New to Climate Change?

What We Know About Climate Change

The Earth’s climate is changing faster today than ever before in the history of our species – and human actions are the main reason why.

The Science

In the late 1700s, humans started burning large amounts of fossil fuels—first coal, and later, oil and natural gas—for heat, to power machines, and to generate electricity. These fuels helped us make significant technological, social, and economic progress and elevated standards of living around the world. As we’ve burned more and more fossil fuels over two centuries, we have added large amounts of carbon dioxide (CO2) and other heat-trapping greenhouse gases to our atmosphere.

Greenhouse gases prevent some heat from escaping the Earth out into space, and while this is a natural phenomenon, human behavior has now added so much greenhouse gas that our atmosphere is keeping in too much heat. In fact, ice core data shows us that there is now more CO2 in our atmosphere than at any point in at least the past 800,000 years. Because of this, our planet is almost 1.8°F hotter than it was in the 1880s.

As the levels of CO2 continue to rise, the planet is still getting hotter—and because CO2 stays in the atmosphere for such a long time, some of the CO2 we emit now will still be trapping extra heat on Earth for many hundreds of years.

This is especially worrisome because many parts of the world are still industrializing, and the global need for energy is growing.

For these facts, the evidence is overwhelming.


Take a look at the 25 warmest years that have ever been measured [since 1880]. If you’re 32 years old or more, you’ve been alive for every single one of them. Even if you’re only 20, you’ve been alive for the great majority of them. We, this generation of people, are living on the warmest planet that has ever been measured in the instrumental record.
Prof. Susan Solomon
who proved that gases called CFCs were creating the ozone hole in Antarctica. She is the Lee and Geraldine Martin Professor of Environmental Studies and Chemistry, MIT Department of Earth, Atmospheric and Planetary Sciences

The Risks

If this warming goes on unchecked, we leave ourselves open to severe risks. Scientists predict that it is highly likely that the rainfall patterns we all need for clean, fresh water will change, drying up in some places while causing floods in others. There is also significant evidence that, as a result of climate change, wildfires will worsen, destroying lives and property; that sea levels will rise, flooding many large cities; that hurricanes will become stronger; that the oceans will grow more acidic and hold less oxygen, threatening sea life and the people who rely on it for food; and that many people around the world would need to move to escape floods, famines or droughts, particularly in the poorest countries with the least capacity to adapt to a changing climate.

In communities across the United States and around the world, people are already experiencing the early effects of this climate change.

It Is Not Too Late

Because of the amount of CO2 we have already added to the atmosphere, some warming has already occurred and some further warming is now unavoidable. In fact, even if we stopped all greenhouse gas emissions today, the planet will maintain this extra warmth for some time, given how long these gases stay in our atmosphere and given the extra heat that has been taken up by the oceans.

But if we act swiftly, it is not too late to prevent much more severe changes to the Earth’s climate.

MIT and many of the world’s leading companies, organizations, and institutions are making a tremendous effort to meet this challenge, and there are options for what can be done. We can, as a species, learn to better adapt to the unavoidable effects of the warming that human behavior has already caused. And we can make choices that will stop adding CO2 to our atmosphere, and work on ways to remove some of what we’ve already emitted.

With a worldwide effort to control our CO2 emissions, we, our children, and our planet can avoid the threats that await us on a hotter Earth.