Understanding Climate Change Part 1 - The Climate Basics - Matter, Energy, Atmosphere, and Oceans

The Climate Basics – Matter, Energy, Atmosphere, and Oceans

(Reading #1 for my course on Climate Change - Alan Holyoak, PhD)

Note: This is the first reading in this series.  This set of 7 readings is designed to help college general education students gain the the foundational background they need to understand the contents of the book "The Climate Crisis" by Archer and Rahmstorf, which I use as a course textbook.

Learning Objectives

By the end of this topic (reading and class discussion) you should be able to understand and explain:

1. The difference between weather and climate
2. The Law of Conservation of Matter
3. The Laws of Thermodynamics
4. The physical structure of the atmosphere
5. The physical structure of the ocean

Introduction

In this reading you will review some basic scientific principles that will help you start to build a foundation of understanding of global climate and climate change.  These include the Law of Conservation of Matter, the Laws of Thermodynamics, and an introduction to the history, composition, and structure of Earth’s atmosphere and ocean. 

Physical Laws of Matter and Energy

The Law of Conservation of Matter

            The law of conservation of matter states that matter cannot be created or destroyed, and that any changes to matter affect only the form or chemical condition of the matter involved.  This means that even if a substance undergoes any physical change (vapor, liquid, solid) or chemical change, the resulting total amount of matter you end up with is the same amount you started with. 

The Laws of Thermodynamics

            The laws of thermodynamics describe the nature of energy.  The first law of thermodynamics is also sometimes referred to as the law of conservation of energy.  It states that energy cannot be created or destroyed, and there is no increase or decrease in the total amount of energy in a closed system.  A closed system has no energy entering or leaving it.  This law also states that heat will always move from a substance or location with higher temperature to a substance or location with a lower temperature.  This means that when you go outside on a cold day you may feel like cold is seeping into your skin, but what is really happening is that heat is seeping out of your body!

The second law of thermodynamics states the total amount of energy available to do work decreases whenever energy is transformed from one form to another.  Entropy is unavoidably generated during any transformation of energy and is released as waste heat.  An example of the second law is when your body converts food that you digest from one chemical form into another one that you can use for energy.  This conversion process is called respiration.  Entropy that accumulates during respiration is released as body heat.  Another example is when you burn gasoline in a car’s combustion engine.  Some of the energy released is used to make the car go, but entropy generated during that process is released as heat.

Introduction to Earth’s Atmosphere and Ocean

The Early Atmosphere and Ocean

When the Earth formed 4.5 billion years ago its atmosphere was significantly different than it is today and there were no oceans – it was too hot for liquid water to exist.  Gases that made up Earth’s first atmosphere are listed in Table 1.  The most abundant gases were hydrogen and helium.  Within 100 million years the atmosphere had changed significantly.  A significant amount of hydrogen escaped into space, and components of the primary atmosphere underwent chemical reactions to make new additions to the atmosphere including water vapor and carbon dioxide, but there was still no free oxygen!

Table 1. Components of Earth’s ancient atmosphere (Table courtesy of Dr. Larry Hipps, Utah State University).

Primary atmosphere	Atmosphere after ~100 million years
Hydrogen	Water vapor
Helium	Carbon Monoxide
Methane	Carbon Dioxide
Ammonia	Ammonia
Water vapor	Nitrogen
	Sulfur Dioxide
	Methane

Earth’s early atmospheric temperature and pressure were also much different than what we experience today.  We currently have one atmosphere of pressure at sea level, and an average global surface temperature of 15^oC  (59^oF).  Earth’s original atmosphere had a temperature of 130-300^oC (266-570^oF) and an air pressure of about 256 atm.  If you wanted to experience 256 atmospheres today you would have to descend to a depth of 2.6 km (1.6 miles)!

By about 4 billion years ago the Earth cooled enough that the water vapor could condense and fall as rain.  That initial downpour probably lasted for thousands of years and filled the oceans. 

Life appeared around 3.5 billion years ago.  This and other significant events in Earth’s history are shown in Fig. 1.  The earliest life included only bacteria.  These single-celled microbes included a group called cyanobacteria.  Cyanobacteria are important because they did something new – photosynthesis. 

Just in case you were struggling to remember what photosynthesis is all about, it is the process where an organism uses sunlight, water, and carbon dioxide to make the energy-rich molecule glucose.  Oxygen is the waste product of this process.  Twelve molecules of oxygen are released for every molecule of glucose that is made: 6H₂O + 6CO₂ = C₆H₁₂O₆ + 12O. 

