Global warming and the greenhouse effect are not necessarily the same thing. While the greenhouse effect can cause global warming, other things can lead to the planet warming or cooling. Other factors include changes in geography (plate tectonics) and cycles of the Earth’s orbit around the Sun.

It is known that global warming is necessary to a certain point: Without the ability of certain gases in the Earth’s atmosphere to help retain radiation from the Sun, our planet would be a cold ice ball in space. These gases act like the glass of a greenhouse (thus the name greenhouse gases), trapping much of the energy emitted from or bounced off the ground and keeping our world warm. This, in turn, allows organisms—plants, animals, and otherwise—to live.

More recently, global warming has been used to describe the unnatural increase in the average surface temperatures around the world. Many scientists (and others) believe humans have pumped excess amounts of greenhouse gases, such as carbon dioxide, methane, and nitrogen oxides, into the atmosphere, causing temperatures to rise. Something has already raised the surface temperatures about 0.5°C (1°F) in the past 100 years, and scientists believe it to be human-induced.