Ch. 21 - Global Climate Change

Class: GEOL-101

Notes:

21.1 Climate and Geology

List the major parts of the climate system and some connections between climate and geology.

Climate system

Presentation content:

• The climate system is a multidimensional system of many interacting parts, which includes:
  • Atmosphere
  • Hydrosphere
  • Geosphere
  • Biosphere
  • Cryosphere (snow, glaciers, ice, and frozen ground)
• When one part of the climate system changes, other components react

Notes from the lecture:

• Spheres interact with each other to drive our climate system

Climate-Geology Connections

Presentation content:

• The climate has a profound impact on many geologic processes
  • Weathering
  • Flooding
  • Mass wasting
• Geologic processes also affect the climate
  • Volcanism
  • Mountain building

Notes from the lecture:

• Carbonic acid is highly effective at corroding materials
• There are seasons where we have a large amount of carob in water, so that can affect weathering of materials
• Use this as geological evidence of pass climate
• Volcanism releases a bunch of CO2, how much does it need to affect climate long term?
  • This means plate tectonics plays a big role in climate chnage

21.2 Detecting Climate Change

Discuss several ways in which past climate changes are detected.

Climate Change Detection

Presentation content:

• Using fossils and many other geologic clues, scientists have reconstructed Earth’s climate going back hundreds of millions of years.

• Earth’s climate can be broadly characterized as being a warm “greenhouse” or a cold “icehouse”.

• Instrumental records only go back a couple of centuries

• Reconstructing past climate change is the field of paleoclimatology

  • Scientists use proxy data (indirect evidence of climate change)

Notes from the lecture:

• proxy records: use those to understand periods of green house vs. icehouse.
  • There are periods of greenhouse and periods of more icehouse
• Despite malinkovich cycles always occurring we have these large periods of greenhouse/icehouse which indicates there are other factors that drive those
• We use this as a proxy for understanding past climate

Climate Change Recorded in Glacial Ice

Presentation content:

• Some ice cores represent over 200,000 years of climate history
  • Ice can be analyzed for:
    • Oxygen isotope analysis.
    • Carbon dioxide and methane (air bubbles trapped in the ice).
    • Dust, volcanic ash, pollen.

Notes from the lecture:

• If you have a large body of water 16 and 18 are uniformly distributed
• But as it is raining out, the first to be removed is that oxygen 18, by the time water is incorporated into ice, it only has oxygen 16 -> there is more oxygen 18 in sea water during times of glaciation
  • Rates of 16-18 oxygen vary over time
• Keep in mind this is not reflecting position of earth, there is something else being reflected here.

Seafloor Sediments - A Storehouse of Climate Data

Presentation content:

• Abundance and types of organic remains are indicative of past sea-surface temperatures
  • Example: foraminifera.

Notes from the lecture:

• Keep in mind these are made of calcium carbonate, organisms incorporate nutrients from the sea water and other minerals
• These organisms evolve very rapidly, so we have a record of these species, identify when they existed, analyze the shell and determine the oxygen composition to see fluctuations along years.

Oxygen Isotope Analysis

Presentation content:

• Oxygen isotope analysis is the precise measurement of the ratio of 18O/16O.
  • Ratios are trapped in calcium carbonate shells of marine organisms.
  • Ratio varies with amount of sea ice and water temperature.

Notes from the lecture:

• Oxygen 16 evaporates, incorporates to clouds, rains out, falls.
• When those glacial ice melts there is a change in 16-18 oxygen ratio.

Tree Rings - Archives of Environmental History

Presentation content:

• Growth rings are added each year
  • Thickness and density of rings reflect environmental conditions
• In certain regions, ring chronologies extend back thousands of years.

Notes from the lecture:

• The idea is that thicker rings reflect periods where the tree has more successful conditions to grow
• Thinner rings represent restrictive conditions for growth
• We can determine what the environment conditions where at that time

Other Types of proxy Data

Presentation content:

• Fossil pollen
  • Pollen can provide high-resolution records of vegetation changes in a region
    • Type of regional vegetation is climate dependent.
• Corals
  • Through oxygen isotope analysis, corals are used as paleothermometers and precipitation proxies
• Historical data
  • Harvest dates
  • Floods
  • Human migration

Notes from the lecture:

• Tells us what the climate was like base on the organisms that travel that area
• Corals lock isotope composition, they are sensitive to temperature, salinity, dust, etc. they need very ideal conditions, we can look at their distribution to get an idea of what the climate and conditions were at that time.
• Look at records of floods, human migration

21.3 Some Atmospheric Basics

Describe the composition of the atmosphere and the atmosphere’s vertical changes in pressure and temperature.