The concentration of free oxygen in the early atmospheric remained very low, only a few parts per million, through about 2.5 billion years ago even though cyanobacteria had been pumping out oxygen for around a billion years.  The reason for the low levels of free oxygen is that most of the oxygen released until this time was quickly bound up in chemical reactions in the air and water.  It is possible, however, that there were “oxygen oases” in the sunlit surface waters of the ocean where cyanobacteria lived, but oxygen diffusing out of the oases reacted almost immediately with other molecules.  The atmosphere and all other areas and depths of the ocean therefore remained virtually anoxic (oxygen free)(see Fig. 2).  

Figure 1. Significant events in Earth’s atmospheric history (Figure courtesy of Dr. Hipps, Utah State University).

Eventually the supply of molecules that reacted with oxygen as soon as it was produced became saturated with oxygen, so starting around 2.5 billion years ago oxygen concentrations in the atmosphere and in oceanic surface waters started to increase. This is called “The Great Oxygenation Event.”  This event sounds good to us since we need oxygen to live, but at the time just about everything alive could not survive in the presence of oxygen.  Oxygen is a highly reactive, poisonous gas, and the only reason it doesn’t kill us is that oxygen is carefully chaperoned while it is in our bodies from the time it enters our blood stream until it gets where it needs to go in our cells (carried by hemoglobin in red blood cells, etc.).  Early microbial species, however, lacked these protective adaptations, and oxygen could kill them.

Gradually increasing concentrations of oxygen in the atmosphere caused many species to go extinct because it disrupted biological processes.  Species that could not find refuge from oxygen or adapt to withstand exposure to died off.   As strange as it may sound, the accumulation of oxygen in the ocean and atmosphere caused Earth’s first mass extinction event. 

  

Figure 2. High and low ranges of oxygen accumulation in the atmosphere (top), ocean surface waters and shallow seas (middle), and deep ocean (bottom).  (Figure modified from Holland, 2006.)

As the amount of oxygen increased in the atmosphere, the concentration of carbon-containing molecules such as carbon dioxide (CO₂), carbon monoxide (CO), and methane (CH₄) decreased.  Oxygen made up 2-5% of the atmosphere by about 1.8 billion years ago, and surface waters of the ocean were also oxygenated to comparable levels, but the deep sea remained anoxic.  Then around 1.5 billion years ago a new form of life appeared – eukaryotic organisms.  These organisms had a nucleus, some were photosynthetic, some were not, but all of them needed oxygen to live.  Also about that same time the oceans became as salty as they are today.  That salinity and the salts that make it that way have not varied significantly since that time, because as more salt is added to the ocean by the world’s rivers, salt is removed from the ocean by chemical processes and sedimentation. 

From 1.8 to about 0.8 billion years ago there was no measurable change in the amount of oxygen in the atmosphere or the oceans.  This is called “The Boring Billion” years.  One thing that did happen during this time is that the deep sea became oxygenated – that’s probably where all the extra free oxygen went.  Then, starting around 850 million years ago oxygen levels began to rise dramatically until 540 million years ago when it made up 10-20% of the atmosphere.  This is when land plants proliferated and added even more oxygen to the atmosphere.  Earth also experienced alternating glaciation and global hothouse conditions.  Toward the end of this time period massive numbers and kinds of animal fossils appeared.  This is called the Cambrian Explosion. 

Lastly, there was a major spike in the amount of oxygen in the atmosphere around 350 million years ago.  At that time oxygen made up as much as 35% of the atmosphere.  This spike was probably produced by the growth of Earth’s first massive forests between 400-300 million years ago.  Just in case you are curious, at that time there were gigantic insects, such as dragonflies with wingspans of up to 2.5 meters long!  Soon after that spike atmospheric oxygen levels dropped to 21%, its current concentration in our modern atmosphere.  The global processes that maintain a constant 21% oxygen concentration are not yet well understood.

The Modern Atmosphere

Earth’s modern atmosphere is the result of geological, chemical, and biological processes that are too complex to explain fully here – we will review and discuss aspects of this later.  The composition of our modern troposphere (the lowest layer of the atmosphere) is shown in Table 2.  The major gases are nitrogen and oxygen that together make up 99% of the troposphere.  There are several other gases present in small concentrations that have significant effects on climate because they are greenhouse gases – gases able to trap and hold energy as heat.  Some of these greenhouse gases are water vapor, carbon dioxide, methane, and chlorofluorocarbons (CFCs).  CFCs are human-produced compounds used for propellants, cleaning electronic components, and refrigeration and air conditioning.  The production of CFCs was banned in the late 1980s they break down stratospheric ozone that protects us from dangerous UV radiation.  We will examine the characteristics and effects of greenhouse gases in another reading later on.

Earth’s atmosphere includes four main layers.  These are the troposphere, stratosphere, mesosphere, and thermosphere.  The atmospheric layers are identified by the temperature profile shown in Fig. 3.

