How the World Warmed: Sources


Script Timeline
One hundred thousand years ago, the world was cold and getting colder. Buried under thousands of feet of ice, North America was descending toward the last Glacial Maximum, when the glaciers blanketing the northern hemisphere would reach their greatest extent. As this Ice Age advanced, mammoths and other fearsome megafauna roamed the Earth, and a new, curious creature began to populate the continent: people. Fast “rewind” back to 100,000 years ago.

~22,000 Years Ago: Last Glacial Maximum1

~25,000 years ago: Humans begin to populate North America2

As temperatures slowly began to climb, the ancestors of Native Americans flourished. The planet cooled and warmed, in turn, and these changes varied by region. When European settlers first set foot on North America, their homelands were experiencing a warm period.

A Revolution was fought and a new nation emerged.

The Industrial Revolution that started in Britain brought change as well to the continent across the Atlantic.

The telegraph and the railroad connected the coasts and the population boomed. So too did fossil fuel emissions from burning coal, and the influx of carbon dioxide into the atmosphere set us on an unprecedented trajectory.

At the same time, some began to investigate and understand humanity’s role in the planet’s climate.

From the discovery that the greenhouse effect keeps Earth warm, to the identification of the atmospheric gases responsible for that effect, and finally to the linkage between human CO2 emissions and worldwide warming, mounting evidence pointed toward a stunning epiphany: we were already affecting the Earth’s future.

Yet, even as this realization unfolded, a Second Industrial Revolution further spurred industrial growth. Human population soared and the First World War encouraged governments to embrace the mobilization of industrial societies.

As the 20th century progressed, new oil fields in Texas and the Persian Gulf dramatically lowered energy prices. The Great Depression struck, followed by World War II, and the Cold War produced the first satellite and a race to the Moon. At the same time, the scientific collaborations of the International Geophysical Year yielded new insights into our own planet and brought new funding and coordination to climate studies. 3

Evidence of Earth’s climate history embedded in minute layers of deep sea sediments and Antarctic ice revealed a delicately balanced system, sensitive to small changes. Two successive energy crises ignited new interest in alternative forms of energy, yet carbon emissions from the burning of fossil fuels continued to climb.

By the end of the 1980s, scientists suspected that the climate was changing, that the world was warming in response to new pressures, as it never had before. Some within the global community saw a need to take action. Efforts to mobilize took shape.

Still others resisted the call to arms, unconvinced by the accumulating evidence — or worse, determined to ignore it.

In 2016, the year of the Paris Agreement, annual average carbon dioxide levels in the atmosphere were already well above 400 parts per million and still rising.4

If we maintain this trajectory, it will be impossible to avoid a catastrophic two degrees Celsius of worldwide warming, or worse. Already, we are seeing extreme weather, floods, and forest fires; if temperatures continue to rise, so too will sea level, endangering coastal communities the world over.

What can we do? The challenge is daunting, but not impossible to overcome. Some nations and individual states in the U.S. are stepping up to address the threat, pledging to stop the warming before it reaches that two-degree threshold.5

The future is in our hands

~20,000 Years Ago: Glaciers begin to melt6

~8,000 years ago: Humans domesticate farm animals and grow rice. 7

~13,000-11,700 Years Ago: Younger Dryas cooling event

Sudden climate shift!8

~950-1250 C.E.: Medieval Warm Period in Europe9

1712: First commercially successful steam engine10

1752: Ben Franklin flies a kite11

~1550-1800: The Little Ice Age cools the Northern Hemisphere.12

1775-1783: American revolution13

1810/1815: Eruptions in Indonesia cause the “year without a summer.” 14

1816: First working telegraph15

1869: First Transcontinental Railroad16

The First Industrial Revolution: Coal powers special purpose machinery, factories, and transportation systems. 17

1850: World population: ~1.3 billion18

1861-1865: U.S. Civil War19

1886: Karl Benz unveils his gas-powered car20

1850: Beginning of modern temperature measurements21

1824: Discovery of Earth’s natural “greenhouse effect.”22

1856/1859: Co2 absorbs long-wavelength radiation, causing a greenhouse effect. 23

1896: The climate system is very sensitive to increased Co2 24

1931/1938: Increasing Co2 and temperature rise are correlated. 25

Fertilizer production, electricity, and public health initiatives further accelerate industrial growth. 26

1878: Thomas Edison invents the lightbulb. 27

1900: World population: ~1.65 billion

1914/1922: Discovery of Vitamins A and D and advent of factory farming. 28

1914-198: World War I29

1920s: Texas and Persian Gulf oil fields open, lowering energy prices.30

1929-1939: The Great Depression31

1939-1945: World War II32

1950s: Oil and natural gas consumption overtakes coal in the United States.33

1969: Neil Armstrong walks on the moon. 34

1955-1957: Discoveries: Doubling Co2 in the air will dramatically raise temperatures.

