05 | 11 | 2020

The nine planetary boundaries

What are they? Why are they so essential to monitor? 

The last fifty years of Economic Development, have led our planet and its delicate mechanisms close to collapse. Since the Industrial Revolution, human activity has been so intense that scientists have declared the end of the Holocene, the geological era characterized by low factors variability that influences our Planet. It has started a new era, the Anthropocene, where human is the main agent of change in our natural systems. As proof of this, floods, fires, hurricanes, and other extreme weather events are now, sadly, the norm across the globe. 

In 2009, the Swedish scientist Rockström and his team of researchers created a framework called “The 9 planetary boundaries” (Johan Rockström, 2009). These nine limits should not be exceeded unless we would like to cause unexpected and irreversible changes to the proper functioning of the Earth system and human survival. 

Unfortunately, in 2009, climatologists admitted that three of these limits had already been crossed: too much carbon dioxide released into the atmosphere, too much nitrogen taken from the atmosphere, and declining biodiversity. A new study published in the magazine Science (Will Steffen, 2015) mentioned that we have also exceeded the limit of change of land use due to wild deforestation. 

What are the 9 planetary boundaries, and which are the consequences of exceeding each of them? 

Source: Steffen et al. 2015

Climate change 

The Earth’s average temperature has already risen by almost 1°C. It is important to consider that even if we remain within the +2°C threshold, established by the Paris Convention on climate in December 2015, there would be high risks of climate change, harmful for the Environment, and for our society. Paleoclimatic data from the last 65 million years suggest that the reduction of CO2 into the atmosphere was one of the main variables that caused the cooling of our planet in the long term. Meanwhile, we can notice that carbon dioxide concentration equal to 450 ppm has caused in the past the total absence of glaciers. Nowadays, we have exceeded 400 ppm of CO2, while the limit set by scientists to prevent catastrophic effects is 350 ppm. 

Other consequences of exceeding this crucial limit are the melting of glaciers, during warm summers, in the Arctic zone, and in the main mountains chains, the widespread deglaciation of Greenland and West Antarctic ice sheets rising sea level, a four-degree latitude pole-ward shift of subtropical regions, the increased bleaching and mortality in coral reefs, the increasing number of major floods and drought events. 

Chemical pollution 

The chemical pollution, such as radioactive components, heavy metals, toxic substances, plastics, and endocrine disruptors, is mostly generated by human activities. It is estimated that between 80,000 and 100,000 chemicals have been released into the environment by humans. Although there is still the scientific uncertainty of neurotoxicity for many of these substances, is possible to affirm that chemical pollution negatively affects human health. 

In 2001, during the Stockholm Convention on persistent organic pollutants, experts declared that some substances such as PCBs, dioxins, DDT, and other pesticides have already crossed the trigger level. 

However, at present, it is not possible to quantify exactly the planetary boundary for any type of pollutants. 

Ozone level 

The ozone layer in the stratosphere protects us from harmful ultraviolet radiation. There are substances of anthropogenic origin capable of destroying the ozone layer, such as, for instance, chlorofluorocarbons. In 1987, the Montreal Protocol banned most of the substances causing damage to the ozone layer, such as chlorofluorocarbons. 

Although, the concentration of these gases in the atmosphere has stabilized and, in some cases, even decreased, the negative effects on the ozone could continue for several decades to come. 

Atmospheric particulate matter 

Particulate matter and fine dust (aerosols) emissions generated by coal, waste, or petrol combustion may cause negative effects on the climate and on human health.  

PM 2.5 is responsible for approx 3% of deaths worldwide related to cardiopulmonary diseases and approx 5% of deaths related to the trachea, bronchi, and lung cancers.  

This causes 800,000 deaths every year due to reasons directly attributable to the pollution of urban and industrial areas. 

Aerosols may also generate other negative effects such as forest degradation and freshwater fishes loss due to acid rain. The complexity of aerosols in terms of particle variety and emission sources are the main reasons why it is not possible to set a precise boundary for these pollutants. 

Ocean acidification 

The oceans play a fundamental role in regulating the Earth’s climatic equilibrium: they currently absorb 25% of total human emissions thanks to their capacity for carbon dioxide dissolution and the carbon absorption by marine organisms. The increase of carbon dioxide present in the oceans aggravates their acidity with negative consequences for many marine organisms, especially for those that use calcium carbonate to create shells. If the current ocean acidification rate continues at this speed (100 times faster than any era in the last 20 million years), we would face the risk of witnessing the death of the coral reefs that represent 90% of the ocean biodiversity. 

