Earth's Climate Part 1

The syllabus says part 1 will take week 2 and 3 to complete.

I completed chapter 1 and half of chapter 2 for week 2 and will complete the second half of chapter 2 and the entire chapter 3 for week 3.

Notes below are the things I highlighted in my book.

Chapter 1: Climate and Climate Change

• the Anthropocene is an era where changes to the climate is caused by human activity predominantly
• Earth is 70% water and 30% land
• Climate is a broad composite of the average condition of a region, measured by its temperature, amount of rainfall or snowfall, snow and ice cover, wind direction and strength, and other factors. Climate change specifically applies to longer term variations (years and longer), in contrast to the shorter fluctuations in weather that last hours, days, weeks, or a few months.
• Climate actual change has been small, but the results have been large such as glaciers

1.1 Geologic time

• Must learn history to understand the current conditions (Earth is 4.55 billion years old)
• 3 primary temperature scales are Fahrenheit, kelvin, and Celsius
• Erosion by water and air made it hard to reconstruct the past.
• Deep time is millions to hundreds of thousands of years

1.2 How This Book Is Organized

• Only covers the last 10% of earths life and covers climate change from the last several hundred years
• Part II mainly covers climatic changes during the last several hundred million years, an interval during which dinosaurs appeared and later abruptly disappeared, while mammals evolved from primitive to diverse forms.
• Part III looks at the last 3 million years, the time span when our primitive ancestors evolved into us.
• Part IV explores changes over the last 50,000 years, an interval that spans large oscillations during the last major glaciation, the maximum development of that glaciation and the subsequent deglaciation that led to our present interglacial climate.
• Part V starts with the story of how our fully human ancestors initially lived a primitive hunting-and gathering life and then developed agriculture, prior to the first human civilizations.
  • Part V then focuses in from the last 1,000 years to the current industrial era and projects forward into the future.
• This book will take an Earth System approach of interdisciplinary studies
• The broad term climate science refers to this vast multidisciplinary and interdisciplinary field of research, and to its linkage of the past, the present, and the future.

1.3 How Scientist study climate change

• Any hypothesis that succeeds in explaining a wide array of observations over a period of time becomes a theory.
  • Unifying theory is one that last the test of time
• Earlier revolutions of knowledge in Earth’s history were
  • The first was the development by Charles Darwin and others in the nineteenth century of the theory of evolution, which led to an understanding of the origin of the long sequence of life-forms that have appeared and disappeared during the history of this planet.
  • The second was the synthesis during the 1960s and 1970s of the theory of plate tectonics, which has given us an understanding of the slow motions of the continents across Earth’s surface through time, as well as associated phenomena such as volcanoes, earthquakes, and mountain ranges.
• Earth’s climate system consists of air, water, ice, land, and vegetation. At the most basic level, changes in these components through time are analyzed in terms of cause and effect, or, in the words used by climate scientists, forcing and response.
• The term “forcing” refers to those factors that drive or cause changes; the responses are the resulting climatic shifts.

1.4 Components of the Climate system

• Picture page 9 Figure 1-5 shows Earth’s climate system and interaction of its components
• Air, water, ice, land and vegetation form major components of the climate system
• Process in the climate systems are precipitation evaporation and winds
• The complexity can be thought of as the operation of a machine: the factors that drive climate change are the input, the climate system is the machine, and the variations in climate are the output.

1.5 Climate Forcing

• Three fundamental kinds of climate forcing exist in the natural world:
  • Tectonic processes generated by Earth’s internal heat alter the basic geography of Earth’s surface. These processes are part of the theory of plate tectonics, the unifying theory of the science of geology. Most of these processes change very slowly over millions of years.
  • Changes in Earth’s orbit around the Sun also affect climate. These orbital changes alter the amount of solar radiation (sunlight and other energy) received on Earth by season and by latitude (from the nearly overhead sunlight in the warm low-latitude tropics to the low-angle sunlight or seasonal darkness at the cold high-latitude poles).
  • Changes in the strength of the Sun also affect the amount of solar radiation arriving on Earth.
  • anthropogenic forcing is an unintended by-product of agricultural, industrial, and other human activities, and it occurs through alterations of Earth’s land surfaces and through additions of carbon dioxide (CO2) and other greenhouse gases, sulfate particles, and soot to the atmosphere.

1.6 Climate Responses

• response time, a measure of the time it takes to react fully to the imposed change.
• The rate of warming is naturally rapid at first but slows as time passes and it nears its equilibrium state
• Each part of the climate system has its own characteristic response time
• The atmosphere has fast response time (hours to days) and land has slower response times
• Liquid water has slower response time than air or land because it can hold more heat
• The response-time concept also applies to vegetation, an organic part of the climate system.

