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What is climate change?

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Climate change – What is it?

Climate or weather?

A short-term state in the atmosphere at a specific location is described as weather – for example, if the sun shines or if it rains, if it is warm or cold. Climate, however, is referred to as the average atmospheric state at a specific location observed over a certain period of time – commonly measured in 30-year periods. While weather is subject to rapid changes, climate or the ‘average weather’ changes only at a very slow pace.

Climate change in the course of history and current developments

Changes in climate have occurred throughout our planet’s history. During the last Ice Age, for example, which ended approx. 10,000 years ago, Germany was almost entirely covered by a thick layer of ice. Even the last 1,000 years were marked by climate change. Following the relatively warm Middle Ages a cold spell came, called ‘short Ice Age’, which lasted until the 19th century.

Then what distinguishes the global warming observed since the second half of the last century from previous climate changes? For the first time, the causes for temperature fluctuations are not to be found in natural processes such as a variability of UV-radiation or volcanic eruptions. Instead, climate experts found that greenhouse gas emissions into the atmosphere have increased at a parallel rate as did the temperature.  

Microprobes from glaciers give an insight about the atmosphere’s composition of the preceding 800,000 years. During this time up until the beginning of the industrial revolution, the CO2 share of the atmosphere ranged between 200 and 300 ppm (parts per million = 0. 0001 percent). Since then, the CO2 concentration in the atmosphere reached a staggering 390 ppm and is expected to surpass the 400 ppm mark in the next couple of years.

The increased amount of greenhouse gas emissions can be attributed to human activity – for the first time, mankind is changing the climate because higher levels of greenhouse gas emissions amplify the natural greenhouse effect. As a consequence, it gets warmer.

The natural greenhouse effect

Illustration: greenhouse effect

Solar energy reaches the earth in form of short-lived UV-radiation. From the surface of the earth, it is then reflected back into the universe in the form of long wave rays (infrared radiation). Part of the radiation, however, stays in the atmosphere where it is retained by steam and greenhouse gases – mostly comprised of carbon dioxide and methane. The remaining radiation in the atmosphere heats up the surface of the earth and its surrounding air. That is why it gets warmer. The natural greenhouse effect is of the utmost importance to life on earth. Without it, global temperature would drop to -18 °C compared to an average +15 °C. Hence, steam and greenhouse gases, which have existed in the atmosphere before mankind’s interference, work somewhat like the glass roof on top of a greenhouse. UV-rays can pass through the glass roof almost unhindered whereas long wave radiation remains ‘caught’ in the greenhouse.

The anthropogenic greenhouse effect

The anthropogenic greenhouse effect describes human-induced climate change. Since the beginning of industrialization, human beings have burned enormous amounts of fossil fuels such as coal, petroleum and natural gas to generate energy. Burning these materials releases gaseous Carbon dioxide (CO2) into the atmosphere. Thereby, the atmosphere’s concentration of CO2 increases, as do those of the other gases relevant to climate. One of these gases is Methane (CH4) which is primarily emitted by agricultural production. Current Methane and Carbon dioxide levels in the atmosphere exceed all measurement records of our earth’s recent history.

An isotope measurement clearly identifies human activity as the main driver of heightened CO2-levels in the atmosphere. This is because the relation between Carbon isotopes 13C and 12C, as observed in Carbon dioxide from fossil fuel combustion, differs from the chemical compound of Carbon dioxide which is emitted from other sources like volcanic eruptions. The anthropogenic greenhouse effect now reinforces the natural one. Temperature rises and the climate changes. The main emitters of greenhouse gases are power plants, traffic, industry, agriculture and deforestation.

Which are the consequences of climate change?

In comparison to the pre-industrial era, temperature has risen by about 0.8 °C. When contrasting these numbers with previous, natural deviations in temperature, this recent surge in temperature is immense and has global implications. Throughout the last decades, the expansion of arctic ice covers dropped by 20 percent in the summer; the last century has also witnessed a rise in sea levels between 12 and 22 cm, with a persistent annual increase by 3.3 mm; the Alpine glaciers have already lost half of their volume – at an accelerating pace; extreme weather events such as hurricanes or floods caused by heavy rainfall are not only occurring more frequently but with more intensity.

Many of these changes can be observed in Latin America. The Andean glaciers have been shrinking dramatically in recent years while others have vanished completely. Increasingly frequent severe droughts threaten both farmers’ yield and domestic water supplies. At the same time heavy rainfall results in earth slides and floods. The spread of diseases like Malaria and Dengue is facilitated by the intrusion of mosquitoes into habitats which are usually too cold for the species. As temperature rises, the area infected by mosquitoes grows larger. Climate change also endangers biodiversity since biodiversity-rich areas, for example the Amazon, are sensitive to alterations in temperature and precipitation levels.

The 2 °C target

International climate politics set the target of keeping global warming at a maximum 2 °C level above the pre-industrial level. A temperature increase above this threshold is expected to have irreparable consequences for the global climate and ecosystems.

The climate of the earth is a highly complex system. If certain thresholds are breached, the probability of abrupt and extreme changes increases which adversely affect the global ecosystem. A major problem are positive feedback effects, which are self-reinforcing in nature and hence further accelerate climate change, ultimately resulting in an irreversible warming of the planet. These processes are called ‘tipping points’. For instance, the melting of permafrost land in Siberia releases great amounts of Methane, thus intensifying the greenhouse effect. If the arctic ice covers evaporate, sea levels will rise as a direct consequence. This further leads to a decrease in the ratio of reflected to absorbed solar radiation, which adds to global warming. This is because bright ice covers reflect solar radiations almost entirely while the ocean beneath absorbs UV-radiation at a much higher rate. Thereby, the ocean and adjacent air layers are getting warmer.

What to do?

There are two strategies to approach climate change:

Greenhouse gas mitigation

One strategy outlined earlier envisions halting climate change at 2 °C in comparison to pre-industrial levels. In this manner the grave consequences of climate change can be moderated on a global scale. According to prognosis, another temperature increase by 0.5 °C is unavoidable additionally to the 0.8 °C rise in temperature up until now. This is because the amount of greenhouse gases capable of causing this increase are already emitted into the atmosphere but are subject to a delayed uptake. The 2 °C target therefore is very ambitious. In order to achieve this goal, greenhouse gas emissions must be curtailed by 50 percent in 2050 at the baseline year rates of 1990. While a 50 percent reduction is proclaimed globally, industrial countries have to cut back emissions between 80 and 95 percent.

Nonetheless, the discharge of global greenhouse gas is currently rising further. The 2 °C target necessitates political and economic actors on a local, regional and global scale to rethink and implement appropriate strategies rigorously within the next couple of years. Generating energy from renewable resources instead of fossil fuels such as coal and raw oil, electro mobility, promoting energy-efficacy in the economy and households, as well as preserving remaining forests are all important concepts to meet the 2 °C target.

The responsibility, however, does not merely rest in the hand of political and economic actors. Every individual’s contribution is needed: Participate politically and challenge companies to produce sustainably, save energy at home, reduce air traffic or switch from car to bicycle and public transport.

Adaptation to climate change

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