Global Climate Change
Magnification of Greenhouse Effect
The greenhouse effect is a very important property of the Earth’s atmosphere, making a substantial contribution to the relatively high temperature of Earth’s surface. The effect consists in the optical component of solar radiation – the visible light, richest in energy – penetrating the planetary atmosphere with but little modification all the way to the surface, where it is absorbed and transformed to heat, which the ground then emits back. It warms up the atmosphere, while part of the thermal radiation is directed from the warmed atmosphere back towards Earth’s surface. This is why the temperature near the ground is much higher than up in the atmosphere. The so-called greenhouse gases are responsible for the absorption of the thermal radiation from Earth’s surface in the atmosphere. They include primarily water vapour, alongside many gases such as carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O). The natural occurrence of these substances means that the temperature differences between night and day or summer and winter are not drastic, enabling life to survive and evolve on Earth.
However, humans have been increasing the concentrations of these gases substantially with their activities, contributing to the gradual warming of the atmosphere and, consequently, Earth’s surface. Carbon dioxide is the most important greenhouse gas beside water vapour, responsible for approximately 35% of the total natural greenhouse effect in the atmosphere. Its concentration in the atmosphere has been rising steadily over the last 200-300 years, though. Combustion of fossil fuels is the single biggest source of its growing concentrations. The other greenhouse gases are much less abundant in the atmosphere, but their concentrations are rising faster than the CO2 concentrations, so that methane in particular may become a pollutant of equal importance to carbon dioxide.
Globally, the CO2 and other greenhouse gas emissions are set to grow for the two or three coming decades at least. The expected warming, although it may not seem dramatic (tenths of degrees to degrees Centigrade), may have very severe implications for the planet’s entire biosphere and thus for many human activities. It is not the warming alone that is the problem: it is the general climate change – a change in the entire climatic regime, which is a very finely balanced system consisting of two large subsystems (the atmosphere and the oceans) and many minor subsystems (e.g., clouds, precipitation, and biosphere). Among other things, climate change may influence the directions and speeds of ocean currents and monsoons, which would entail catastrophic consequences for humans. It will be accompanied almost certainly with extreme events, such as periods of heat and frost, strong winds, rains and droughts. The effect on precipitation will be particularly noticeable: it may decrease or increase significantly in various regions. As a result of global warming, river flow rates may be altered substantially.
The rising sea level many be one of the side effects. Predictions are uncertain as yet in this respect, but it cannot be ruled out that the sea level may rise by up to several decimetres, even metres in a distant future. In fact, the warming will inevitably cause ocean waters to swell due to its increased temperature and thermal expansivity. Huge amounts of water from melted glaciers will contribute to the sea level rising, especially if the giant ice masses of Greenland and Antarctica melt: both the Antarctic and Arctic glaciers are shrinking. The rising sea level is a threat mainly to coastal countries, particularly those with densely populated coastal plains. The adverse consequences of the sea level rising may have severe negative manifestations in the form of more frequent extreme weather events, including stormy winds causing blustery surf, typhoons precipitating breaker waves and other phenomena. Floods caused by these events are highly destructive, as proven for example in the Caribbean region in 2005.
The economic activities likely to suffer include agriculture, which is very sensitively adapted to the current climatic conditions, and any change, however small, will necessitate swift adaptation, which will not be easy. The higher frequency of natural disasters will affect all economic activity, particularly transportation and construction. Moreover, the risk of tropical diseases (such as malaria) may increase in the temperate zone.
Even though the Earth’s ecosystems cannot adapt to the rapid climate change and many of them will be affected by its progress (coral reefs are likely in the greatest and most immediate peril: they will suffer from the increased sea water temperature; about 50% of them are seriously disrupted globally), organisms have always coped with previous climate changes, which have been the side effect of the planet’s evolutions. Some have become extinct, others have adapted or produced other viable forms. The fundamental problem of the current global climate change is the adaptive capacity of human society, its economic and political systems: major climatic changes may bring about dangerous clashes, which have always been more deadly to man than environmental effects.
Disruption of the Ozone Layer
The solar spectrum contains a certain part of ultraviolet radiation (UV), some of the components (wavelengths) of which are seriously adverse to life. However, most of the UV energy hardly reaches Earth’s surface because it is absorbed in the ozone layer. Ozone is a toxic substance, but its presence is very welcome in the stratosphere, where the so-called protective ozone layer occurs. Some 90% of all atmospheric ozone is concentrated in a layer between approximately 15 and 40 km high above the planet’s surface. Here, molecular oxygen is split into atomic oxygen by the short-wave ultraviolet (UV-C) radiation, which then combines with other oxygen molecules to form a triatomic ozone molecule. This ozone is then further decomposed by medium-wave UV-B from the Sun. Both reactions – ozone creation and disintegration – are normally in balance and bind all the UV-C energy and most of the UV-B energy, preventing it from reaching the surface.
Many laboratory tests, calculations and later also direct measurements of atmospheric ozone concentrations have confirmed that the ozone is disappearing due to the presence of certain substances produced and used by humans (e.g. CFCs and other, similar substances). The most serious reductions have been detected above the south pole, above Antarctica, where the zone layers becomes so thin during the local winters that it has given rise to the term Antarctic ozone hole. However, the reduced ozone layer is global in nature, not limited to the Antarctic region or even the southern hemisphere. Roughly speaking, each per cent of reduction in the ozone content leads to a two-percent increase in the UV-B input to Earth’s surface. This implies that the radiation is magnified by about 10% on average in the temperate zones. The increased ultraviolet input has a harmful effect on all living organisms.
Ultraviolet radiation (more precisely, its UV-B component, which may reach the surface in large quantities) increases the probability of the dangerous form of skin cancer (melanoma) and affects the cornea. Since UV-B is harmful to almost all organisms, other animals and plants too suffer from the increased input of this radiation. It slows down photosynthesis and has an adverse effect on plant production, including crop harvest.
Everything is further complicated by the fact that although international treaties have made it possible to significantly reduce or even halt the production and consumption of ozone-damaging substances,this has not resolved the problem. Most CFCs (chlorofluorocarbons) – substances used formerly in refrigeration, electrotechnicals and other industries – are very stable, lasting up to decades in the atmosphere. Their impact on the ozone layer is thus going to continue.