Ruled Out

The Sun

The facts: Since the 1970s, the sun has been cooling slightly. Over this same time period, the Earth has gotten warmer. Most of the warming has occurred in the lower atmosphere near the Earth's surface.



The Earth's Orbit

The facts: The way the Earth tilts on its axis and the way it circles the sun can influence the amount of the sun's energy that reaches the planet. As a result, changes in the Earth's orbit can cause the climate to change, but these changes happen very slowly, over tens to hundreds of thousands of years.



Volcanoes

The facts: When volcanoes erupt, they add a small amount of greenhouse gases into the atmosphere. They also release dust, ash, and other particles called aerosols. Some volcanic explosions are so strong that they throw these aerosols high enough into the atmosphere that they block some sunlight from reaching the Earth.

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