The urban heat island effect is a direct result of adding concrete ,asphalt , and brick buildings  where they did not exist before, absorbing more solar radiation .Nothing to do with the oceans.
Oceans are warmed by solar radiation ,always have , always will. Nothing to do with man made CO2. Compare solar radiation penetration of sea water to I.R. penetration of sea water.The planet is 70% covered by water, all that  sea water has a 1000x's the heat capacity of the entire atmosphere.About the top 3m of the sea water is the equivalent of the entire atmosphere in heat capacity .Glaciers ,arctic ice , permafrost melting has been happening since the start of this inter glacial started about 10000 years ago. We only started to build a accurate ocean  temperature historical data base with the argo buoys in the last 17 years.
Recently it only started to warm again in the last 150 odd years ending the L.I.A. & every body knows that.