In this video lesson, you will learn about the five main greenhouse gases and how their unnaturally high concentrations are leading to the enhanced greenhouse effect and global climate change on Earth.
Earth's Changing Climate
Melting polar ice caps. Hurricane Katrina. Superstorm Sandy. Extreme droughts in the Midwest. Dangerous blizzards on both the east and west coasts. Mile-wide tornadoes in Oklahoma, and the recent wildfires in Colorado and the Southwest United States. All of these examples are the direct result of an unprecedented increase in greenhouse gas concentration in the atmosphere - a problem that is rooted in human activity.
Greenhouse gases are gases in the atmosphere that allow sunlight to pass through and reach the Earth's surface. Some of this sunlight is captured as heat on Earth, and some of it is radiated back towards space. When greenhouse gases are present in the right amounts, they trap just enough heat to keep the Earth warm enough for organisms to survive, while letting some of that heat back into space. This is very much like cracking the windows in your car while it sits in the sun. If you left the windows closed, the car would be way too hot when you got back, so you open the windows just enough to let some of that heat escape.
Without greenhouse gases the temperature on Earth would be well below freezing. This trapping of heat under the atmosphere is called the greenhouse effect, and it is both natural and beneficial to life on Earth. So, if greenhouse gases are so good for us, why do they get such a bad reputation? The problem with greenhouse gases is that they need to be present in specific amounts.
When too little gas is present, not enough heat is trapped under the atmosphere to keep the Earth warm. When too much gas is present, too much heat gets trapped, which warms the Earth more than usual. The types and amounts of greenhouse gases in the atmosphere are only beneficial when they are present in just the right balance.
The Enhanced Greenhouse Effect
You now know that the greenhouse effect is both natural and necessary for our survival because it keeps Earth warm and hospitable. However, the rapid increase in greenhouse gas concentrations in the atmosphere has led to the enhanced greenhouse effect, which is when too much heat is trapped on Earth, resulting in an overall increase in global temperatures.
While we do not know exactly how much damage such high concentrations of greenhouse gas can do, we have already seen some of the effects. Rising temperatures on Earth have produced severe changes in weather patterns, such as hotter summers, colder winters and stronger storms, like hurricanes and tornadoes.
Increasing global temperature will also lead to a rise in sea levels as the glaciers and polar ice caps melt. As sea levels rise, many organisms, such as polar bears, birds, fish and plants, will lose valuable habitats, and people will be forced to move farther inland. Industries, such as agriculture and forestry, will also be negatively affected by temperature changes, which could have worldwide consequences, such as food shortages and extreme land erosion.
The Greenhouse Gases
So, what are the greenhouse gases that are enhancing the greenhouse effect? As mentioned before, greenhouse gases naturally occur in the atmosphere, but human production has been increasing the concentration of certain ones faster than they can break down. This increase is mainly due to human activities such as burning fossil fuels (like coal, oil and natural gas) and excess methane production from livestock and landfills. The most important greenhouse gases are water vapor, carbon dioxide, methane, nitrous oxide, ozone and fluorinated gases.
Water vapor is the most abundant and possibly the most important greenhouse gas. Water vapor is not only very good at trapping heat on Earth but also amplifying the effects of other greenhouse gases. Water vapor does this through a vicious cycle: as the amount of water vapor increases in the atmosphere, the temperature on Earth increases as well, which then causes more water vapor absorption in the air, which again increases the warming of the Earth…you can see how this is an issue!
Carbon dioxide (CO2) comes from the burning of fossil fuels and is important because even though it's not the most potent greenhouse gas, it is one of the most abundant. CO2 concentrations naturally fluctuate over time, but recently reached a milestone concentration of 400 parts per million. To put this in perspective, in the past 800,000 years it has not been over 300 parts per million.
The real worry though is how quickly CO2 is accumulating in the atmosphere. Since the beginning of the Industrial Revolution (about 1750), human activity has continually increased atmospheric CO2 levels from 280 parts per million to the current high. There is no other period in the history of Earth where CO2 levels have increased so quickly.
Methane is also rapidly increasing in the atmosphere. Methane is released into the air from fossil fuels and livestock. Atmospheric methane has increased 151% since the beginning of the Industrial Revolution and is currently at its highest concentration in at least 650,000 years.
Nitrous oxide is a gas that comes from feedlots, chemical manufacturing plants, emissions from vehicles and nitrogen fertilizers in agriculture. The level of nitrous oxide has increased about 18% since 1750, and while this number may seem small, think about this: the warming impact of one pound of nitrous oxide is over 300 times that of one pound of carbon dioxide!
In another lesson, we learned about the benefits of the ozone layer, but ozone also plays a critical role as a harmful greenhouse gas. When found in the lower levels of the atmosphere, ozone can cause respiratory illnesses and damage vegetation. Since the Industrial Revolution, concentrations of ozone have increased by 36%.
Last but certainly not least are fluorinated gases, which come from aerosols and coolants. Not only do these take thousands of years to break down in the atmosphere, but they also destroy that beneficial ozone that protects us from harmful UV radiation.
The greenhouse effect is the trapping of heat under the atmosphere, which is a natural effect caused by greenhouse gases. These gases allow sunlight to pass through the Earth's surface, warming the Earth and allowing us to live. However, when greenhouse gas concentrations are too high, they trap too much heat and increase the temperature on Earth, causing the enhanced greenhouse effect.
There are many greenhouse gases present in the atmosphere, but the most important are water vapor, carbon dioxide, methane, ozone, nitrous oxides and fluorinated gases. These gases are currently present in higher concentrations than have been seen for hundreds of thousands of years. Additionally, the rate of increase is unprecedented and cause for great alarm.
It's difficult to say just how much of the current increase in greenhouse gas concentration is due to human energy use, since some natural variation does occur. However, many scientists believe that because the increases are so large and are happening so quickly that most of the change is not natural. Slowing the emission of greenhouse gases is the most important step we can take to prevent further greenhouse gas build-up in the atmosphere and reduce the effects of global warming.
When you finish the lesson, you should be able to:
- Define the greenhouse effect
- Describe the five greenhouse gases and where they come from
- Recognize the possible environmental consequences of the enhanced greenhouse effect