The Earth's climate is enormously complex, involving subtle and imperfectly understood relationships between the Sun, atmosphere, oceans, lithosphere (Earth's crust), pedosphere (soils), and terrestrial biosphere (forests, mostly). But over the course of the twentieth century, in particular from the late 1950s onward, knowledge of the Earth's climate advanced very quickly. By the late twentieth century, scientific research had reached near-consensus on the accuracy of a long-advanced and troubling forecast for the Earth's climate. This, of course, was the idea that human activities since the beginning of the Industrial Revolution had altered climate and begun heating the Earth. Variously labeled the “enhanced greenhouse effect,” “global warming,” or “anthropogenic climate change,” the problem centered mostly on human interference in the planet's carbon cycle. (p.63)
They add:
The Earth's atmosphere is the reason the planet is neither freezing cold nor burning hot. In highly simplified terms, almost one-third of solar radiation is instantly reflected back into space. A bit more than two-thirds of the incoming solar radiation that strikes the Earth is absorbed and converted into infrared energy (heat) by the Earth's surface, oceans, or atmosphere, and re-radiated in all directions. Greenhouse gases (GHGs), of which there are several types, absorb most of this infrared (or long-wave) energy. Naturally occurring greenhouse gases include water vapor, methane, carbon dioxide, and nitrous oxide…Very recently, at the onset of the industrial revolution, the naturally occurring concentrations were about 0.7 parts per million (ppm) for methane, 280 ppm for CO2, and 288 parts per billion (ppb) for nitrous oxide. The concentration of every one of these has risen since. (p.64)
The primary reason why a rise in GHG concentrations is so detrimental is because it prevents some of that one-third of solar radiation that would normally be instantly reflected back to space from being able to escape our atmosphere. The solar radiation is essentially trapped by the extra GHGs, which then warms the planet beyond the current “goldy-locks zone” that has enabled the explosion of life we have enjoyed. But, how have humans added to the GHG concentrations? The authors discuss how “human interference in the natural cycling of carbon during the industrial era” has led to excess carbon in the atmosphere. (p.65) They write:
In essence, the climate change problem arises from the fact that humans have removed carbon from the Earth and placed it in the atmosphere at rates much faster than occurs naturally…There are two basic ways humans have added carbon to the atmosphere. First, carbon is released through deforestation, via burnt or decaying wood and from newly exposed, carbon-rich soils… Second, and more importantly, carbon is released through the burning of fossil fuels. Humans have shifted carbon stored in the lithosphere (in the form of coal, oil, and natural gas) to the atmosphere and thereby to the oceans…Carbon dioxide concentrations are now…[above]...400 ppm, compared with the 280 ppm pre-industrial baseline. This concentration is the highest CO2 level reached in the last several hundred thousand years and possibly the last twenty million years. (p.65-67)
These concentrations have already led to higher global average temperatures, warmer and more acidic oceans, melting of glaciers, and higher levels of evaporation and moisture in the air. These primary effects then lead to secondary effects, such as sea level rise due to thermal expansion of the oceans and glacial melt, increased likelihood of hurricanes and cyclones over warmer oceans, and both extreme droughts leading to wildfires and more rainfall and snow due to higher levels of evaporation and more moisture in the air. Additionally, areas such as oceans and forests that historically acted as ‘carbon sinks’ by pulling excess CO2 out of the air and storing it are now unable to continue to provide this vital service. This can happen for one of two reasons, either because they are at or over their storage capacity (oceans) or because human actions or wildfires are destroying them and causing them to release the carbon dioxide they once stored (forests).
