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Causes of global climate change

Definitions

  • The atmosphere: it consists of the mixture of solids, liquids and gases that are held to the earth by gravitational force. It consists of two elements – Weather & Climate.
  • Weather refers to the state of the atmosphere at a local level, usually on short term timescale from minutes to months. It includes temperature, precipitation, atmospheric pressure, wind speed and wind direction.
  • Climate is the average weather condition of a place taken over a given period of time, usually about 30 years. It is long term behavior of the atmosphere in a specific place. Climatic data temperature, precipitation, atmospheric pressure, wind speed and wind direction are used to predict elements of weather for daily, monthly or annually averages.

Climate change: What do all the terms mean?

The Atmospheric System

Most of our atmosphere is located close to the earth’s surface where it is most dense. The air of our planet is 79% nitrogen and just under 21% oxygen; the small amount of the remaining is composed of carbon dioxide and other inert gasses such as argon, neon etc.

There are four distinct layers of the earth’s atmosphere. These include: Troposphere, stratosphere, mesosphere and thermosphere.

Click on layers of the atmosphere to learn more.

Source: Randy Russell, UCAR

Energy balance in the atmosphere
The main source of the earth’s energy is the sun. The earth receives incoming energy in the form of short-wave radiation or solar radiation. The amount of energy received is determined by various factors as passes through the atmosphere, including either absorption, reflection, scattering, transition or refracted.
1. Absorption
Absorption is mainly by ozone, carbon dioxide, particles of ice or dust.

2. Reflection
Reflection takes place mainly by clouds and to a lesser extent, the surface of the earth. The ratio between in-coming radiation and the amount of energy reflected, expressed as a percentage is known as albedo. Albedo varies with cloud type: 30- 40% in thin clouds, 50 – 70% in thick stratos clouds, 90% in cumulo-nimbus clouds.

3. Scattering
Scattering occurs when solar radiation is diverted. It takes place in all directions and may reach the earth as diffuse radiation. Scattering or incoming solar radiation is diverted by particles of dust, molecules of gas, volcanoes and deserts.

4. Transmission occurs when both shortwave and longwave energy, instead of scattering, pass through the atmosphere.

5. Refraction takes when energy moves from one type of space to another, such as from air into water. As the energy moves, it changes its speed and direction when reacting with the particles present in it. The shift in direction often causes the energy to bend and release the various light colors within it, similar to what happens as light passes through a crystal or prism.

Only 46% of solar radiation reaches the earth due to the combined effect of absorption, scattering, reflection, transmission and refraction. When solar radiation reaches the earth, it is converted into heat energy. This energy is what is needed to keep the earth warm at a temperature suitable for our habitation of this planet.

The energy that is radiated from the surface of the earth back into the atmosphere is called long-wave or infra-red radiation. About 94% of this energy is trapped by the ozone layer or absorbed by CO2, clouds (stratocumulus) and water vapour. This energy is re-radiated and 6% is lost to space. This process is called the natural greenhouse effect. The natural greenhouse effect keeps the earth’s temperature at a level that makes it possible for living things to survive on this planet. This is summarized in the diagram below.

The natural greenhouse effect keeps the earth’s temperature at a level that makes it possible for living things to survive on this planet. This is summarized in the diagram below:

The heat energy that reaches the surface of the earth is not always uniformly distributed across the planet: the tropical regions (between Lat 35N and 35S) have energy surpluses whilst the polar regions have net losses. Atmospheric circulation is therefore necessary to prevent the topical areas from overheating and the polar regions from freezing. Two major transfers take place to prevent tropical areas from overheating. These are:

The Greenhouse effect

Horizontal heat transfers – horizontal movement of air across the globe. This is done through (winds) jet stream, hurricanes, depressions(80%) and ocean currents (20%).

Vertical heat transfers:Vertical movement of heat into the atmosphere.
This is achieved through radiation, conduction, convection and latent heat (the amount of energy needed to change the state of a substance without affecting its temperature. E.g ice – water- vapour)

Changes in global energy balance and the role feedback loops

External factors contribute to climate change in a number of ways which are generally described as part of the atmospheric forcings. These forces take place outside the earth’s atmosphere and have nothing to do with human activities. These may increase or decrease global temperatures.

Feedback loops:

In any system, there are inputs, processes and outputs. In the case of the atmospheric system the input is shortwave radiation and the output is long-wave radiation from the earth. As a system the output of energy can be reinvested into the atmospheric system when long wave radiation is re-radiated to the earth. This is what is described as the feedback loop. The feedback can be positive or negative.

