Scientists said Thursday they had found evidence of a natural thermostat that may limit ocean surface temperatures to a monthly average of about 89 degrees.

A study of the tropical Pacific Ocean found that when the water got warm enough, it limited further warming by triggering the formation of clouds that provided shade.Scientists said it is not clear whether such a phenomenon would help counteract global warming, the expected result of a buildup in the atmosphere of heat-trapping gases.

The work was presented in Thursday's issue of the British journal Nature by Veerhabdran Ramanathan and William Collins of the California Space Institute.

The cloud-shading effect had been suggested before, but the new study provides experimental evidence, Col-lins said.