Before teaching a unit on how energy influences climate it is important to review some basics of energy. Energy is defined as the capacity to do work. 1 There are six forms of energy: chemical, electrical, radiant, mechanical, thermal and nuclear.2 Chemical energy is the energy stored in the bonds between atoms. Electrical energy is energy generated from the movement of electrons. Radiant energy is the energy that is associated with electromagnetic waves. Mechanical energy is the energy attributed to an object because of its movement or position. When the nuclei of atoms are split or fused the type of energy produced is nuclear energy. Thermal energy is the energy of moving or vibrating molecules also known as heat energy.3 The types of energy focused on in this unit will be thermal and radiant energy. The flow of incoming energy from the sun (radiant energy) and outgoing energy from the earth (thermal energy) is what drives the earth’s climate.
In order to more fully comprehend how the earth’s climate may be influenced we need to explore the first law of thermodynamics. The first law of thermodynamics or the law of conservation of energy states that energy can neither be created nor destroyed only transferred from one system to another. Types of heat transfer include radiation, conduction or convection. Heat always moves from the warmer area to the cooler one. Radiation is a type of energy transfer where two objects exchanging energy do not have to be in direct contact, for example the sun heats the earth through radiation.4 Conduction is where the heat exchange is done through direct contact for example a pan on an electric burner is heated through conduction.5 Convection has to do with fluids both liquid and gaseous. Here the warmer fluid will rise and expand while the cooler fluid will sink.6 Convection explains how a baseboard heater near the floor of a room can heat the whole space.
It is the movement of incoming energy from the sun and outgoing energy from the earth that drives the climate. If the net energy in and out are equal then the climate stays the same. If there is more energy out than in the earth’s climate it will get colder and if the opposite is true then the climate gets warmer.7 This concept is comparable to maintaining weight. If you wish to gain weight you need to eat more calories than you are using. If you want to lose weight you need to use more calories than you are eating and to maintain a steady weight, calories in need to equal calories out. However, if the earth did not trap some energy it would be too cold for life. It is the atmosphere that traps heat close to earth creating the comfortable living conditions for those in the biosphere.
For this unit the earth will be thought of as a system. A system may be opened or closed. In terms of matter, earth is a closed system; our planet does not exchange matter with space (meteorites are the exception).8 In terms of energy however earth is an open system. Energy from the sun enters earth's atmosphere and warms the surface of the earth and this energy is then re-radiated by the earth back into space. Earth systems science is the study of the different earth spheres and their interactions with the other spheres. Four major earth spheres include the atmosphere, biosphere, geosphere and the hydrosphere.
Atmosphere: is the layer of gases that extends several hundred kilometers away from Earth’s surface and it is divided into several layers.
Biosphere: includes all life on earth.
Geosphere: includes all of the rocks, minerals and soils on earth.
Hydrosphere: includes all the water on earth.
Cryosphere: includes all of the frozen water on earth.9
Nearly all of the energy available at Earth’s surface is from the sun. The energy travels through space and arrives in the form of electromagnetic waves. Electromagnetic waves are waves that travel at about the speed of light (300,000 km/s), have both electrical and magnetic properties and can pass through solids, liquids, gasses and even empty space. The different characteristics of a wave include amplitude, crest, trough, wavelength and frequency. Amplitude is the height of a wave from rest position. A crest is the high point of a wave while a trough is the lowest point on a wave. Wavelength is the distance between two crests or two troughs. Frequency is how many complete waves pass a given point in a second. The shorter the wavelength the higher the frequency. In order to get our bearings on what has a longer wavelength infrared radiation or ultraviolet radiation we will need to look at the electromagnetic spectrum.10
The electromagnetic spectrum begins with radio waves which have the longest wavelengths. Items such as radios use radio waves. Microwaves are shorter than radio waves and are used in microwave ovens and radar. Next is the infrared region of the electromagnetic spectrum which transmits heat.11 With shorter wavelengths from approximately 700 nm to 400 nm is visible light, this range of wavelengths is what humans can see. Ultraviolet radiation has a higher frequency than visible light. Also known as UV rays this type of electromagnetic radiation can be used to sterilize and cause sun burns. X-rays have an even higher frequency than UV rays and have many medical purposes such as allowing people to see inside the body. Finally, the highest frequency and shortest wavelength EM waves are gamma rays. Electromagnetic rays are important for climate studies because sunlight is made up of a range of EM waves and sunlight provides the energy that warms the earth. Sunlight is made up of a range of wavelengths including some infrared all visible light and a portion of the UV region of the electromagnetic spectrum.12
The greenhouse effect is where incoming energy from the sun enters earth’s atmosphere as shortwave radiation and the earth’s surface reradiates this energy as longwave radiation (i.e., heat) which can then be lost to space or trapped by greenhouse gasses. Several things can happen to incoming shortwave energy from the sun 1) it can be reflected back to space while in the atmosphere 2) It can be reflected by earth’s surfaces with a high albedo 3) it can be absorbed by the earth’s surface.13 Clouds have a high albedo which means that they reflect lots of shortwave energy. Albedo is a measure of something’s reflectivity. Snow and ice have a high albedo while the open ocean is a darker color and has a very low albedo. Light colors have a higher albedo while darker colors have a lower albedo.14 This is why you are hotter in a black t-shirt on a sunny day than in a white one.
