Global warming refers to the increase in average temperatures of the Earth's atmosphere and oceans since the mid-20th century. According to the IPCC, global surface temperatures increased 0.74°C over the 20th century. Climate change is defined as a long-term change in weather patterns over decades to millions of years that may be natural or human-caused. The Copenhagen Climate Summit brought together 193 countries to forge an agreement to mitigate global warming but they only agreed to "take note" of the eventual accord between China, US, Brazil, India and South Africa which was deemed insufficient.