Sawing Off the Limb
“From an ecological systems perspective, grossly
disrupting global ecological balances, as we have been doing,
is akin to slowly sawing off the limb on which humanity itself perches.”
At the top of the list of human activities that severely damage ecosystems is agriculture. This should not be surprising as it is the largest interface between humans and the environment. Land conversion for agriculture destroys habitat, increases soil erosion, and accelerates loss of species diversity. About 12 percent of our current land surface is under crop cultivation. Much of this land degrades over time, and we are already exceeding the regenerative capacity of the Earth’s soil resources. Approximately 40 percent of cultivated land is experiencing soil erosion, reduction in fertility, or overgrazing. Soil loss rates exceed soil formation rates by at least tenfold. The conversion of land in the Amazon rainforest for cattle ranching and for feed, for example, could tip the basin into an irreversible transformation to a semi-arid savanna, that in turn triggers unpredictable changes to the global climate system.
Insects are globally dying en masse, risking a catastrophic collapse of Earth’s delicate, interdependent ecosystems that could present a real existential threat to the survival of human civilization. This alarming insect apocalypse is being driven by habitat loss because of intensive agriculture, the heavy use of pesticides, climate change, and invasive species. More than 40 percent of insect species are dwindling globally and a third of species are endangered. The total mass of insects is falling by 2.5 percent annually. If the decline continues at this rate, insects could be wiped off the face of the Earth within a century. The proportion of insects in decline is currently twice as high as that of vertebrates and the insect extinction rate is eight times faster than that of mammals, birds, and reptiles. Insects play a critical role in the proper functioning of Earth’s ecosystems. They are a food source for many animals, critical pollinators, and recyclers of nutrients back into the soil. A world with no insects would likely be a flowerless and less vibrant world, a world of still and silent forests, a world of dung and old leaves and rotting carcasses accumulating in cities and roadsides.
Over the past 10,000 years, the biomass of wild animals has been dramatically decimated, while human and livestock numbers have skyrocketed. In just the last 50 years, animal populations have fallen by 68 percent. The tropical Americas have seen animal populations decline 94 percent in the same period. The size of observed animal communities in or near freshwater globally have fallen by 84 percent. By mass, humans and domesticated livestock now make up 97 percent of all animals on land. Wild mammals and birds (elephants, mice, kangaroos, lions, raccoons, bats, bears, deer, wolves, moose, chickadees, herons, eagles, etc.) have been reduced to a mere 3 percent. The biomass of chickens (livestock) alone is more than double the total mass of all other birds combined. Food production and other human activities are destroying the ecosystems other animals rely upon. Before the advent of agriculture 10,000 years ago, humans made up just a tiny fraction of animal biomass, and domesticated livestock did not exist at all. With this massive loss of mammals, birds, amphibians, reptiles, and fish goes the security of ecosystems that have always supported humanity.
As a result of decades of unsustainable business-as-usual commercial fishing practices, peak fish may have occurred in 1996, as global marine catches have been declining ever since. Since 1950 we've wiped out around 90 percent of the big fish in the ocean — swordfish, marlin, and grouper. What does it say that just one bluefin tuna can bring hundreds of thousands of dollars on the Japanese market. Upwards of a quarter million sharks are killed each day, mostly for just their fins, to bolster the status of the soups they are destined for. Every year, an undersea area twice the size of the continental United States is plowed with trawlers, callously leveling everything on the sea floor.
More than half of all of the fish eaten worldwide is now produced through aquaculture — underwater meat production. Each pound of cage-raised salmon costs fifteen pounds of fish from the ocean. Anchovies, herring, and sardines are the most fished fish in the world, and almost all of the catch is used as fish meal for aquaculture.
Rates of habitat destruction and of species extinction have led to the sixth major extinction event in history — and the first one to be caused by human activity. A majority of the world’s most species-rich habitats — such as tropical forests and coral reefs — have been destroyed or are being significantly impacted. The extinction rate has increased to 100 to 1,000 times that of normal background levels. It is projected to increase another tenfold before the end of this century. Much of the recent extinctions have occurred on the main continents from land-use changes, introduction of invasive species, and climate change. The extinction rate that humans are now causing has not been seen since the Cretaceous–Paleogene extinction event 65 million years ago when an asteroid impact wiped out the dinosaurs. The collective human impact on biodiversity increasingly resembles, in fact, a slow-motion asteroid impact on the planet. Biodiversity is not adequately protected because its value is not included in the market signals that guide the economic decisions of producers and consumers and dictate the overall operation of the economic system.
