An Alaska aquarium says it has replaced 98 percent of its fossil-fuel heating requirements with a system that draws heat from seawater.

The Alaska SeaLife Center's second seawater system has been operating since January.

The center is in Seward on Resurrection Bay, which absorbs solar heat over summer months and retains much of it throughout winter.

Seawater from the bay warms a loop of water and glycol, which then heats a loop of liquid carbon dioxide, causing the liquid CO2 to boil into a vapor.

When the CO2 vapor is compressed, the vapor temperature rises dramatically and heats water that circulates through conventional baseboard heaters.

The center has cut its heating bill by more than half and estimates it has reduced annual carbon emissions by 1.24 million pounds.