Planetary Boundaries

What are they and why are they important?

There are nine planetary boundaries. Just like any boundary, you cannot push past the limit without receiving consequences. Exceeding the limits of Earth's boundaries put us at risk of creating an unhabitable environment, threatening our own existence. All life on Earth relies on the balance of biochemical systems that keep the planet and its ecosystems stable.

Four of the nine planetary boundaries have already been pushed past the "safe zone," that being climate change, biodiversity loss, land system change, and biochemical flows. Society's impact has been most apparent over the past two centuries, with rapid change and exploitation coinciding with modern advancements.

Currently, the Earth is in it's Holocene state, which began after the end of the last ice age. During this time period, the Earth has been at an incredibly stable state. For the majority of this time, dating back 11,700 years, little change has occurred to Earth's climate, allowing for such rich biodiversity. However, the trend of the past two centuries shows an increase in the mean global temperature, threatening 12,000 years of a stable climate. The year 2020 saw the highest temperatures in the Holocene period, potentially the highest temperatures seen in 128,000 years.

It is generally agreed upon that human activity is the largest contributor to climate change and pushing the limits of all nine planetary boundaries that are cues of the Earth's welfare. When we go out and explore the world around us today, we are not seeing an untapped version of nature. We do not see nature's at its best potential and richness and no one alive today has seen what beauty the world held before human activity slowly started destroying the planet that provides for us.

Climate Change

Climate change is not solely dependent on CO2 levels, though CO2 is important to track as it has a large lifespan in the atmosphere and the drastic levels in which humans are emitting them. Prior to the industrial revolution, CO2 levels were at 280 ppm. Today, that number is 414 ppm, and rising. The "safe" level is regarded as 350 ppm, a number we surpassed in May of 1986. Some studies suggest, without changes in policies, CO2 levels will be at 685ppm by 2050, almost twice the amount of the "safe" level.

Already, we have seen the irreversible effects of climate change. Ice sheets melting, resulting in sea levels rising, which on its own has it's implications such as erosion, flooding and soil contamination (from salt), are some of the prominent irreversible effects in motion. Massive loss of our rainforest result in a loss of natural carbon sinks, contributing to rising levels of CO2.

Biosphere Integrity

The term biosphere refers to the parts of the world wear life exist. From deep trenches to sky-high mountains, the atmosphere and everything in between is all apart of Earth's biosphere. Life exist in many forms, most familiar to us are plants and animals, many of which are facing threats of habitat loss and climate change. There have been massive population decreases among birds, mammals and reptiles since 1970, several predicted to go extinct by the end of the century.

Aside from whole species going extinct, there is an effect on individual ecosystems and the biosphere as a whole. In respective ecosystems, each species play a role in maintaining order and stability. Grazing animals fertilize pastures. Birds and insects help pollinate abundance of flora. Predators stabilize population of grazers so fields are not overgrazed. Food webs are reliant on each member of the community, some playing a larger role then others, known as key stone species, whom existence are imperative to the whole community. There are Keystone species who are threatened for extinction.

Genetic biodiversity is integral for Earth's biosphere integrity. It allows for the biosphere to adapt to both sudden and gradual change, so that entire species do not go extinct or the welfare of ecosystems are not under siege. It is unknown what levels of extinctions or biodiversity loss will spiral into irreversible changes that the Earth system cannot cope with.

The leading cause of biodiversity loss is the result of an increased demand and exploitation of food, water and natural resources to sustain modern society's desires and the increasing global population. There is little of the world left untouched by mankind. 23% of Earth's surface (not including Antarctica) and 13% of the ocean is considered "wilderness."

Land-system change

All across the planet, forrest, wetlands, and grasslands alike have been converted to human use, particularly agricultural land. This change in land-use is a leading cause behind deforestation, biodiversity loss, changes in water-flow, and the alteration of the biochemical cycles of carbon, phosphorus and nitrogen, among other integral elements.

Forest, above all else, play a vital role in climate stability. Changes in evapotranspiration, the process of water transferring from the surface to the atmosphere, gives feedback to climate change as tropical forest are subjected to deforestation. Boreal forest, characterized by coniferous forest growing at high-altitudes, likewise play a large role as their distribution affects the energy exchange of their respective region, or the albedo of the land surface. Land surface albedo is the ratio between reflected radiance from Earth's surface to incoming radiance across the solar spectrum.