The authors next discuss the history of climate science. They explained that:
[Due to]...the complexity of Earth's climate,...[s]cientific understanding has required a high degree of interdisciplinary cooperation involving geophysicists, oceanographers, meteorologists, biologists, physicists, geologists, mathematicians, and specialists from a host of other disciplines. [And,] as a global phenomenon, climate change has provoked scientific collaboration across international boundaries. The history of climate science thus has been marked by both of these forms of cooperation. (p.72)
Throughout history, the science behind the Earth's climate was discovered in a piecemeal fashion. In the 1820s, the philosopher Jean-Baptiste Joseph Fourier “...argued that the atmosphere traps a portion of incoming solar radiation, thereby raising its temperature far above what would otherwise be the case.” (p.72) He was the first to compare the effects of the atmosphere to that of a greenhouse. Then, in the 1850s, the physicist John Tyndall “...discovered the infrared absorptive capacity of CO2.” (p.73) In the late 1800s, “...the Swedish scientist Svante Arrhenius…outlined the basic relationship between CO2 and climate…[and]...calculated the global temperature changes that might result if levels of the gas were to increase or decrease. (p.73) Between World War I and II, “...Serbian mathematician Milutin Milankovic refined the theory that the Earth's oscillations and solar orbit were responsible for the ice ages.” (p.73) The authors add:
At about the same time in the Soviet Union, the geochemist Vladimir Vernadsky was working on the natural carbon cycle. He argued that living organisms in the biosphere were responsible for the chemical content of the atmosphere, adding much of its nitrogen, oxygen, and CO2. Hence, plants and other living organisms were foundational to the Earth's climatic history. (p.73)
However, one of the most interesting aspects of the history of climate science is how technology initially introduced during the Cold War was able to catapult scientists’ understanding of the global climate. The authors explain:
In the 1950s a group of scientists at Scripps Institution of Oceanography, near San Diego, funneled small amounts of defense-related funding toward their studies of CO2 in the atmosphere and oceans. two of them, Charles Keeling and Roger Revelle, created the first reliable atmospheric carbon dioxide monitoring station. They placed newly developed, sophisticated equipment atop Hawaii's Mauna Loa volcano, chosen because the air circulating about the remote location was not contaminated by emissions from local power plants or factories…The Mauna Loa time series has produced data continuously since 1958; in the process, its sawtooth upward curve has become one of the most widely known visuals of anthropogenic climate change. The sawtooth pattern represents the seasonal changes in CO2 in the Northern Hemisphere: in the summer months when the leaves are out, more carbon is in the trees and bushes and less in the atmosphere. in the winter the atmosphere has a little more CO2.
Additional technological advancements of the Cold War that have been used to further climate science are satellites and computers that were used to help develop global climate models and polar explorations that produced ice core samples allowing scientists to see what historic levels of CO2 were in the trapped air bubbles. All of these new technological advancements and the scientific findings that resulted from them led, in the 1960s, to many prominent scientists addressing the issue of anthropogenic climate change.
However, beginning in the 1980s, the issue of anthropogenic climate change became politicized, and the same countries whose scientists were able to collaborate in order to identify the problem now found themselves at odd odds when discussing how to address it. Though the United Nations was able to create the Intergovernmental Panel on Climate Change (IPCC), and that panel was able to ascertain, with ever-increasing certainty, that climate change was a serious global problem caused by human actions, the individual countries of the world could not seem to come to any real agreement on how to solve the problem. The authors explain:
The two largest polluters, the United States and China, resisted binding agreements on emissions. in general, both China and the United States took self-serving positions in climate diplomacy, content to let the perfect become the enemy of the good…
A sizable chunk of the American public did not accept the consensus of climate change science, and interested Industries both encouraged that skepticism and lobbied Congress to prevent emissions agreements…Nonetheless, the US diplomatic position emphasized the need for the largest developing countries, in particular China, India, and Brazil – all of which had much lower per capita emissions [than the United States] – to be party to any mandatory greenhouse gas emission cuts framework.
