The National Oceanic and Atmospheric Administration (NOAA) has created a climate portal as an attempt to organize the sources and kinds of climate information. It opens onto "ClimateWatch", an online magazine. Other tabs are "Data & Services", "Understanding Climate" and "Education"
Here is a good summary: About NOAA Climate Services Portal
The Center for Climate and Energy Solutions is a source of reliable information about the causes and potential consequences of climate change.Here are some of their articles to get you started.
U.S. Federal Agency Websites: