Space-based measurements of carbon dioxide () are used to help answer questions about Earth's carbon cycle. There are a variety of active and planned instruments for measuring carbon dioxide in Earth's atmosphere from space. The first satellite mission designed to measure was the Interferometric Monitor for Greenhouse Gases (IMG) on board the ADEOS I satellite in 1996. This mission lasted less than a year. Since then, additional space-based measurements have begun, including those from two high-precision (better than 0.3% or 1 ppm) satellites (GOSAT and OCO-2). Different instrument designs may reflect different primary missions. Purposes and highlights of findings There are outstanding questions in carbon cycle science that satellite observations can help answer. The Earth system absorbs about half of all anthropogenic emissions. However, it is unclear exactly how this uptake is partitioned to different regions across the globe. It is also uncertain how different regions will behave in terms of flux under a different climate. For example, a forest may increase uptake due to the fertilization or β-effect, or it could release due to increased metabolism by microbes at higher temperatures. These questions are difficult to answer with historically spatially and temporally limited data sets. Even though satellite observations of are somewhat recent, they have been used for a number of different purposes, some of which are highlighted here: Megacity enhancements were observed with the GOSAT satellite and minimum observable space-based changes in emissions were estimated. Satellite observations have been used for visualizing how is distributed globally, including studies that have focused on anthropogenic emissions. Flux estimates were made of into and out of different regions. Correlations were observed between anomalous temperatures and measurements in boreal regions. Zonal asymmetric patterns of were used to observe fossil fuel signatures. Emission ratios with methane were measured from forest fires. emission ratios with carbon monoxide (a marker of incomplete combustion) measured by the MOPITT instrument were analyzed over major urban regions across the globe to measure developing/developed status. OCO-2 observations were used to estimate emissions from wildfires in Indonesia in 2015. OCO-2 observations were also used to estimate the excess land-ocean flux due to the 2014–16 El Niño event. GOSAT observations were used to attribute 2010-2011 El Niño Modoki on the Brazilian carbon balance. OCO-2 observations were used to quantify emissions from individual power plants, demonstrating the potential for future space-based emission monitoring. Challenges Remote sensing of trace gases has several challenges.