The troposphere is lowest layer and extends to an altitude of 6-20 km (3-12 mi).  The troposphere is thickest in the tropics and thinnest near the poles.  Eighty percent of the mass of the atmosphere and 99% of all water vapor is found here.  Virtually all weather events take place in the troposphere.  The troposphere is warmest at the Earth’s surface where there is a global average temperature of about 15^oC (59^oF), and temperatures drop to about -45^oC (-49^oF) at the top of the layer.  This temperature difference exists because there is a higher concentration of greenhouse gases near the planet surface than there are near the top of the troposphere.   

Heat from the sun heats the troposphere, and friction between the lower troposphere and the earth’s surface together with the Coriolis Effect produce prevailing surface winds.  The formation of these surface winds will be discussed in a later reading.  The atmospheric layer that lies on top of the troposphere is the stratosphere.

Table 2. Atmospheric components of the modern troposphere (Data courtesy of Dr. Hipps, Utah State University).

Major Gases	Percentage of the atmosphere
Nitrogen	~78%
Oxygen	~21%
Argon	<1%
Important Trace Greenhouse Gases	Percentage of the atmosphere
Water vapor	0.1-7%
Carbon Dioxide	~390 ppm (parts per million)
Methane	~1.7  ppm
N2O	~320 ppb (parts per billion)
CFC 11	~250 ppt (parts per trillion)
CFC 12	~540 ppt

The stratosphere extends to an altitude of about 50 km (30 mi).  It contains most of the remaining 20% of the mass of the atmosphere and it is extremely dry. Unlike the troposphere, temperatures increase in the stratosphere with increasing altitude.  The bottom of the stratosphere is coldest at -45^oC (-49^oF), and the top is warmest at about -3^oC (27^oF).  This temperature difference exists because ozone is produced naturally at higher altitudes where oxygen (O₂) is split apart by UV radiation and individual oxygen molecules bond with molecules of atmospheric oxygen (O₂) to form ozone (O₃).  Ozone is extremely efficient at absorbing ultraviolet radiation and some other wavelengths of light, thus warming the stratosphere, but ozone allows many other wavelengths of light to pass through and these wavelengths of light warm the troposphere as well as the Earth and ocean surfaces.

The mesosphere, the layer above the stratosphere, extends from 50km (30 mi) to 85 km (53 mi) in altitude.  There are fewer gas molecules here than in the lower layers of the atmosphere, and the concentration of molecules becomes progressively smaller as altitude increases.  Because of the small number of molecules in the mesosphere, these molecules are constantly bombarded by the complete spectrum of solar radiation.  As a result they are said to be in an excited state, i.e., they are constantly absorbing and releasing energy.  Temperatures in the mesosphere range from -3^oC (27^oF) at the lowest altitude to -93^oC (-135^oF) at the top.  There are still enough molecules in the mesosphere, though, that this is where meteorites become visible as “shooting stars” as they burn up due to friction with the atmosphere.

Figure 3. Temperature profile and layers of Earth’s atmosphere. (Figure from Wikimedia Commons.)

The outermost layer of the atmosphere is the thermosphere.  It extends to an altitude of about 600 km (372 mi).  There are very few molecules there.  Because there are fewer molecules at increasing altitudes there is less and less matter to absorb or block solar radiation so temperatures climb from -93^oC (-135^oF) at the bottom of the thermosphere to over 1700^oC (3090^oF) at the top.  The aurora borealis forms near the base of the thermosphere, and the thermosphere is the layer of the atmosphere where the shuttle flies and most satellites are in orbit. 

The Earth’s Oceans

The Early Ocean

The size, shape, and location of oceans change constantly but very slowly.  This is because the forces of plate tectonics move continents as new oceanic crust is produced in some places and old oceanic crust is subducted (forced down) into the mantle in other places.  The resulting movement of continental plates sometimes causes continents to be largely isolated from each other as they are today, and at other times to be pushed together to form supercontinents.  Supercontinents have existed at least five times during Earth’s history.  Their names and the times they were formed are listed in Table 3.  The most recent supercontinent was Pangea.  It formed about 250 million years ago, about the same time that dinosaurs appeared, and broke up between 200 and 65 million years ago. 

When a supercontinent exists the rest of the Earth is covered by one massive ocean.  When continents are mostly isolated, like they are today, there are several smaller oceans.  The locations and sizes of continents affect the size, strength, and direction of surface and deep oceanic currents, and these currents affect climate.  We will discuss the formation and effects surface and deep-water oceanic currents in a later reading.

Table 3. Names and ages of some of Earth’s supercontinents.

