What effect does the ozone layer have on the EM waves from the Sun? What is currently threatening the ozone layer?

Ultraviolet (UV) radiation is a form of electromagnetic (EM) energy emitted by the sun. UV radiation is divided into three types based on wavelength: UVA, UVB, and UVC. UVA has longer wavelengths and is less harmful, but it can still cause skin aging and contributes to some forms of skin cancer. UVB, with shorter wavelengths, can cause more severe damage such as sunburn and most skin cancers. The shortest wavelengths belong to UVC, which is the most dangerous form of UV radiation.

Fortunately, Earth's ozone layer absorbs almost all of the highly energetic UVC and a significant portion of UVB, shielding all forms of life from these harmful rays. Without this layer, UV radiation would penetrate our atmosphere almost unimpeded, leading to increased risks for skin cancer, cataracts, and other health issues related to sun exposure. Moreover, it could also harm ecosystems by affecting delicate biological processes.

Ozone-depleting substances (ODS) are chemicals that can significantly harm the stratospheric ozone layer. The most notorious ODS are chlorofluorocarbons (CFCs), but the category also includes substances like halons, carbon tetrachloride, and methyl chloroform. ODS are mainly used in air conditioning, refrigeration, foam blowing agents, and solvents.

When ODS reach the stratosphere, they are broken down by ultraviolet light, releasing chlorine and bromine atoms. These atoms are highly reactive and catalyze the breakdown of ozone (O3) into oxygen (O2), depleting the ozone layer. As a result, the more ODS that are released into the atmosphere, the greater the reduction in the ozone layer, allowing more damaging UVB and UVC rays to reach Earth's surface.

The Montreal Protocol, formally known as the Montreal Protocol on Substances that Deplete the Ozone Layer, is an international treaty designed to protect the ozone layer by phasing out the production of numerous substances responsible for ozone depletion. Adopted on September 16, 1987, the protocol is considered a landmark agreement in terms of its global adoption and success.

The treaty has been revised several times, leading to the phase-out of many ODS, including CFCs and others. As a consequence of this unified global action, the ozone layer has shown signs of recovery, although it may take several decades to completely heal. The success of the Montreal Protocol is often cited as an inspiring example of international cooperation in addressing a major environmental issue.

The environmental impact of ozone depletion is far-reaching and severe. Increased UV radiation due to a thinner ozone layer can cause an array of ecological disturbances. For humans, the health effects include a higher incidence of skin cancers, cataracts, and weakened immune systems.

For wildlife, particularly those in aquatic ecosystems, excessive UV radiation can disrupt the base of the food chain by damaging phytoplankton. Plants and crops are also susceptible, as heightened UV levels can interfere with their growth and photosynthesis processes. Furthermore, the broader impacts of disrupted ecosystems can lead to diminished biodiversity and altered water cycles, highlighting the complex and interconnected nature of our environment's response to ozone depletion.