Positive feedback tends to amplify or enhance changes to the initial system by changing its equilibrium state. When there is an increase or decrease in the amount of inputs injected into the system it results in a similar impact on the system i.e the increased inputs lead to increased output.

Source: Global Emergency Institute

An example of positive feedback in relation to changes in global temperatures could be an increase in the melting of ice in the polar regions may lead to a decrease in permanent glaciers and ice sheets. This reduces albedo (note that fresh snow reflects solar radiation) which, in turn, leads to an increase in solar radiation, thereby resulting in an increase in global temperatures.

On the other hand, negative feedback tends to dampen the initial system, with the addition of inputs, causing the system to slow down or decrease the output of the system.

Negative feedback could be explained in terms of an increase in evaporation in tropical areas, leading to increasing precipitation, and a subsequent increase in the amount of fresh water in ice caps in the polar regions. This results in lowering global temperatures. Again, when there is an increase in the amount of carbon dioxide in the atmosphere, it could lead to an increase in plant growth due to increasing amount of solar radiation need by plants for photosynthesis. The increase in plant growth will further result in increasing levels of oxygen in the atmosphere, which would reduce global temperatures. Click here for more examples on negative feedback.

Positive and negative feedback. Source:Climate Emergency Inst.

Notwithstanding the benefits of the negative feedback in reducing global temperatures, it is important to note that the effects might not be felt in the short term. Therefore, scientists are worried that the positive feedback would far more exceed the negative and there is the need to find solutions to reduce the amount of greenhouse gases in the atmosphere. The diagram below summarizes the positive and negative feedback in relation to global warming.

The diagram below shows examples of positive and negative feedback loops.

Click here to try an assignment on feedback loops.

a. Variations in solar radiation

Data collected over the past several years suggest that global temperatures have fluctuated over time. Sea-level changes, changes in the length of growing season for certain crops and other observed evidence have suggested that world temperatures have changed in the past due to variations in solar radiation. Some possible explanations for such variations are:

Milankovitch cycles

Variations in the tilt and/or orbit of the earth around the sun refers to the three dominant cycles through which variations in the earth’s eccentricity (measure of the shape’s deviation from being a circle), axial tilt and procession occur.

The earth’s eccentricity theory suggests that as the earth orbits around the sun, there comes a time, (about 100,000-413,000 years) when it changes from a less elliptical (nearly perfect) to elliptical (nearly imperfect) orbit. This increases the amount of solar radiation from the sun.

Besides, the axial tilt theory suggests that about every 41,000 years, the earth tilts on its axis (at angles between 22.1-degrees and 24.5 degrees) as it orbits around the sun, thereby affecting solar radiation.

The procession theory suggests that the earth wobbles on its axis every 26,000 years, causing further changes in the earth’s temperature. These three combined effects have led to significant heating and cooling of the earth’s temperature (Universe Today). Details on this subject can be found here: Atmospheric forcings. Visit NASA’s Global Climate Change website for a animation and an interesting discussion on Milankovitch’s theory

Global dimming due to volcanic eruptions

Global dimming refers to a reduction in the amount of solar energy received from the sun resulting from an increase in suspended particulate matter in the atmosphere. This reflects the sun’s energy, thereby “dimming” the energy from the sun. This can be caused by factors such as volcanic eruptions, which ejects large amounts of dust particles in the atmosphere. The volcanic dust in the atmosphere can shield the earth from incoming solar radiation, thereby lowering global temperature.

For example, the eruption of Mount Pinatubo in 1991 caused a dip in global temperatures in the early 1990s. Also, the eruption of a volcano in Chile in 2015 produced dust that traveled around the earth. Other volcanic eruptions include Krakatoa in 1873 and Laki fissure (Iceland) in 1783, had a major impact on the amount of solar radiation reaching the earth. Laki led to a reduction in temperatures in the northern hemisphere by about 1 degree Celsius whilst Pinatubo also led to a 0.5 degree reduction in temperature in the northern hemisphere.

Global warming due to human factors such as industrialization leads to the production of particulate matter and carbon dioxide in the atmosphere. Even though the particulate matter reflects the sun’s energy to reduce the amount of solar radiation reaching the earth (cooling the earth), carbon dioxide increases global temperatures (heating the earth) by trapping long-wave radiation from leaving the earth’s atmosphere.

Sunspots- Source:ak3q.com

Variations in solar energy

Sunspot activity raises global temperatures. These are dark spots on surface of the sun with intense solar energy output. They occasionally emit high amounts of solar output with intense magnetic storms which sometimes lead to the formation of ‘northern lights’ in the northern hemisphere. These storms can increase global temperatures and may decrease temperatures in periods without sunspots.

