One of the clearest signs of global warming, unless you live next to a glacier, are rising oceans. Now a joint mission involving the US and European countries is launching a pair of satellites to monitor the rising sea levels. The two satellites will monitor the oceans until 2030.
There’s more to rising oceans than melting glaciers and ice sheets. Ocean rise is also caused by the warming of the atmosphere. The oceans are like heat sinks, and as they absorb the heat from the atmosphere, they expand and rise. The pair of satellites will track that rise, providing important data for our efforts to adapt to climate change.
The pair of satellites are identical, and will be launched five years apart. Each one has an expected lifetime of about 7 years, guaranteeing that the two will overlap, and there will be no gap in the data. The mission is called Sentinel-6/Jason-CS (Jason Continuity of Service.) The satellites are named Sentinel-6A and Sentinel-6B. They’re built by German company IABG, and will be launched from Vandenberg Air Force Base in the US on a SpaceX Falcon 9 rocket.
By the end of this mission, Sentinel-6/Jason-CS will have added to an almost 40 year record of rising oceans. The mission follows in the footsteps of four other joint U.S.-European satellite missions:
Collectively, the data from those missions shows that the Earth’s oceans are rising at an average rate of 3 mm (0.1 inches) every year. According to the IPCC, that rate has accelerated in recent history, and by 2100 the oceans could rise by a meter. While lowering emissions can potentially change that, these satellites will provide data needed to plan for it.
“Global sea level rise is, in a way, the most complete measure of how humans are changing the climate,” said Josh Willis, the mission’s project scientist at NASA’s Jet Propulsion Laboratory in Pasadena, California. “If you think about it, global sea level rise means that 70% of Earth’s surface is getting taller – 70% of the planet is changing its shape and growing. So it’s the whole planet changing. That’s what we’re really measuring.”
The oceans play a key role in the Earth’s climate. They’re able to absorb CO2; in fact some data shows they absorb about 26% of the carbon dioxide released through human activity. They also absorb heat, and as they heat, they expand. But that warming means they also absorb less CO2, which means more warming, which means more expansion and sea level rise.
The Sentinel-6/Jason-CS satellites will measure the ocean rise down to the millimeter. They’ll map up to 95% of Earth’s ice-free oceans every 10 days. It’s radar altimeter will also measure the shape of the ocean, the hills and valleys that make up its topography, providing data for mapping ocean currents. Along with the radar altimeter, the satellites will carry a microwave radiometer, Precise Orbit Determination (POD) instruments, a GNSS- Radio Occultation instrument, and other equipment.
The satellites will also help gather data that can aid weather forecasts.
“Global sea level rise is one of the most expensive and disruptive impacts of climate change that there is,” said project scientist Josh Willis. “In our lifetimes, we’re not going to see global sea level fall by a meaningful amount. We’re literally charting how much sea level rise we’re going have to deal with for the next several generations.”
And that exact amount of rise is difficult to determine. The IPCC estimate is based on 7,000 separate studies. But the issue of tipping points means the IPCC’s estimate of one meter of sea rise by 2100 needs to be looked at in context.
Only a few years ago, back in 2007, the IPCC predicted a 59 centimeter rise by 2100. Now, only a dozen years later, that has almost doubled. Some estimates show a rise greater than 5 meters by 2300. What actually happens will depend on our efforts to reduce GHG emissions, and on tipping points, like melting permafrost. Melting permafrost could release vast quantities of methane into the atmosphere and speed climate change up, making a 5 meter rise a realistic scenario.
Sentinel-6/Jason-CS is being jointly developed by the European Space Agency (ESA), the European Organisation for the Exploitation of Meteorological Satellite (EUMETSAT), NASA and the National Oceanic and Atmospheric Administration (NOAA.) France’s CNES and the European Commission are supporting the mission.
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