Supercontinent name	Age formed
Vaalbara	3.6 billion years ago
Kenorland	2.7 billion years ago
Columbia or Nuna	1.8 billion years ago
Rodinia	1.0 billion years ago
Pangea	250 million years ago

Structure of the Ocean

           

            Like the atmosphere, the world’s oceans are separated into divisions based on the conditions there.  The bottom contour of ocean basins is bounded on its edges by continental margins that include a continental shelf and a continental slope.  The abyssal plain is at the bottom of the continental slope.  Mid-oceanic ridges exist someplace in the middle of abyssal plains, as do oceanic trenches.  New oceanic crust is formed along oceanic ridges, and old crust material is subducted at trenches along plate margins (see Fig. 4).

Figure 4. Ages of oceanic plate material and locations of mid-oceanic ridges and trenches.  The youngest oceanic plate material is shown in red and the oldest in blue.  Examples of ridges and trenches are indicated. (Image courtesy of NOAA.)

            The divisions of the ocean are shown in Fig. 5, and Fig. 6 may give you a better handle of the relative scale of depth of the ocean and other water masses.  The intertidal zone is the thin margin of the ocean where seafloor is covered when tides are high and are uncovered when tides are low.  All other parts of the ocean are referred to as the pelagic zone.  The pelagic zone is divided into two main subdivisions.  The portion of over continental slopes is called the neritic zone.  The rest is called the oceanic zone.  The pelagic zone is also divided into horizontal layers by depth and other physical conditions such as light penetration and temperature. 

            The surface layer of the pelagic zone is called the epipelagic zone.  This layer usually extends to a depth of several hundred meters.  In most areas, only about 1% of the sunlight that strikes the surface penetrates to the bottom of the epipelagic zone.  The epipelagic zone is extremely important to Earth’s ecology because the majority of our planet’s photosynthesis happens there, and this is where most marine life exists.

            The mesopelagic zone is next deepest layer, and extends from the bottom of the epipelagic zone to a depth where water temperatures cool to ~10^oC.  This zone is in perpetual twilight.  Most of the animals here have bioluminescence.  This is an important layer because many animals that live there migrate vertically into the epipelagic zone each evening to feed on plankton and then migrate back to the mesopelagic zone each morning.  This vertical migration matters because the migrating animals ingest huge amounts of carbon at the surface and move that carbon to deeper waters. 

            The bathypelagic zone extends from the 10^oC temperature mark to the 4^oC temperature depth.  This is a zone of perpetual darkness.  No light penetrates to this depth, and animals there survive by eating each other and material that drifts down from above. 

Figure 5. Divisions of the oceans.  The 10^oC and 4^oC lines are based on data from tropical waters in the Atlantic Ocean.  Actual depths of water at these temperatures at a given location depend on latitude, season, and weather conditions. The depth of the photic zone also varies with location, season, and water conditions.  (Image courtesy of NOAA).

            The abyssalpelagic zone extends from the 4^oC depth to the abyssal plain, which in most places averages a depth of about 6,000 meters (3.7 miles).  Animals that live there tend to stay close to the bottom where they can pick food off of the bottom as well as particles that drift down from above.

            The hadalpelagic zone exists only where there are oceanic trenches, and can extend to depths greater than 10,000 meters (6 miles).  Little is known about life at these depths, but fishes and invertebrates are known to exist in trenches.

            The vertical profile of ocean water from the surface downward to deeper water also includes a thermocline (Fig. 7).  A thermocline is the depth of water where there is rapid temperature change with increasing depth.  The thermocline is particularly important when measuring and considering the movement of heat and nutrients throughout the ocean, because water above the thermocline is warmer and less dense than the water below the thermocline, and water of different densities do not easily mix.

            Oceanographers have discovered complex sets of surface and deep-water currents in the oceans.  These currents carry water, plankton, dissolved gases, heat, and other things that affect the global climate.  We will investigate the formation and effects of these currents later in the course. 

Figure 6. Depths of the ocean and some major lakes. Vertical depth scales are accurate, horizontal scales are not.  (Courtesy of aquaticsports.com)

Figure 7. The thermocline exists where when water undergoes rapid temperature change in its vertical profile.  (Image courtesy of marinebio.org)

Review Questions

1.        What does the first law of thermodynamics have to do with climate?

2.        Why does it matter that we know that the atmosphere has changed in the past?  

3.        Why are the trace gases in the modern atmosphere so important?

4.        Why does tectonic movement of the continents matter to global climate?

5.        Why does it matter that you have a basic understanding of the structure of the ocean?

Source material

Hipps, LE. 2010. Personal communication and materials produced and provided by Dr. Hipps. Professor of Atmospheric Science, Dept of Plants, Soils, and Climate.  Utah State University.

Holland, HD. 2006. The oxygenation of the atmosphere and oceans. Philosophical Transactions of The Royal Society Ser. B. 361 (1470): 903-915.

Nybakken, JW, and MD Bertness. 2005. Marine Biology: An Ecological Approach. 6^th Edition. Pearson Benjamin Cummings Publishers, N. Y. 578