Millions of people across the world have marked Earth Hour by switching off lights.
Earlier, Minister for the Environment John Gormley appealed for everybody across Ireland to join in by turning off lights for an hour from 8.30pm.
Last year, Ireland was the only country in Europe to support Earth Hour.
Public buildings in Dublin including Government buildings, Leinster House, the Custom House, and the Four Courts turned off their lights.
The Rock of Cashel along with Cahir Castle, Ormonde Castle, Donegal Castle and Trim Castle in Co Meath were all plunged into darkness at 8.30pm.
In Belfast, the dome at Victoria Square shopping centre, the Belfast Wheel and the City Hall building it stands beside, along with Queen's University went dark.
During Earth Hour, Belfast International Airport in Co Antrim turned off all non essential lights throughout the terminal building, as well as the 'Welcome to Belfast ' sign that millions of travellers see as they touch down.
The initiative aims to reduce emissions and promote awareness of climate change.
Up to 1bn people worldwide were expected to take part.