Climate Literacy

Session: Causes

Peter CoombeAugust 5, 2015

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Causes: Anthropogenic Climate Change

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The “Keeling Curve”

1. Energy from the Sun – Radiation2. Albedo – How Much Reflectivity3. Atmospheric Composition

SUN

Mercury Venus MarsEarth

What Factors Influence Climate?

1. Energy from the Sun – Radiation2. Albedo – How Much Reflectivity3. Atmospheric Composition

Mercury Venus MarsEarth

What Factors Influence Climate?

Equilibrium T (°F)

Actual Surface T (°F)

324

35614

847-2

59

-67-45

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IceOceanLand

Sub-surface Earth

Atmosphere

Heat fromSurface

About 31%reflected into space

69% absorbed at surface

Solarradiation

Earth’s Climate System

Greenhouse Gases

59°F

Sun

Land

Sub-surface

AtmosphereHeat fromSurface

Extract and burn fossil fuelsadd CO2 to atmosphere

More greenhouse gases, more radiation absorbed

Additional heat retained, higher surface temperatures

Earth’s Climate SystemEnhanced Greenhouse Effect

“Anthropogenic Climate Change”

Ocean Ice

More greenhouse gases, more

radiation absorbed

Compound 

Formula 

ContributionApprox. (%)

Water vapor and Clouds H2O

50% Water Vapor 25% Clouds 

Carbon dioxide CO2 20%

Methane CH4 4%  Other GHGs 1%  

When ranked by their direct contribution to the greenhouse effect, the most

important GHGs are:

More greenhouse gases, more

radiation absorbed

Compound 

Formula 

Global Warming Potential- (GWP)

Carbon dioxide CO2 1

Methane CH4 25

Nitrous oxide  N2O 298

Chlorofluorocarbons (CFCs) 1,000- 10,000s

Greenhouse GasesAnthropogenic Sources:

GWP is used to calculate Carbon Dioxide Equivalents [CO2e] for emissions reporting

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Changes in GHG Concentrations

Image created by Robert A. Rohde

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CO2 Changes since the Industrial Revolution

Image created by Robert A. Rohde

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Visualization of the history of CO2 

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So we’ve reached 400 ppm.…  Now what happens?

https://scripps.ucsd.edu/programs/keelingcurve/

Carbon Dioxide (CO2)

Absorption

Emission

Greenhouse Gases trap heat because they absorb radiation in the infrared range, according to specific bond geometries and vibrational modes (ex CO2 below)

IPCC(2007)

Warming from increasesin greenhouse gases

www.ncdc.noaa.gov

What do models tell us?

Meehl et al. (2004)

The dominant mechanisms (to which recent climate change has been attributed) are anthropogenic:

• Increasing atmospheric concentrations of greenhouse gases• Global changes to land surface, such as deforestation• Increasing atmospheric concentrations of aerosols

What about natural mechanisms?

• Changes in solar activity • Volcanic activity

What do models tell us?

Meehl et al. (2004)

Global Temperature and CO2 CO2 level

today > 400 ppm

Take Home Points

• A basic physical understanding of the climate system: greenhouse gas concentrations have increased and their warming properties are well-established.

• Historical estimates of past climate changes suggest that the recent changes in global surface temperature are unusual.

• Computer-based climate models are unable to replicate the observed warming unless human greenhouse gas emissions are included.