Climate change is the direct consequence of global warming. An in-depth look at everything you need to know about the causes and consequences of one of the most serious threats of our time.
The discovery of the phenomenon of global warming dates back to the end of the nineteenth century, when Svante Arrhenius, a Swedish chemist and physicist who received the Nobel Prize for Chemistry in 1903, first set out the theory that carbon dioxide has an influence on the climate, thereby causing climate change.
From that point on, awareness that humanity has an influence on the climate and causes effects of an anthropogenic nature (climate change) grew considerably. In the first half of the twentieth century, many scientists believed — and perhaps hoped — that the oceans would manage to keep CO2 levels in the atmosphere constant by absorbing the greater part of anthropogenic emissions.
In 1957, however, this assumption was called into question by the study of scientists Roger Revelle and Hans Suess, who demonstrated that the oceans, while absorbing excess CO2, do so at a much slower rate than previously expected, and that over the years a rise in average global temperature could occur.
The research was subsequently confirmed during the 1960s and 1970s, when several chemists began to carry out accurate measurements of greenhouse gases from the observatory at the summit of the Hawaiian volcano Mauna Loa, leading them to assert that the concentration of carbon dioxide in the atmosphere was progressively increasing.
In particular, Charles David Keeling of the Scripps Institution of Oceanography in San Diego, California, who died in 2005, succeeded in building a long-term analysis that resulted in a diagram known worldwide as the "Keeling Curve" (see graph above), which tracks month by month, year by year, the concentration of carbon dioxide in the atmosphere. The oscillation of the concentration subsequently led researchers to describe the graph as a representation of the Earth's breathing. The ups and downs are, in fact, comparable to the technique of inhaling and exhaling.
On the basis of this new data, the issue was placed on the agenda at the most important international scientific conferences, where — by the 1980s, with technologies becoming more advanced and precise — it began to be explored in greater depth.
Within a short time it was discovered that it is not only carbon dioxide (CO2, also known as carbon dioxide) that causes global warming, but a group of gases including methane (CH4), nitrous oxide (N2O), ozone (O3) and, indirectly, water vapour (H2O). All of these contribute to what is known as the "greenhouse effect". To these must be added chemically derived gases such as CFCs, or chlorofluorocarbons, which were however regulated by the Montreal Protocol of 1987 because of their responsibility for the thinning of the ozone layer.
Calculations published as early as 1985 showed that all these other gases combined influence global warming to the same degree as CO2, making the issue doubly serious and problematic compared to what had previously been anticipated.
The greenhouse effect, however, is a natural phenomenon that can be described as the ability of the atmosphere surrounding our planet to absorb and retain, within a certain level of equilibrium, the moisture and heat of the sun's rays. The presence of these gases is therefore fundamental to making life on Earth possible. Without greenhouse gases — that is, without the Earth's atmosphere — the average temperature would in fact be around -18 degrees Celsius, whereas the greenhouse effect ensures that the average global temperature is around 14–15 degrees.
The problem of global warming therefore concerns a rise in the average temperature on Earth caused by an excessive concentration of CO2 and other gases present in the atmosphere as a result of emissions that are no longer solely natural in origin but also anthropogenic. The main drivers of a global increase in carbon dioxide are fossil fuels, which are burned without limit by humans to produce energy (responsible for 75.2 per cent of greenhouse gas emissions) used to meet electricity and heating consumption (32.6 per cent) and for the transport sector (14.2 per cent, such as cars and aeroplanes). The increase in methane and nitrous oxide, on the other hand, is mainly attributable to the agricultural sector (responsible for 16.1 per cent).
Deforestation also contributes to the increase of carbon dioxide in the atmosphere: forests, especially tropical ones, are true sinks that absorb and retain CO2, which is why their destruction, as well as preventing regular absorption, releases into the air additional carbon dioxide that was previously "naturally stored". Since the early 1990s, deforestation is estimated to have contributed to a CO2 increase of approximately 15–25 per cent. If one then adds the emissions from agriculture and the deforestation associated with it, this amounts to covering around one fifth (21 per cent) of the total CO2 emitted into the atmosphere in the period 2000–2010 (equivalent to approximately 44 billion tonnes).
The concentration of CO2 in the atmosphere has risen from a value of 280 parts per million (ppm — that is, the ratio between the number of greenhouse gas molecules and the total number of dry air molecules; for example, living in a world at 350 ppm means that in the atmosphere there are 350 greenhouse gas molecules for every 1 million dry air molecules) recorded before the industrial revolution to 400 ppm in 2017. The record so far stands at over 420 ppm, and new records are a regular occurrence. A record that is the product of a level of CO2 emissions into the atmosphere of 41 billion tonnes per year.
Growth has become exponential in recent decades. The Intergovernmental Panel on Climate Change (Ipcc, the United Nations intergovernmental body that studies climate change) typically uses 1750 as the reference year from which to begin studying climate change.
