People should not cross certain boundaries, so as not to come to an ecological catastrophe, which will become a serious threat to the existence of mankind on the planet.
The researchers say there are two kinds of such borders. University of Minnesota environmentalist Jonathan Foley says one such boundary is that tipping point when something catastrophic happens. In another case, these are gradual changes, which, however, go beyond the range established in the history of mankind.
Here are seven such boundaries that are currently under active discussion:
Ozone in the stratosphere
The Earth’s ozone layer could reach the point where people can get a tan in minutes if scientists and political leaders don’t work together to control the release of ozone-depleting chemicals. The Montreal Protocol in 1989 banned chlorofluorocarbons, thereby saving Antarctica from the specter of a permanent ozone hole.
Environmentalists believe that the critical point will be a 5% reduction in the ozone content in the stratosphere (upper layer of the atmosphere) from the level of 1964-1980.
Mario Molina, head of the Center for Strategic Studies in Energy and Environmental Protection in Mexico City, believes that a 60% depletion of ozone around the globe would be a disaster, but losses in the region of 5% would harm human health and the environment.
Currently, environmentalists set a limit of 15% on the use of land for agriculture and industry, which gives animals and plants the opportunity to maintain their populations.
Such a limit is called a “sensible idea”, but also premature. Steve Bass, senior fellow at the International Institute for Environment and Development in London, said the figure would not convince policymakers. For the human population, land use is too beneficial.
Restrictions on intensive land use practices are realistic, Bass said. It is necessary to develop sparing methods of agriculture. Historical patterns have already led to soil degradation and dust storms.
Fresh water is a basic need for life, but people use a huge amount of it for agriculture. Foley and his colleagues suggested that water withdrawal from rivers, lakes, underground reservoirs should not go beyond 4000 cubic kilometers per year – this is approximately the volume of Lake Michigan. Currently, this figure is 2600 cubic kilometers each year.
Intensive agriculture in one region may consume most of the fresh water, while in another part of the world rich in water, there may be no agriculture at all. So restrictions on fresh water use should vary from region to region. But the very idea of ”planetary boundaries” should be the starting point.
High levels of carbon dioxide can dilute minerals needed by coral reefs and other marine life. Ecologists define the oxidation boundary by looking at aragonite, the mineral building block of coral reefs, which should be at least 80% of the pre-industrial average.
The figure is based on results from laboratory experiments that have shown that decreasing aragonite slows coral reef growth, said Peter Brewer, an ocean chemist at the Monterey Bay Aquarium Research Institute. Some marine life will be able to survive the low levels of aragonite, but increasing ocean acidification is likely to kill off many of the species living around the reefs.
Loss of biodiversity
Today, species are dying out at a rate of 10 to 100 per million per year. Currently, environmentalists say: the extinction of species should not go beyond the threshold of 10 species per million per year. The current rate of extinction is clearly exceeded.
The only difficulty is with species tracking, said Christian Samper, director of the Smithsonian National Museum of Natural History in Washington. This is especially true for insects and most marine invertebrates.
Samper proposed dividing the extinction rate into threat levels for each species group. Thus, the evolutionary history for the various branches of the tree of life will be taken into account.
Cycles of nitrogen and phosphorus
Nitrogen is the most important element, the content of which determines the number of plants and crops on Earth. Phosphorus nourishes both plants and animals. Limiting the number of these elements can lead to the threat of extinction of species.
Ecologists believe that humanity should not add more than 25% to the nitrogen that comes to land from the atmosphere. But these restrictions turned out to be too arbitrary. William Schlesinger, president of the Millbrook Institute for Ecosystem Research, noted that soil bacteria can alter nitrogen levels, so its cycle should be less human-influenced. Phosphorus is an unstable element, and its reserves can be depleted within 200 years.
While people try to keep to these thresholds, but harmful production tends to accumulate its negative impact, he said.
Many scientists and politicians consider 350 parts per million as a long-term target limit for atmospheric carbon dioxide concentrations. This figure is derived from the assumption that exceeding it would result in a warming of 2 degrees Celsius.
However, this figure has been disputed as this particular level could be dangerous in the future. It is known that 15-20% of CO2 emissions remain in the atmosphere indefinitely. Already in our era, more than 1 trillion tons of CO2 have been emitted and humanity is already halfway to a critical limit, beyond which global warming will get out of control.