Modern observations mostly come from weather stations, weather balloons, radars, ships and buoys, and satellites. The Global Historical Climatology Network daily (GHCNd) contains records from more than 100,000 stations in 180 countries and territories. A surprisingly large number of U.S. measurements are still made by volunteer weather watchers. There are more than 8,700 citizen observers in the National Weather Service's Cooperative Observer Program, who log daily weather data. On the ocean, moored and drifting buoys have begun to replace ships in recent decades as the primary method for measuring temperatures at sea.
The U.S. organization responsible for preserving the global climate record is NOAA. It's primary station data set, the Global Historical Climatology Network (GHCN) is an integrated database of daily climate summaries from land surface stations across the globe, including a common suite of quality assurance reviews. NOAA’s National Centers for Environmental Information (NCEI) produces the GHCN data set. Other nations also maintain archives of global weather and climate observations.