What is climate change?
Global climate change is a reality. The changing climate in the 20th and 21st centuries is primarily attributable to human greenhouse gas emissions.
The climate and climate system have always been changing, for which there are various reasons, as the climate system is influenced by many different factors. Along with human greenhouse gas and aerosol emissions and changes in land use, there are also numerous natural factors at play, including volcanic eruptions, changes in solar activity and the earth’s orbit around the sun, changes in the chemical composition of the atmosphere, vegetation changes and many more besides. All of these factors influence climate over varying timescales. While human developments are bringing about very rapid changes in the grander scale of earth’s history, certain natural factors are responsible for very long-term changes in the climate. In the NAP, we work with the term "climate change" as it relates to the period in climate history between the start of the industrial revolution and the end of the 21st century – the period covered by our climate scenarios. The term thus includes changes in the climate system that are caused by human as well as natural factors.
Is current climate change being caused by humans?
The changes in climate over the past 150 years and up to the present day are, to a great extent, caused by human greenhouse gases. This has become particularly apparent for the past 50 to 60 years. Model simulations that do not take anthropogenic emissions into account are not able to reproduce the temperature changes that have been measured on a global and continental scale since the middle of the twentieth century.