1.7 Time scales of forcing versus response

• The forcing is very slow in comparison with the response of the climate system
  • Tectonic plate moves slowly, and change is hard to notice but has large effect in the future
• The forcing is fast in comparison with the climate system’s response
  • Solar eclipse is so fast and creates small change then back to normal
• The time scales of forcing and climate response are similar
  • This situation produces a more dynamic response of the climate system.
• Forcing usually create changes that commonly occur in smooth continuous cycles.
• If the forcing occurs in slower (longer) cycles, it produces a larger response (larger maxima and minima) because the climate system has more time to react before the forcing turns back in the opposite direction.
• In contrast, forcing that occurs in faster (shorter) cycles produces a smaller response because the climate system has less time to react before the forcing reverses direction
• The two responses differ in size, even though the forcing moves back and forth between the same maximum and minimum values in both cases.
• The approximate match of the time scales of forcing and response sets up cyclic interactions very greatly

1.8 Differing Response Rates and Climate System Interactions

• One way to grasp the impact of these differences in response is to imagine that some change is abruptly imposed on the climate system from the outside
• The faster-responding parts of the climate system will warm up more quickly, and the slower responding parts will do so more slowly.
• These differing response rates can lead to complicated interactions in the climate system like some response rates might lag and other will be observable
• Earth’s climate system is dynamic, with numerous interactions at different scales.
• The response-time concept is directly relevant to projections of climate change in the near future.
• The changes in the next few centuries will be unusual because the large climate forcing caused by humans and the warming it will bring will arrive at a speed much faster than the large changes known from Earth’s history.
• Within a few centuries, the fossil fuels that generate excess CO2 in the atmosphere will be largely used up, CO2 emissions will fall, and Earth’s climate will begin to return toward its previous cooler state. But before that happens, Earth will face centuries of very substantial warmth, along with many other changes.
• Scientists, and the public in general, want to know how large the disruption caused by these oncoming centuries of very high CO2 concentrations will be, and the answer to this question requires understanding the different response times of the major components in the climate system.
• A large part of the challenge facing climate scientists is to sort out these different responses and all their interactions.

1.9 Feedback in the climate systems

• Feedbacks is a process that alter climate changes that are already underway, either by amplifying them (positive feedbacks) or by suppressing them (negative feedbacks).
• The strength of a feedback on temperature, called the feedback factor
• Positive feedbacks produce additional climate change beyond the amount triggered by the initial forcing
  • For example, a decrease in the amount of heat energy sent to Earth by the Sun would allow snow and ice to spread across high-latitude regions that had not previously been covered. Because snow and ice reflect far more sunlight (heat energy) than bare ground or open ocean water, an increase in the extent of these bright white surfaces should lessen the amount of heat taken up in polar regions and amplify the climatic cooling in those regions.
• Positive feedback processes also occur when climate is warming. If more energy arrives from the Sun and causes climate to warm, high-latitude snow and ice will retreat and allow more sunlight to be absorbed at Earth’s surface.
• Regardless of the direction of change (warming or cooling), positive feedbacks amplify whatever changes are underway
• Negative feedbacks work in the opposite sense, by muting climate changes
• In response to an initial climate change, some components of Earth’s climate system may respond in such a way as to reduce the initial amount of change.
• These two examples focus on temperature feedbacks. But other feedbacks can amplify or suppress other climatic responses, such as precipitation.

Chapter 2: Earth’s Climate System Today

• Earth’s climate system is driven primarily by heat energy arriving from the Sun.
• Energy travels through space in the form of waves called electromagnetic radiation.
• These waves span many orders of magnitude in size, or wavelength, and this entire range of wave sizes is known as the electromagnetic spectrum
  • The energy that drives Earth’s climate system occupies only a narrow part of this spectrum.
• Much of the incoming radiation energy from the Sun consists of visible light at wavelengths between 0.4 and 0.7 μm, sometimes referred to as shortwave radiation.
• Some ultraviolet radiation from the Sun also enters Earth’s atmosphere, but radiation at still shorter wavelengths (X rays and gamma rays) does not affect climate

2.1 Incoming Solar Radiation

• Radiation from the Sun arrives at the top of Earth’s atmosphere with an average energy of 1,362 watts per square meter (W/m2).
• Earth is a three-dimensional sphere, not a flat disk. A sphere has a surface area of 4πr2 that is exactly four times larger than the surface area of a flat one-sided disk .
• Because the same amount of incoming radiation must be distributed across this larger surface area, the average radiation received per unit of surface area on a sphere is only one-quarter as strong (1,362/4 = 340 W/m2).
• The 340 W/m2 of solar energy arrives at the top of the atmosphere, mainly in the form of visible radiation.
  • About 70% of this shortwave radiation passes through Earth’s atmosphere and enters the climate system.
    • Of the 70% of solar radiation that is retained within the climate system, about two-thirds is absorbed at Earth’s surface and about one-third by clouds and water vapor in the atmosphere. This absorbed radiation heats Earth and its lower atmosphere and provides energy that drives the climate system.
  • The other 30% is sent directly back out into space after reflection (or scattering) by clouds, dust, and the more reflective regions at Earth’s surface.
  • As a result, the average amount of solar energy retained by Earth is 238 W/m2 (0.7 3 340 W/m2).

