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The Earth’s atmosphere consists of many chemical compounds, including greenhouse gases. Some of the sunlight incident on the Earth’s surface is reflected back into the atmosphere as infrared radiation and can then be absorbed by greenhouse gases present in the Earth’s atmosphere. Over time, the amount of energy sent from the sun to the Earth’s surface is roughly equal to the amount of energy radiated back into space. This leaves the surface temperature of Earth roughly constant.
There are several factors that affect the impact a greenhouse gas can have on the Earth’s atmosphere and climate. These factors include:
- Concentration and amount of the greenhouse gas
- How long the greenhouse gas remains in the atmosphere
- How potent the greenhouse gas is
Gases Exhibiting Greenhouse Gas Properties
A number of gases exhibit greenhouse properties. Some gases such as water vapor, carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O) occur in nature, while others, including some aerosols, are man-made.
Carbon dioxide is released into the atmosphere by burning fossil fuels, including coal, natural gas, and oil. Burning solid waste, trees and other wood products also releases CO2 into the atmosphere, along with it being a by-product of certain chemical reactions in manufacturing. Plants absorb carbon dioxide from the atmosphere as part of the biological carbon cycle.
Methane is released during the production and transportation of coal, natural gas, and oil. Livestock, agricultural practices, and decaying organic waste also produce a large amount of methane.
Nitrous oxide comes from both agricultural and industrial practices, along with being released as a result of burning fossil fuels and solid waste.
Fluorinated gases include hydrofluorocarbons, perfluorocarbons, sulfur hexafluoride, and nitrogen trifluoride. They are synthetic greenhouse gases produced through a variety of industrial practices. They are sometimes referred to as High Global Warming Potential (High GWP) gases, due to the fact that, although they are produced in small amounts, they are potent greenhouse gases.
What are the Sources of Greenhouse Gases?
The levels of a number of important greenhouse gases have increased since large-scale industrialization began around 150 years ago. Since 1970, emissions of CO2 have increased by approximately 90%. Around 78% of the total greenhouse gas emissions from 1970 to 2011 came from fossil fuel combustion and industrial processes. Agriculture and widespread deforestation are thought to be the second largest contributors to greenhouse gas emissions.
Greenhouse gas emission mostly comes from the use of energy, which is driven largely by economic growth and the fuel used for the generation of electricity.
In 2014, China (30%), the US (15%), and the European Union (9%) showed the three largest global CO2 outputs.
Between 1990 and 2016, emissions of greenhouse gases from transport have increased by 21.5%. Agriculture has seen the second biggest percentage increase at 17.2%, with industry increasing by 14.3%. Both residential and commercial greenhouse gas emissions decreased by 3.7% and 3% respectively.
Carbon Dioxide Concentrations in the Earth's Atmosphere
Carbon dioxide concentration in the atmosphere is regulated naturally by a number of processes commonly referred to as the carbon cycle. The carbon movement between the land, the ocean and the atmosphere is dominated by natural processes such as photosynthesis of plants.
Although these natural processes can absorb some of the man-made carbon dioxide emissions, it is estimated that about half is added to the atmosphere annually. The Earth’s positive imbalance between absorption and emission results in the continual growth in greenhouse gases in the atmosphere.
The Effect of Greenhouse Gases on Climate Change
Increasing amounts of CO2 in the atmosphere causes higher global air temperatures. Higher temperatures increases decomposition rates in soil which then releases more CO2 into the atmosphere, continuing the cyclical. Ocean temperatures also rise with air temperatures, altering ocean ecosystems that may lead to changes in the oceanic carbon cycle and impeding the ocean’s ability to absorb and store carbon.
Rising global temperatures cause changes in sea levels, land use, and weather. This phenomenon is commonly referred to as climate change.
Climate change is a hotly debated and controversial topic that is often politicized. Not everyone believes that the Earth’s climate is really changing, but the past 650,000 years have seen seven cycles of glacial advance and retreat that have been attributed to climate changes caused by variations in the Earth’s orbit affecting the levels of solar energy the planet receives. The end of the last ice age around 7,000 years ago was the beginning of the modern “climate era”.
Since then, the Earth’s atmospheric CO2 levels have not reached above 300 parts per million. However, the current level is 400 parts per million, having increased since the industrial revolution. Links between significantly increased levels of human activity since the mid-20th century have been made with the increased global temperatures. Activity rates are continuing that has not been seen over decades to millennia.
There are many natural elements that can be studied to find evidence of climate change. These include:
- Ice cores
- Tropical mountain glaciers
- Tree rings
- Ocean sediments
- Coral reefs
- Sedimentary rock layers
Evidence taken from ancient sources, such as tree rings, have shown that global warming is progressing ten times faster than the average rate of ice-age-recovery warming.
Ice sheets in Greenland and the Antarctic have decreased in mass, with ice loss in Antarctica tripling in the last decade. Glaciers have retreated in the Alps, Himalayas, Andes, Rockies, Alaska, and Africa, and snow cover in the Northern hemisphere during spring months has also decreased.
Sea levels have risen globally by eight inches in the last 100 years. Extreme weather, in particular high temperature related weather events, is also becoming more and more common, with storms and intense rainfall increasing in the US.
2016 marked the warmest year on record worldwide, with eight of the twelve months of the year from January to September, excluding June, surpassing the previous highs.
Climate Change in the Future
It is thought that even if greenhouse gas emissions ceased entirely, global temperatures would continue to rise for a few decades into the future. Despite this, worldwide efforts to reduce pollution, greenhouse gas emissions and waste from industry are underway, with awareness being spread through a huge number of organizations.
Sources and Further Reading
This article was updated on the 2nd April, 2019.