Global warming and climate change

The Earth is warmer than it ought to be, given its distance from the Sun, because some of the gases in the atmosphere create what is called a greenhouse effect. The extra warming is caused by so-called greenhouse gases as more heat is retained in the atmosphere than otherwise would be. The main greenhouse gases are carbon dioxide, methane, nitrous oxide and water. Greenhouse gas emissions are mainly driven by population size, economic activity, lifestyle, energy use, land use patterns, technology and climate policy, and there is a consistent, almost linear, relationship between cumulative CO₂ emissions and projected global temperature change up to the year 2100. The UN's Intergovernmental Panel on Climate Change (IPCC) has set out four scenarios that describe different pathways for future greenhouse gas emissions. The IPCC says that many species will face increased extinction risk during and beyond the twenty-first century.