Background to the problem of global warming

The energy we use to heat our homes, drive our vehicles, produce electricity, and in many industrial processes comes, for the most part, from the burning of so-called fossil resources, namely, oil, natural gas, and coal. The burning of fossil resources has risen sharply with increasing industrialisation and with increasing mechanization over the last 150 years and the atmospheric concentration of CO₂ produced by combustion increases, consequently, faster and faster.

Effects of CO₂ concentration in the atmosphere since the beginning of industrialisation

From the beginning of industrialization in the 19^th century, researchers have been wondering whether the smoke gases from the factories, which were visible everywhere at that time, could have harmful effects beyond the immediately noticeable smog. It was recognised early that CO₂ in the atmosphere has an influence on the temperature. The CO₂ is very similar to clouds of water vapor. The short-wave heat radiation from the sun passes through the atmosphere, but CO₂ blocks the counter- radiation reflecting from the earth. It acts like a permeable insulation layer in one direction only. These effects were then understood in the laboratory, and there were already first rough calculations on how the atmosphere could warm up due to a rising CO₂ content.¹ Even then, the term “greenhouse effect” was used to describe the mechanism of warming the atmosphere, comparing this process with the warming of air under the glass roof of a greenhouse. It must also be mentioned that besides CO₂, other gases also have similar effects. These include methane (CH₄) and nitrous oxide (N₂O) as so-called climate-impacting gases.

Observation of weather and climate

As early as in the 19^th century, with the invention of the thermometer, interested laymen began to systematically describe the weather on the basis of measured values. If one observes the weather over longer periods of time and averages out temperature and also precipitations, one speaks about climate, characterized by just these averaged values ​​and other statistically determined factors. Regarding the time before the possibility of direct thermometer measurements, conclusions about the weather and the climate could be drawn indirectly from reports on the crop cycles, characteristics of the seasons and also on  cultivated plant species. From historical events and descriptions, conclusions were drawn on the prevailing climate, for example during the Roman period, the warm period in the High Middle Ages, and finally the “little ice age” that came to an end in the mid-19^th century.

The role of CO₂ in changing cold and warm periods of the earth is well understood

Earth history, dating back to Earth’s birth about 4.5 billion years ago, is a helpful example to understand the effect of CO₂ on the Earth’s climate in more detail. Ice ages and warm periods followed each other, always accompanied by low or high CO₂ concentrations in the atmosphere. Glacier traces in the landscape, traces of the respective vegetation and the animal world give indications of warm periods and cold periods in the history of the earth.
The greatest insight into the recent history of the earth and especially about the history of climate could be made in the early seventies. Specimen, so-called ice cores, were then, for the first time, extracted in ever greater depth in the ice sheets of Greenland and later also in the Antarctic.² The ice has formed in layers, the time of their origin could be assigned. Using modern measuring methods, for example by measuring the proportion of oxygen isotopes in the ice, it was possible to deduce the temperatures at the time of ice formation and, with the analysis of trapped air bubbles, it was also possible to determine the CO₂ concentration and the concentration of other gas traces in the atmosphere at the time of ice formation. It became possible to accurately determine the CO₂ content of the atmosphere and the prevailing temperatures during the last 400,000 years and in further projects with deeper drilling, even for the last 800,000 years. There was a clear simultaneity between high atmospheric temperatures and high levels of CO₂ in the atmosphere. Conversely, there were ice ages or cold periods in which the CO₂ content in the atmosphere was low. It showed a regularity. Prolonged cold periods of about 90,000 years followed warm periods of about 10,000 years. The explanation was provided by the so-called Milankovitch cycles. It was known that this cycle was determined by the not always equal distance of the Earth from the Sun.³ In new drilling projects, the goal is to gain more precise insights with ice cores from deeper ice-layers that are 1.5 million years old.⁴

Various effects overlapping and reinforcing each other

Overlapping effects create a complex picture. In the ocean, CO₂ is bound or dissolved on a large scale in very slow processes. Due to warming, for example resulting from the Milankovitch effect, the sea releases large quantities of CO₂, thus leading to an increased warming. On the other side, cooling leads to an increase in the CO₂ absorption by the sea, a reduction of the CO₂ concentration in the atmosphere and a self-reinforcment of the cooling process. The same applies to an increased ice formation on the earth’s surface. The ice surfaces reflect more sunlight, which in turn causes an increase in cooling. Decrease of ice leads to self-reinforcing warming. There are further cyclical effects, each one with its own temporal dynamics. They overlap and sometimes lead to a seemingly chaotic development which science can understand and in which the role of CO₂ is quite fully understood.

