GLOBAL CHANGE & EARTH SCIENCE/ What Makes a Planet Habitable?

Lecture 1: Introduction to Global Change

Learning Objectives:

What is global change and what causes it?

What are the timescales of global change and why are timescales of such changes important?

How has life changed Earth?

Why is Earth unique?

What changes are currently happening?

What is the role of science in understanding and dealing with these changes?

Next lecture: Earth systems, cycles, and feedbacks

What is Global Change?

Many view Earth as static and unchanging –Not true!

active plate tectonics, vigorous hydrologic cycle, and dynamic climate system

What do we mean by dynamic? Change is the only constant!

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What is Global Change?

Changes in climate and its components

atmosphere, hydrosphere, biosphere, geosphere

Caused by variety of processes that operate on different time scales

Most are natural… but human activities have become a major driver of global change over last 50-100 years

What is the Earth System?

Inter-related and inter-acting components

Atmosphere, hydrosphere, geosphere, biosphere

Fluid earth, solid earth, living earth

Interact to produce climate and plate tectonic systems

Change in one part of system drives change elsewhere in system

What Causes Global Change?

External drivers: solar output, orbital cycles

Internal drivers: changes within atmosphere, hydrosphere, biosphere, geosphere

Changes in carbon cycle - movement of carbon between atmosphere, biomass, and geologic materials

Changes in energy absorption or retention –albedo, greenhouse effect

Changes in ocean and atmosphere circulation – land-ocean geography, heat exchange, ice sheets

External – outside the earth system

Internal – within the earth system – change within one “sphere” of earth system affects the other “spheres” – biosphere, atmosphere, hydrosphere, geosphere – listed examples

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What Causes Global Change?

Plate tectonic activity

Rearranges continents and oceans, builds mountains, recycles earth materials

Main driver of global change on long timescales

Earth when first dinosaurs evolved

Modern world took shape by 14 mya

Plate tectonic system – part of geosphere – affects atmosphere, hydrosphere, biosphere - producing global change on long timescales. Why? Plate tectonics are slow processes (cm/yr) requiring long periods of time to produce significant change

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What Causes Global Change?

Changes in climate most recognizable form of global change

Ice sheets and sea level change 18,000 years ago

Last Glacial Maximum

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Maximum extent of ice sheets 18,000 years ago at the last glacial maximum. Also note the drop in sea level which resulted in exposure of the continental shelves and altered coastlines worldwide.

Why is Timescale Important?

Last ice age ended 11,750 years ago

Was this a long time ago? Or a short time ago?

Last Glacial Maximum

Today

Washington’s Olympic Peninsula

Why is Timescale Important?

Timescale of change provides insight into its causes

Geologic processes operate on long timescales

Difficult to comprehend in human terms

Consider recent geologic event: end of last Ice Age 11,750 years ago

People lived through it

Why is Timescale Important?

Although geologically recent, was about 400 generations ago:

During your great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, grandparents lifetimes

Human knowledge of Ice Ages did not survive to present

19th century geologists reconstructed this knowledge from geologic record – by studying rocks

What Causes Global Change?

Changes in past driven by processes still observed today

Study modern processes to understand past global changes

Study past changes to understand causes of current changes

Modern moraines, Alaska Ice Age moraines, California

TECTONIC

ORBITAL

MILLENNIAL

HISTORICAL

What are the Timescales of Global Change?

Millions of years

10,000s – 100,000s of years

Thousands of years

Decades to Centuries

Different processes operate at different rates, producing global change on different timescales

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What are the Causes of Global Change on Different Timescales?

Millions of years (geologic time)

plate tectonics

Tens of thousands of years (ice ages)

Changes in earth’s orbit and rotational axis

Thousands of years (within last ice age)

ice sheet dynamics and deep ocean circulation

Years to decades (industrial revolution to present)

sunspot cycle, volcanic eruptions, deforestation, agriculture, and fossil fuel use

How Are the Geologic and Biologic Histories of Earth Related?

Geologic events have affected origin, diversification, and extinction of entire groups of organisms

Origin and development of life changed global environment in a way that makes Earth unique

Representation of geologic time scale with major groups of organisms living at different times

Why did Life Begin on Earth?

Extraordinarily balanced in favor of life

Right distance from Sun: not too cold (Mars) or too hot (Venus)

Right size: enough gravity to hold an atmosphere

Not too large: result in thick atmosphere of nebular gases (H, He)

Not too small: still has hot interior and active tectonics

Recycles earth materials including atmospheric CO2

Magnetic field to shield surface from cosmic radiation

Molten metallic outer core and fast rotation

Why did Life Begin on Earth?

