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Chlorofluorocarbons (CFCs) and hydrofluorocarbons (HFCs) are both types of compounds that are used in various industrial applications such as refrigeration, air conditioning, and as propellants in aerosol sprays. However, because of their different chemical structures, their impacts on the Earth's atmosphere and environment differ significantly.

CFCs are known to cause significant damage to the Earth's ozone layer, leading to depletion particularly in the polar regions. This depletion increases the amount of harmful ultraviolet (UV) radiation reaching the Earth’s surface, which can cause various health and environmental problems, such as skin cancer, and damage to crops and marine life. The release of CFCs also contributes to climate change as they have a strong greenhouse effect.

HFCs are considered a better alternative to CFCs because they do not cause ozone depletion. The reason lies in their chemical structure – HFCs do not contain chlorine atoms, which are responsible for catalyzing the destruction of ozone molecules in the stratosphere. Though HFCs have long lifetimes in the stratosphere, their lack of a chlorine atom makes them safer for the ozone layer.

While HFCs do not contribute to ozone depletion, they still have a greenhouse effect and can contribute to climate change. However, their global warming potential is generally lower than that of CFCs. Moreover, efforts are being made to develop and use HFCs with lower global warming potentials, further reducing their climate impact.

International agreements such as the Montreal Protocol have been put in place to phase out the use of ozone-depleting substances like CFCs. This treaty has been successful in significantly reducing the production and use of CFCs since the late 1980s, leading industries to find alternatives such as HFCs, which do not harm the ozone layer. The Kigali Amendment to the Montreal Protocol aims to phase down the use of HFCs due to their greenhouse effect and encourage industries to use more environmentally friendly alternatives. In conclusion, HFCs are used to replace CFCs primarily because they do not contribute to ozone depletion, despite their long lifetimes in the stratosphere. While they still have a greenhouse effect, their global warming potential is generally lower than CFCs, and efforts are being made to minimize their climate impact.