The Climate Institute, founded in 1986, is possibly the oldest single-issue group focused on climate change. Its style is more informational than advocacy-driven, and large conferences and symposia are characteristic activities.
The Pew Center on Global Climate Change is supported by the Pew Charitable Trusts, which is ultimately based on the family fortunes of the descendants of the founder of the Sun Oil Co. The Pew climate program is a centrist, non-profit advocacy organization "working to create a policy environment that leads to the adoption of mandatory federal limits on emissions that contribute to global warming." Pew works intensely with Fortune 500 companies.
UNEP is the administrative umbrella for most major UN environmental efforts, including those on climate change. Their site is a good place to look for current and upcoming events, reports, and documents.
The UNFCCC is a treaty that was negotiated at the 1992 Earth Summit in Rio de Janiero, was ratified by some 189 countries, and went into effect in March 1994. It initially had no mandatory controls or deadlines. The 1997 Kyoto Protocol, which did set mandatory limits, was an add-on to the UNFCCC.
The IPCC is the umbrella organization that articulates not only the consensus among climate scientists, but also the breadth of opinion among them. It assembles and synthesizes the work of some 2,000 scientists in scores of disciplines from about 150 countries. Wikipedia. Press Contact.
Massachusetts Institute of Technology
MIT has several entities involved in climate research. The Joint Program on the Science and Policy of Global Change is a cross-cutting program that melds work from MIT's Center for Global Change Science and the MIT Center for Energy and Environmental Policy Research.
A major research institute with over 200 scientists focusing on all earth sciences, especially strong on climate-related topics.