Composition of the Atmosphere

Presentation content:

• Air is a mixture of many discrete gases
• Clean dry air
  • Air is mostly nitrogen (78%) and oxygen (21%).
  • Carbon dioxide is a minute component (0.04%) of air but can absorb heat and affect global climate.

• Water vapor
  • Amount varies from 0 percent to 4 percent of air.
  • Source of clouds and precipitation.
  • Can absorb heat and affect global climate.
• Ozone
  • A combination of three oxygen atoms (O3) in one molecule.
  • Thin layer of gas concentrated in the stratosphere.
  • Absorbs harmful ultraviolet radiation.
• Aerosols
  • Tiny solid and liquid particles found in the air are called aerosols.
    • Sea salts
    • Fine soil
    • Smoke and soot from fire
    • Pollen and microorganisms
    • Ash and dust from volcanoes
  • Can attract moisture for cloud formation
  • Can block sunlight from reaching Earth

Notes from the lecture:

• Although carbon dioxide is a very small portion of the atmosphere it has a lot of heating capacity
  • Effective greenhouse gases because of the size of their molecules
  • Not letting heat escape (traps heat)
  • CH4 is also one of those
• O3 is important to block a lot of that harmful ultraviolet radiation coming from the sun
  • It also plays a role in trapping greenhouse gases
• Aerosols are helpful to trigger atmospheric processes like seeding and precipitation

Extent and Structure of the Atmosphere

Presentation content:

• Pressure changes with height
  • Pressure is the weight of the air above.
    • Pressure at higher altitudes is less.
    • Average sea level pressure is 1 kg/cm2 (14.7 psi).
• Temperature changes with height
  • Earth’s atmosphere is divided into four layers based on temperature.
  • Troposphere.
  • Stratosphere.
  • Mesosphere.
  • Thermosphere.

Notes from the lecture:

• As you move up the air gets thinner -> less pressure

Temperature changes

Presentation content:

• Troposphere
  • The bottom layer of the atmosphere.
  • We live in the troposphere.
  • Temperature decreases with an increase in altitude.
  • Weather occurs in the troposphere.
  • Bounded on the top by the tropopause.
• Stratosphere
  • Temperature remains constant until 20 kilometers, then it increases.
  • Ozone is concentrated in the stratosphere.
  • Bounded on the top by the stratopause.
• Mesosphere
  • Temperatures decrease with height to the mesopause.
  • Coldest temperatures in the atmosphere are found in the mesosphere.
• Thermosphere
  • Contains only a tiny fraction of the atmosphere.
  • Temperatures increase due to the absorption of solar radiation.
  • No defined upper limit.

Notes from the lecture:

• This shows how variable the atmosphere is in terms of temperature changes
• It has a profound impact on our daily activities
• Also protecting us from UV radiation

Understanding Weather in the Troposphere

Presentation content:

• The temperature decrease in the troposphere is called the environmental lapse rate.
• Its average value is 6.5°C per kilometer (3.5°F per 1000 feet), a figure known as the normal lapse rate.
• The environmental lapse rate is not a constant; it changes over time and from one place to another, and it must be measured regularly.
• To determine the environmental lapse rate at a particular time and place, as well as to gather information about vertical changes in pressure, wind, and humidity, radiosondes are used.
• A radiosonde is an instrument package that is attached to a weather balloon and transmits data by radio as it ascends through the atmosphere

Notes from the lecture:

• This circulation of temperature drives our climate system
• Cheapest way to profile temperature is a radiosonde:
  • Weather balloon with a Radiosonde (instrument package) and a radar unit for tracking radiosonde

21.4 Heating the Atmosphere

Outline the basic processes involved in heating the atmosphere.

Energy from the Sun

Presentation content:

• The Sun emits electromagnetic radiation in the form of rays, or waves.
  • As an object absorbs radiation, molecule movement increases, causing temperatures to increase
  • Key difference among electromagnetic radiation is the wavelengths

• Basic laws governing radiation
  • All objects emit radiant energy.
  • Hotter objects radiate more total energy than do colder objects.
  • The hotter the radiating body, the shorter the wavelengths of maximum radiation.
  • Objects that are good absorbers of radiation are good emitters as well.