These physical causes of global temperature change have always existed and have been responsible for alternate heating and cooling cycles of the earth’s temperature.

b. Terrestrial albedo changes and feedback loops

Terrestrial albedo is the ratio between in-coming solar radiation reaching the earth and the amount of energy reflected, expressed as a percentage. Albedo, as we noted early on, vary over different land surfaces: >10% over ocean and dark soils, 15% over coniferous and urban areas, 25% over grassland and deciduous forest, 40% over light-colored desert and 85% over reflecting fresh snow.

Albedo plays in a significant role in terrestrial heating and cooling. When albedo is reduced due to an increase in global temperatures, it will cause the melting of ice in the polar regions and this will further cause a decline in the reflectivity of short wave radiation from snow, thus increasing global temperatures even further. This will result in a positive feedback, as intense solar radiation reaching the earth will cause ice under the sea to melt further, thus increasing the amount of fresh water in the ocean, lakes and other areas of snow. This will further lead to evaporation, which will increase the amount of water vapour in the air, resulting in the formation of clouds, increasing the reflectivity solar radiation at high altitudes (negative feedback). The clouds could fall back as rain, thereby reducing global temperatures. The cycle then continues over and over again.

c. Methane gas release and feedback loops

Another important gas that has an impact on global temperatures is Methane. Recent studies show that large deposits of methane under permafrost, among other natural sources of methane such as from wetlands and termites, have the capacity to increase global temperatures. They are formed from the decomposition of organic matter in areas without oxygen. Methane traps longwave radiation from returning to space, just as carbon dioxide. However, methane does not last as long (maximum of about 20 years) as carbon dioxide does in the atmosphere as a greenhouse gas that causes global warming. Consequently, the impact of methane is often been ignored, yet methane is 80-85% effective in increasing global temperatures.

Natural causes of increasing methane gas include:

  • increasing global temperatures results in a reduction in albedo in the polar regions due to excessive melting of snow, thus exposing the decomposed organic matter which contains methane. (This creates a positive feedback loop: increasing global temperature have the capacity of triggering the release of methane in permafrost areas which further increases global temperature by trapping longwave radiation from escaping back to space).
  • Waterlogging in some lowlying areas due to excessive rainfall resulting form increasing global temperature. This means organic matter found out water bodies will decompose to release methane into the atmosphere.

Other human causes include:

  • increase demand for meat which leads to large scale cultivation of livestock; another important source of methane gas (cattle dung contain methane)
  • burning of biomass and fossil fuels also release large quantities of methane into the atmosphere
  • landfill sites containing organic matter also decompose over time to release methane.
Global methane gas

The enhanced greenhouse effect

Human factors have also played a key role in increasing the among of green house gases in the atmosphere. They include carbon dioxide, nitrous oxide, water vapor, methane and chlorofluorocarbons, and troposphere ozone. According the Intergovernmental Panel on Climate Change (IPCC) report for 2013, the concentration of greenhouse gases in the atmosphere have reached unsustainable levels not seen in the last 800,00 years. For example, statistics indicate that CO2 levels have risen from about 315 parts per million (ppm) in 1950 to 406 in 2017 ppm and are expected to reach 600ppm by 2050.

Carbon Dioxide:
This is the most important human factor causing global warming. It is produced by vehicles and burning fossil fuels in power stations, especially in HICs, where large amounts of fossil fuels are used to produce energy.

According to Forbes, “in April 2018, the Mauna Loa Observatory in Hawaii recorded an average concentration of atmospheric carbon dioxide above 410 parts per million (ppm). This was the highest monthly average in recorded history, and in fact according to ice core records it is the highest value in at least 800,000 years” (Forbes.com).

Increasing levels of carbon dioxide also has a positive feedback in increasing the amount of methane, another greenhouse gas, which is trapped under snow. This means rising temperatures will lead to ice melting thereby triggering the release of methane.

Sources of carbon dioxide

  • The production of carbon monoxide, combining with oxygen, produces carbon dioxide, which significantly contributes to global warming by trapping longwave radiation.
  • Deforestation and the burning of the tropical rainforests also contributes to global warming by increasing the amount of carbon dioxide in the atmosphere (note: vegetation/forest serves as a carbon sink). Therefore the reduction in vegetative cover will significantly reduce the natural ability of the forest to absorb carbon dioxide.
https://ichef.bbci.co.uk/news/624/cpsprodpb/5294/production/_110504112_total_emissions_v2-nc.png

Further readings:

Methane:

The second largest contributor to global warming, increasing at a rate of 1% per annum. It is released from decaying organic matter such as peat bogs, swamps, landfill sites, animal dung and farms. It is estimated that cattle produce about 100 million tons of methane by converting 10% of their food. 150m tons of methane is produced annually by paddy fields. Bogs also melt at high temperatures to release methane into the atmosphere.

