Environmental problems and their evolution
The electronics industry cleaned its boards with the same compounds that punched a hole in the ozone layer. The Montreal Protocol phased them out, and it is considered the most successful environmental agreement.
01From the smokestack to the planet
Environmental problems have changed scale as human activity has grown. The first ones were local and visible; today’s are global, slow, and unevenly distributed between those who cause them and those who suffer them.
| Scale | Example | Feature |
|---|---|---|
| Local | The London smog of December 1952, which caused thousands of deaths in a few days | Cause and effect in the same place and at the same time |
| Regional | Acid rain in Europe and North America in the 1970s and 1980s | The emissions of one country damage the forests and lakes of another |
| Global | The ozone hole and climate change | Everyone contributes and everyone is affected, with a delay of decades |
In Argentina there are examples at every scale: the pollution of the Matanza–Riachuelo basin, which led to the 2008 ruling of the Supreme Court in the Mendoza case; the loss of native forests in the Chaco, which led to the Forest Law 26,331, and the retreat of the glaciers, protected by Law 26,639. The chemical bases of pollution were covered in chemistry and the environment, in General Chemistry.
02The ozone layer: a global problem half solved
Chlorofluorocarbons (CFCs), used in refrigeration, aerosols and in cleaning electronic boards, release chlorine in the stratosphere and destroy the ozone that filters ultraviolet radiation. In 1985 the measurement of the hole over Antarctica was published, and in 1987 the Montreal Protocol was signed, which progressively phased out their production. It is considered the most successful environmental agreement: scientific assessments foresee the layer recovering by the middle of the century. The electronics industry had to change its cleaning solvents, which is why no-clean fluxes are used today.
03Climate change
Carbon dioxide, methane and other gases absorb the infrared radiation emitted by the Earth. As their concentration increases, the surface has to warm up in order to re-emit as much energy as it receives from the Sun. CO₂ went from about 280 parts per million before industrialization to more than 420 today. Its effect is measured with the radiative forcing, the energy imbalance it produces, and the response of temperature with the climate sensitivity:
The equilibrium warming corresponding to CO₂ alone, for a given concentration and climate sensitivity. The band is the range of 2.5 to 4 °C per doubling; the dot, the chosen concentration.
The warming observed so far, a little more than 1 °C, is different from the equilibrium warming: the oceans take decades to warm up, the aerosols from pollution cool, and other gases such as methane warm. But the logarithmic relationship and the sensitivity are what determine where the system is heading.
04Planetary boundaries
In 2009, a group of scientists led by Johan Rockström proposed nine planetary boundaries: processes of the Earth system with thresholds that, if crossed, can lead to abrupt changes. Besides climate and ozone, they include biodiversity loss, the nitrogen and phosphorus cycles, land and freshwater use, ocean acidification, aerosols and novel entities, such as plastics and synthetic compounds. Waste electrical and electronic equipment, which is covered in the unit on ICT and the environment, falls into this last category because of its metals and flame retardants.
05In the laboratory
Download the CO₂ concentration series from the Mauna Loa observatory, plot it and fit the trend and the annual oscillation. Estimate the growth rate per decade.
Build a CO₂ meter with a non-dispersive infrared sensor and a microcontroller, and record the concentration in a classroom over the course of a class.
Choose an environmental problem of the region and describe its scale, its causes, whom it affects and which rules regulate it.
06Common mistakes
- Confusing the ozone hole with climate change. They are different problems, with different causes and effects.
- Expecting the warming to be proportional to the concentration. The forcing grows with the logarithm.
- Reading the equilibrium warming as the current one. The ocean delays the response by several decades.
- Thinking that a global problem has no local component. Its causes and its damages are local and unequal.
07Self-assessment
What forcing does doubling the preindustrial CO₂ produce?
\( 5.35 \ln 2 \approx 3.7 \) W/m².
With a sensitivity of 3 °C, what equilibrium warming corresponds to 420 ppm?
\( 3 \cdot \ln 1.5/\ln 2 \approx 1.75 \) °C, from CO₂ alone.
Which international agreement phased out CFCs?
The Montreal Protocol, of 1987.
Why is acid rain a regional problem?
Because the emissions travel hundreds of kilometers and damage ecosystems far from the source, often in another country.
08Further reading
- IPCC. Climate Change 2021: The Physical Science Basis. Sixth Assessment Report, Working Group I, Cambridge University Press, 2021. The reference assessment on forcing, sensitivity and scenarios.
- David Archer. Global Warming: Understanding the Forecast. 2nd ed., Wiley, 2012. The physics of the greenhouse effect explained with simple models, for science students.
- Johan Rockström et al. A safe operating space for humanity. Nature, 461, 2009. The article that proposed the planetary boundaries.