To understand what it means to live in a world at 400 ppm, it suffices to cite the natural range of CO2 over the past 650,000 years, which has always been between 180 and 300 ppm. Methane, meanwhile, has risen from a value of 715 ppb (parts per billion) recorded in 1750 to the current value, which has broken through the 1,880 ppb mark. Nitrous oxide, finally, has risen from 270 ppb to 328 ppb.
All of this has already caused an increase in average global temperature of more than 1 degree, according to the World Meteorological Organization (WMO), compared to the pre-industrial era.
According to forecasts, even if the concentration of all greenhouse gases were kept at year-2000 levels, a further increase of around 0.1 degrees per decade would be inevitable given the slow response of the oceans in terms of absorption. By 2050, the concentration of CO2 in the atmosphere would thus reach double pre-industrial levels (around 550 ppm). The reality, unfortunately, is that current emissions will bring us to the 550 ppm threshold as early as 2035.
To counter the catastrophic development of the phenomenon, it would be at the very least desirable to achieve the minimum objective of not exceeding 450 ppm by 2050, relative to the aforementioned current value of 400 ppm, according to many scientists. This objective would make it possible to keep the increase in average temperature well below 2 degrees, as stipulated by the Paris Agreement on climate, reached in 2015 during the climate conference (Cop 21). It should be noted that the international treaty asks the parties to do everything within their power "to attempt not to exceed 1.5 degrees". To succeed in this endeavour, global emissions would need to peak by the end of the decade and then fall by at least 5 per cent per year, until they decrease by 80 per cent compared to current emission levels by 2050. The greenhouse gas reduction pledges made so far by states realistically point to a temperature increase of more than 3 degrees.
The phenomenon described thus far is producing tangible effects on the Earth's ecosystem and on populations. Here is a list of those we are already experiencing firsthand.
The most visible effects are the melting of the ice — of the cryosphere, that is the part of the Earth's surface covered by water in its solid state, such as the polar ice caps, mountain glaciers and permafrost (a term referring to those areas of the planet where the ground is permanently frozen). According to some forecasts, the Arctic ice could even be subject to complete melting during the warmest periods of the year (such as in late summer) as early as the end of this century. The cryosphere, of course, plays a fundamental role in the global climate system, and a change in its extent can bring about shifts in the system itself. Fragile ecosystems such as those of seas, mountains and wetlands risk being permanently compromised.
A reduction in the Antarctic ice sheet and the Greenland ice sheet has almost certainly contributed to a rise in sea levels of 3.1 millimetres per year between 1993 and 2003, according to the Ipcc. By 2100, the rise is expected to be between 15 and 95 centimetres.
The increase in CO2 in the atmosphere will also lead to ocean acidification, causing irreparable damage to the marine ecosystem — for example, to the Great Barrier Reef, listed among the assets protected by Unesco in 1981 because it is home to "more than 400 types of coral, 1,500 species of fish, 4,000 types of mollusc. It is also considered of enormous scientific interest as it is the habitat of endangered species such as the dugong and the green turtle." A wealth that the consulting firm Deloitte has quantified at 56 billion Australian dollars, the equivalent of around 37.8 billion euros, and which provides employment for 64,000 people.
Desertification (and with it heatwaves) will spread towards regions that currently enjoy a temperate climate, such as the areas to the north and south of the Sahara Desert — including the Mediterranean region (Italy included) — causing serious damage to agriculture. Crop yields will fall and the number of people at risk of malnutrition will rise. In particular, yields of maize and wheat fields could drop by as much as 50 per cent over the next 35 years due to global warming. A risk to be avoided and prevented, especially now that the number of people suffering from hunger worldwide is showing a slight decline. The report State of food insecurity in the world 2015, produced by the International Fund for Agricultural Development (Ifad) and the World food programme (Wfp), calculated that nearly 795 million people still do not have enough to eat today. The figure stood at one billion in the period 1990–1992.
Phenomena such as El Niño — a variation in the southern oscillation that typically occurs every nine years and causes severe climate changes such as hurricanes, storms and floods in Central America, as well as prolonged droughts often linked to devastating wildfires in the western Pacific region — will increase in frequency and intensity, causing casualties and enormous damage costs. All of this could also lead to the spread of diseases, such as malaria, in areas where they were previously unknown.
Not solely because of climate change, but certainly because of human beings, an unstoppable mass extinction — the sixth, to be precise — is under way on Earth. This translates into a significant decline in our planet's biodiversity. The rate of extinction of terrestrial species is vertiginous, and by the end of the century half of all living species risks disappearing forever. This phenomenon will have "serious and far-reaching implications for human well-being," according to John Knox, a human rights expert and professor of international law at Wake Forest University. Knox is also the United Nations Special Rapporteur on human rights and the environment, as well as the author of the first UN report to recognise that biodiversity and healthy ecosystems are essential for human rights. As with desertification, the loss of biodiversity — in particular the disappearance of plants — could slow the fight against disease and increase the spread of infectious and autoimmune conditions.