There are natural and anthropogenic causes of climate change. According to the Intergovernmental Panel on Climate Change (IPCC) global warming is caused by human activities such as the burning of fossil fuels, deforestation and agriculture. These human activities have resulted in elevated concentrations of greenhouse gases (CO2, CH4, N2O) in the atmosphere since the start of the industrial era around 1750 (IPCC, 2007). The carbon dioxide concentration in the atmosphere increased from a pre-industrial concentration of about 280 parts per million by volume (ppm) to 379 ppm in 2005. The same applies to the methane concentration (from 715 parts per billion by volume (ppb) to 1774 ppb), and nitrous oxide concentration (from 270 ppb to 319 ppb) in the atmosphere (IPCC, 2007). The 2007 assessment report of the IPCC concluded that “an increase in anthropogenic greenhouse gas concentrations is very likely to have caused most of the increases in global average temperatures since the mid-20th century.” However, according to other scientists, the current emphasis on the role of carbon dioxide may not be correct and the history of climate change has been insufficiently taken into consideration. They argue that changing solar activity also has a strong influence on the climate system and showed that decreased volcanic activity and increased solar activity were plausible explanations for the observed global warming in the first half of the 20th century (Verweij et al., 2010). A colder intermezzo from 1970 until 1995 was caused by high volcanic activity in that period. Natural factors, such as volcanic eruptions and El Niño events, have only caused short-term temperature variations over time spans of a few years but cannot explain any longer-term climatic trends. The remaining global warming in the second half of the past century can be explained by anthropogenic forcing.