Weather is the state of the atmosphere at a given place and time: temperature, rainfall, wind and cloud. Climate is the average weather of a region measured over a long period, usually 30 years or more. Climate change is a significant, long-term change in these average patterns.Global warming is the increase in the Earth's mean surface temperature. It is one part of climate change: a warmer planet also has changed rainfall patterns, rising sea levels and more frequent extreme weather. Since the late 19th century the mean global temperature has risen by about 1.1 to 1.2 °C.The climate has always changed naturally, because of:
• variation in the Earth's orbit and tilt (Milankovitch cycles), which drive the ice ages over tens of thousands of years;
• changes in the Sun's output;
• large volcanic eruptions, which release ash and sulfur dioxide that cool the Earth for a year or two.However, the current warming is happening far faster than these natural changes and matches the rise in greenhouse gases from human activity. Change caused by humans is called anthropogenic climate change. Most climate scientists agree that human activity is the main cause of the warming since the mid-20th century.In the lessons that follow you will look at how the greenhouse effect works, the evidence for warming, how reliable that evidence is, and how climate change affects living organisms.
• variation in the Earth's orbit and tilt (Milankovitch cycles), which drive the ice ages over tens of thousands of years;
• changes in the Sun's output;
• large volcanic eruptions, which release ash and sulfur dioxide that cool the Earth for a year or two.However, the current warming is happening far faster than these natural changes and matches the rise in greenhouse gases from human activity. Change caused by humans is called anthropogenic climate change. Most climate scientists agree that human activity is the main cause of the warming since the mid-20th century.In the lessons that follow you will look at how the greenhouse effect works, the evidence for warming, how reliable that evidence is, and how climate change affects living organisms.