China, on the other hand, argued that the industrialized countries should make commitments first, on the grounds that their cumulative emissions over the centuries were highest and that they had already benefited economically from heavy use of fossil fuels in ways that China had not…
[Additionally,] India lobbied hard for the transfer of mitigation technologies and expertise from the rich to the poor world, and for a sliver (0.7 percent) of the rich-world GDP to help poorer countries limit their emissions. (p.78-79)
The countries of the European Union and many island nations were the most receptive to proposals to cut emissions. However, though the US and China announced a “joint promise to reduce carbon emissions,” and many countries have reduced their emissions voluntarily over time, there is still no binding agreement with repercussions for failure to comply between the nations of the world and current cuts will not be enough to limit the harshest effects of climate change. (p.81)
Next, the authors discuss how biological diversity has suffered in the Anthropocene. The authors explain:
Scientific, philosophical, and occasional public concern about certain vanishing species can be traced back centuries, but until recently few people worried that humankind was capable of systematically decreasing the Earth's living heritage. This began to change only in the postwar era, when a small number of scientists started to ponder cumulative human impacts on the world's biomes…The terms biological diversity and the shorthand biodiversity were largely unknown within the scientific community until the 1970s and 1980s. But the scientific and popular use of both exploded during the 1980s, especially after a 1986 conference on the topic organized in Washington, DC, by the eminent biologist E.O. Wilson. The conference proceedings, published as a book under the apt title Biodiversity, sounded an alarm. (p.82,84)
Though biodiversity loss is of grave concern, there remains difficulties with both defining biodiversity and measuring the losses with any accuracy. For example: “Did biodiversity mean,...genetic diversity, species diversity, or ‘population’ diversity (meaning geographically distinct populations of animals or plants within a species)?” (p.84) The authors go on to explain that, though there still remains some debate, most “...scientists [now] acknowledge that species diversity is a simple, readily understandable measure that has powerful popular resonance. Even if flawed, so the argument goes, species extinction is still the most tangible way to measure global biotic decline.” (p.84) However, the primary issue may be measuring biodiversity loss accurately. This is due to the fact that scientists have not been able to identify or count the number of species currently on the planet. Inability to accurately account for the total number of species on the planet greatly affects our ability to objectively determine how many species are going extinct in any given timeframe. Many species may be going extinct before we even know they exist. The authors continue:
Estimates very widely, ranging from a few million to one hundred million species are more…[Yet,] fewer than two million species have been identified and “described” by scientists, and only a small percentage of these have been thoroughly assessed…
[However,] there is…agreement about where most life forms are located. Tropical forests in South America, Africa, and Southeast Asia contain the bulk of the world’s species. Just 10 percent of the Earth's terrestrial surface is thought to hold between one-half and two-thirds of its species…[Additionally,] terrestrial species form only a portion of the world's biodiversity. The rest exists in the world's oceans and seas and, to a lesser extent, in its freshwater. Some scientists have estimated that perhaps 15 percent of the world’s species live in the oceans, but this is admittedly guesswork…As with tropical rainforests, some aquatic ecosystems are incredibly rich in species. The continental shelves, coral reef systems, and those parts of the oceans exposed to nutrient-rich currents (such as Newfoundland’s Grand Banks) possess enormous species abundance and/or diversity…Otherwise, much of the ocean is relatively barren, akin to the world's land deserts. (p.84-86)
Recently, the primary concern has been on human activities causing the ‘sixth mass extinction’. The authors write: “Scientific worry about mass extinctions emerged coincidentally with heightened concern about tropical deforestation and its effects during the 1970s and 1980s…Again E. O. Wilson was one biologist at the forefront in mainstreaming the idea, calculating in 1986 that extinctions in the world's rainforests were one thousand to ten thousand times greater than normal due to human activities.” (p.86-87) Though other scientists have reached different conclusions about the current extinction rates, “[a]ll…Concede that current rates are many times higher than background [rates].” (p.87) Data suggests that: “The background level of extinction known from the fossil record is about one species per million species per year, or between 10 and 100 species per year (counting all organisms such as insects, bacteria, and fungi, not just the large vertebrates we are most familiar with). In contrast, estimates based on the rate at which the area of tropical forests is being reduced, and their large numbers of specialized species, are that we may now be losing 27,000 species per year to extinction from those habitats alone.” (pbs.org) These changes, according to scientists, are occurring as a result of “...increased human interference in the planet's ecosystems.” (p.87)
