Chapter 18

GLOBAL CLIMATE CHANGE

Weather Vs. Climate

• Weather: Short term variations in the atmosphere phenomena that interact and affect the environment and life

• Climate: The long-term average of variation in weather for a particular area

What is Global Climate Change?

• Global climate (temperature) is changing and humans are influencing the change in climate

• Global climate has changed in the geological past, various factors influence global climate change

• Climate will probably change in the future too

Past Global Climate Change (1A)

• Medieval Warming Period (1100 A.D. – 1300 A.D.)• Global climate was relatively warm• Glaciers receded in many parts of the world• Sea temperature 4°C -- 7°C warmer than it is now (?)• Allowed people to settle into colder regions and

navigate waters that were normally hazardous due to icebergs

Past Global Climate Change (1B)

• During the Medieval Warming Period, the Vikings colonized Greenland

• It is suspected that the waters were much warmer and the climate was warmer than in current Greenland

Sea routes of the Vikings Artists conception of the Viking explorers

Past Global Climate Change (2A)

• After the end of they Medieval Warming Period, scientists and historians now know that the Little Ice Age took place

• Very cold winters existed and greatly affected Europe (around 1400)

• Other conditions that persisted during the Little Ice Age included severe storms, wet periods, dry periods, extreme hot and cold conditions

- Viking settlements abandoned in Greenland

Little Ice Age in Spain

Past Global Climate Change (2B)

• Good book to check out• Discusses how humansadjusted to climatic changesduring the Little Ice Age- History of Europe a result of climate?

"Climate change is the ignored player on the historical stage," writes archeologist Brian Fagan. But it shouldn't be, not if we know what's good for us. We can't judge what future climate change will mean unless we know something about its effects in the past: "those who do not learn from history are doomed to repeat it". And Fagan's story of the last thousand years, centered on the "Little Ice Age," reminds us of what we could end up repeating: flood, fire, and famine--acts of God exacerbated by acts of man. -Comment in a book review from http://www.amazon.com

• Climate changes: Contributing to the complex evolutionary history of the Earth system

• Earth system: Interactions between the atmosphere, the oceans, solid Earth, and the biosphere, Earth System Science a big component of studying global climate change

• The effects of human activities: Extensive on aglobal scale

Overview

• Uses of the geologic records to study climate• Fossils, sediments, and rocks can tell the story about

how environments have changed over time• Using various dating techniques, the fossils,

sediments, or rocks can be dated Ice cores e.g., carbon dioxide concentration in

glacial ice (pockets of air preserved when the snow falls)

Ocean sediment cores, also contain information about global climate change (small microorganisms that thrive in certain temperature conditions)

Lake sediment cores, varves

Tools for Studying Global Change (1A)

Tools for Studying Global Change (1B)• Glacial tillite: Glacial till lithified to rock• Evidence of ice age• Precambrian Gowganda Formation of Ontario,

Canada (can be found in glacial drift in Ohio too) Angular rocks

surrounded by fine-grained matrix (diamictite)

Tools for Studying Global Change (1C)

• Deep ocean sediment core• Organic and inorganic materials from the ocean can be used to study past environmental conditions and past climates- Ocean Drilling Program (ODP)

Scientists inspecting an ocean sediment core

Tools for Studying Global Change (1D)

• Ice cores, studying trapped air pockets in ice• Ice caps, alpine glaciers, other places

Tools for Studying Global Change (1E)

• Varves, layers that are deposited in a water environment (such as a lake)

• If the layers in the varve deposited are annual, then they can be used to reconstruct the climate

• Glacial lake varves

Tools for Studying Global Change (1F)

• Carbonates can include something called Speleothems • Type of mineral formation which can be found in

caves • The precipitation of calcium carbonate by groundwater• Can be dated via radiometric dating (U)

• Increased movement of GW = thickerlayers• Decreased movement of GW = thinnerlayers

Example of a speleothem

Tools for Studying Global Change (1G)

• Dendochronology: Study of tree rings, tree rings can be used to date archaeological sites and certain climatic events

• Wet year = thick ring• Dry year = thin ring• Only works in certainareas and with certain trees

Tree rings (Notice that they are not all the same thickness)

Tools for Studying Global Change (2)

• Real-time monitoring: Collecting data on a regular basis in order to better understand and keep track of climatic changes

• (1) Temperature• (2) Concentrations of atmospheric gases• (3) Composition of the ocean• (4) Other variables• Collecting data is necessary to track climatic

trends and to calibrate data from the geological record

Tools for Studying Global Change (3A)

