaping. This causes the greenhouse to heat up and keeps the plants warm enough to live in the winter.
The natural greenhouse effect
The Earth is wrapped in a blanket of air called the 'atmosphere', which is made up of several layers of gases. The sun is much hotter than the Earth and it gives off rays of heat (radiation) that travel through the atmosphere and reach the Earth.The Earth’s atmosphere is all around us. It is the air that we breathe. Greenhouse gases in the atmosphere behave much like the glass panes in a greenhouse. Sunlight enters the Earth's atmosphere, passing through the blanket of greenhouse gases. As it reaches the Earth's surface, land, water, and biosphere absorb the sunlight’s energy. Once absorbed, this energy is sent back into the atmosphere. Some of the energy passes back into space, but much of it remains trapped in the atmosphere by the greenhouse gases, causing our world to heat up.
The atmosphere is changing
The Earth's atmosphere is made up of 78 per cent nitrogen and 21 per cent oxygen. Only about 1 per cent is made up of natural greenhouse gases, but this comparatively small amount of gas makes a big difference. Before the Industrial Revolution (which started in England about 200 years ago) the mix of gases that made up the atmosphere was relatively constant. The Industrial Revolution brought new industrial processes, more extensive agriculture, and a rapid increase in the world's population. This rapid increase in human activity meant that more of the gases which cause the greenhouse effect were released into the atmosphere. We know this because of measurements made over the last 35 years and the analysis of air bubbles trapped in ancient ice. There is now clear evidence that levels of carbon dioxide, methane, nitrous oxide and halocarbons are increasing.
The Greenhouse Gases
There are more and more greenhouse gases in the atmosphere, more heat is trapped which makes the Earth warmer. Atmospheric greenhouse gases play a critical role in shaping our global climate. Naturally-occurring trace gases in the atmosphere include water vapor, carbon dioxide, methane, nitrous oxide, and ozone a few other gases are greenhouse gases.
The Effects of Global Warming
- Water vapour- Water vapor is the most common greenhouse gas in the atmosphere, accounting for about 60 to 70 percent of the natural greenhouse effect. Humans do not have a significant direct impact on water vapor levels in the atmosphere. However, as human activities increase the concentration of other greenhouse gases in the atmosphere (producing warmer temperatures on Earth), the evaporation of oceans, lakes, and rivers, as well as water evaporation from plants, increase and raise the amount of water vapor in the atmosphere.
- Carbon dioxide- Carbon dioxide constantly circulates in the environment through a variety of natural processes known as the carbon cycle. Volcanic eruptions and the decay of plant and animal matter both release carbon dioxide into the atmosphere.
Oceans, lakes, and rivers absorb carbon dioxide from the atmosphere. Through photosynthesis, plants collect carbon dioxide and use it to make their own food, in the process incorporating carbon into new plant tissue and releasing oxygen to the environment as a byproduct. Humans cut down huge tracts of trees for lumber or to clear land for farming or building. This process, known as deforestation, can both release the carbon stored in trees and significantly reduce the number of trees available to absorb carbon dioxide.
- Methane- Many natural processes produce methane, also known as natural gas. Decomposition of carbon-containing substances found in oxygen-free environments, such as wastes in landfills, release methane. Ruminating animals such as cattle and sheep belch methane into the air as a byproduct of digestion. Microorganisms that live in damp soils, such as rice fields, produce methane when they break down organic matter. Methane is also emitted during coal mining and the production and transport of other fossil fuels. Methane is an extremely effective heat-trapping gas—one molecule of methane is nearly 30 times more efficient at trapping infrared radiation radiated from the Earth’s surface than a molecule of carbon dioxide.
- Nitrous oxide- When plants die and rot, nitrous oxide is produced. Nitrous oxide is released by the burning of fossil fuels, and automobile exhaust is a large source of this gas. In addition, many farmers use nitrogen-containing fertilizers to provide nutrients to their crops. When these fertilizers break down in the soil, they emit nitrous oxide into the air. Plowing fields also releases nitrous oxide.
- Ozone- Ozone is both a natural and human-made greenhouse gas. Ozone in the upper atmosphere is known as the ozone layer and shields life on Earth from the Sun’s harmful ultraviolet radiation, which can cause cancer and other damage to plants and animals.
- Fluorinated Compounds- A group of greenhouse gases called the chlorofluorocarbons, which are usually called CFCs, because the other word is much too long! - have been used in aerosols, such as hairspray cans, fridges and in making foam plastics. They are found in small amounts in the atmosphere. They are dangerous greenhouse gases because small amounts can trap large amounts of heat.
The greenhouse effect is important. Without the greenhouse effect, the Earth would not be warm enough for humans to live. But if the greenhouse effect becomes stronger, it could make the Earth warmer than usual. The changes in climate will affect everyone, even a little extra warming may cause problems for humans, plants, and animals. But some populations will be at greater risk.