Unit A

Module 2 ~Lesson 1


  Human Activities

 The biogeochemical cycles in the biosphere maintain a natural state of equilibrium. The amount of any one nutrient in the biosphere is fixed but each nutrient can exist in the biosphere in a variety of compounds and molecules. Sometimes, human activities can cause an excess or deficit of a nutrient in a particular form. You read about one example of this in the last module, eutrophication. One example of disruption of biogeochemical cycles is the increase in atmospheric carbon dioxide due to human activities. 

 


What is the Greenhouse Effect? Does it occur naturally?
© US EPA, via Wikimedia Commons 
D7.13 The greenhouse effect
The natural greenhouse effect is the term used to describe the absorption of thermal energy by the atmosphere. As we studied previously in this unit, this happens naturally and it helps to keep Earth’s climate warm enough for organisms to survive. Without the greenhouse effect, the temperature of Earth would be about 33 ˚C lower. Remember, different gases have different abilities to absorb thermal energy. Some gases absorb large amounts of thermal energy, while others do not absorb any. Gases that absorb and re-emit large amounts of thermal energy are called greenhouse gases.

An increase in these greenhouse gases has led to what is known as the enhanced greenhouse effect. This is the main cause of the increased climate change that Earth is undergoing. Let’s look at each greenhouse gas in detail.

Water vapour is the most natural of the greenhouse gases and is one that, generally, humans have little effect on. Water is the main cause of the natural greenhouse effect; it causes about two-thirds of this effect and is key to keeping temperatures on Earth habitable. The problem lies in what happens to water vapour as the climate warms unnaturally. As other greenhouse gases increase and the enhanced greenhouse effect takes place, more water evaporates into the atmosphere. This increases the amount of water vapour in the atmosphere and increases the contribution of water vapour to the greenhouse effect. This continues to warm global temperatures, causing more water to evaporate and the cycle to continue. NASA’s Earth Observatory website states that if this trend continues, water vapour has the ability to double the warming caused by carbon dioxide alone. This means that the extra water evaporating into the atmosphere due to the warming caused by carbon dioxide will cause the warming to double. 

Previously in this lesson, it was mentioned that the more water vapour entering the atmosphere, the more clouds created. It was suggested clouds block sunlight and therefore cool the temperature of Earth. So this excess water vapour should balance itself out with the extra clouds created, right? 

Unfortunately, it depends on where the clouds are created. If low clouds are created, this is definitely the case; however, studies have shown this extra water vapour is forming high clouds—clouds that sit higher in the atmosphere. These high clouds act like a greenhouse gas and block thermal energy from escaping back into space, enhancing the greenhouse effect.
D7.15 Low level clouds over prairies

The next biggest greenhouse gas is carbon dioxide, and this greenhouse gas is directly tied to human activity and the problem caused by an increase in water vapour in the atmosphere.

D7.16 Forest fire—a carbon source
There are carbon sources and carbon sinks. Carbon sources release carbon dioxide into the atmosphere. Some examples of carbon sources are forest fires, combustion of fossil fuels, such as oil and gas, and animals breathing. Carbon sinks remove carbon dioxide from the atmosphere. Forests and oceans are examples of carbon sinks, as the plants in forests use carbon dioxide for photosynthesis and carbon dioxide dissolves in oceans and lakes.

When carbon sources and carbon sinks are in equilibrium—meaning the amount of carbon dioxide released into the atmosphere is equal to the amount taken out of the atmosphere—the amount of carbon dioxide in the atmosphere remains stable. If this was the case, we would not be seeing the rapid climate change we are experiencing. Unfortunately, they are not equal.

Deforestation is the removal of forested areas on Earth, dramatically reducing carbon sinks. Large scale deforestation has been occurring for the last 200 years, as people migrate into forested land to create farms and as cities and urban centres have expanded. Deforestation is still a problem today. Deforestation occurs when the trees removed are not replaced. This occurs when trees are removed for agricultural reasons or for human habitat, not necessarily as part of the forestry industry.

Deforestation causes the balance between carbon sources and carbon sinks to shift. When there are more carbon sources than sinks, excess carbon dioxide is released into the atmosphere, increasing the greenhouse effect.
D7.17 Deforestation for agriculture

D7.18 Vehicle emissions
Other human activity has also changed this balance between carbon sources and sinks. Many human activities, such as driving vehicles, heating homes, and generating electricity, burn fossil fuels, which releases large amounts of carbon dioxide into the atmosphere, enhancing the greenhouse effect. In fact, carbon dioxide is the main emission released during fossil fuel combustion. Water vapour and nitrous oxide is also formed, and both of these enhance the greenhouse effect as well.

Right now, the carbon sinks are absorbing about half of the carbon dioxide released due to human activities. This is very important, as this slows the increase of carbon dioxide in the atmosphere, therefore slowing climate change. However, this may not be the case for much longer.

