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I was surprised you didn’t mention the effect of salinity in ocean water in this article. Warming climate has melted much of the glaciers, bringing fresh water into the North Atlantic. That water isn’t dense enough to sink and carry on the conveyor belt that usually brings warm currents from the tropics. This slowing of the conveyor belt happened during the Little Ice Age, and apparently, it’s happening again.

Bella C. Chiu
Arlington, Mass.

Isn’t it likely that the accelerated breakup of polar ice holds the key to the missing heat? Massive amounts of heat are absorbed by the solid-to-liquid phase change when ice melts, and recent observations have shown a striking reduction of ice thickness.

David Roper
Grand Junction, Colo.

Perhaps the heat is going into the atmosphere and is the origin of what we measure as “global warming.”

Paul Etzler
Cedar City, Utah

As far as scientists can tell, top-layer cooling of the world’s oceans isn’t an effect of melting ice in the polar regions. Some of the heat may be warming the atmosphere, scientists say. However, much of the missing heat remains unaccounted for. —S. Perkins