Climate change: Warmer... but why? | Upsetting the balance | Mammals on the move
Connecting climate and disease | How do sea shells record temperature change?
Taking Earth's temperature

Earth's climate has had its ups and downs over the planet's five billion year history. At times it's been so cold that ice has covered much of North America and Eurasia. At other times, long periods of warm weather have made oceans rise, covering much of Earth.

Over the past 100 years, our planet has warmed by about one degree Fahrenheit. Is this warming just part of a natural cycle, or is it due to human activities that have changed the chemical composition of the atmosphere, resulting in an enhanced greenhouse effect?

Leading climate scientists say most of the climate’s warming is due to things people are doing.


The past 100 years have been different from the rest of Earth’s history, because during this time, people have burned fossil fuels at unprecedented rates to run cars and trucks, to heat and light homes and businesses, to keep computers and electrical appliances humming, and to power factories.

What are greenhouse gases?

Burning fossil fuels produces water vapor, carbon dioxide, methane, and nitrous oxide, known collectively as greenhouse gases, because they trap heat in the lower atmosphere, just as the glass roof of a greenhouse keeps heat from escaping. Greenhouse gases also occur naturally in the atmosphere and play an important role in regulating Earth's energy balance. But adding extra amounts of greenhouse gases to the atmosphere upsets this balance.

The stylized diagram above shows energy from the Sun coming to Earth as a yellow arrow. Earth absorbs some of the energy, warming its surface, but radiates some back into space. Greenhouse gases, shown as a white layer, trap some of the outgoing energy, retaining heat like the glass panels of a greenhouse roof. Since the beginning of the industrial revolution, atmospheric concentrations of carbon dioxide have risen nearly 30%, methane concentrations have more than doubled, and nitrous oxide concentrations have increased by about 15%. Carbon dioxide causes the greatest concern because it accounts for about two-thirds of all greenhouse gas emissions. These increases in greenhouse gases have enhanced the natural heat-trapping capability of Earth’s atmosphere, leading to global warming.
The first clues: Trend-spotting scientists

In 1956, a forward-looking scientist named Roger Revelle, then at the Scripps Institution of Oceanography, began a bold and ambitious experiment to sample carbon dioxide in Earth's atmosphere every day, at multiple locations around the world, over a period of many years.

Revelle and coworker Charles David Keeling established their main research station atop Mauna Loa, an enormous volcanic mountain that covers half the big island of Hawaii. They used weather balloons to collect daily air samples, and they analyzed the carbon dioxide concentrations in the air they collected.

Revelle and Keeling's research helped lead to the realization that many of our actions are contributing to climate change.

This chart shows monthly average carbon dioxide concentrations at the Mauna Loa Observatory in Hawaii, dating from 1958 to 2004. It didn't take long for the scientists to see from their data that the amount of atmospheric carbon dioxide was on the rise. The longer the experiment went on, the clearer the trend became.

What’s ahead?

Predicting what will happen with greenhouse gases and global climate change in the future is difficult, because economic and demographic trends, as well as developments in technology and policy, will influence the outcome. Scientists have come up with several scenarios, based on data they already have and assumptions about the near future...

In one such scenario, carbon dioxide concentrations are projected to be as much as 150% higher than today’s levels by the   year 2100.

The average global surface temperature could rise another 1 to 4.5 degrees Fahrenheit over the next 50 years and 2 to 10    degrees Fahrenheit in the next century.

With that warming, evaporation will increase, leading to higher average precipitation and a greater number of intense,    destructive storms.

Sea levels are rising partly because of melting glaciers and sea ice. If this trend continues, sea levels are likely to rise at   least several feet, inundating coastal areas and cities.

Upsetting the balance >

Climate change: Warmer... but why? | Upsetting the balance | Mammals on the move
Connecting climate and disease | How do sea shells record temperature change?
Taking Earth's temperature