World Resources Institute
The World Resources Institute (WRI) publishes free environmental data aimed at geographic information system (GIS) work, climate research, and sustainability projects. Its holdings include Global Forest Watch, which tracks forest change around the world, alongside other flagship monitoring datasets.
Most of the data is released under the Creative Commons Attribution licence (CC BY 4.0), which lets you reuse it, including for commercial products, as long as you credit WRI. A few datasets carry different terms, so check the licence on each one.
Related sources
Copernicus (EU Earth Observation)
The EU's flagship Earth observation programme. The Copernicus Climate Change Service portal provides authoritative information about past, present, and future global climate, derived from Sentinel reference products alongside other satellite observations and in-situ measurements.
Met Office DataPoint / CEDA
The Centre for Environmental Data Analysis hosts UK atmospheric and Earth observation data, including Met Office archives, climate model outputs, and satellite data.
NASA Earthdata
The home for full and open access to NASA's Earth science data collections. The umbrella portal for the largest collection of freely available Earth science data in the world, with over 12,400 datasets spanning land, ocean, atmosphere, and cryosphere, collected by satellite missions, airborne campaigns, and ground stations.
NOAA Open Data Dissemination (NODD)
Free, full, and open access to NOAA data through partner platforms including Amazon Web Services, Google, and Microsoft Azure. Covers climate data records and atmospheric, oceanic, and terrestrial datasets from one of the largest climate archives in the world.