Forbes said declaring this emergency was to give climate change the recognition it deserved.
"It's also to raise awareness of the impacts we're already starting to feel here close to the coast," he said.
"To avoid the worst effects of climate change, we will need to take local and global action. We will need to make changes as councils, as businesses and as individuals.
This declaration is our way of raising awareness of the changes and the extent and speed with which we all need to act," Forbes said.
The UK, Ireland, Wales, Canada and France have all declared a climate change emergency.
More than 50 New Zealand scientists have called on the Government to declare a national climate emergency.
Prime Minister Jacinda Ardern previously said the Government was keen to do so but work was needed to get more MPs to come on board.