Nitrogen and phosphorus cycles balance 

Human interference in the nitrogen and phosphorus cycle has caused sudden and dangerous changes in the lacustral and marine ecosystems biochemistry. Nowadays, we have already largely exceeded the safety threshold regarding the nitrogen level. Human activity including the industrial processes to transform nitrogen into ammonia, agricultural processes related to leguminous crops, fossil fuels, and biomass combustion convert more molecular nitrogen (N2) than all natural processes combined. The threshold set by scientists within nitrogen should be 35 Mt per year, which is 25% of the current level we have reached. 

Phosphorus, a mineral that unlike nitrogen must be extracted, is an essential fertilizer for modern industrial agriculture. Every year we extract 20 Mt of phosphorus. It is estimated that more than half of it ends up in the oceans causing eutrophication and anoxic phenomena. The planetary boundary for phosphorus has been set 10 times the natural flow. At present, it has reached 8-9 times the natural flow

Freshwater consumption rate 

The global limit for the use of blue water is set at around 4,000 km3. Exceeding this threshold would seriously put in danger the supply of green water and terrestrial ecosystems. Humans currently use approximately 2,600 km3 of rivers and lakes water per year. Although we still have some margins, pressures on water resources are increasing due to the food growing demand to feed the world population. It is estimated that by 2050, the consumption of blue water will increase from 25% to 50%. 

Land use  

Intensive agriculture is the main factor behind the change in land use. Forests yield space to cultivated fields or to pastures. This conversion, with an average annual rate of 0.8% over the last 40-50 years, contributes to climate change (by decreasing the ability of ecosystems to absorb CO2), by increasing nitrogen and phosphorus present in the water, and by reducing Planet’s biodiversity. The boundary where to allocate land for crops and pastures is 15% of the land surface (free from ice). In 2005, about 12% of the planet’s land was cultivated, so scientists still consider the presence of a certain margin for agricultural land expansion up to 400 million hectares. However, it is very likely that this limit will be reached within a few decades. 

Humanity should implement measures to avoid soil fertility loss such as shifting to organic farming, building more efficient irrigation systems such as drop system, changing eating habits like reducing meat and food consumption per capita, and decreasing waste in the food distribution chain.  

Biodiversity loss 

Biodiversity plays an essential role in increasing the resilience of Earth systems. Ecosystems with a low level of diversity are more vulnerable to external impacts and more exposed at risk of a sudden and catastrophic downgrading of structural conditions. We are currently experiencing the sixth major extinction of life on the planet and we should bear in mind that past extinctions have always led to permanent changes in the biotic composition and functioning of the Earth System. Currently, 25% of known species are threatened with extinction. Among the causes, there are changes in land use, climate change, intensive fishing, and chemical pollutant contamination. 

The average extinction rate in the past, estimated thanks to the study of the fossil record, is between 0.1 and 1 species per million per year. Nowadays, the extinction rate stands at 100 species per million per year. Meaning we have already entered the red zone for the biodiversity limit. The extinction rate must urgently be brought back to around 10 species per million. Moreover, efforts must be made to ensure the survival of those species considered essential for the functioning of ecosystems such as corals or some types of algae. 

The crucial aspect to consider is that planetary boundaries are all deeply connected and if one is crossed, the risks of overcoming the others start to rise. 

The recent work on monitoring these boundaries, conducted by Rockström and his researchers, highlights how for the first time in the history of humanity, we are forced to consider the real risk of destabilizing the entire Planet. The new generations do not hesitate to protest asking world leaders to act. Sadly, it is not easy to understand, objectively, and concretely, which are the real issues threatening our planet and its delicate mechanisms. 

This type of scientific framework helps us to have a more precise idea of ​​the problems we are facing, clarifying the current situation and in which areas we need to act urgently. 

Society and science must act towards a single goal: the stabilization of our Planet. We need to drastically reduce global emissions as soon as possible by decarbonizing the energy-intensive sectors. We need to transform agriculture from a source of emissions to a carbon sink and we need to seriously protect our oceans and the natural ecosystems that absorb half of our emissions. 

We can do that! We have the technology, we have the knowledge, and the awareness is growing among the society. This is our only home. Preserving it is our mission to protect the future of our children.

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