A strong, fast and unprecedentedincrease in CO₂ in our time

For the times of early earth, the very slow increase in CO₂ concentration at that time over millions of years can be determined approximately on the basis of traces in sediment layers. In the last million years before our time, CO₂ concentration was about 180 ppm in cold periods and never higher than 280 ppm in warm periods. The last warm period, our present warm period, has started about 12,000 years ago. In this warm climate men have been settling down and have been  able to develop and successfully practise agriculture and livestock breeding. CO₂ levels and temperature have been relatively constant in this short geological period.
However, after first signs at the beginning of industrialization in the 19^th century, CO₂ concentration in the atmosphere has risen rapidly and increasingly from the fifties of the 20^th century on. Today, the increase is about 100 times faster than ever in the long history of the earth. Logically, this can also be explained by the fact that fossil resources like oil, coal and gas had been formed over millions of years, fixing carbon somewhere in the earth’s crust. This fixed carbon in our coal, oil and gas, is now released back into the atmosphere as CO₂ in one millionth of the  time span of its formation, leading to those heat effects known to us in principle from earth’s history and which are also fully understood physically. Men have started exploiting fossil resources to an unprecedented extent in the shortest possible time in earth’s history, and it seems logical to assume that the increase in CO₂ observed today is man-made.
CO₂ in today’s world
All processes releasing CO₂ into the atmosphere and those leading to a reduction in CO₂ concentration are very slow. Accordingly, it is expected that a reduction of today’s high CO₂ concentration in the atmosphere to pre-industrial levels by natural processes will take about 1,000 years.⁵ Phenomena emerging today will be remaining in the long term, they may intensify and have effects for many generations.
Men and future generations will have to adapt to climate changes caused by the rapid and strong, unprecedented increase in CO₂ level. The increase cannot be reversed with reasonable efforts in the short term. However, this does not mean that measures to avoid a further increase do not make sense in the long term.
There are examples of environmental problems tackled through joint action by all states. The problem of forest dieback in the 1970s was largely solved by consistent regulations on smoke gas, desulphurisation of power plants, and the elimination of sulphur content in fuels. The hole in the ozone layer over the Antarctic could be significantly reduced with international cooperation through regulations laid down in the 1987 Montreal Protocol and the use of substitute materials.
In the case of CO₂, international agreements on CO₂ reduction have been entered into, but until now they have had practically no effect. One example is carbon (CO₂) certificate trading in which the problem is left to “market-based” mechanisms. Highly ambitious targets have been formulated, but actual emissions in all countries are not or just slowly decreasing, so that the ambitious targets can hardly be achieved or fulfilled. Approaches reasonable on the longterm  should be pursued. A “wait and see” policy has no place here. Moving beyond fossil energy generation in a thoughtful way promoting renewable energies is certainly not the wrong way to go.    •

1    Fourier 1824, Tyndall 1860, Arrhenius 1896 nach Rahmstorf/Schellnhuber. Der Klimawandel: Diagnose, Prognose, Therapie. München 2006, ISBN-13: 978 3 406 50866 0
2    Nature 399 (1999), Petit et al, Climate and Atmospheric History of the Past, 420 000 years from the Vostok ice core, Antarctica
3    Milankovitch, M. (ed.). Mathematische Klimalehre und astronomische Theorie der Klimaschwankungen. Berlin, 1933
4    Auf der Suche nach dem ältesten Eis. «Neue Zürcher Zeitung» 5. April
5    Solomon, Plattner, Knutti. ETH Zürich. Irreversible climate change due to carbon dioxide emissions. In: Proceedings of the National Academy of Sciences of the United States of America, February 2009