• Mathematical models: Numerical means to represent real-world phenomena and the linkages and interactions between the processes involved

• Used to solve complex problems• Help to understand atmospheric circulation and

groundwater movement (among other things)

e.g., global circulation models (GCMs)

Tools for Studying Global Change (3B)

• Diagram showinghow a GCM is useddata for each cell isinput into a computerprogram and thenanalysis is done usinga supercomputer- Weather and climate modeling

What is Climate?• Weather and climate are often confused• Weather: is a term that encompasses phenomena in the

atmosphere of a planet. The term is normally taken to mean the activity of these phenomena over short periods of time, usually no more than a few days. *

• Climate: The statistical properties of the atmosphere, including measures of average conditions, variability, etc…. (Over a period of time longer than days or weeks, usually seasons to decades.)

• Understanding climate can be very complex (processes between all of the earth spheres.)

* Taken from http://en.wikipedia.org

Characteristic temperature and precipitation

conditions

• Climate change: Change of atmosphere conditions and its relationships with lithosphere, hydrosphere, and biosphere

• Atmosphere as a complex chemical factory: With many little-understood chemical reactions

• Changes in greenhouse gases, variable temp, and water vapor

- Greatest variable within the Earth’s atmosphere is the concentration of water vapor

Atmosphere and Climate Change

• Temp of the Earth: Three factors (1) The amount of sunlight received (2) The amount of solar energy reflected and

absorbed (3) The amount of retention by atmosphere

• Earth: Absorbing the short wavelength solar energy, then radiating long wavelength IR radiation

• Global warming: Greenhouse effect

Global Warming

Earth’s Energy Balance (1)

Greenhouse

Earth’s Energy Balance (2)

• Greenhouse gases are actually needed to keep the Earth warm. Without the greenhouse effect the water on the Earth’s surface would be frozen. Earth would be a very cold place!

• However, excessive greenhouse gases could potentially warm the Earth too much

• Venus = “runaway greenhouse effect”

The planet Venus

• Several atmospheric gases: CO2, CH4, CFCs, nitrogen oxides trapping more heat and warming up the lower atmosphere, similar to the effect of a greenhouse

• The concentration of greenhouse gases increased recently due to human activities, anthropogenic gases (especially burning fossil fuels)

• Natural greenhouse warming occurs, water vapor the main culprit

The Greenhouse Effect (1)

The Greenhouse Effect (2)

*

The Greenhouse Effect (3)

Incoming infrared radiation has short wavelengths but the outgoinginfrared radiation has longer wavelengths

Figure 18.8C

Carbon Dioxide in the Atmosphere (1)

-Cycles of carbondioxide are seasonal,more CO2 is takenout of the atmosphereduring the summergrowing season in the northernHemisphere.-Most of the vegetation is located in the northern hemisphere

Carbon Dioxide in the Atmosphere (2)

-CO2 concentrations over the past 160,000 years-Note the swift upward trend in CO2 concentrations

-Low CO2

concentrations =glacial episodes

-High CO2

concentrations =interglacials

Exponential growth in CO2 concentrations

• The Pleistocene Ice Age: ~ 2 MYA, “Beginning of the Ice Age”

• Numerous changes in Earth’s mean annual temperature since then

• Warming trend over the last 150 years, especially since 1940s with the warmest in 1980s and 1990s

• Mean temp increased about .8°C (1.36°F) in the past 100 years

Global Temperature Change (1)

Global Temperature Change (2)

• Climate has changednumerous timesduring the Pleistocene-Glacials vs. interglacials-Sea level going up anddown-Greenhouse gases goingup and down

• Changes in long cycles (100,000 yrs) separated by short cycles (20,000 to 40,000 yrs)

• First identified in 1920s, Milankovitch hypothesis

• Long cycle: The variability in Earth’s orbit aroundthe Sun (100,000 year cycles)

• Short cycle: The wobble effect of Earth’s axis (20,000 / 40,000 year cycles)

Why Climate Change?

• Climate system even unstable in shorter cycles, a few decades (not a few days as depicted by Hollywood)

• The ocean conveyor belt, global circulation of ocean water, contribute to the change

• Warm surface water is transported westward and northward (increasing in salinity owing to evaporation) to near Greenland, where it cools from contact with cold Canadian air. As the water increases in density, it sinks to the bottom and flows south, then east to the Pacific, where upwelling occurs. The masses of sinking and upwelling waters balance, and the total flow rate is about 20 million cubic meters (700 million cubic feet) per second. The heat released to the atmosphere from the warm water keeps northern Europe 5 degrees to 10 degrees C (8.5 degrees to 17 degrees F) warmer than it would be if the oceanic conveyor belt were not present

• Taken from Keller (2005)

Why Climate Change?

