Climate Change 101

Nashville Youth Climate Summit

Jonathan Gilligan

Saturday, February 20 2021

What Is Climate Change?

What Is Climate?

  • Weather is what is happening now
    • Temperature, wind, rain, clouds, etc.
  • Climate describes patterns of weather over several decades:
    • Average temperature
    • Range of variation (hottest, coldest, etc.)
    • How likely is it to rain on an average day?
  • Climate is what you expect.
    Weather is what you get.

Photo of sunny day with fair weather cumulus clouds

Photo credit: Mabel Amber, Pexels

City in snow

Photo credit: wal_172619 on Pixabay

Climate vs. Weather

  • Predicting weather is hard:
    • Will it rain on Feb. 5, 2025?
  • Predicting climate is much easier:
    • On average, will February be colder than July from 2025–2055?
    • On average, will Texas be hotter than Alaska from 2025–2055?
  • A few unusually hot or cold days doesn’t prove or disprove climate change.
    • Climate change means a consistent pattern of changing weather
      over 30 years or more.

The Greenhouse Effect

Light and the Atmosphere

  • Light has different wavelengths (like colors)
  • Everything gives off light
  • Visible light and ultraviolet light are shortwave
    • Very hot things
    • Sun is almost 10,000° F
    • Light bulbs are about 5,000° F
  • Infrared light is longwave
    • Cooler things
    • Earth is about 68° F on average

Workers with red-hot metal ingot in a forge

Photo credit: Kateryna Babaieva on Pexels

Photo of a light bulb

Photo credit: Burak K, Pexels

infrared thermometer

Photo credit: Yongrow Medical

My Dog Finley

Finley in visible light

Finley in infrared light

The Greenhouse Effect

  • The atmosphere is transparent to shortwave light.
    • That’s why we can see!
  • Greenhouse gases are opaque to longwave light.
    • Carbon dioxide, water vapor, methane, …
  • Shortwave sunlight brings heat to the surface
  • Longwave light takes heat away
    • Greenhouse gases block longwave light & trap heat
  • The natural greenhouse effect is good
    • Without the greenhouse effect, all water on earth would be frozen
    • Life would be impossible
  • Fossil fuels put extra greenhouse gases in the atmosphere
    • Stronger greenhouse effect
    • The earth gets hotter

Longwave radiation from earth

Photo credit: NASA Terra/CERES mission

History of Climate Science

Cartoon: Two people looking at Munch’s “The Scream”, saying “It was commissioned in the 1890s by climate scientists”

Cartoon by Peter Ommundsen

Greenhouse Effect (1820s)

Title page of Fourier’s article General Remarks on the Temperature of the Terrestrial Globe and the Planetary Spaces

Joseph Fourier

Portrait of Joseph Fourier

Greenhouse Gases (1850s)

Title page of Eunice Foote’s 1856 paper Circumstances affecting the heat of the sun’s rays

Eunice Foote, "Circumstances affecting the heat of the sun’s rays, American Journal of Science 22, 382–383 (1856).

Eunice Foote

Roll of Honor for Seneca Falls Convention with Eunice Foote

Greenhouse Gases (1860s)

Title page of John Tyndall’s 1872 book Contributions to the Molecular Physics in the Domain of Radiant Heat

John Tyndall

Photograph of John Tyndall

Photograph by Elliott & Fry, public domain

Global Warming (1896)

Title page of Svante Arrhenius’s 1896 article On the Influence of Carbonic Acid in the Air upon the Temperature of the Ground

Svante Arrhenius

Photograph of Svante Arrhenius

Photo: University Archives, University of Würzburg

Modern Theory of Greenhouse Effect (1956)

Title page of Gilbert Plass’s 1956 article The Carbon Dioxide Theory of Climatic Change

Gilbert Plass

Photograph of Gilbert Plass

Photo: Emilio Segré Visual Archives, American Institute of Physics

Media Coverage (NY Times 1956)