Water Vapour

This is abundant in the atmosphere, however it does contribute to global warming to some extent. This comes about as a result of industrial production, agricultural production, deforestation and electricity generation from thermal plants. These activities contribute in the the production of steam/water vapor into the atmosphere. Water vapor has a positive feedback effect: high temperatures results in high rate of evaporation. This will lead to an increase in the amount of water vapor present in the air, which eventually forms clouds. Clouds trap long wave radiation from escaping into space. The further increase global temperatures and the process continues.

There can also be a negative feedback: the formation of clouds from water vapor can lead to the high albedo in the upper atmosphere, leading to low levels of shortwave radiation reaching the earth, thus lowering temperatures. Again, the clouds may fall as rain to lower temperatures. However, it must be noted that the effects of water vapor on global temperatures are only temporary and they might not be felt in years to come.

Nitrous Oxide

Nitrous oxide is emitted through combustion from cars and power stations,nitric acid production, agricultural fertilizer and biomass burning. Nitrous oxide can be obtained from agricultural activities such as the application of artificial fertilizers such as nitrogen (accounting for about 66%), burning of fossil fuels for energy and transport (15%) and biomass production as well as well forest fires (11%).

Chlorofluorocarbons (CFCs)

These are gases produced from aerosols, air conditioners, foam packaging and refrigerators. They destroy the ozone layer and also absorb long wave radiation. Their production is increasing at a rate of 6% per annum and they are more efficient at trapping heat.

International variations in greenhouse gas sources and emissions in relation to economic development, globalization and trade

Even though there is a steady rise in the amount of greenhouses gases produced in a given year, the level of increase is not uniform. The pie chart below shows the top polluters in the world and the interactive map also shows the extent to which various countries are contributing to the global warming.

Source: Boden, T.A., Marland, G., and Andres, R.J. (2017).

This interactive chart explains world’s top 10 emitters, and how they’ve changed over time.

It is worth noting that there is a correlation between the level of economic development/trade/globalization and the emission of CO2 gases. The top polluter is an emerging economy – China. This can be explained by the fact that China is the world’s manufacturing hub, and most industries in the developed world have relocated their industries, especially polluting industries, to China not only to take advantage of their lax environmental laws, but also the cheap labour offered by its citizens.

Countries like the United States have always developed their economies through industrialization, but a large sector of population is now engaging in the tertiary sector, thus accounting for the declining level of CO2 emissions in the country. Developed countries like Germany, the UK, US and Japan are beginning to introduce policies to reduce their CO2 emissions and this partly explains the decline in the production of greenhouse gases in these countries.

This relationship is similar to the environmental Kuznet curve development by Simon Kuznet, which assumes that as human activities contribute to economic growth and development, there is the tendency to increase environmental degradation as a result of the use of inefficient energy sources. However, as countries continue to advance economically, they tend to adopt energy efficient ways to reduce environmental pollution and also shift from agrarian based economies to tertiary economies, further reducing pollution.

This principle can be adopted to explain the relationship between the level of economic development and the level of greenhouse gas production. Greenhouse gases are produced as a country develops economically, however the production of these gases may reduce when the country further advances economically due the adoption of energy efficient sources. This is summarized in the curve below:

How can globalization enhance the production of Greenhouse gases?

  1. Globalization leads to the relocation of polluting industries from HICs to LICs or MICs, where environmental laws are relaxed. This can be seen in China, India and Mexico, where polluting industries from the US and Europe are located.
  2. Globalization promotes trade between countries. This means goods produced in one country can be transported over long distances to different parts of the world. Goods are mostly transported by air and by sea. For example, sea transport contributes about 4% of the amount of CO2 generated by humans and 9% of nitrous oxide. Thus, increase in sea travel will lead to increase in GHS emission.
  3. Give other reasons

What is Climate Change: A really simple guide

Question:

Distinguish between global climate change and the enhanced greenhouse effect

Global climate change is the change in the global pattern of climate precipitation,temperature, winds, pressure systems). The enhanced greenhouse effect is the increasing amount of greenhouse gases in the atmosphere as a result of human activities.

Distinguishing characteristics could be:

  • Global Climate Change (GCC) can relate to any aspect of climate whereas the Enhanced Greenhouse Effect (EGE) specifically impacts upon temperature
  • GCC can have natural causes whereas the EGE is anthropogenic
  • GCC can involve cooling/glacial periods whereas EGE is associated with global warming
  • EGE is a major cause of GCC.

Source: IBO

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