Excess Co2 will stay in the atmosphere, not the oceans. 35,36

1958: New measurements demonstrate a rise in Co2.37

1966: Deep sea sediments and ancient corals reveal the climate’s sensitivity to small changes.38

1973: An oil embargo and elevated prices create an energy crisis. 39

1979: Second oil energy crisis. 40

1980: First large wind farms installed in California. 41

1987: Montreal Protocol restricts chemicals that damage the ozone layer. 42

1988: Intergovernmental Panel on Climate Change (IPCC) founded. 43

1990: World population: ~5.3 billion

1997: The United Nations establishes the Kyoto Protocol, pledging to reduce emissions by an average of 5% by the period 2008-2012.44

1997-2000: First hybrid electrical and modern electric cars45

2001: President George W. Bush removes the U.S. from the Kyoto process. 46

2009: China overtakes the U.S. as the world’s biggest greenhouse gas emitter.47

2016: World population: ~7.3 billion

April 22, 2016: On Earth Day, the U.S. and 174 other nations join the Paris agreement. 48

May 31, 2017 President Trump withdraws the U.S. from the Paris agreement. 49

January 2018: Data show that 2015, 2016, and 2017 were the 3 warmest years on record50,51

General timelines

How the World Warmed Annotations

  1. Recent glacial history (Britannica)
  2. History of the Bering Land Bridge (PBS)
  3. The International Geophysical Year (National Academies of Science)
  4. Time Machine exploring Climate (NASA)
  5. Cities and States supporting Paris Accord (PBS)
  6. Climate throughout the history of humans (Britannica)
  7. Anthropocene Era begins (Climate Change: An Encyclopedia of Science and History)
  8. Evidence that abrupt climate change has happened before (Columbia University)
  9. The Medieval Warm Period (Britannica)
  10. Thomas Savery, patented the steam engine (Spartacus Educational)
  11. Benjamin Franklin and the Kite Experiment (The Franklin Institute)
  12. The Little Ice Age (Britannica)
  13. World History Timeline (Library of Congress)
  14. Explosion of Mount Tambora (Britannica)
  15. Invention of the Telegraph (American Institute of Physics)
  16. First transcontinental railroad is completed (Smithsonian Institute)
  17. The Industrial Revolution (American Institute of Physics)
  18. World population: Using a combination of estimates from HYDE and UNDESA, summarized here:
  19. U.S. Civil War (Library of Congress)
  20. History of the Automobile and the Environment (University of Michigan)
  21. Beginning of modern temperature measurements (Climatic Research Unit, University of East Anglia)
  22. Discovery of the greenhouse effect (American Institute of Physics)
  23. Discovery that CO2 absorbs long-wavelength radiation (American Institute of Physics)
  24. Discovery that the climate system is very sensitive to increased CO2 (American Institute of Physics)
  25. Discovery that increasing Co2 and temperature rise are correlated (American Institute of Physics)
  26. The Industrial Revolution (American Institute of Physics)
  27. Edison invents the lightbulb (Smithsonian Institute)
  28. Discoveries of Vitamin A and D (Nobel Prize)
  29. World War I (American Institute of Physics)
  30. Texas and Persian Gulf oil fields open (American Institute of Physics)
  31. The Great Depression (American Institute of Physics)
  32. World War II (American Institute of Physics) , (Library of Congress)
  33. Graphs showing United States energy usage (NPR)
  34. Apollo 11 Mission to the Moon (NASA)
  35. Doubling CO2 in the atmosphere will affect temperatures (American Institute of Physics)
  36. Excess CO2 will stay in the atmosphere (American Institute of Physics)
  37. Measurements of atmospheric CO2 begin (Scripps Institution of Oceanography, UC San Diego, American Chemical Society) ,
  38. Evidence for climate change in deep sea sediments and ancient corals (American Institute of Physics)
  39. 1973 Oil Embargo (The History Channel)
  40. The second oil energy crisis in 1979 (American Institute of Physics)
  41. First Wind Farms in California (U.S. Department of Energy)
  42. Montreal Protocol (American Institute of Physics)
  43. Intergovernmental Panel on Climate Change founded (American Institute of Physics)
  44. Kyoto Protocol (American Institute of Physics)
  45. Hybrid electrical and modern electrical cars (American Institute of Physics)
  46. U.S. removal from the Kyoto Protocol (American Institute of Physics)
  47. China overtakes U.S. as top greenhouse gas emitter (Nature)
  48. Paris Agreement (United Nations)
  49. U.S. withdraws from Paris Agreement
  50. The warmest years on record (Climatic Research Unit, University of East Anglia)
  51. The warmest years on record (NASA)