Explanation:

The Intergovernmental Panel on Climate Change (IPCC) is the leading international body for assessing climate change. Established in 1988, its primary role is to provide comprehensive scientific assessments on climate change, its implications, and future risks, including the impact of increasing carbon dioxide. Option (1) UNEP co-founded IPCC but focuses on environmental policy. Option (3) IUCN focuses on nature conservation and biodiversity. Option (4) WHO addresses public health, although climate change has health impacts, it doesn't primarily assess the scientific mechanisms of climate change.