History of climate change science

The history of the scientific discovery of climate change began in the early 19th century when scientists first noticed changes in Earth's climate, such as ice ages. They learned about the greenhouse effect.

Important scientists like Joseph Fourier, Claude Pouillet, Eunice Newton Foote, and John Tyndall discovered how gases in the air can trap heat. Later, Svante Arrhenius predicted in 1896 how more carbon dioxide could warm the Earth.

By the 1960s, scientists had proof that human actions were changing the climate. They also found that some pollutants could make the planet cooler, called global dimming. In the 1990s, using advanced computer models, scientists confirmed that human-made greenhouse gases were causing global warming.

Today, climate science keeps growing. Researchers study how climate change affects weather. Reports from the Intergovernmental Panel on Climate Change share this important knowledge with everyone.

Prior to the 20th century

People have always wondered if the climate of a place could change over many years. For example, a student of a famous ancient thinker noticed that draining swamps made areas colder, and thought cutting down forests might warm places up. Chinese scholars noticed that some plants found far underground grew in warmer places, suggesting climate changes over time.

In the 1800s, scientists began studying Earth’s past climates. They found signs that huge glaciers had moved across places that are now warm. One scientist noticed that giant rocks in valleys looked like they had been pushed there by glaciers and shared this idea with others. This idea was met with doubt at first, but later became widely accepted. Another scientist, Joseph Fourier, discovered that Earth’s air keeps it warmer than it would be in space. He thought human activities might change the climate, especially by changing how land is used.

Later, a scientist named Svante Arrhenius calculated that if the amount of a certain gas in the air doubled, Earth’s temperature would rise significantly. He also thought that human activities, like burning coal, could slowly change the climate over many years.

20th century onwards

Early scientists started to learn that human activities might change the Earth’s climate. In the early 1900s, they looked at old climates in lake mud and tree rings. They noticed patterns linked to changes in the Sun’s activity. Some thought sunspots caused climate changes, but others were unsure.

By the 1950s, better tools showed that carbon dioxide in the air could trap heat. Scientists found that oceans could not absorb all extra carbon dioxide quickly. In the 1960s, studies of deep-sea cores and ancient corals suggested that Earth’s climate could change quickly with small shifts.

In the 1970s, some people worried about cooling from pollution, but evidence showed that the Earth was warming. Scientists used computers to predict that doubling carbon dioxide would raise global temperatures. By the 1980s, more agreed that human activities were warming the planet. International efforts started to study and address climate change.

Discredited theories and reconciled apparent discrepancies

See also: Climate change denial

Early scientists learned that the Earth gets warmer because of something called radiation trapping. This is like how a greenhouse stays warm, leading to the idea of the "greenhouse effect."

Some scientists, like Prof. R. W. Wood in 1909, thought greenhouses stayed warm only because of air moving, not radiation trapping. But later tests proved that radiation trapping is the main reason greenhouses heat up. So, the idea of the greenhouse effect in our atmosphere is correct.

There have been discussions about where weather stations are placed and how they measure temperature. Some people thought these stations might give wrong results, but studies show these effects are small and do not change the overall warming trend. Scientists have checked these measurements and found that the Earth is warming as expected.

Scientists also studied temperature changes high in the atmosphere and found they match what we would expect from human-caused climate change, not just natural changes like the Sun's activity. Studies show the Sun’s energy has not increased since 1978, so it cannot explain the recent warming. Models that include human influences match what we see happening today.

Past estimates of greenhouse gas emissions and temperature rises

Previous estimates for the year 2020

In 2011, the United Nations Environment Programme studied how world emissions might change up to the year 2020. They used scientists and experts from many countries.

If no new steps were taken to cut emissions, global emissions in 2020 could be about 56 gigatonnes of CO₂-equivalent.

If countries followed the promises made in the Copenhagen Accord, emissions would still be around 50 gigatonnes by 2020. Without strong action, there was a concern of a temperature rise by the end of the century, which could cause problems.