Scan of 1956 New York Times article "Warmer climate on the earth may be due to more carbon dioxide in the air

President’s Council of Advisers on Science & Tech (1965)

Cover page of 1965 PCAST report “Restoring the Quality of our Environment”

Roger Revelle and Lyndon B. Johnson

Portrait of Roger Revelle

Photo: Roger Revelle Papers, Special Collections & Archives, University of California San Diego

Quotation from PCAST report: “The climatic changes that may be produced by the increased CO2 content could be deleterious from the point of view of human beings”

Recognition of Great Severity (1975)

Title and abstract of Wallace S. Broecker, “Climatic change: Are we on the brink of a pronounced global warming”

National Academies Report (1979)

Title page of the 1979 National Research Council report “Carbon Dioxide and Cliamte: A Scientific Assessment”

Jule G. Charney

Portrait of Jule G. Charney

Photo: MIT Museum

Quotation from the Charney Report: “A wait-and-see policy may mean waiting until it is too late.”

What Does Science Know?

What Does Science Know?

  • Carbon dioxide in the atmosphere has risen by almost 50% since people started using fossil fuels
    • Chemical analysis of the atmosphere proves that the rise in carbon dioxide is almost entirely caused by burning fossil fuels.
    • The amount of carbon dioxide in the atmosphere is the highest it’s been in 3 to 5 million years.
  • The earth’s average temperature has risen by 2.2° F since the late 19th century.
    • Human activity caused almost all of this warming.

Studying Ancient Climates

Ice Cores

Ice core

Ice core

Inside the Ice Core

Ice core section

Image credit: National Ice Core Laboratory

Inside the Ice Core

Ice Ages

Last Glacial Maximum in North America

Image credit: Ron Blakey

Last Glacial Maximum

Image credit: Ron Blakey

What Scientists Have Learned

  • Climate has changed throughout Earth’s history
  • Those changes were mostly caused by natural changes in carbon dioxide
  • If carbon dioxide did not cause climate change, the Ice Ages could not happen

Could Something Else Be Causing Global Warming

  • Some people say changes in the sun are causing warming, not greenhouse gases.
  • Different causes produce different patterns of climate change
    • Compare patterns to find the true cause
    • Example: Greenhouse gases:
      • Nights warm faster than days
      • Winter warms faster than summer
    • Observed patterns match greenhouse theory.
    • No other theory matches patterns nearly as well.
  • Once you eliminate the impossible, whatever remains, no matter how improbable, must be the truth.
    — Sherlock Holmes


Photo: NASA/Goddard/SORCE

Climate Change and People’s Lives

  • Extreme heat waves are now 50 times more frequent than they used to be.
    • Six of the ten deadliest heat waves in history happened since 2000.
      • 2003 European heat wave: 70,000 deaths
      • 2010 Russian heat wave: 50,000 deaths
    • A heat waves, combined with drought caused wildfires in Australia and California.

Bond fire, Silverado, Orange County, California, Thursday Dec. 3, 2020

2020 Bond fire, Silverado, Orange County, CA
Photo: Noah Berger/AP

Climate Change and COVID-19

  • No direct connection between weather and COVID-19
  • Air pollution is linked to COVID deaths
    • Air pollution causes inflammation and lung damage, affects immune system
      • Easier to transmit COVID
      • Infections are more severe
    • Places with worse air pollution have:
      • greater COVID infection rates
      • greater death rates from infections
  • Air pollution also makes other lung infections worse:
    • SARS
    • 2015 avian flu
  • Rising temperature makes air pollution worse

Smog in Hong Kong

Photo: David Holt, Flickr CC BY 2.0

Sea-Level Rise

  • Sea level rise is causing increasing flooding in coastal cities
    • “King tides” in Miami are flooding the city even in good weather.
    • When hurricanes come, storm surges are higher and more destructive

King tide flooding in Miami

Photo: Arianna Prothero/WLRN Miami

Nashville Winters

  • Average winters through 1980:
    • 12.4 inches of snow
    • One day below 0° F
  • The last time it went below zero was Feb. 5, 1996
  • Average for the last 20 years:
    • 4.3 inches of snow.

