Top Ten Environmental Concerns of the 21st Century
What are the top ten environmental problems facing the world today?
A recent scientific paper published in Nature attempted to answer this question, with a twist. The Earth has spent roughly the last 12,000 years in a period of unusual climate stability known as the Holocene era. To put this era in perspective, all major human civilizations have existed since the beginning of the Holocene. In fact, humans have only practiced agriculture for roughly the last 10,000 years. This all-important development, which allowed civilizations from the ancient Sumerians to our own to thrive, was made possible by the stable climate of the Holocene
Unfortunately, this stable, pleasant period is currently coming to an end, and there is strong reason to believe that this is not the result of a change in the natural cycles of the Earth, but rather that the change is caused by human activity.
The authors of Planetary Boundaries: Exploring the Safe Operating Space for Humanity,
attempted to identify the most serious environmental threats the human
race currently faces, and identify the potential "tipping points"
beyond which the pleasant Holocene era would disappear and the Earth's natural resources would be seriously depleted.
The ten most serious environmental problems they identified were:
10. The Stratospheric Ozone Layer
The ozone layer filters out the most harmful wavelengths of UVB ultraviolet radiation from the sun before it reaches the earth's surface. A depleted ozone layer would mean increased rates of skin cancer for humans, as well as damage to plants and ecosystems. Ozone depletion received a lot of attention in the 1970s and 80's when scientists discovered a giant and growing "hole" in the ozone layer above Antarctica.
Fortunately, the scientists were able to convince the world community to act quickly to limit the production of ozone depleting substances such as CFCs and halons and the problem of ozone depletion today seems to be on the path to successful resolution, though due to the long lifetime of ozone depleting compounds the Antarctic ozone "hole" is not expected to recover completely until 2050 and the overall levels of ozone in the atmosphere will recover to pre-1980 levels only about 2060-2075.
The goal for the future will be to maintain the progress we have already made on this issue.
9. Land Use Changes
The authors of Planetary Boundaries chose Land Use Changes as one of their top environmental concerns, which I felt was a slightly redundant choice, because changes in land use, for the most part, have the same negative effects as several of their other choices. For example, loss of wildlife habitat leads to loss of biodiversity. Depending on what the habitat is replaced with, the change can also lead to air or water pollution from factories and farm fields, depleted groundwater reserves due to impervious surfaces such as city roads, and carbon emissions from almost any human activity you could name.
Land Use Changes are also particularly difficult to define a "tipping point" for because their effects vary so significantly, so that in fact the exact environmental impact of one land use change is different from the impact of every other land use change ever made.
I feel a less redundant and easier to measure choice might have been soil depletion due to erosion, desertification, and unsound agricultural practices, among other factors.
(Bonus) Learn More About Soil Depletion
8. Atmospheric Aerosol Pollution
Atmospheric aerosols can be either natural or man-made. Unlike greenhouse gases, most aerosols have a net cooling effect on the climate because they reflect sunlight back into space, instead of allowing it to warm the Earth. The famous Year Without a Summer in 1816 was the result of large amounts of natural aerosols being thrown into the atmosphere by the 1815 eruption of Mount Tambora.
Unfortunately, excessive aerosols are nevertheless undesirable because of their damaging effects on human and animal health, among other things. Smog and other forms of air pollution contribute to chronic respiratory illnesses and even deaths for millions of people every year. In fact the World Health Organization estimates that 2.4 million people every year die as a direct result of aerosols and other forms of air pollution. This problem is most severe in industrialized areas and areas that use "slash-and-burn" agriculture methods or wood fires for cooking.
7. Chemical Pollution
Pollution of air, water, and soil by long-lasting chemical compounds is another tipping point that is hard to quantify, in part because many of the chemicals in question simply have not been around long enough for their long-term effects to be clear. These include many compounds suspected of being endocrine disruptors, chemicals that interfere with the natural balance of hormones in the body. Some of these endocrine disrupting chemicals are blamed for a sudden rise in hermaphroditism among aquatic creatures such as fish and frogs. Others are believed to contribute to the rise in breast cancer, prostate cancer, and other hormone-related cancers in humans.
Other pollutants, such as some heavy metals, are already known to be both harmful and persistent.
6. Ocean Acidification
Ocean acidification is a lesser known side effect of excessive CO2 production. About 1/4 of the CO2 produced by human activities every year is dissolved in the oceans, where it reacts to form various compounds, including carbonic acid, that increase the acidity of seawater. Over the last 250 years, surface acidity of the ocean has increased by an estimated 30%. The acidity is expected to increase by 150% by 2100.
The effects of this change are still poorly understood. However, what is known is that increased acidity decreases the amount of carbonate in seawater, an important component of shells for many shellfish and plankton, and skeletons for coral. The effect of more acidic seawater is similar to that of the disease osteoporosis on human bones - the shells and skeletons gradually become softer and weaker. Eventually, the shells and skeletons dissolve completely. Since shellfish and plankton provide food for many other creatures and coral reefs offer one of the richest and most biodiverse ocean habitats, this could result in a disastrous domino effect for ocean ecosystems, leading to the collapse of many fisheries and eventual extinction of thousands of species.
The Water Crisis
5. The Water Cycle
Many experts believe that water depletion will be one of the most pressing issues of the 21st century. Currently, one third of humans have inadequate access to clean, fresh water. By 2025, the number is expected to reach one half to two thirds of the human population, thanks to a combination of many factors, including water pollution, climate change, and water depletion from unsustainable water uses.
