The 20th century: The great Acceleration and environmental globalization

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Earth
Earth from space.
Image courtesy NASA

The space age created an environmental revolution during the 1960s. NASA’s Apollo missions and their view of the small blue Earth floating in space is the first global image of the environment that is home to all humans and living things known to humanity. It reminds us of how fragile and unique the Earth’s systems are and it forces us all to imagine ourselves globally. The image also a testament that humanity has become a global dominant species with global environmental impacts such as global warming and ozone depletion.

The most remarkable development of the 20th century was the "Great Acceleration", the sharp increase in human population, economic activity, resource use, transport, communication and scientific, in particular since World War II and which has continued into the 21st century. The “engine” of the Great Acceleration is an interlinked system consisting of population increase, rising consumption, abundant cheap energy, and liberalised political economies.

j-curve
J-curves: increase of poplation, gdp, resource use, etc. since 1750.
source: Photobucket

With the Great Acceleration came also a globalization of environmental problems. Embedded in the idea of the Great Acceleration is the J-curve, statistical graphs that turn progressively upwards. Whether it is population, economies, extinctions or numbers of cars, the story is all about growth. But this growth has its limits and beyond certain thresholds starts to impact on the global environmental systems, which are most visible as global warming and ozone depletion.

 

Acid Rain

Acid Rain affected forest
Acid rain affected forest in the Jizera Mountains,
Czech Republic. Source: Wikimedia Commons

Acid rain or deposition can damage terrestrial and aquatic ecosystems, attack vegetation and disrupt food webs. It can also cause severe damage to buildings and stonework. The problem of acid rain in urban and industrial areas probably started during the first stages of the industrial Revolution in the 18th century. But the real impact and scale of acid rain became only visible during the second half of the 20th century. Acidification of the environment is caused by emissions of sulfur dioxide and nitrogen oxides from power and chemical plants and traffic. Since the introduction of tall chimneys the problem intensified in rural areas because the tall chimneys allow the wind to transport pollutants over long distances. Around 1980 scientists became alarmed by the state of the European forests. These were affected by acid rain, which damaged foliage and could even kill trees. In 1984 it was reported that almost half of the trees in the famous Black Forest in Germany had been severely damaged by acid rain. The impact of acid deposition was even worse in the communist countries of Eastern Europe where air pollution was much less regulated than in the west. In 1988, as part of the United Nations-sponsored Long Range Transboundary Air Pollution Agreement, 25 industrial nations agreed to limit nitrogen oxide emissions to 1987 levels. Legislation that sets targets has now been introduced to lower nitrogen emissions. The UK has reduced its nitrogen oxides emissions by 30 percent compared to 1980 levels and mast cars are now fitted with catalytic converters to combat these emission

A hole in the ozone Layer

The story of the hole in the ozone layer started in 1928. It was then that Thomas Midgley invented CFC (Chloroflourocarbon), a gas that was perfectly suited to refrigerating and for use in spray cans. Midgley is an interesting individual and historian John McNeill has remarked that Midgley “had more impact on the atmosphere than any other single organism in earth history.” Not only did he invent CFCs but also discovered that adding lead to fuel makes engines run better. One could argue that Midgley's inventions symbolize how humankind, by developing technology, is supposedly killing itself. However this view is too simplistic since it was thought initially that CFCs were harmless. In addition, the gas is highly stable: it does not react with any other gas or substance. This remarkable chemical stability made people confident that there would be few, if any, environmental side effects, so the chemical was embraced by industry.

Ozone hole
Stratospheric ozone thinning, 1981-1999.
Image courtesy NASA

In 1974, Sherwood Rowland and Mario Molina discovered that CFCs are agents that can destroy stratospheric ozone under the influence of ultraviolet light. By 1977 it was almost certain that these gases, which were used on a large scale in spray cans and refrigerator systems, was almost certainly damaging the ozone layer, which protects us from harmful UV-B radiation. However, governments, pressurised by the chemical industry, refused to act since the mechanisms by which ozone was destroyed were by then not fully understood. It was argued that more data and research was needed to warrant action.

By the mid-1980s a severe seasonal thinning of ozone over the Antarctic was observed and by 1987 the world’s media were reporting on a ‘Hole in the Ozone Layer’. It was during that year that the Montreal Protocol established a scheme that led to a total global ban of the production of CFCs by the late 1990s. In 2003, observed levels of chlorine in the atmosphere peaked and then began to fall. However, they will remain high for decades to come and it is expected that atmospheric concentrations of ozone will not return to natural levels before the middle of the century.

Greenhouse gasses

Another major by-product of industrial activity, transport and agriculture in the increased emission of carbon dioxide (CO2) and methane, the two most important of the so called “greenhouse gases”. The earth’s atmosphere acts like a blanket. Once the sun’s energy heats up the earth, the heat is radiated back into space but the atmosphere traps part of this heat so the earth is warmer than it would be if it had no atmosphere. This is essential for life and without greenhouse gases the earth would be permanently frozen. However a rise in the concentration of the greenhouse gases caused by industrial processes has meant that more heat than usual is being trapped, leading to a slight but significant rise in the earth’s average temperature.

Industrialisation and population growth has led to an annual increase of 5 billion tonnes of CO2. Methane from land fill sites and agriculture is increasing at a rate of over 1% per year. Plant life cannot absorb this rapid increase of greenhouse gases so the overall concentration of CO2 is rising, and the temperature with it. The release of greenhouse gases is now recognised as a hazard for the planet. International legislation is trying to decrease the levels of pollution but the industrialised countries, although reducing their levels of pollution, still contribute most to the problem.

Keeling Curve
The graph shown at the right shows the history of atmospheric carbon dioxide concentrations as directly measured at Mauna Loa, Hawaii, between 1958 and 2007. This curve is known as the Keeling Curve, and is an essential piece of evidence of the man-made increases in greenhouse gases that are believed to be the cause of global warming. The Mauna Loa observations are the longest record of carbon dioxide increase available and confirm that human activity is increasing the amount of this gas in the atmosphere.  The annual fluctuations in the graph are caused by seasonal variations in carbon dioxide uptake by vegetation. Since more forest is concentrated in the Northern Hemisphere, more carbon dioxide is removed from the atmosphere during Northern Hemisphere summer than Southern Hemisphere summer. This annual cycle is shown in the inset figure by taking the average concentration for each month across all measured years. The black line shows the average monthly concentrations of CO2.