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Climate change

november clouds (photo by Gisela Baudy)Climate change is a natural phenomenon. However,  most climatologists agree that our (industrialized) way of life is the very cause of dramatic climatic changes today and tomorrow - with all their ecological, economical and social changes.

The main cause goes by the name of global warming: The earth's temperature is on the rise and since this upward trend is expected by experts to have a disastrous effect on the entire eco-system, we must make sure that the rise in temperature does not exceed another two degrees Celsius - to keep the impact of global warming manageable. This is mainly achieved by a drastic cut in CO2 emissions at 750 Gt until 2050.

In the following we will provide some background information on the issue as well as useful links for anyone willing to dig for further details.

Defining the term "climate"

Climate refers to the meteorological weather conditions of a specific region measured over a longer period of time (usually 30 years) such as temperature, precipitation (amount of rain, snow, sleet, or hail falling to the earth's ground), wind, air pressure, hours of sunshine and cloud cover. Latitude, the tilt of the earth's axis, the movements of the earth's wind belts, the difference in temperatures of land and sea and topographical aspects influence the climate. Gerhard Petschel-Held of the Potsdam Institute for Climate Impact Research (PIK) explains it this way: "Our climate is determined by the differences between temperatures in the tropics and the polar zones as they drive the circulation of the air and ocean currents." Another important factor is the chemical composition of the atmosphere: oxygen (O2), nitrogen (N) and water vapour are the main natural components next to small amounts of trace gases (< 1 % in volume of the earth's atmosphere) such as carbon dioxide (CO2) and methane (CH4),. These atmospheric gases are also called "natural greenhouse gases" (GHGs) as they are responsible for the so-called natural greenhouse effect.

Greenhouse effect

About half of the sun's energy reaches the Earth's surface - one half of the rest is absorbed by the atmosphere, the remaining 25 % are reflected by clouds and sent back into space. GHGs let the sun's (short-wave) radiation pass through the atmosphere to the earth's surface, capture the warm (long-wave) radiation from the Earth and send them back to the Earth's surface - as if in a greenhouse. Due to this greenhouse effect, the global average temperature is around 14 or 15C. Without the greenhouse effect, the global average temperature would be around minus 18C and life on this planet would be quite impossible or at least quite different from life as we know it. The higher the concentrations of these atmospheric gases, the more heat is trapped on the Earth's surface and temperatures go up accordingly.

Climate Change

Climate changes from one place to the next. For instance, tropical climates differ (greatly) from the continental ones. Climate also changes over time - and global warming can be one out of many causes. Spanning thousands of years and thus giving the planet's flora and fauna a fair chance to adapt to the new situation, variation in the average global temperature covered between 9 and 16 degrees C.

There are a number of factors that can produce climatic change such as alterations
(i) in the state of the sun's or the earth's orbit (astrophysical change altering the solar radiation on the earth), (ii) on the earth's surface, (iii) in the chemical composition of our planet's atmosphere and (iv) in the balance of energy in the earth's surface and atmosphere. All these changes can occur naturally (like an eruption of a volcano leading to the blocking of solar radiation through dust and ashes and thus having a cooling effect on the climate). Except for astrophysical changes, alterations can also be caused by human intervention (anthropogenic or man-made climate change).

Global warming

The natural cause of global warming or the increase of the earth's average temperature is intensified solar radiation.  Throughout its history, our planet has experienced quite a number of episodes of global warming. The current increase in temperature, however, is different and generally attributed to an intensified anthropogenic greenhouse effect, ie one that is caused by increased concentrations of greenhouse through human activities pertaining in particular to an industrialised life style.

There is clear scientific evidence that with industrialisation (for the benefit of the economy, consumption and well-being) rapid changes in the chemical balance of the atmosphere have occurred and produced  a rise in the global  mean annual temperature by 0.74 degrees Celsius over the past  100 to 150 years with a rather sharp increase since the end of the 1970s.  This is a fairly short stretch of time considering the fact that before the industrial revolution, global warming of such scale would occur over a period of a 1,000 years! Furthermore, compared to pre-industrial times, the concentrations of carbon dioxide (CO2) have gone up by roughly 40 % , i.e. from 280 ppm [parts per million] to 389 ppm in 2010. The levels of  methane (CH4) have risen by 145 % and dinitrogen oxide (N2O, aka laughing gas) levels have increased by 15 %. And they are still rising.

The greatest impact for the current upward trend of temperature is assigned to increasing levels of carbon dioxide. Human activities such as burning coal, oil and natural gas (fossil fuels)  to generate electric power for heating, cooling, production, traveling & transporting, etc as well as land-cover changes due to cutting and burning tropical trees to gain agricultural areas add huge amounts of carbon dioxide to the natural carbon cycle that exists between the atmosphere, vegetation, soils and oceans: Whilst power generation via fossil fuels emits carbon emissions into the atmosphere, far-reaching tropical deforestation reduces the absorption or storage of CO2 in vegetation (one of the natural carbon sinks) and more CO2 remains in the atmosphere. Additionally, mass livestock farming accounts for higher levels of methane and nitrous oxide (produced by animal dung) in our atmosphere.

The effects of climate change

Global warming is due to a higher level of the average global temperature, which is one factor of the complex climate system. Since (even rather small) changes in one factor can (slightly, moderately, seriously) alter the interaction between all climate factors and possibly cause rapid changes in the entire climate system, problems for both the earth's ecosystems and human civilization are inevitable and already reality. 

So far, climatologists have observed a number of changes in our natural environment and linked them to today's anthropogenic global warming. For example, spring commences earlier in the Northern Hemisphere than it used to, the plant distribution is shifting and the glaciers in the Alps are melting as do the polar ice caps, and over the last 100 years the sea level rose by an average of 17 cm.

Making exact predictions, however, it is difficult. As is the case with the climate factors, the interplay between atmospheric processes and the earth's hydrosphere (water systems), geosphere (land masses), cryosphere (ice caps) and biosphere (lifeforms), too, is a complex matter, and changes in one parameter can result in various changes in the others.

Climate researchers base their estimates on complex computer models which are and will be under constant revision. Future scenarios includfluctuations in temperature and precipitation, further melting of the polar ice caps and glaciers, rising sea levels, acidification of the oceans, more  flooding, more frequent and stronger hurricanes, frequent drought and heatwaves, desertification and forest fires, less agricultural productivity, shortage of drinking water, more food insecurity and health risks, accelerated migration and security problems, and a loss of biodiversity. Experts assume that by the year 2100 the mean global annual temperature  will go up by between 1.8 and 6.4 degrees C and that the sea level will rise between 18 and 59 cm by 2100.

Although many climate-related issues remain to be studied very closely and on a long-term basis, climate change has entered the political debate at the local, regional, national and international  level and  features also in our everyday lives.

Useful links

> Assessment Reports [ARs] (Intergovernmental Panel on Climate Change IPCC)
> Assessment of Knowledge on Impacts of Climate Change – Contribution to the Specification of Art. 2 of the UNFCCC  (Berlin 2003)

> WBGU/publications

> WBGU/factsheets
> Climate Change: Scaremongering by Scientists? 
> GHS concentration assessment (Jan 2012, European Environmental Agency)
> Research News (Max-Planck-Instutute for Meteorology/Max-Planck-Insitut für Meteorologie)

> Tipping points (Potsdam Institute for Climate Impact Research/Potsdam Institut für Klimafolgenforschung)