Upper ocean heat content has increased significantly over the past two decades. An estimated 70 percent of the excess heat has accumulated in the top 2,000 feet of the ocean, and the rest has flowed into deeper ocean layers.
The ocean is the largest solar energy collector on Earth. More than 90 percent of the warming that has happened on Earth over the past 50 years has occurred in the ocean. Not all of that heating is detectable at the surface because currents move some of the heat to deeper layers of water, where it can "hide" for years or decades.