News report on Nashville winters

Davis Nolan, WKRN News, Nov. 15, 2017

Warming Winters and Agriculture

  • Cold winters are important
    • Freezing temperatures kill pests
    • Many trees need cold winters to tell them to reset for growing in the spring
      • Peach trees need more than 800 hours below 40° F to make good fruit
      • The winter of 2016–2017 had less than 500 “cold-soaking” hours in Georgia
      • 85% of the Georgia peach crop was lost.

Summer Temperatures

  • In the South, many people work outside
    • Construction, farming, logging, etc.
    • Summer heat waves could make it dangerous to be physically active outdoors
    • Loss of working hours, lower economic productivity, less money

Photo: Yang Hui/Global Times

What Does the Future Hold?

Future Projections for the U.S.

  • Extreme heat in 2070-2099 even with serious emission reductions.

Trends in future heat waves

K. Dahl et al., Environ. Res. Commun. 1, 075002 (2019), doi:10.1088/2515-7620/ab27cf

Football Practice in Heat

Football practice health/safety rules:

  • Heat index of 104 or more is considered dangerous
    • Constant observation and supervision for overheating
    • No pads or equipment
    • 5 minutes mandatory rest and water break every 15 minutes
  • After 2070:
    • Average of 3 weeks per year in US
    • 2 months per year in most of South and Midwest

Photo credit: Nathaniel Rutherford/RTI

Severe Heat Waves

  • Severe heat waves even with serious emission reductions.

Trends in future heat waves

K. Dahl et al., Environ. Res. Commun. 1, 075002 (2019), doi:10.1088/2515-7620/ab27cf

Dust Bowl in Context

  • 1930s Dust Bowl:
    • Lower 48: hottest years since 1880
    • 6 years of drought
    • Plains states: 25% less rain
  • Medieval Megadroughts:
    • N. America: 1–2°C hotter than today
    • 60–240 year droughts
    • Plains states: 40% less rain
    • Affected everything west of Mississippi

Global Warming is Already Affecting Economic Inequality

Impact of Global Warming on Economic Inequality

N.S. Diffenbaugh & M. Burke, Proc. Nat’l Acad. Sci. 116, 9808 (2019) 10.1073/pnas.1816020116

Future Economic Damages

Fugure economic damages from global warming

M. Burke et al., Nature 527, 235 (2015) 10.1038/nature15725

Benefits of Reaching International Climate Goals

Economic benefits from limiting warming to 1.5° C

M. Burke et al., Nature 557, 549 (2018) 10.1038/s41586-018-0071-9

Prospects for Clean Energy

Solar Power

Solar Energy over Time

Top-10 Nations for Solar PV

Wind Power

Wind Energy over Time

Top-10 Nations for Wind

Prospects for Future Renewable Energy

Cost of Renewable Power

  • Cost of solar energy is 90% less than in 2009
  • Cost of wind energy is 70% less than in 2009
  • Cost of wind and solar is now one third the cost of coal power
  • Cost of battery storage is down 87% since 2010.
  • Most car companies say the future of cars is electric
  • Politics and government regulations are preventing the rapid expansion of renewable electricity
  • Many tech companies like Amazon, Facebook, Google, Microsoft, and Apple want to install more renewable electricity
  • Vanderbilt University just signed a deal to build a 35 million Watt solar power facility.

What Can You Do?

  • Reduce energy waste at home:
    • Drive less, walk, bicycle, and take the bus more
  • Don’t waste food
    • Growing and preparing food takes energy.
    • Food in landfills generates greenhouse gases
  • Eat less meat
    • Especially beef
    • Switching from beef to pork or chicken does a lot of good
  • Demand that adults behave responsibly
    • Make your voice heard
  • When you turn 18, register to vote and vote in every election