Climate change refers to altered long-term weather patterns. Global warming - a rise in the average global temperature - is one measure of climate change. Long-term changes to weather patterns can largely be associated with human activity through the pollutants emitted by burning fossil fuels. The pollutants entering the atmosphere effectively change its composition and prevent heat from escaping the earth's surface. This results in rising global average temperatures that have increased roughly 0.76 degrees Celsius since 1900. It is widely believed that a 2 degree Celsius rise would be a tipping point where climate change effects would be acutely and dangerously apparent with extreme weather events, record temperatures, retreating glaciers, rising sea levels and habitat loss.