FIGURE 1-1 “The Keeling Curve.” Time series of annual departures from the 1961 to 1990 base period mean of 334 ppmv using direct measurements from Mauna Loa. SOURCE: Compiled by J. Hurrell, National Center for Atmospheric Research.

… [T]he observing system available today is a composite of observations that neither provide the information nor the continuity in the data needed to support measurements of climate variables. Therefore, above all, it is essential to ensure the existence of a long-term observing system that provides a more definitive observational foundation to evaluate decadal-to century-scale variability and change.


Long-term observations sustained over decades are a critical first step in providing the climate data necessary for scientists, decision makers, and stakeholders to make adaptive choices that could improve resiliency to climate change and vulnerability, and maintain economic vitality. Many international and national activities and reports concur on the need for

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