2.2 Receipt and Storage of Solar Heat

• heat loss, called back radiation, occurs at wavelengths lying in the infrared part of the electromagnetic spectrum and is also called longwave radiation.
• The amount of heat radiated by an object increases with its temperature
• Earth’s atmosphere contains greenhouse gases that absorb 95% of the longwave back radiation emitted from the surface, thus making it impossible for most heat to escape into space.
• The two main gases in Earth’s atmosphere are nitrogen (N2) at 78% of the total and oxygen (O2) at 21%, but do not traps outgoing radiation. The three most important greenhouse gases form very small fractions of the atmosphere. Water vapor averages less than 1% of a dry atmosphere, but it can range to above 3% in the moist tropics. Carbon dioxide and methane occur in much smaller concentrations of 0.04% and 0.00018%, but they are also important greenhouse gases.
• Clouds also contribute to the retention of heat within the climate system by trapping outgoing radiation from Earth’s surface.
• Many important characteristics of Earth’s climate, such as the amount of incoming sunlight, vary with latitude.
  • Incoming solar radiation is stronger at low latitudes, than at high latitudes, where the Sun’s rays strike Earth at a more indirect angle and cover a wider area.
• This unequal distribution of incoming solar radiation is aggravated by unequal absorption and reflection by Earth’s surface at different latitudes
• The percentage of incoming radiation that is reflected rather than absorbed by a particular surface is referred to as its albedo. Radiation and albedo also vary seasonally.
• Absorption and storage of solar heat are strongly affected by the presence of liquid water because of its high heat capacity, a measure of the ability of a material to absorb heat. Heat capacity = Density x Specific Heat
•  These differences in amplitude and timing of response between land surfaces and the upper ocean layers are referred to as differences in thermal inertia. The fast-responding land has a low thermal inertia; the slower-responding upper layers of the ocean have a high thermal inertia.

2.3 Heat transformation

• Sensible heat is the product of the temperature of the air and its specific heat. It is also the heat that a person directly senses as it is carried along in moving air masses.
  • The heated air expands in volume like any heated gas, becomes lighter (less dense), rises higher in the atmosphere, and carries sensible heat along with it in a large-scale process known as convection.
• The second form of heat transfer within the climate system involves the movement of latent heat. This more powerful process of heat transfer also depends on the convective movement of air, but in this case, the heat carried by the air is temporarily hidden in latent form as water vapor.
  • the heat energy liberated during the freezing process was in effect hidden in the water, this released energy is called the latent heat of melting
• The amount of water vapor that can be held in air is limited
• Attempts to add more water vapor to fully saturated air will cause condensation (dew point temperature).
  • This limit of full saturation, measured in grams of water per cubic meter of air and called the saturation vapor density, roughly doubles for each 108C increase in air temperature
• Evaporation of water from Earth’s surface in warmer regions stores excess heat energy in the warm atmosphere. This energy stored in water vapor is carried along with the moving air, both vertically and horizontally.
• When condensation and precipitation occur, the stored latent energy is released as heat, far from the site of evaporation. The average parcel of water vapor stays in the air for 11 days and travels.

2.4 Overcoming Stable Layering in the atmosphere

• Air is highly compressible with 50% of the air molecules below 7 kilometers and 75% below 10 kilometers
• The pull of gravity compresses the atmosphere and increasing their density. 
  • atmospheric pressure - pressure exerted by the weight of the overlying column of air increases toward the lower elevations.
• two opposing forces, the downward pull of gravity and the resistance directed upward, tend to remain in a stable but delicate balance that limits the amount of vertical air motion.
• parcels of heated air rise to higher elevations, processes come into play that involve changes in temperature and in the density of the moving air due to changes in pressure. Climate scientists refer to these changes as adiabatic processes
• Latent heating is the second process that can destabilize the atmosphere, and it occurs as a wet process driven by water vapor, which weighs roughly a third less than the mixture of gases that form Earth’s atmosphere.
  • Evaporation goes up and condensation goes down
• The rate at which Earth’s atmosphere cools with elevation is called the lapse rate.
  • This rate ranges from 5C/km to as high as 9.8C/km but typically averages 6.5C/km both at middle latitudes and for the planet as a whole.

