Warming seas, overfishing and pollution mean it is vital to improve the system for monitoring the world's oceans, says a group of distinguished scientists.
The researchers say more data is needed to ensure the world is able to respond effectively to any potential threats.
An "adequate initial system" would include an integrated network of buoys, research vessels, satellites and tagging marine animals, they added.
The scientists want the global scheme to be completed within the next decade.
The call for action has been made by the Partnership for Observation of the Global Oceans (Pogo), which includes many of the world's leading oceanographic research centres.
A delegation of Pogo members will make their case at the annual ministerial meeting of the international Group on Earth Observations (Geo) in Cape Town, South Africa.
Tony Haymet, chairman of the Pogo's executive committee, said the international community had agreed to "construct a comprehensive, integrated ocean observing system two decades ago".
Technological advances are helping unlock the oceans' secrets
But he added that the venture was less than half completed.
"The good news is that we have demonstrated that a global ocean observing system can be built, deployed and operated with available technologies," said Dr Haymet, director of the US's Scripps Institution of Oceanography.
"Now we must move from experiment and proof-of-concept to routine use. Let's complete the task before we are struck by more tsunamis or comparable calamities."
According to Pogo, completing such a system over the next 10 years would cost an estimated $2-3bn (£1-1.5bn), and would include:
- A network of satellites - to survey the oceans' vast surfaces
- Fixed monitoring stations - for continuous measurements on the sea bed, water columns and surface
- Small robot submarines - some will drift with ocean currents, while others will follow pre-determined routes
- Tagging - electronic devices will relay information about the areas marine animals visit
- Research vessels - to be used for scientific surveys
The scientists say a better understanding of how the oceans behave would have a range of benefits, from improving short-term forecasting of potentially devastating storms and hurricanes, to the possible impact of warming waters on marine and coastal ecologies.
"Marine scientists could authoritatively diagnose and anticipate changing global ocean conditions - something akin to the system that enables meteorologists to predict weather," Dr Haymet explained.
The Pogo delegation will present its case on Friday to the GEO ministerial meeting, which will review progress on the Global Earth Observation System of Systems (GEOSS) and agree a roadmap for the coming decade.