a) NASA Goddard Space Flight Center Image by Reto Stöckli (land surface, shallow water, clouds). Enhancements by Robert Simmon (ocean color, compositing, 3D globes, animation). Data and technical support: MODIS Land Group; MODIS Science Data Support Team; MODIS Atmosphere Group; MODIS Ocean Group Additional data: USGS EROS Data Center (topography); USGS Terrestrial Remote Sensing Flagstaff Field Center (Antarctica); Defense Meteorological Satellite Program (city lights) from https://visibleearth.nasa.gov/images/57730/the-blue-marble-land-surface-ocean-color-and-sea-ice b) Wikimedia Commons contributors, "File:World-airline-routemap-2009.png," Wikimedia Commons, the free media repository, https://commons.wikimedia.org/w/index.php?title=File:World-airline-routemap-2009.png&oldid=374115880 c) Southern most routes and sea ice markings highlighted.  https://doi.org/10.6084/m9.figshare.11566707.v1