Global Circulation of Ocean Water

• Global warming: Need to consider major forcing variables—solar, volcanic, and anthropogenic gases

• Quite complicated to take all of these variables into consideration

• History of the past 1000 years

• Medieval warm period corresponding to a time increased solar radiation

• The little ice age (14th century) corresponding to the minimum solar activity

Solar Forcing (1)

Solar Forcing (2)• Observation of sunspots for hundreds of years• Gives an idea of solar activity and how it has affected

climate on Earth• Maunder Minimum occurred during the coldest part of

the Little Ice AgeColdest part ofThe Little Ice Age

•Taken from http://en.wikipedia.org/

Solar Forcing (3)

• Some scientists argue that the solar cycles affect climate more than greenhouse gas concentrations such as carbon dioxide

• Controversial topic

• Taken from http://en.wikipedia.org/

• Volcanic eruption: Vast amount of aerosol particles into the air

• Aerosols: Reducing solar radiation to the Earth surface, reflect incoming solar radiation

• Aerosols may have a counteracting effect on global warming

• Episodes of volcanic eruptions have significant contribution to the cooling of the Little Ice Age (pulse of volcanic eruptions

Volcanic Forcing (1)

Volcanic Forcing (2)

• Eruption of Mount Pinatuboin the Philippines• Global climate was coolerfor several years after theeruption

Eruption of Mount Pinatubo

• Natural variability failing to explain the warming at end of the 20th century

• Mathematical modeling on the anthropogenicforcing: Increase of temperature due to the doubling of CO2

• Significant global warming as a result of human activities

Anthropogenic Forcing

Aerosols Causing Global Dimming (1)

• Human processes could cause cooling too• Reflection from atmospheric particles could

reduce incoming solar radiation by 10%• Called global dimming

Aerosols Causing Global Dimming (2)

• Good documentary movie to check out:

http://www.pbs.org/wgbh/nova/sun/

• Doubling the greenhouse gases, then 1.5–6°C (2.6−10.2°F) increase in average global temp

• Significant rise of sea level and melting of glacierice due to the increase in temp (affecting island nations most seriously, increased coastal erosion worldwide)

• The number of retreating glaciers accelerating in many areas of the world

• Some remote communities rely on glacial meltwater as a water supply

Potential Effects of Global Climate (1)

• Global warming leads to significant changes of rainfall, soil moisture

• Agricultural activities and world food supplies affected greatly by climatic factors

• Global warming affects the frequency, intensity, and distribution of natural hazards, such as hurricane and other storms

Potential Effects of Global Climate (2)

Potential Effects of Global Climate (3)

• Desertificationchanging of regional / globalclimates- Expanding deserts

Sahara Desert

Migrating sand dunes Sahel Region

• An estimated 40 cm (16 in.) rise in sea level for the next century

• Increases in coastal erosion: Up to 260 ft on open beaches

• Landward shift of existing estuaries

• Disastrous impact on the existing developmentsalong coastal zones

Sea Level Rise and Global Warming

• Causing a number of changes in biosphere, both people and overall ecosystem

• Risk of extinction due to land-use change and habitat shift

• Spread of infectious and other diseases due to migration of organisms

Biosphere and Global Warming

Increased El Nino Events

• (1) Identify the historic changes that have occurred

• (2) Predict the potential changes in the future

• (3) Reduce greenhouse gases

• (4) Political commitment: Reconciling the conflicts between the environmental need for reduction of greenhouse gases and the economic demands for more fossil fuel

Reducing the Impact of GW (1)

Reduce the emission of CO2

• Use fossil fuels releasing less CO2

• Conservation of energy• Store CO2 in forests, soils and rocks (sequestration of

CO2)• Use alternative energy

Reducing the Impact of GW (2)

• The coupling of the greenhouse and ozone depletion problems from CFCs

• Burning of fossil fuels and acid rain problems

• Use of fossil fuels and volcanic eruptions problems and atmospheric cooling

• Emphasis on the principle of global environmental unity in action

Coupling of Global Change Processes

• Rapid economic development in developingcountries occurs at the expense of environment. Should people put environment first? Why or why not?

• What can individual citizens do to help battle the global warming problem?

• Will new technologies be part of solution on problem in global warming? Explain

Applied and Critical Thinking Topics

End of Chapter 18