The International Energy Agency is an OECD sponsored autonomous intergovernmental organization. The IEA acts as a policy adviser to its member states, comprising most OECD countries, but also works with non-member countries.
The IEA provides excellent data, charts and reports on energy and greenhouse gas emissions.
The Intergovernmental Panel on Climate Change is the United Nations body for assessing the science related to climate change..
The IPCC provides excellent data, charts and reports on greenhouse gases.
The United States' Energy Information Agency is a US sponsored national organization. The US Department of Energy and Environmental Protection Agency websites typically link to this site.
The EIA provides excellent data, charts and reports on energy and greenhouse gas emissions for the United States.