Check out ICECAP (International Climate and Environmental Assessment Project) to find out more about the earth's temperature changes.
ICECAP "is the portal to all things climate for elected officials and staffers, journalists, scientists, educators and the public. It provides access to a new and growing global society of respected scientists and journalists that are not deniers that our climate is dynamic (the only constant in nature is change) and that man plays a role in climate change through urbanization, land use changes and the introduction of greenhouse gases and aerosols, but who also believe that natural cycles such as those in the sun and oceans are also important contributors to the global changes in our climate and weather. We worry the sole focus on greenhouse gases and the unwise reliance on imperfect climate models while ignoring real data may leave civilization unprepared for a sudden climate shift that history tells us will occur again, very possibly soon."
So, if you want to know more about global warming (and cooling), ICECAP is a great starting place!