Observed climate changes
Climate study is a complex field of research because of the many factors involved. The Earth's climate has never been static, but is subject to variations on all time scales from decades to thousands and millions of years. Among the recent climate variations dated on European soil during the Pleistocene stresses in the last million years, a sequence of at least four glacial periods, followed by interglacial periods.
More recently, and within the historical scale, paleoclimatic studies conducted mainly in Europe point to the fourteenth century as the beginning of a period of several centuries characterized by a significant deterioration in the thermal conditions and changes in the normal behavior of precipitation, known as little Ice Age which came to an end in the nineteenth century.
Nowadays, studies from observations of climate variables conclude that increased temperature is a global phenomenon, but more pronounced in the Arctic regions. The warming has been detected on the surface of the Earth, in the atmosphere and in the first few hundred meters in the oceans. Land areas have warmed faster than the seas.
But global warming we are witnessing is of a different nature to those discussed variations, as their explanation must be sought in anthropogenic causes.
Article 1 of the Framework Convention of the United Nations on Climate Change, from 1992, defines climate change as a variation directly or indirectly attributed to human activity that alters the composition of the global atmosphere and which is added to natural variability of the climate observed over comparable time periods.
There is now an almost widespread scientific consensus around the idea that our way of energy production and consumption are causing a global climatic change, which will lead, in turn, to serious impacts on both ecosystems and socio-economic systems on Earth.
The Intergovernmental Panel on Climate Change, better known by its acronym IPCC, creates reports prepared periodically in order to disseminate the available scientific and technical knowledge on climate change. The increase in global average surface temperatures combined between land and oceans during the period 1880-2012 was estimated at 0,85ºC, as recorded by the Fifth Assessment Report of Working Group 1 of the IPCC, published in 2013.
Regarding temperatures, each of the last three decades has been successively warmer at the surface of the Earth with no precedent since 1850. In the Northern Hemisphere, from 1983 to 2012 was probably the warmest period of the last 1,400 years.
As for precipitation, according to the data studied by the IPCC, since 1901 increases were experienced in certain regions of the world, such as the mid-latitudes of the Northern Hemisphere. In addition, there are more regions where the number of heavy precipitation events has increased than regions where has decreased. The frequency of heavy precipitation events has increased in North America and Europe.