The Antarctic and Arctic ozone holes are slightly different (and these conditions can change depending on the conditions during a specific year). The first ozone “hole” over the Antarctic was discovered in 1985; in 2002, the hole split into two distinct holes, but by 2012, the hole had decreased to the second smallest in twenty years. Most scientists believe this is because of the warmer temperatures (the global average temperatures have gone up) in the Antarctic’s lower stratosphere, the layer above the troposphere where humans live.

The Arctic ozone hole tends to be milder and shorter-lived than the one over the Antarctic, but the ozone levels are still often significantly higher than at the South Pole. The Arctic hole is found in a region of the so-called polar vortex—a place in which fast-blowing circular winds intensify in the fall, isolate an air mass within the vortex of the winds, and keep the area very cold. In most years, atmospheric waves push the vortex to lower latitudes in the late winter and break it up, unlike the Antarctic hole, which is much more stable and lasting until midspring. And “good news” may be in the far future for the ozone layer above the Arctic: according to a study in 2013, some scientists believe the ozone layer over the North Pole should recover to its original nonhole state by around 2100.

The greenhouse effect is a warming of the Earth’s atmosphere that results when gases in our atmosphere trap the Sun’s heat. This effect was first described by Irish physicist John Tyndall (1820–1893) in 1861; it was given the greenhouse analogy much later, in 1896, by the Swedish chemist Svante Arrhenius (1859–1927). Simply put, greenhouse gases, such as methane, water vapor, and carbon dioxide, absorb some radiated heat (infrared radiation) from the ground that passes through the atmosphere toward space; the heat is then reradiated back to the Earth, keeping us warm. The greenhouse effect is not bad—it’s what makes Earth habitable. Without the presence of the greenhouse gases, too much heat would escape, and Earth would be too cold to sustain life. It is only when an excess amount of greenhouse gases is present in the atmosphere that an increase in global temperatures occurs—and thus, as we’ve seen in the past decades—changes in the Earth’s climate.