Inadequate water resources have led to violent conflict throughout human history, but never on the scale that is likely to affect the 21st century. In addition to human suffering and armed conflicts, unsustainable water use also affects the environment as a whole. For example, irrigation of crops can lead to salinization of soil, ultimately leading to desertification and loss of habitat and biodiversity. Another concern is rising ocean levels. Recent studies have linked groundwater depletion around the world to rising sea levels. Rising sea levels already threaten many island nations and low-lying coastal regions.
The Real Dead Zone
4 and 3. The Phosphorus and Nitrogen Cycles
Although the effect of human activities on the carbon cycle is better known, the effect of human activities on the nitrogen cycle has been even more dramatic.
The human race's use (and abuse) of the nitrogen cycle has been one of the most beneficial for our own species for many years. Every year, humans convert 120 million tons of nitrogen from the atmosphere into reactive forms such as nitrates, mainly in the production of nitrogen-based fertilizer for crops. The widespread introduction of nitrogen fertilizers to the world's farmers was one of the driving forces of the remarkable Green Revolution of the 20th century, which increased crop yields in most regions of the globe by up to ten times.
However, human activities now remove more nitrogen from the atmosphere than all natural processes combined, and much of this nitrogen ends up as a pollutant. A particularly serious problem is nitrate pollution from agricultural runoff in ground and surface water supplies, which can not only poison humans and other living creatures drinking polluted waters, it can also significantly change freshwater and marine ecosystems. The Gulf of Mexico "Dead Zone" is caused by nitrate and phosphate pollution, primarily from agricultural runoff in the American Midwest. The fertilizers cause massive algae blooms, which consume all the oxygen in the water, leaving it too low in oxygen for anything to survive. The size of the Dead Zone varies from year to year, but it generally covers about 6000-7000 square miles and has seriously impacted fisheries in the area, as well as the health of the local ecosystem. Other Dead Zones exist in the Baltic Sea, the Black Sea, Chesapeake Bay, and some parts of the Pacific Ocean, as well as freshwater lakes and rivers around the world.
Phosphate pollution contributes to the problem as well, though to a far lesser degree. Unlike nitrogen, which is extracted from the air, phosphorus is mined.
The authors of the Planetary Boundaries report believe that the nitrogen cycle has already long passed its tipping point and the the human race should strive to reduce its consumption of atmospheric nitrogen to 35 million tons per year to return to sustainable levels.
One way to reduce nitrogen consumption is to increase use of nitrogen-fixing cover crops such as clovers and other legumes, and use of compost and animal manures as fertilizer.
The Sixth Extinction
2. Loss of Biodiversity
Of the three "tipping points" the authors of Planetary Boundaries believe the human race has already passed, the loss of biodiversity is the most dramatic. The Earth is currently in the midst of the greatest mass extinction since the death of the dinosaurs 65 million years ago. As many as half of all plant and animal species that exist today could be extinct by 2100, a rate that is an estimated 1000 times the natural rate of 0.1-1.0 species per million species per year.
This catastrophic loss of biodiversity is already likely to affect the development of life on earth for millions of years to come. Following the largest mass extinction in Earth's history - the Permian-Triassic extinction event that occurred about 251 million years ago - it took 50 million years for land-dwelling species to regain their previous diversity, and more than 100 million years for ocean biodiversity to recover.
The cause or causes of the Permian-Triassic extinction are still unknown, but the cause of the current mass extinction sadly is not. The majority of modern extinctions are directly or indirectly caused by human activity. Habitat destruction, overhunting/overharvesting, competition from invasive alien species, and climate change are a few of the most common causes of extinction.
In addition to an almost unimaginably impoverished world, mass extinction also threatens to lead to the collapse, domino-style, of entire ecosystems, ecosystems that the human race depends on for its own survival. So-called "ecosystem services" are believed to save human societies trillions of dollars every year by performing functions such as the following:
- purification of air and water
- crop pollination
- production of seafood, game, and other wild foods
- pest control
- waste decomposition
- soil creation
- drought and flood mitigation
- and more
Healthy ecosystems perform ecosystem services more effectively than stressed or destroyed ecosystems.
The Science of Climate Change
1. Climate Change
The most controversial of the planetary tipping points named by the Planetary Boundaries Report is climate change. Climatology is a complex science, and there are some who believe that the changes of the past few decades are nothing but natural variations. The overwhelming majority of climate scientists, however, believe that human activities are currently affecting the climate and, like many other scientists, the Planetary Boundaries team believes that the tipping point has already been passed.
In order to maintain the stable Holocene climate humans have enjoyed for the last 12,000 years of our existence, a majority of scientists now believe that atmospheric carbon dioxide levels must remain below 350 parts per million (ppm). (This level is still 75 ppm higher than pre-industrial levels of 275 ppm.) Beyond 350 ppm, we begin to risk catastrophic and effectively irreversible changes, such as the disappearance of the Greenland ice sheet, which is already melting at a rate of 48 cubic miles (200 cubic kilometers) per year. Currently, the atmospheric carbon dioxide level is 390 ppm and climbing by nearly 2 ppm every year.
Reducing atmospheric carbon levels is likely to be one of the most difficult challenges in a century of difficult challenges. It will require a worldwide improvement in energy efficiency and conservation, a massive push to more carbon neutral forms of energy generation, and a revolution in land use practices.
The good news is that climate change is intimately connected with each of the other environmental problems outlined in this article, so by solving climate change we can help to solve other environmental problems, and by solving other environmental problems, we can likewise help reduce the problem of climate change. Pick an issue, study it, and set about creating the change you want to see in the world.