Evidence that the global climate has changed

We know that the global climate has changed because of evidence from a number of factors that is taken and collated by scientists all around the world.  Today, with orbiting satellites and other modern technological instruments and techniques it is now possible measure and record with accuracy how and where changes in climate have taken place in many different parts of the world on a daily basis.   By various means this information is then put together to construct a meaningful insight into what is happening with the global climate. 

The Earth taken by the crew 

of  Apollo 17, NASA - Public Domain

NASA point out that while it is known that the global climate has changed a number of times in the past these were caused by natural changes in the way the planet orbits the Sun resulting in changes to the solar energy levels received on Earth.  With temperatures now rising at an exceptionally unparalleled rate over the last 1300 years they believe the present trend is caused by human activities.  Read more