The energy absorbed by earth's surfaces is then reradiated as longwave radiation in the infrared region of the electromagnetic spectrum that can be lost to space or trapped by greenhouse gases such as carbon dioxide CO₂, nitrous oxide N₂O, methane CH₄ and water vapor H₂O. This is a normal process that keeps the earth a livable temperature.15 Humans however are altering this process by adding immense amounts of CO₂ from burning fossil fuels into the atmosphere every year changing the amount of energy leaving the earth and the troposphere.16
Carbon dioxide is a molecule made up of a carbon atom with an oxygen atom bonded to each side in a linear shape. When infrared radiation reradiated from the earth comes into contact with a CO₂ molecule it causes the bonds between the atoms to move. These bond motions include both bending and stretching. When the molecule returns to its normal shape the energy is then released back into the atmosphere in random directions. This process only happens with electromagnetic energy in the infrared region. Visible light and UV rays do not cause this to happen. (video)
Greenhouse gases heat the Earth by absorbing reradiated heat from the Earth’s surface and limiting the energy that escapes back to space. Different greenhouse gasses can affect the Earth’s average temperature differently. Two ways that greenhouse gases are different from each other include their ability to absorb energy known as radiative efficiency and how long they stay in the atmosphere or lifetime.17
The Global Warming Potential (GWP) according to the EPA “is a measure of how much energy the emissions of 1 ton of a gas will absorb over a given period of time, relative to the emissions of 1 ton of carbon dioxide (CO2).”18 (EPA website) This means that a larger GWP for a gas the more or less that it warms the atmosphere compared to CO2 during that time period. Usually for GWPs the amount of time is 30 or 100 years.19 GWPs are important for policy makers; they provide a unit of measure, which allows the policy makers to determine which gases have the most impact and compare ways to most effectively reduce climate change through targeted emissions reduction.20
Greenhouse gases
Carbon dioxide or CO₂ is a molecule made up of one carbon atom and two oxygen atoms. Carbon dioxide is released naturally through processes such as respiration and volcanic eruptions.21 Respiration, the metabolic process of breaking down sugar for energy releases CO₂. Anthropogenic sources of atmospheric CO₂ include deforestation, land use changes, and burning fossil fuels. Fossil fuels include coal, crude oil and natural gas which are burned for energy. The process of burning organic matter such as fossil fuels or wood is known as combustion which releases CO₂. Energy rich fossil fuels were formed over a very long time from organic matter that eventually was stored underground. Because of their slow rate of formation fossil fuels are a nonrenewable resource. As a result humans are burning a nonrenewable resource and putting many billions of tons of carbon into the atmosphere from the combustion reaction of these fossil fuels. Humans are taking carbon that was stored in the geosphere and are adding it to the atmosphere. This is a problem because CO₂ is a greenhouse gas with a very long lifetime in the atmosphere, ~1000 years.22
Methane or CH₄ is another greenhouse gas that is made up of one carbon atom and four hydrogen atoms bonded together. It is 30x stronger than CO₂ at absorption of long wave radiation over a 100-year time scale. Methane is present at much smaller quantities than CO₂ in the atmosphere and has a much shorter atmospheric life, approximately 8-12 years. Methane is produced by anaerobic decomposition. This means it is found both in natural ecosystems such as wetlands and anthropogenic sources such as landfills, flooded rice fields, and the guts of cattle.23 A future source of methane scientists are concerned about is methane from permafrost thaw.24 As permafrost thaws they become waterlogged and go through anaerobic decomposition of the organic matter that has been stored for thousands of years.
N₂O or nitrous oxide is another greenhouse gas found in the atmosphere. It is a gas produced by soil cultivation practices, especially the use of commercial and organic fertilizers, fossil fuel combustion, nitric acid production, and biomass burning.25 Another source of nitrous oxide is internal combustion engines. N₂O also has a long lifetime in the atmosphere and is also a very powerful greenhouse gas.
