Forty million years ago, when the earth was warmer because there was more carbon dioxide in the air as a result of volcanic eruptions, the oceans are thought to have been 70 meters (or 229 feet) higher.
Encouraging cloud formation over the oceans by spraying seawater into the air would be roughly as helpful as pumping the stratosphere full of particles.
It's important to remember that around half of the 25 billion tons of air-borne CO2 emissions humans produce each year also gets absorbed by the oceans.