Environmental Defense Fund

 How we know human activity is causing warming

We know the planet is warming — scientists have a clear understanding why

The theory of global warming is nothing new. The Nobel Prize-winning chemist Svante Arrhenius first proposed the idea of global warming in 1896. Carbon dioxide, he knew, traps heat in the Earth's atmosphere. He also knew that burning coal and oil releases carbon dioxide (CO₂).
Arrhenius speculated that continued burning of coal and oil would increase concentrations of CO₂ in the Earth's atmosphere, making the planet warmer. It's called the greenhouse effect.

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