Continuing from yesterday, the third Planetary Boundary we must consider is ozone depletion. Gradual thinning of Earth’s ozone layer in the upper atmosphere caused by the release of chemical compounds containing gaseous chlorine or bromine from industry and other human activities. The thinning is most pronounced in the polar regions, especially over Antarctica. Ozone depletion is a major environmental problem because it increases the amount of UV radiation that reaches the earth’s surface, which increases the rate of skin cancer, eye cataracts, genetic and immune system damage. Where were we in 2015? Depletion was still safely inside the boundary except over Antarctica where during spring levels it dropped to 200 DU (Dobson Units). As a result of continued international cooperation on this issue, the ozone layer is expected to recover overtime.
The fourth PB is pollution caused by excessive flow of nitrogen (N) and phosphorus (P). The biogeochemical cycles of N and P have been radically changed by humans as a result of many industrial agricultural processes. N and P are both essential elements for plant growth, so fertilizer production and application are the main concern. Farmers use nitrogen and phosphorous and other nutrients in farm soils to ensure decent production. Problem is that much of the fertilizer is not taken up by plants. A portion of the unused fertilizer returns to air and the other portion is carried down to pollute water bodies including groundwater. Nutrients give rise to ‘algal bloom.’ When these algae die, they are consumed by bacteria, which in turn deplete oxygen in the water giving rise to hypoxic dead zone and killing the fish and other marine life. This process of ‘eutrophication’ is already occurring in many countries.
The fifth PB arises from the overuse of freshwater resources. In the planet more than 97 per cent of water is salty, 2 per cent is fresh in the form of snow and ice, and only one per cent is left for humans. Water is finite. Of the total amount of freshwater that humans use, about for 70 per cent goes to agricultural production and about 20 per cent is used in industry. And the remaining 10 per cent is for households. Humanity is now using so much, especially for food production purposes, that many parts of world societies are depleting their critical sources of freshwater. Groundwater depletion is now a worldwide phenomenon. Freshwater scarcity will be exacerbated by countless other problems. The PB of freshwater will pose a major crisis for the many regions of the world in the decades to come. By 2050 about half a billion people are likely to be subject to water -stress.
The sixth PB is land use. Humanity uses a massive amount of land to grow food, graze animals, produce timber and other forest products, and expansion of expanding cities. Many regions of the world that were once dense forests are now farmlands or cities. Such deforestation adds CO2 to the atmosphere. Human land-use change is causing a massive disruption to ecosystems and species survival in many parts of the world. Status as in 2015: 62 per cent of the land system has been changed.
The seventh PB is biodiversity. Biodiversity not only defines life on the planet, but also contributes in fundamental ways to the functions of ecosystems, the productivity of crops, and ultimately to the health and survival of humanity. We depend on biodiversity for our food supply, our safety from many natural hazards. When biodiversity is disturbed, the ecosystem changes markedly, usually in adverse ways. Humanity is massively disrupting biodiversity. The National Geographic reports: ‘More than 99 per cent of all organisms that have ever lived on Earth are extinct.’ Many species are declining in numbers, genetic varieties, and resilience. The history of life on earth has included at least five periods during which huge numbers of species vanished forever, primarily due to changes in climate and sea level. Some scientists worry that a sixth extinction has begun because of humanity’s gross misuse of the earth’s resources. The status on 2015: biodiversity has dropped to 84 per cent in parts of the world such as Africa.
The eighth PB is called aerosol loading. When we burn biomass, hydrocarbon fuels, coal, forests and crop waste etc. small particles called aerosols are put into the air. We have more than doubled the global concentration of these aerosols since pre-industrial times. Very small particles less than 2.5 micro meters in diameter can cause life-threating lung diseases. Aerosols can have an indirect effect on climate. Status in 2015: within limit.
The nineth PB is chemical pollution. Industries and mining not only use land and water for their processing but also add a tremendous load of pollutants back into the environment. Pollutants are deadly for humans and as well as other species.
The PBs define, as it were, the boundaries of the ‘planetary playing field’ for humanity if major human-induced environmental change on a global basis is to be avoided. Transgressing one or more PBs may be highly damaging or even catastrophic. It is estimated that humanity already transgressed three PBs: climate change (1st), rate of biodiversity losses (7th) and changes to global nitrogen cycle (4th). Many environmentalists alarmed by humanity’s trespassing of PBs have concluded that economic growth must end now. Most importantly, it is also argued that by choosing the appropriate technologies we can achieve continued economic growth and also honour the PBs for sustainable development.
Most environmental economics studies the question of how to use the various kinds of incentives ~ both market based and socially based ~ in order to reduce externalities. However, growth of material well-being per person is best protected if the astounding rise in global population is brought under control this century through a voluntary reduction of fertility rates to their replacement rate or below, thereby leading to a peak and then gradual decline in the global population during the twenty-first century.