Notes from the lecture:

• Sun emits the full range of electromagnetic radiation
• Hotter objects irradiate more energy

Paths of Incoming Solar Energy

Presentation content:

• 50% of solar energy passes through atmosphere and is absorbed on Earth’s surface.
• 20% is absorbed by clouds and atmospheric gases.
  • Including oxygen and ozone
• 30% is reflected back to space.
  • By clouds, atmosphere, snow, and ice
  • Called albedo

Influence of surface material on Albedo

Presentation content:

Notes from the lecture:

• Lighter-bright materials tend to reflect a lot more of the energy/heat emitted by the son

The Greenhouse Effect

Presentation content:

• Shortwave solar radiation passes through the atmosphere and heats Earth.
• Longwave radiation emitted by Earth is absorbed by gases in the atmosphere.
  • Such as carbon dioxide and water vapor
• The longwave radiation heats the atmosphere, which radiates heat both out into space and back to Earth.
• This selective absorption and reheating of Earth is called the greenhouse effect and results in warming of the atmosphere.

Notes from the lecture:

• Venus has a much thicker atmoshpere and it traps a lot more of that gas
  • Traps them more effectively and allows it to reach warmer temps

21.5 Natural Causes of Climate Change

Discuss hypotheses that relate to natural causes of climate change.

Plate Movements and Orbital Variations

Presentation content:

• Moving landmasses
  • Landmasses move closer or further from the equator
  • Moving landmasses can affect ocean circulation
• Variations in Earth’s orbit
  • Changes in eccentricity, obliquity, and precession cause fluctuations in distribution of solar radiation

Notes from the lecture:

Volcanic Activity and Climate Change

Presentation content:

• Volcanic ash and dust
  • 1815 was “the year without summer” due to the Mt. Tambora eruption
• Sulfuric acid droplets
  • 1982 eruption of El Chichón released large amount of sulfur dioxide gas; Remains in the stratosphere for up to several years
    • Lowered global temperatures by 0.5ºC
• Volcanism and Global Warming
  • Cretaceous period was one of the warmest in Earth’s history
    • Extensive volcanism
      • Lava plateaus
    • Increase atmospheric CO2

Notes from the lecture:

• Volcanism releases large amount of ash and CO2
• Keeps solar radiation from coming in and also from escaping to the sun so it is a little bit uncertain to know what the effect would be and if it will be leaning towards either side.
• CO2 can serve as both blocking from solar radiation from coming in and going out

Solar Variability and Climate

Presentation content:

• No long-term variations in solar intensity have been measured outside the atmosphere.
• Sunspot cycles
  • Sunspots are huge magnetic storms on the Sun
    • Appear as dark spots on the Sun
  • Sunspots reach a maximum every 11 years
    • Cycle is too short to have an effect on global temperatures

Notes from the lecture:

• Very profound but very short in terms of geologic timescale

21.6 Human Impact on Global Climate

Summarize the nature and cause of the atmosphere’s changing composition since about 1750. Describe the climate’s response.

Human impact

Presentation content:

• Humans have been modifying the environment for thousands of years.
  • Ground cover has been altered by:
    • Fire
    • Overgrazing
  • Results in modification of reflectivity, evaporation rates, and surface winds.
• Rising CO2 Levels
  • Carbon dioxide is a greenhouse gas.
  • Humans add carbon dioxide to the atmosphere.
    • Burning fossil fuels
    • Deforestation
• CO2 levels are highest in the past 600,000 years.

Notes from the lecture:

• Our historical record of CO2 oscillated back and forth but today we are braking the rule, this means we are having a great impact in the earth's climate system.

• Fluctuates back and forth reflecting seasonal oscillations

The Atmosphere's Response

Presentation content:

• Global temperatures have increased in response to increased atmospheric carbon dioxide.
  • Global temperatures have increased 0.8°C in the past century
    • The warmest 16 years (since 1850) have occurred since 1995
  • Temperatures are expected to continue to increase in the future.
• Amount of increase depends on amount of emitted greenhouse gases

Notes from the lecture:

• In general CO2 concentration is increasing, basically heating up the earth as a greenhouse -> increasing the temperature -> starts melting globe's ice -> changes the albedo -> impacts the amount of solar radiation reflected
• As we start warming the earth, the temperature compoundly increases exponentially
• At 2025 we have almost double 2015 temperature +1.5 C degrees
  • When will we reach 3 C? -> this is a big concern
• Different areas are being impacted differently
  • We see increase in temperature but we also see an increase in precipitation
• Projections

The Role of Trace Gases

Presentation content:

• Methane
  • Less abundant than carbon dioxide, but more effective at absorbing outgoing radiation.
• Nitrous Oxide
  • Greenhouse gas that lasts for 150 years in the atmosphere.
• CFCs
  • Commercially produced chemical that depletes the ozone.
• A combined effect!
  • CO2 is not the only contributor to global warming, but it is the single most important cause.

