An Introduction to the Greenhouse Effect and Greenhouse Gases
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What is the Greenhouse Effect?
When discussing climate change and global warming, the term ‘greenhouse effect’ is often used.
It refers to a group of gases that trap heat within our atmosphere and warms our planet, and the term comes from the analogy of greenhouses. A greenhouse is most commonly made from glass, which allows sunlight to pass through its walls and ceiling. The heat from the sunlight remains trapped within the greenhouse, creating a warmer internal environment which enables gardeners to grow certain crops year-round without them being effected by the colder seasons.
This is very similar to our own atmosphere. The heat from the sun’s rays radiate off of the earth’s surface and back into the atmosphere in the form of invisible infrared light. Only 10% of this infrared lights escapes into space - the other 90% gets absorbed by the greenhouse gases and redirected toward the earth, causing further warming. As more emissions are generated, our atmosphere thickens and traps the more heat from the sun, which contributes to the warming of the Earth and the pollution of our environment (NASA, 2018).
You may have heard some people argue that the greenhouse effect is something that occurs naturally and has happened for millions of years, and they’re not wrong. The greenhouse effect has contributed to creating an environment suitable for life on Earth, and without it our planet would be a lot more frozen and inhospitable - somewhat like Mars. However, mankind’s voracious burning of fossil fuels for energy is producing an inordinate amount of greenhouse gases which are causing the earth’s surface to warm at an alarming and dangerous rate. For the past 800,000 year - long before human civilisation - the concentration of greenhouse gases in our atmosphere was between roughly 200- and 280 parts per million. In the past century alone though, that concentration has jumped to more than 400 parts per million (Denchak, 2019).
What are Greenhouse Gases?
There are six main gases responsible for the greenhouse effect. Some of these gases occur naturally, such as carbon dioxide (CO2), Methane (CH4), and Nitrous Oxide (N2O); whilst the remaining three are synthetic, fluorinated gases - Sulphur Hexafluoride (SF6), Chlorofluorocarbons (CFCs), and Hydrofluorocarbons (HFCs). But what influence do these gases have individually on global warming? This depends on multiple different factors:
The greenhouse gases all have different chemical properties and are removed from the atmosphere by different processes over varying durations of time. Carbon dioxide, for example, can be absorbed by carbon sinks. Carbon sinks can be natural or artificial systems that absorb more carbon dioxide than they give out, thus storing the carbon dioxide and preventing it from being in the atmosphere (Ocean & Climate Platform, 2016). Plants do this naturally through photosynthesis, with the most commonly occurring carbon sinks being plants, soil, and the ocean. Fluorinated gases, meanwhile, are only destroyed by sunlight in the far upper atmosphere, and are considered the most potent and long-lasting of the greenhouse gases (USEPA, 2017).
Another crucial factor regarding a greenhouse gas’ effect on global warming is how much of that specific gas exists in the atmosphere. As briefly mentioned above, the concentrations of gases in the atmosphere are measured in parts per million (ppm), parts per billions (ppb), or parts per trillion (ppt). Not only are the concentrations of the greenhouse gases important, but also the lifetime of the gas - meaning how long it remains in the atmosphere.
Global Warming Potential
The final, key factor in determining a greenhouse gas’ effect on global warming is how effective it is at trapping heat, which is known as global warming potential (GWP). A gas’ GWP is essentially a measure of the total energy that a gas absorbs over a given period of time, relative to the emissions of 1 tonne of carbon dioxide (USEPA, 2019). GWP isn’t the only way to measure greenhouse gases. There are several other factors that can contribute to climate change, such as the sun’s brightness or large volcanic eruptions. This is known as radiative forcing, or climate forcing, and it quantifies the difference between how much of the sun’s energy gets absorbed by the earth and how much is released into space of any one climate driver. A climate driver with a positive RF value indicates that it has a warming effect on the plant, whilst a negative RV value represents a cooling effect (Denchak, 2019).
Where do Greenhouse Gases Come From?
