Planetary Boundaries is a central concept in the framework of Earth System science that defines the danger of irreversible and rapid environmental changes that cannot be reversed after human activities have crossed a certain critical point. Here, in light of the low awareness of the crisis, the aim is to raise awareness about the sustainable future of the planet. Planetary Boundaries is a concept developed by Rockstrom and others at the Stockholm Resilience Center. At present, the pressure that humans are exerting on the earth's system has reached saturation, and irreversible changes can occur if the natural resilience of the climate, water environment, ecosystem, etc., exceeds the limits. It is important to know where these limits ("critical points") lie so that humankind can avoid passing them (the planetary boundary) and prevent catastrophic changes.

There are nine planetary systems that represent the Earth's environmental capacity chemically.
 

1. Climate change (Global warming)
2. Ocean acidification
3. Destruction of stratospheric ozone
4. Circulation of nitrogen and phosphorus
5. Global freshwater use
6. Land use change
7. Biodiversity loss
8. Atmospheric aerosol load
9. Pollution by chemical substances

In this article we will clarify the current problems with these nine items and recommendations for the future so as not to exceed their boundaries ("critical points").

1. Climate change (Global warming)

Global warming means that if there is too much greenhouse gases (carbon dioxide, methane, and chlorofluorocarbons) in the atmosphere, and too much heat on the earth's surface trying to escape to space, the temperature will rise and the global climate will change, as it is now. Since the Industrial Revolution in the 18th century, burning fossil fuels such as coal and oil for energy has resulted in a rapid increase in atmospheric carbon dioxide. This is the main cause of global warming. The concept of a "critical point" where the entire planet cannot be reversed was introduced 20 years ago by the IPCC (Intergovernmental Panel on Climate Change). In the past, it was thought that the climate exceeded the "critical point" when a warming of 5°C or more occurred. However, the IPCC warned in a 2018 report that it could occur with just a 1-2°C warming increase. Global measures have been taken, such as the Paris Agreement with countries pledging to reduce greenhouse gas emissions. The solution is to reduce carbon emissions to zero and reduce global warming to around 1.5°C.

2.Ocean acidification

Ocean acidification is the reduction of pH in seawater caused by the increased concentration of carbon dioxide in the atmosphere that dissolves into the ocean. Ocean acidification is an "other carbon dioxide problem" and needs to be addressed and minimized on a global scale. Some studies have shown that marine ecosystems will be at significant risk and that by 2040 suitable areas for reef-building corals will disappear from around Japan. As a countermeasure, it is necessary to create a low-carbon society with reduced fossil fuel consumption, that is, the same countermeasures as global warming countermeasures.

3. Depletion of stratospheric ozone

The ozone layer that surrounds the earth absorbs most of the harmful ultraviolet rays contained in sunlight and protects living things. CFC (chlorofluorocarbon) is a typical fluorocarbon widely used in refrigerants, cleaning agents, foaming agents and the like. Once these chlorofluorocarbons are released into the environment and reach the stratosphere they are exposed to intense UV light that causes them to release chlorine which destroys the ozone layer. As a result, the amount of harmful ultraviolet rays that reach the surface of Earth increases, which may cause an increase of skin cancer and have adverse effects on ecosystems. On a global scale, the ozone layer continues to decline over the long term and globally, except in the tropical zone. The depletion of ozone is most prominent over Antarctica. As an international initiative, efforts are being made to reduce the production of specific CFCs and halons, to set schedules, and to reduce the use of restricted substances, so that the ozone layer will not be further depleted.

4. Circulation of nitrogen and phosphorus
 
It is possible to use biofuels to build a low-carbon society (centered on measures against global warming gas), but an increase in the production of fuel plants requires nitrogen and phosphoric acid as chemical fertilizers. Organic compounds of nitrogen and phosphorus, also found in garbage, sewage, sludge, and livestock manure, that are released into water can cause eutrophication of sea areas, lakes and marshes. Excessive accumulation in ecosystems causes a risk of seriously affecting diversity. One measure is to promote organic agriculture.

