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OUR eyes around Earth are seeing less. US environmental satellites that helped forecasters predict superstorm Sandy are failing. By 2020, the fleet could have just a quarter of the sensors it has today.

In a posted online, of the National Center for Atmospheric Research in Boulder, Colorado, warns that new launches are not keeping up with the failures of older instruments. As a result, NASA and the National Oceanic and Atmospheric Administration could have just 20 sensors in orbit by 2020.

“We are basically going blind in terms of our ability to monitor the planet,” says at the University of Maryland in College Park, who contributed to a recent .

There have been delays sending satellites into polar orbits. The first of NOAA’s new won’t launch until 2017, which last year forced NASA to launch a stop-gap satellite called . Any failures before 2017 will leave a gap in weather data.

Climate research is sensitive to launch delays, as new instruments need to operate simultaneously with old ones for a year to calibrate their sensors. Suomi’s sensors may fail before 2017, warns Trenberth.