A build-up of greenhouse gases from human activities, mainly the burning of fossil fuels, is warming the atmosphere and the oceans.

Washington - The US space agency said it would attempt to launch on Friday a satellite to observe levels of salt on the surface of the world's oceans and how changes in salinity may be linked to future climate.

The launch of Aquarius/SAC-D was delayed from June 9 to June 10 to allow engineers time to review an “inconsistency found in the Delta II launch vehicle flight profile for wind conditions on the day of launch,” Nasa said.

The weather forecast on Friday shows a 100 percent change of favourable launch conditions. Launch from Vandenberg Air Force Base in California is set for 7:20am Pacific time (1420 GMT).

The orbiting science instrument will aim to map the entire open ocean every seven days from its position 408 miles (657 kilometres) above Earth, producing monthly estimates that show how salt levels change over time and location.

While a European satellite was launched in 2009 to measure soil moisture and ocean salinity, the Aquarius/SAC-D is a global collaboration - with partner Argentina as well as France, Brazil, Canada and Italy - that will add to scientists' knowledge of the oceans in novel ways, Nasa said.

Earlier this year, Nasa lost Glory, a $424 million Earth-observing satellite that failed to separate properly from its rocket launcher and plunged into the ocean. - Sapa-AFP