5. Global Freshwater Use
 
97.5% of the earth's water is seawater and 2.5% is freshwater, of which only 0.01% is readily available for use. The current state of the world water problem is:
 

1. Drinking water: 1.2 billion people worldwide do not have access to safe water.
2. Sanitation: 2.4 billion people do not have access to adequate sanitation.
3. Illness and death: About 2 million children die from water-borne illnesses each year.
 

On these three points efforts are being made on a global scale to treat seawater with a membrane, desalinate it, and use it for drinking water, industrial water, and agricultural water.

6. Land use change

Changes in forest carbon dioxide emissions and absorption, changes in land cover, heat and water cycles, and changes in land use could have an impact on future climate. In order to consider future temperature changes, establishment of a global impact assessment is expected as a countermeasure. We can asses assess the impact of global land use with these 4 steps:
 

1. Spatial refinement of socio-economic scenarios: Promote patterns of changes in the geographical distribution of population and GDP with urban growth.
2. Develop global land use scenarios: Promote patterns of land use change such as farmland and pastures with forests.
3. Evaluate carbon balance due to land use change: Promote carbon dioxide absorption patterns associated with ecosystem models that result in the regeneration of deforestation.
4. Climate Impact Assessment by Land Use Change: Evaluate the impact of each land use scenario on land surface temperature using an integrated earth system model.

7. Biodiversity loss
 
One-fourth of amphibians, coral and plant life are at stake as loss of organisms has resulted in:
1. The extinction of species.
2. A decrease in the average vertebrate population between 1970 and 2006 by about a third.
3. The size and continuity of natural habitats such as freshwater wetlands, seawater areas, salt marshes, coral reefs, seagrass beds, etc. decreasing.
4. The fragmentation and degradation of ecosystems, such as forests and rivers, leading to loss of biodiversity and ecosystem services.
The three "critical points" of biodiversity loss:
 

1. Amazon forests transition to savanna-like vegetation as a result of deforestation, forest fires and climate change.
2. Pollution from agricultural fertilizers and sewage causes eutrophication of inland waters such as lakes and marshes.
3. In addition to seawater acidification, bleaching, eutrophication and overfishing will cause catastrophic losses in the functioning of coral reef ecosystems.
Beyond this "critical point", the risk of dramatic loss of biodiversity and degradation of ecosystem services increases. Species extinction, habitat loss, and changes in species distribution and abundance are expected to occur much more rapidly than what has occurred in history over the 21st century. Effective action at international, national and local levels is needed.

8. Atmospheric aerosol load
 
Fine particles released or generated in the atmosphere as a result of burning fossil fuels are called atmospheric aerosols. Although these aerosols have a cooling effect on Earth's temperature, the greenhouse effect of greenhouse gases overtakes that of the aerosols. These aerosols find their way deep in human lungs causing various health hazards. Additionally, they also cause acid rain and adversely affect ecosystems such as forests and lakes. Finally, air pollution is also severe. As a countermeasure, there is an urgent need to curb the consumption of fossil fuels, which are the source of these aerosols.

9. Pollution by chemical substances

Environmental pollution due to chemical substances has a serious impact on people and the environment in developing countries, especially in the area of ​​widespread chemical pollution through environmental media, international trade and logistics. Global measures include:
 

1. Evaluation of exposure to chemical substances 8n the environment and the development of technologies to render them safe.
2. Basing purchases on products and services with low generation of chemical substances and waste offered by socially conscious companies.
3. Establishment of social principles that advocate for a comprehensive framework of risk management of wastes and chemicals.
4. International efforts on transboundary pollution can be cited.

Now that you've read about the above nine issues and their countermeasures, I hope that this will give you an awareness of the limits of humanity's survival (planetary boundary). In the future, we must strive to possess the appropriate knowledge of these planetary boundaries so that we can live on this earth for a long time to come.