2.5 Tropical-Subtropical Atmospheric Circulation

• Tropical heating drives a giant tropical circulation pattern called the Hadley cell
• Hadley cell flow prevents condensation from occurring in much of the subtropics and makes these latitudes a zone of low average precipitation and high evaporation, in regions such as the Sahara Desert.
• The region near the equator where the northern and southern trade winds meet is called the intertropical convergence zone (ITCZ).
• Because solar heating is the basic driving force behind the Hadley cell circulation, the seasonal shifts of the Sun between hemispheres also affect the location of the ITCZ.
  • It moves northward during the Northern Hemisphere’s summer (June to September) and southward during the Southern Hemisphere’s summer (December to March).
  • The slow thermal response of the land and oceans causes the seasonal shifts of the ITCZ to lag more than a month behind those of the Sun.
• Important seasonal transfers of heat between the tropical ocean and land, called monsoons, arise from the fact that water responds more slowly than land to these seasonal changes in solar heating because of its larger heat capacity and high thermal inertia.
• The summer monsoon circulation is basically an in-and up flow of moist air that produces precipitation. The strong, direct solar radiation in summer at low and middle latitudes heats Earth’s surface
• The strongest summer monsoon circulations on Earth today occur over India. Heating of the large high landmass of southern Asia focuses a strong wet summer monsoon against the Himalaya Mountains
• The winter monsoon circulation is the reverse of the summer monsoon. 

2.6 Atmospheric Circulation at Middle and High Latitudes

• The giant Hadley cells are a simple and convenient summary of basic atmospheric circulation across that half of Earth’s surface area lying between 30S and 30N latitude
• The circulation at latitudes above 30 is more difficult to summarize.
• The Coriolis deflection produces a clockwise spin of air around subtropical highs in the Northern Hemisphere and a counterclockwise spin in the Southern Hemisphere.
• Water vapor condenses from the cooling air and produces heavy precipitation on the sides of mountains that face upwind toward warm oceans, such as the Olympic Mountains of Washington State. This is referred to as orographic precipitation.
• At higher elevations in the mid-latitude atmosphere, winds flow more steadily from west to east. Narrow ribbons of faster flow called jet streams occur at altitudes of 5 to 10 kilometers in two regions: a persistent but weaker jet near 30 latitudes in the subtropics, near the sinking branch of the Hadley cell; and a more mobile jet that wanders between latitudes 30 and 60 above the moving high- and low-pressure cells.
• The uppermost layer of the ocean is heated by solar radiation. Like air, water expands as it warms and becomes less dense, but in this case the warmest layers are already at the top of the ocean, so they simply float on top of the colder, denser deep ocean.
• Winds mix the stored solar heat to maximum depths of 100 meters, a small fraction of the 4,000-meter average depth of the oceans. Some of this warm water is transported from the tropics toward the poles, and this poleward flow carries about half as much heat as is transported by the atmosphere.

2.7 The Surface Ocean

• Most of the surface circulation of the oceans is driven by winds, and one of the most prominent results is huge gyres of water at subtropical latitudes
  • gyres are mainly the result of an initial push (or drag) of the winds on the ocean surface and of the Coriolis deflection of the moving water
• The Coriolis effect turns this surface flow of water to the right in the Northern Hemisphere (and to the left in the Southern Hemisphere).
• The edges of the continents also play a role in forming these gyres by acting as boundaries that contain the flow within individual ocean basins.
• In the North Atlantic, the poleward transport occurs in the Gulf Stream and its continuation, the North Atlantic Drift
• The effects of this circulation cell are felt even beyond the North Atlantic. The surface circulation typical of most oceans carries heat from the warm equator to the cold poles, as partial compensation for the imbalances set up by uneven solar heating and heat absorption at the surface.
• The net northward transport of heat in the North Atlantic is often referred to as a “conveyor belt”, but the overall flow has also been compared to an airport baggage carousel.
  • Most of the luggage (heat) spins around and around the carousel (warm water recirculating in the subtropical gyre), while only a small amount enters the carousel (comes across the equator from the South Atlantic) or is removed (heads farther north in the Gulf Stream and its continuation).
• This warm, northward-moving water in the Atlantic transfers a huge amount of heat to the atmosphere. At latitudes above 50N, the large temperature contrast between the warm North Atlantic waters and the cold overlying air produces a loss of sensible heat from the ocean to the atmosphere that is comparable to the amount of heat delivered locally by incoming solar radiation.
• The fundamental circulation and heat transport of the oceans are less well understood than those of the atmosphere, mainly because of the difficulty of maintaining long-term monitoring stations at sea.