Towards a Wholistic and Sustainable Atmospheric/Earth Observing System

US and global Earth observation capabilities have evolved dramatically since the International Geophysical Year of 1957/58, which kickstarted an era of exploration and dicovery. Many satellite and in situ measurement techniques and data analysis systems are mature and support operational applications for Numerical Weather Prediction (NWP) and beyond. Computing and communications have kept pace with sensor development, and we are well into the age of "big data" and machine learning/AI. Societal benefits and technological potental for expanded and sustained observations now far exceeds available government resources, and this situation predates recent efforts to reduce federal spending by cutting programs and reducing the federal workforce. For example, the 2017 Decadal Survey of Earth Science and Applications from Space identified many more high-value observables than can realistically be supported by the US government in the foreseeable future and did not attempt to define or scope crtical in situ observations. We will present examples of potential new, targeted atmospheric observations to support climate science, applications, and decision support, including measurements of aerosols, greenhouse gases and radiation, with emphasis on the use of platforms of opportunity (e.g. cargo ships and commercial aircraft) and emerging mechanisms for engaging private sector and philanthropic partners. We will focus on the feasability and potential for expanded "reference quality" measurements to anchor the atmospheric observing system and unlock unrealized potential value of existing and candidate new observations, by ensuring compabitility across sensors and platforms over timescales of decades.