The current rate of ocean acidification is at least 100 times faster than at any time in the last 20 million years, and surface ocean pH has decreased by about 0.1 units relative to pre-industrial times. The oceans, covering 70 percent of the planet's surface, currently absorb about 25 percent of human-emitted carbon dioxide through dissolution into the seawater and through uptake of carbon by marine organisms. The portion of this carbon dioxide that turns into carbonic acid has the destabilizing side effect of increasing the acidity (reducing the pH) of surface seawater, making it more corrosive and threatening to normal ecosystem functionality. Corals are sensitive to pH levels and warming waters, and stressed reefs are undergoing negative shifts in dynamics, productivity, and species composition. Marine plankton are also vulnerable to pH reductions. As water acidifies, the small phytoplankton at the very base of the planet's food chains struggle to form carbonate for their skeletal parts. This loss of productivity would directly impact the food chain all the way up.
Though we are naturally more aware of the destabilizing climate-change effects of the extra heat in the atmosphere around us resulting from fossil fuel combustion, over 90 percent of the additional heat is, in fact, absorbed by the sea. It has been estimated that, without the massive watery heat sink capacity of the world's oceans, the average air temperature around the globe would already have increased by a staggering 97 degrees Fahrenheit. The deep sea is now warming about nine times faster that it was in the 1960s, '70s, or '80s.
Record-breaking ocean temperatures from a changing climate have damaged more than two-thirds of the Great Barrier Reef — the largest living structure on Earth. The potent combination of warming and acidifying water has resulted in more and more mass coral reef bleaching events around the globe. Though they only take up a very small area in the world's oceans, coral reefs are home to a quarter of all marine species. Already half of the world's coral reefs have been lost over the last thirty years. Ocean scientists, in a 2013 report to the United Nations, expressed their worry that by 2050, virtually all of he world's coral reefs could be dead. And by the end of the century, we will have indeed turned the sea the into a much harsher hot, sour, breathless habitat for the remaining marine life.
More heat in the atmosphere also cranks up the dial on the hydrologic cycle, with rising rates of water storage and circulation in the atmosphere producing drier droughts and wetter floods around the globe. Cyprus and other countries in the eastern Mediterranean, for example, are increasingly vulnerable to drought as the changing climate brings higher temperatures and less precipitation. These conditions invariably lead to mass migrations of climate refugees inevitably followed by social and political instability from clashing populations.
Groundwater aquifer depletion from expanding human populations and from competition for water resources is threatening the long-term economic viability of agricultural regions. Food production is artificially inflated by unsustainable practices of mining for groundwater creating a pernicious and precarious food-bubble economy.
Almost all of the world's rivers have been altered, and about 25 percent of global river flows no longer reach the ocean due to these river-flow diversions. These dramatic reductions of global freshwater supplies affect not only the biodiversity of river systems, but also the food sources, health, and security of local communities, climate regulation, and carbon sequestration. Tipping points may be reached that result in the collapse of regional hydrologic cycles.
Human activities now convert more nitrogen from the atmosphere into reactive forms — mostly to enhance food production via fertilizers — than all of the Earth’s terrestrial processes combined. The majority of it ends up in waterways and coastal zones. The sudden unintended introduction of very high levels of nutrients into formerly lower nutrient systems, eutrophication, like human agricultural runoffs of nitrogen and phosphorus, have caused abrupt shifts in lakes and marine ecosystems where the species of primary producers adapted to the lower nutrient conditions are outcompeted by faster growing species adapted to the anomalous high-nutrient conditions. The suddenness of the shift only affects the primary producers, resulting in a disorganized and out-of-balance collection of species, which in turn trigger plankton blooms and mass fish die-offs.
Toxic chemicals are a form of unnatural, human-made pollution that no existing natural systems have experienced before and that no existing natural systems can benefit from in a positive way. Out of some 80,000 chemicals in commerce, 1,000 are known to be neurotoxic. Different chemicals have different pathways through Earth’s biosphere. Some, such as mercury or DDT, can undergo long-range transport via ocean or atmospheric dynamics. Chronic, low-dose exposure may lead to subtle non-lethal effects that hinder development, disrupt endocrine systems, impede reproduction, or cause mutagenesis. These are usually most visible in top predators and human populations. In fact, toxic chemicals are so pervasive in the natural world that it is difficult to find a sample of ocean water anywhere with no sign of some chemical pollution as polychlorinated-biphenyls (PCBs), other persistent toxic chemicals such as DDT, and heavy metal compounds continue to accumulate throughout the world's widely dispersed marine ecosystems.
Tragically, our woeful management of natural habitats has allowed for the destructive exploitation of land, forest, and water resources for too long with unsustainable levels of harvesting and cultivation. And too little attention has been given to the proper handling and disposal of toxic chemicals. Our efforts to protect Earth's ecosystems have been sadly lacking in scientific rigor and in a deep understanding of, or concern for, complex and dynamic ecological interrelationships.
From an ecological systems perspective, grossly disrupting global ecological balances, as we have been doing, is akin to slowly sawing off the limb on which humanity itself perches.