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How Did We Get Here?

The Handwriting on the Wall

Today, atmospheric CO2 is at a level that has not been seen on Earth for at least 800,000 years, and probably much longer.

how-handwriting_graph_540.jpg

The line on this wall-sized graph tracks levels of carbon dioxide in Earth's atmosphere over the last 400 years.

Denis Finnin/AMNH


Coal and heat

By the 1600s, coal was replacing wood as a common fuel. In addition to being readily available, coal had another great advantage over wood: it is more energy-dense. That is, it takes less coal than wood to produce an equivalent amount of heat.

Coal and transportation

The early 1800s saw the invention of boilers that could hold steam under high pressure. Within decades, these boilers were driving more powerful coal-fired engines that could pull heavy trains and power steamboats. A steam-powered ship first crossed the Atlantic Ocean in 1833.

The World Gets Wheels

The first mass-produced Model T Ford left the factory in 1908; by 1915 Ford was selling 500,000 a year. Most were powered by oil, although these internal combustion engines were also capable of running on ethanol, a plant-based fuel. Oil eventually became the fuel of choice for engines designed to move from place to place.

On The Move

There were fewer than 50,000 cars and trucks on the world's roads in 1900. By 2000, there were more than 700 million. And personal mobility is only gaining in appeal; in 2008, Indian automakers unveiled an inexpensive five-seater car with a small, 33-horsepower engine. They expect annual demand of up to one million cars.

1600

Estimated world population: 545-579 million
 Estimated size of world economy: $77 billion
 Estimated atmospheric carbon dioxide: 274 ppm*

*This abbreviation stands for parts per million. It is the ratio of the number of CO2 molecules to the total number of molecules of dry air. That is, 274 ppm means 274 molecules of CO2 per million molecules of dry air, or 0.0274 percent.

1650

Estimated world population: 470-545 million
 Estimated size of world economy: $82 billion
 Estimated atmospheric carbon dioxide: 277 ppm

1700

Estimated world population: 600-679 million
 Estimated size of world economy: $100 billion
 Estimated atmospheric carbon dioxide: 277 ppm

1750

Estimated world population: 629-961 million
 Estimated size of world economy: $135 billion
 Estimated atmospheric carbon dioxide: 277 ppm

1800

Estimated world population: 813 million-1.1 billion
 Estimated size of world economy: $175 billion
 Estimated atmospheric carbon dioxide: 284 ppm

1850

Estimated world population: 1.1-1.4 billion
 Estimated size of world economy: $360 billion
 Estimated atmospheric carbon dioxide: 286 ppm

1900

Estimated world population: 1.5-1.8 billion
 Estimated size of world economy: $1.1 trillion
 Estimated atmospheric carbon dioxide: 300 ppm

1940

Estimated world population: 2.4-2.6 billion
 Estimated size of world economy: $4.1 trillion
 Estimated atmospheric carbon dioxide: 311 ppm

2000

Estimated world population: 6.07 billion
 Estimated size of world economy: $41 trillion
 Estimated atmospheric CO2 in 2000: 369 ppm

2008

Estimated atmospheric CO2: 385 ppm

Additional Resources

What's the big idea about climate change?

This isn't the first time Earth's climate has changed, but it's the first time human activity has caused it. Learn more about global warming and how -- and why -- we should slow it.

What do you know about climate change?

Think your an expert on our changing climate? Test your knowledge with this interactive quiz.

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