Water vapor is the most abundant greenhouse gas and acts as a feedback to the climate. Water vapor increases as the Earth's atmosphere warms, so does the possibility of clouds and precipitation create possibilities for both positive and negative feedback loops.26
Ozone (O3) is also a greenhouse gas but a potential source of misconception for students. Ozone in the stratosphere protects the Earth from harmful UV rays. However in the 1970’s a hole in the ozone layer was observed and attributed to the use of chlorofluorocarbons or CFCs. With the Montreal protocol in 1987 the world came together around this issue to ban the future use and phase out the current use of CFCs. The misconception among students is that the hole in the ozone layer is what is causing climate change.
Feedback Cycles
With a changing climate it is important to make predictions for what the future climate will look like. In order to do this several important feedback loops, need to be taken into consideration. A feedback loop is where the product of a change is used as the input and results in an enhanced effect or a mitigating effect.27 For example our body needs to regulate our internal temperature. When we get too hot we sweat. Sweating results in evaporative cooling lowering our body temperature. This feedback is an example of negative feedback. Here the reaction to the change brings our body back to a normal temperature maintaining homeostasis. A climate example of negative feedback is where warming atmospheric temperatures will result in more water vapor in the air. This water vapor could increase cloud cover. Clouds have a high albedo and could result in a cooling of the climate. A positive feedback loop is where a change to a system results in an amplification of the initial change. For example, in a warmer world snow and ice are melting. Snow and ice have a very high albedo and help keep the planet cool by reflecting lots of light. When snow and ice melt they are replaced by darker surfaces such as ground or open water both have a much lower albedo and would result in increased warming of the atmosphere amplifying the initial warming. When making predictions of future climates feedbacks need to be considered.
By adding many tons of carbon, in the form of CO2, to the atmosphere and other greenhouse gasses humans are increasing the global average temperature as a result.28 We are able to determine how carbon added to the atmosphere will continue to increase the global average temperature. One way we know this is by looking at paleo-climate data such as ice core samples. Other sources of past environmental conditions include very old tree rings and corals. Thousands of years old the layers of ice on some ice sheets contain air bubbles which are able to tell us about past atmospheric conditions. With this and other data it is possible to look back into the earth’s climate history and see the gasses in the atmosphere that most affect the earth’s climate.
How do we know CO₂ is increasing in the atmosphere? Data has been collected regularly and frequently measuring the concentration of CO₂ at the Mauna Loa observatory since 1958.29 Charles David Keeling from the Scripps Institution of Oceanography made several discoveries with his data collection. One was that the earth “breathes” with a yearly max and min CO₂ concentration. The max is in the fall when the plants become dormant in higher latitudes, and the min is when the plants grow in the spring with the increase of photosynthesis.30
A rising global average temperature is a problem for many reasons. Effects of this temperature and CO₂ increase include; sea level rise, weather pattern changes, increase in frequency and severity of storms, ocean acidification and a frost-free growing season.31 Sea level is rising not just from the melting of glaciers and sea ice. As water heats up and the molecules move faster and farther apart: the water expands.32 Drastic changes in weather patterns leads to change in precipitation and can lead to both floods and droughts.33 With a warmer global average temperature come warmer ocean waters. Ocean warming leads to more water vapor in the atmosphere. Warmer ocean also creates stronger convection currents which consequently speeds up storms and increase severity.34 Increasing temperatures mean a frost free growing season. This lack of a freeze can increase ranges for disease vectors such as mosquitoes and ticks.35 One effect of increasing CO₂ levels in the atmosphere is ocean acidification caused by change in ocean pH. CO₂ can dissolve in the ocean and make carbonic acid. This acidification of the ocean has many reaching effects including negatively impacting calcifying organisms such as corals and mollusks.36
A rising global average temperature is a problem not just for the natural world but for humans too. Changes in weather patterns are resulting in many destructive forces such as wildfires, flooding and frequent severe hurricanes.37 These climate change fueled forces damage infrastructure and cost lives. Everyone is affected but there are more vulnerable groups.
Since climate change has been recognized by global policy makers there have been two major UN Climate agreements: the Kyoto Protocol and the Paris agreement.38 The Kyoto Protocol was created in 1997 and was a legally binding agreement to decrease greenhouse gas emissions with the goal of decreasing them by 5% from 1990 levels. This agreement only required developed nations to participate.39 Paris Agreement was signed in November 2016 this agreement’s goal was to limit global average temperature increase to 1.5 degrees Celsius above pre-industrial levels and requested that all nations participate.40 These are two historic pieces of global legislation to combat climate change.
There is hope! Humans need to focus both on adaptation and mitigation strategies. Adaptation refers to adapting to the current and future impacts of climate change.41 For example adaptation strategies for dealing with sea level rise could be building a sea wall. A mitigation strategy is different in that its goal is to address and limit the cause of climate change and example of this is carbon sequestration or finding a way to store large amounts of carbon, maybe by putting it underground or into the deep ocean.42 Other mitigation strategies include alternative energy sources, and tax on industry for adding CO₂ to the atmosphere.
