Lots of new data from satellites. Now faster and bigger computers can analyze the large mass of data generated from satellites. We notice these elements first and they have a great day to day impact on our lives. In general, we know and understand more about the elements that are commonly measured than about those for which we have only a small number of observations. For different needs, there are different elements to assist us.
Most sites use standardized equipment with required exposures and procedures.
Temperature - measurements are made at 1.5 meters above ground, because that is were humans, animals and many plants live. Precipitation - measurements are made at the surface where the water is used by plants, runs off in rivers, soaks into the ground. Usually, a surface-based measurement is used to characterize the climatic conditions in weird locations and to characterize climatic differences between locations. Because of their long record these measurements provide a means to identify how various climate elements change over time. Potential changes in station location, exposure, observer techniques, obs time, equipment, etc.