According to the Intergovernmental Panel on Climate Change (IPCC), there are seven main broad forcings that are the drivers for almost all greenhouse gas emissions created by humans (IPCC, 2014). These include population size, economic activity, lifestyle, energy use, land use patterns, technology, and climate policy. Any one of these factors can have a varying effect on the sources of greenhouse gases, as detailed below:
Electricity and Heat Production
- Electricity and heat production most commonly comes from the burning of coal, oil, and natural gas.
- This is the largest, single source of greenhouse gas emissions, and is responsible for one quarter of worldwide, human-driven emissions (IPCC, 2014).
- Carbon dioxide is the primary gas produced, along with small quantities of methane and nitrous oxide, and is mainly caused by coal combustion.
Agriculture and Land Use Changes
- Roughly a quarter of global greenhouse gas emissions are caused by agriculture and other land-use activities, such as deforestation (Smith et al., 2014).
- The vast majority of greenhouse gases caused by agriculture are methane, and nitrous oxide. Methane is produced as manure decomposes, and as beef and dairy cow pass gas. Nitrous oxide, on the other hand, is released with the use of nitrogen-heavy fertilisers.
- Deforestation and the tilling of soil play a huge role in agricultural emissions, since they destroy the carbon sinks that plants and soil provide. (Climate & Weather, 2020).
- One-fifth of global human-driven emissions come from the industrial sector (IPCC, 2014).
- This included the manufacturing of good and raw materials, such as cement and steel; food processing; and construction.
- The majority of emissions caused by industry consist of carbon dioxide, methane, nitrous oxide, and fluorinated gases.
- 14% of global greenhouse gas emissions come from the burning of petroleum-based fuels, such as petroleum and diesel (IPCC, 2014).
- Carbon dioxide is the primary gas emitted, though fuel combustion also releases methane and nitrous oxide.
- Air conditioning used in transportation systems, as well as refrigerated transport, release fluorinated gases.
- Planes are the largest producers of emissions out of all modes of transportation. On average, planes create 285g of CO2 per passenger, per kilometer, whereas a small car produces on average 42g CO2 per passenger, per kilometer (European Environment Agency, 2019).
- Construction and operating buildings produces almost a third of the world’s carbon dioxide emissions, and 6.4 percent of global greenhouse gases (IPCC, 2014).
- The emissions are mostly made up of carbon dioxide and methane, which stem from the burning of natural gas and oil for heating and cooking. Other sources of greenhouse gases also include managing waste, and wastewater, and leaking refrigerants from air-conditioning and refrigeration systems.
- If the greenhouse gas emission doesn’t fall into one of the above categories of sources, then it most likely comes from other energy-related activities other than fossil fuel combustion. This included the extraction, refining, processing, and transportation of oil, gas, and coil.
- Whilst it is not a side of greenhouse gas emissions that the majority of the public witness, the production of fossil fuels for use accounts for 9.6 percent of emissions (IPCC, 2014).
More than 2000 billion tonnes of carbon dioxide has been released into the atmosphere by human activities since the start of the Industrial Revolution (Global Carbon Project, 2020). With today’s greenhouse gas emissions higher than ever, the planet is warming rapidly. If the warming trends continue at their current rate, it’s estimated global warming will reach 1.5 degrees Celsius above pre-industrial levels between 2030 and 2052 (IPCC, 2017). These changes in temperature will not only pose a threat to plants and wildlife but also to mankind directly. Warmer temperatures mean insects that spread diseases, such as dengue fever and Zika virus, can thrive. Heat waves will become hotter and more lethal. Droughts and flooding - as well as other weather extremes - will increase, which will effect crop yields. According to a recent National Research Council study, crop yields were predicted to decrease by 5 - 15 percent with every one degree Celsius increase in the Earth’s temperature. These are just a few of the reasons as to why it is imperative that we understand where our greenhouse gases are coming from. We, as a species, need to reduce our emissions and capture those that are already in our atmosphere if we are going to delay, and ultimately prevent, any further global warming.
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