Freshwater use

A growing global population and human modification to land continues to put pressure on freshwater systems worldwide. Fresh water is becoming increasingly scarce as a consequence of global river flow changes and vapor flows resulting from human interference. These abrupt and intrusive changes in hydraulic systems leave little to no room for freshwater systems to adapt, causing permanent affects.

Biochemical flows- Nitrogen and Phosphorus

The importance of nitrogen and phosphorus lies in the fact that they are essential to plant growth. Biochemical cycles of both these elements have drastically changed as a result of agricultural and industrial practices. Their use as fertilizers has become the primary concern.

Human activities has changed the abundance of nitrogen in the atmosphere as opposed to being consumed by crops. Atmospheric nitrogen has been converted to reactive forms of nitrogen which is then in turn the nitrogen being emitted back into the atmosphere, contaminating rain. This rain pollutes waterways.

Likewise, much of the phosphorus that is used in human activities, such as in fertilizers, does not get consumed by plants and enters waterways and aquatic systems. Due to the abundance of nutrient flows, these waterways can become oxygen-starved with algae blooms responding to the nutrients and bacteria eating off the algae.

Ocean Acidification

The ocean is vast, covering 71% of Earth's surface. It holds many several mysteries and untold stories. It also holds roughly 25% of emitted CO2. When the ocean absorbs excess CO2, carbonic acid is formed and the chemistry of the ocean is altered. The pH level of the surface water decreases, increasing the surface acidity (the lower the pH level, the more acidic a substance is). The result of higher acidity is a decrease in carbonate ions, an essential element several marine species use to form their shells and/or skeleton, species like coral.

Increasing acidity in the ocean makes it more difficult for coral, shellfish and species of plankton to survive, all of which are essential to the stability of their ecosystems. Coral reefs are sensitive to changes in their environment, including heat and pollution that lead to coral bleaching. Between ocean acidification, heat and pollution, the stress of coral reefs are significant enough to destroy entire groves of coral. This not only impacts the survival or coral reefs, but all that depends upon them for their habitats and shelter. An estimated 25% of all marine life live among coral reefs, even though they only account for less than 1% of the ocean. A drastic change in these ecosystems that rely on coral reefs would lead to a significant decrease in fish stocks.

It is important to note that many human impacts on the environment can be considered localized. However, ocean acidification cannot be contained to one particular location. There is no one boundary that collects all excess CO2, leading to global ramifications.

Atmospheric Aerosol Loading

Many people when they hear "aerosol" will think of hair spray or spray paint. But what is "aerosol" in terms of physics and chemistry? In simple terms, aerosol is particle matter suspended as a gas, such as dust or smoke.

How does human activity load aerosol into the atmosphere? Particle matter, sometimes referred to as nanoparticles, reach the atmosphere through pollution and land-system changes that increase the amount of particle matter being produced. Not only dust and smoke, but sulfates, nitrates, sea salt and mineral dust are all groups, among others, that are key in determining aerosol's impact on human and environmental health.

Aerosols impact Earth's climate systems, such as the hydrological cycle that determines cloud formation and atmospheric circulation, from a regional to global scale. At the regional level, the most notable impacts can be seen through monsoon systems in tropical regions. Aerosols also change the amount of solar radiation that is being absorbed or reflected in the atmosphere.

Stratospheric Ozone Depletion

This boundary is fairly simple and one many people are aware of. At the very least, many have heard of the "ozone layer." The ozone layer is responsible for filtering out the ultraviolet (UV) radiation from the sun. The depletion of this layer will decrease its effectiveness in controlling the amount of UV radiation. reaching Earth's surface. UV radiation is harmful to humans as well as biological systems on both the land and in the ocean. Too much exposure to UV radiation can cause skin cancer and the depletion of this vital layer would only increase cases of skin cancer among humans.

Release of Novel Entities and Chemical Pollution

The dominating factor of what defines a novel entity is that it is "new" to the environment in the sense that it has been created or an existing substance has been modified by humans. These novel entities can have adverse affects on public health and the environment.

Typically, these chemicals and entities are toxic and have long lives, exhibiting persistence and the ability to spread on large scale. The release of synthetic chemicals and entities can have unforeseen consequences when the Earth is exposed to the engineered material. Consequences that can have irreversible impacts on organisms, the atmosphere and the environment. Many compounds have been linked to loss of fertility and permanent genetic mutations.

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