© US EPA, via Wikimedia Commons 
D7.19 Carbon sources larger than carbon sinks
The oceans play a huge role in absorbing the carbon dioxide being released into the atmosphere, as they are the main carbon sink. The problem is that as the oceans warm up due to climate change, they can hold less carbon dioxide. So as the climate warms due to carbon dioxide in the atmosphere, the oceans become warmer and can remove less carbon dioxide from the atmosphere, increasing the rate of climate change.

As the climate warms and places such as the tundra, which are normally frozen all year, start to thaw, carbon that had been trapped may be released into the atmosphere. The surrounding plants will help to absorb some of the extra carbon; however, once the plant takes up all the carbon it needs, it will not take up anymore. Once the plants reach their limit, all the carbon released from the melting permafrost will go into the atmosphere, enhancing the greenhouse effect.

Please note: Earthobservatory.nasa.gov was used as a reference for the information in this section.

D7.20 Coal burning power plant
Nitrous oxide is the next common greenhouse gas. The correct IUPAC name for this gas is dinitrogen monoxide, but it is commonly referred to as nitrous oxide. As noted above, nitrous oxide is released during the burning of fossil fuels though not to the same degree as carbon dioxide. Nitrous oxide is released anytime a substance is burned, as the oxygen needed for combustion comes from the atmosphere. Remember, the atmosphere contains 78% nitrogen, so the oxygen used often includes some nitrogen as well. This gas has enormous potential to enhance the greenhouse effect, but there is less of it being released into the atmosphere compared to carbon dioxide. An increase in nitrous oxide in the atmosphere has been observed since the start of the industrial revolution, with the biggest increase occurring in the last century. The concentration of nitrous oxide in the atmosphere is steadily increasing as our energy needs increase. Nitrous oxide contributes to about 6% of the enhanced greenhouse effect, and its concentration in the atmosphere has increased by 15% since 1800.

Agriculture is another source of the increase in nitrous oxide in the atmosphere. The manure and chemical fertilizers used release nitrous oxide into the atmosphere. This is an extremely common worldwide practice.
Methane is the third natural greenhouse gas affected by human activity. It does not last long in the atmosphere before it breaks down, and it has less potential to enhance the greenhouse effect than nitrous oxide, however, it contributes to 20% of the enhanced greenhouse effect. The concentration of methane in the atmosphere has increased by 146% since 1800. Methane is also known as natural gas, and it is a common fuel used in most Albertan homes.

D7.21 Sources of methane
Methane gas is released during the mining and drilling process for extracting fossil fuels. It can be leaked through the pipelines when transporting natural gas from one place to another, though efforts are made to stop this from happening. Methane is also released into the atmosphere by rice patties and the digestive systems of farm animals (as well as humans). As the amount of farming and energy resources needed to support a growing human population increases, the amount of methane released into the atmosphere increases as well.

Other sources of methane include decaying garbage in landfills, decaying vegetation in areas flooded by dams, and decaying organic material (such as dead plants and animals). About 60% of the methane released into the atmosphere is due to human activities.

Technology has improved around the capture of methane from landfills to be used for energy in homes. Landfills are the second largest cause of methane in the atmosphere, so this could be an important step in fighting climate change.

  Digging Deeper

© U.S. Geological Survey, via Wikimedia Commons
D7.22 Discovered and inferred locations of methane hydrate
There is another form of methane being researched for energy purposes called methane hydrate. Methane hydrate is methane combined with water, and it is found mostly in very deep oceans. It needs a specific temperature and amount of pressure to form. The supply of methane hydrate could contain up to twice the amount of energy from the natural gas supply. Research is being done into how we can extract it without causing further harm to the environment. Go to the following link for more information on methane hydrate.

Learn More
Halocarbons are human made compounds containing halogens and carbon. The most common of these compounds are chlorofluorocarbons (CFCs), hydrochlorofluorocarbons (HCFCs), and hydrofluorocarbons (HFCs). These halocarbons have the largest potential to enhance the greenhouse effect. They were developed in the 1930s to be used as coolants in a variety of appliances and as propellants in aerosols. CFCs are particularly dangerous, because they also cause the thinning of the ozone layer. Because of this, the use of CFCs was banned in 1996 as part of the Montreal Protocol.

Ground-level ozone is another human-made problem. Ground-level ozone differs from the ozone layer. The ozone layer plays a part in the natural greenhouse effect and protects us from some of the sun’s more harmful rays, such as ultra-violet (UV) rays. Ground-level ozone enhances the greenhouse effect, increasing climate change. This compound is formed when emissions from vehicles, solvents, and oil-based paints react with heat and sunlight. These emissions are known as photochemical smog, and you can see this grey cloud hovering over a city on a sunny day.
D7.23 Photochemical smog over Vancouver

  Did You Know?

© National Oceanic and Atmospheric Administration, via Wikimedia Commons
D7.24 Hurricanes Katia, Irma, and Jose in a row

The summer of 2017 was ranked the fifth most active hurricane season since 1851. It saw 17 named storms, with 6 classified as major hurricanes. These storms resulted in over 882 deaths, made Barbuda uninhabitable, and caused over $369.76 billion US dollars in damage. Experts agree climate change contributed to the increased activity, though it was not the only reason for it.