The authors conclude this section by discussing the human activities that have led to biodiversity loss and conservation efforts. First, they examine changes in terrestrial biodiversity. They explain that on land the primary cause of biodiversity loss was habitat destruction as a result of land-use changes. Land-use changes are best described as the various ways that humans alter the land to provide for our wants and needs, examples include clearing forests for agriculture and livestock and mountain-top removal for mining, to name just a couple. The authors write:
This was the greatest threat to terrestrial species, because heterogeneous landscapes containing great plant and animal diversity were replaced by highly simplified ones managed by human beings for their own purposes…Replacing native habitat with other land uses systematically reduced the spaces for wildlife. Cropland and pastures, for instance, host only a fraction of the birds counted in the world's remaining intact grasslands and forests…
After land-use changes, the next biggest threat to biodiversity came from exploitation due to hunting, harvesting, and poaching for subsistence or trade. In addition, invasive species were a major problem for biodiversity…Finally, by the end of the century some scientists reported instances of species beginning to suffer from the adverse consequences of climate change. (p.88-89)
Next, the authors address changes in aquatic biodiversity. They write:
After World War II humans accelerated their campaign of taming the world's rivers, to the point where few big ones anywhere were left in their original states. Engineers built tens of thousands of dams, reservoirs, levees, and dikes…Engineers dredged streambeds and river bottoms and rerouted entire rivers, changing water flow patterns and temperature levels. Pollutants from cities and industry added chemicals of many different types and toxicities. Agricultural runoff increased the load of organic nutrients in streams and rivers. This led to the eutrophication of downstream water bodies and the creation of oxygen-deprived “dead zones”...Increased siltation from mining, agriculture, and deforestation also reshaped stream, river, bay, and estuarine habitats…Marshes and wetlands were converted into other types of uses, filled in to make land for agriculture or cities. (p.91-92)
Additionally, invasive species, often transported by humans from one locale to another, were very disruptive to both freshwater and estuary systems.
Human impacts on the world’s oceans also resulted in biodiversity loss. Improved technologies after World War II allowed the fishing industry to wreak havoc on the fish populations. The authors explain:
Humans began interfering in the ecology of the deep ocean, which until then had felt little or no human presence of any kind. Commercial fishing was by far the most important activity. Humans had fished the oceans and seas for millennia, but the postwar era saw unprecedented increases in the scale, location, and impact of oceanic fishing. Global demand for fish increased rapidly along with rising wealth and growing world population. Supply increased in large part because postwar technologies allowed fishers to catch ever-larger quantities of fish in ever-deeper waters…Sonar, for instance, had been refined during World War II to track and hunt submarines, but after the war it was also used to locate schools of fish…Moreover, states subsidized the construction of oceangoing vessels that were capable of not only catching greater amounts of deep water fish but also processing and freezing the fish on board. These “factory” ships could stay at sea for long stretches, giving their prey no rest…
Deepwater fishing, made ever more efficient by the new methods, severely reduced the number of top predators such as bluefin tuna. Pelagic net fishing took huge numbers of unwanted and unlucky species, euphemistically termed the “bycatch,” including seabirds, dolphins, turtles, and sharks. Trawling reached increasingly deeper areas of the seafloor, scouring and removing everything. These benthic environments contained rich marine life that was hauled to the surface, the unmarketable portion of which would be thrown overboard. By the 1980s and 1990s, the world's major fisheries were showing signs of stress, with most going into decline and a few and to collapse. (p.93-95)
Aside from the deep sea environments, humans also caused biodiversity loss around coral reefs as we fished them for both food and exotic fish trade. And, the authors also mention our affects on whale populations during the late nineteenth century’s whaling industry.
The realization of global biodiversity loss has also led to major conservation efforts. The period after World War II also saw a rise in environmental awareness and activism. The authors write:
Wildlife-themed television programming became popular in North America and Europe from the 1950s. New conservation organizations emerged, such as the World Wildlife Fund…Within another decade the mass environmental movement had succeeded in placing species conservation on the popular agenda in some parts of the world. In 1973 the United States passed the landmark Endangered Species Act (ESA)…During the 1970s organizations such as Greenpeace spearheaded global campaigns to ban whaling, leading to the global moratorium in 1986…
Major international agreements and initiatives focused on biodiversity conservation, beginning when UNESCO hosted a 1968 biosphere conference…Since the 1970s, biodiversity concerns have increasingly garnered political attention, both domestically and internationally.
Nature reserves and national parks were the most common conservation tools…
[And,] toward the end of the twentieth century the reserve idea was also applied to the oceans. (p.98-99)
Though these efforts are not enough to reverse the sixth mass extinction yet, they are enough to provide hope that we can make a positive change.
In the next section, we will discuss “Cities and the Economy.”