Notes from the lecture:

• Methane, Nitrous Oxide are very large molecules that have a relatively short residence time in the atmosphere
• CO2 has a very long residence time (it is not easy to remove it from the atmosphere)
• CFCs start doing holes in the ozone layer
• Methane mostly comes from Natural gas and kettle
  • In recent years we flare it, we burn natural gas because it is safer for the atmosphere, instead it goes as CO2, which we know also has an impact
• We are trying to eliminate a lot of these harmful gases

Aerosols

Presentation content:

• Aerosols are tiny particles and drops of liquid
  • Produce a cooling effect by reflecting sunlight back to space
    • The effect on today’s climate is determined by the amount emitted over the course of a few weeks.
    • By contrast, carbon dioxide remains for much longer spans and influences climate for many decades.
  • Most human-generated aerosols come from the sulfur dioxide emitted during the combustion of fossil fuels
    • Black carbon is soot generated by combustion processes and fires.
    • Black carbon warms the atmosphere because it is an effective absorber of solar radiation.

Notes from the lecture:

• They are important
• You can see their effect with volcanic eruption impact on temperature records (i.e. El Chichon eruption)
• Note: natural gas is a lot cleaner than coal

21.7 Predicting Future Climate Change

Contrast positive- and negative-feedback mechanisms and provide examples of each.

Climate, a complex system

Presentation content:

• The climate is a very complex system
  • When any component is altered, scientists must consider many possible outcomes
  • The different possible outcomes are called Climate-Feedback Mechanisms.
• Types of Feedback Mechanisms
  • Changes that reinforce the initial change are called Positive-Feedback Mechanisms.
    • Example: Warmer temperatures at high latitudes cause sea ice to melt, which is replaced with a lower-albedo ocean, which increases solar radiation absorbed at Earth’s surface, which increases temperature.
  • Negative-Feedback Mechanisms produce results that are the opposite of the initial change and tend to offset it.
    • Example: An increase in global temperatures would increase evaporation, which increases cloud cover, which would reflect more solar radiation back into space, lowering global temperatures.

Notes from the lecture:

• Positive feedback:
  • Warmer temperature -> melts ice -> decreases the albedo on the surface -> warms it even more
• Negative feedback
  • Increase albedo surface -> reflect more solar radiation -> cools it a little bit

Computer Models of Climate

Presentation content:
Important Yet Imperfect Tools

• General circulation models (GCMs) are based on the fundamental laws of physics and chemistry
  • Incorporate human and biological interactions
  • Can predict climate-change scenarios

Notes from the lecture:

21.8 Some Consequences of Global Warming

Discuss several likely consequences of global warming.

Complex climate system

Presentation content:

• Because the climate system is so complex, predicting specific regional changes related to increased levels of CO2 is speculative
  • Magnitude of temperature increase is not globally uniform.
  • Precipitation changes will also vary across the globe.

Notes from the lecture:

• Probabilities become more certain as time progresses and we do not do anything to address this issue

Sea Level Rise

Presentation content:

• Sea level has risen 25 centimeters since 1870.
• Will affect low-lying countries and regions with a gently sloping shoreline
  • Atlantic coast of the U.S.
• Sea level rise driven by:
  • Melting glaciers
  • Thermal expansion

Notes from the lecture:

• Sea level rise is not only about adding volume, is also about heating water
• A few thousand years ago, sea level was much more lower than today

The Changing Arctic

Presentation content:

• Arctic Sea Ice
  • Amount of sea ice has declined by 13 percent since 1979.
• Permafrost
  • Thawing permafrost is a positive feedback mechanism.
    • Organic material stored in the permafrost will start to decay and release carbon dioxide and methane

Notes from the lecture:

• We are seeing smaller and smaller volume of CI
• Significant volume difference

Increasing Ocean Acidity

Presentation content:

• When atmospheric carbon dioxide dissolves in seawater, the oceans become acidic
  • Makes it harder for calcite-secreting marine organisms to grow hard parts

Notes from the lecture:

• The oceans buffers it in terms of limestones, carbonate rocks, coral reefs

The Potential for "Surprises"

Presentation content:

• Due to the complexity of Earth’s climate system, we might experience relatively sudden, unexpected changes or see some aspects of climate shift in an unexpected manner
• A constant state of change is very likely

Notes from the lecture:

• There are a lot of different impacts that we don't really understand