Oxygenated atmosphere came well after life began

Provides ozone layer and allows aerobic metabolism

Life first evolved when atmosphere was very different

Atmosphere similar to Mars and Venus

Rich in CO2, trace amount of oxygen

Earth would still have CO2 atmosphere today if not for evolution of photosynthesis

What was Earth Like when Life Evolved?

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How Did Life Change Earth?

Photosynthesis changed atmosphere from CO2-rich to O2-rich

Made Earth more hospitable to life

Allowed evolution of complex organisms

Earth supports life because life evolved on earth, not vice versa

Where would you rather live?

Too much GHGs

Too few GHGs

Just right

Biologic processes help regulate the concentration of greenhouse gases (like CO2) in the atmosphere – geologic processes do too

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Earth only planet with lots of water in all three phases

liquid water, water vapor, ice

Temperature range makes this possible

Right distance from Sun

Right amount of GHGs in atmosphere

Why is Earth Unique?

Earth is unique in the solar system, being the only planet whose surface conditions allow water to exist in liquid form, a requirement for all life as we know it.

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Why is Earth Unique?

Would Earth’s surface conditions allow liquid water if life had not evolved on Earth?

Too few GHGs

Too much GHGs

Just right

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Maybe, but not a lot – without biologic processes like photosynthesis, Earth would still have a CO2 rich atmosphere producing a stronger greenhouse effect and warmer surface temperatures (near the boiling point of water given Earth’s distance from the Sun). But with no greenhouse effect at all (like Mars), earth would be much colder than it is today (given its distance from the Sun), and all the water on Earth would be frozen.

CO2 traps heat in atmosphere warming surface - greenhouse effect

Without greenhouse effect average temperature -73o C (-100o F)

Too cold for liquid water and life

Why is Earth Unique?

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Certain atmospheric trace gases such as water vapor, carbon dioxide, and methane absorb certain wavelengths of terrestrial infrared radiation. This energy is the remitted in all directions as heat, including back to the earth’s surface. The greenhouse effect therefore traps heat near the surface, warming the planet. Without the natural greenhouse effect, earth’s average surface temperature would be only about -73 C (-100 F); similar to the coldest parts of interior Antarctica where all water is permanently frozen and no life exists. Alternatively, a "runaway" greenhouse effect like that found on the planet Venus would result in surface temperatures as high as 500 C (932 F).

Why is Earth Unique?

Too Much GHGs

Too Few GHGs

Just Right

Water only as vapor

Water (if present) only as ice

Water abundant in all three phases liquid, vapor, ice

Mars probably had liquid water in the distant past when more GHGs in atmosphere resulted in warmer surface temperatures – but Mars is too small to have enough gravity to hold its atmosphere and is too small to have active tectonics to maintain its atmosphere – without tectonic processes to recycle geologic materials, all its CO2 is now locked up in geologic material

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What Global Changes are Happening Now?

Changes in greenhouse gas concentrations

Changes in climate

temperature, precipitation, glaciers, sea ice, hurricanes, sea level rise, etc.

Changes in ecosystems

distribution (range) and behavior (adaptation) of plants and animals, migration, habitat loss, extinction

Global change is much more than warming temperatures and melting glaciers (in contrast to how global change is portrayed in the media).

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What are the Human Dimensions of Global Change?

Global change affects people too, not just natural systems

Freshwater availability

Agricultural production

Population growth and resource availability

Energy supply, demand, and price

Economic development and sustainability

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What Questions About Global Change are Answerable by Science?

Science (knowledge) vs. Policy (choice)

These are scientific questions: get answers by gathering data, developing and testing hypothesis, making predictions

What changes are taking place?

What are the causes of those changes (natural and human)?

What are the consequences of these changes?

Are these changes expected to continue – or increase?

How will these changes affect us?

In this class we will mostly focus on how we answer scientific questions and what this knowledge tells us about how and why climate is changing – the choice of what to do with this knowledge could be a class in itself. Note that this is very different from how global change is portrayed in the media and politics where little or no distinction between scientific knowledge (how and why climate is changing) and decision making (what should we do with this knowledge) is made.

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What Questions About Global Change are NOT Answerable by Science?

What should we do about climate change? Should we limit carbon emissions from fossil fuel use?

Choice - informed by values, not knowledge alone

Science can help us make more informed and hopefully better choices but cannot tell us what choices to make

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Questions for Review

Each lecture will end with a set of review questions. Although you do not need to turn them in, you should take the time to answer these questions to make sure you understand the key points of the lecture.

Provide some examples of global changes, the processes that cause them, and the timescales these processes operate on.

In what ways is Earth unique in our solar system? How does this help explain the existence of life on Earth but not elsewhere?

What global changes have been observed over the last century? What issues are related to these changes and their causes?

Review the syllabus carefully and make sure you understand how this class is structured and what is expected of you.