Working Group I

Working Group I (WGI) is one of three standing working groups of the Intergovernmental Panel on Climate Change (IPCC), the UN-affiliated body established in 1988 by the World Meteorological Organization (WMO) and the United Nations Environment Programme (UNEP). WGI focuses specifically on the physical science basis of climate change: it assesses the peer-reviewed literature on observed warming, atmospheric and ocean processes, the carbon cycle, climate models, attribution of extreme events, and projections of future climate under different emissions scenarios.

The other two groups handle complementary questions. Working Group II addresses impacts, adaptation, and vulnerability, while Working Group III covers mitigation. Together they produce the IPCC Assessment Reports roughly every 6–8 years, which are then summarized in a Synthesis Report. WGI's contribution is typically the longest and most heavily cited volume.

Each WGI report is drafted by hundreds of volunteer scientists nominated by governments and observer organizations, reviewed in multiple rounds, and concludes with a Summary for Policymakers (SPM) that is approved line-by-line by government delegations in a plenary session. This dual scientist–government approval gives WGI findings unusual political weight: governments cannot later claim the conclusions were imposed on them.

Key WGI outputs have shaped international negotiations:

• The First Assessment Report (1990) underpinned the 1992 UN Framework Convention on Climate Change.
• The Third Assessment (2001) strengthened language on human influence.
• The Fifth Assessment (2013) stated human influence on the climate system is clear.
• The Sixth Assessment (AR6) WGI report, released in August 2021 and titled Climate Change 2021: The Physical Science Basis, concluded that it is "unequivocal" that human activities have warmed the atmosphere, ocean, and land.

For Model UN delegates and researchers, WGI is the authoritative reference for physical climate data — global mean temperature trends, sea-level rise, carbon budgets — that is cited in UNFCCC, COP, and General Assembly debates.