In 2015 Auckland's gross greenhouse gas emissions increased by 3.8 per cent - much more than previous years.

Auckland is releasing more greenhouse gases than ever.

But it's not all doom and gloom, with emissions per capita falling and Auckland Council taking action to reduce the city's carbon footprint.

A report recently released by Auckland Council, which looked at different sectors in Auckland in 2015, said emissions were increasing at a faster rate than previously.

JASON OEXENHAM/STUFF Road transport made up 35.7 per cent of emissions.

Between 2009 and 2015 Auckland's gross greenhouse gas (GHG) emissions increased on average by 1.2 per cent per year, yet in 2015 they increased by 3.8 per cent.

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Greenhouse gases absorb radiation, which traps and holds heat in the atmosphere and is one of the main factors responsible for global warming.

SIMON MAUDE/STUFF Mayor Phil Goff says tackling climate change is one of humanity's most pressing issues.

In 2015 Auckland's GHG emissions were 11,309 kilotonnes of carbon dioxide, the report said. One kilotonne is equal to 1 million kilograms.

By comparison a 2014 United Nations report said New Zealand's total GHG emissions were 81,104 kilotonnes, which was 1 per cent higher than 2013, and up 23 per cent since 1990.

Road transport made up 35.7 per cent of emissions, by far the worst GHG emitter for the city, the report said.

JAMES PASLEY/STUFF Auckland Council chief sustainability officer says Auckland needs faster emission reduction progress in coming years, especially as population grows.

Industrial practises and product use, including steel production and glass making, accounted for 21 per cent of emissions in 2015, the report said.

Despite the rise in emissions, per capita GHG emissions had decreased from 2009 to 2015, which meant emissions weren't tied to population and economic growth, the report said.

​The report was released in the same month mayor Phil Goff entered into a non-binding C40 fossil free streets declaration along with mayors of Barcelona, Cape Town, Los Angeles, Milan and Paris.

"Tackling climate change is one of humanity's most pressing issues. In a city such as Auckland that grows by 50,000 people per year and where 800 cars are added to our roads each week, the task is significant," Goff said.

Auckland Council had been making changes in transport, urban development, waste minimisation and the planting of trees, he said.

"These are all reducing emissions."

For example the electrification of rail reduced Auckland's rail emissions by 80 per cent, translating to a reduction from 30.2 kilotonnes to 6.1 kilotonnes and a saving of more than 9 million litres of diesel a year, he said.

"Next year we are trialling electric buses with the aim of progressively replacing our fleet of diesel buses."

Goff also had his petrol mayoral car replaced with an electric one.

"It is clear that we can do more and I am committed to ensuring that Auckland Council show leadership and reduces its carbon emissions where possible."

Sustainable Business Council executive director Abbie Reynolds said businesses weren't a homogenous entity, but it was a hopeful time and many businesses were reframing climate issues as an opportunity to improve.

"We're seeing a bunch of businesses make long-term carbon targets," Reynolds said.

Auckland was likely to experience the impact of these targets by about 2020 because goals had been set over the last 12 months, she said.

Auckland Council chief sustainability officer John Mauro said there were positives from the report.

Per capita emissions starting to decline was a sign that better transport choices, waste prioritisation and energy improvements were happening, Mauro said.

"However the economic, social and environmental success of our city requires an ambitious and accelerated reduction in emissions as we also prepare for the impacts of a changing climate.

"We need to see far faster and greater progress in coming years, especially as Auckland's population continues to grow."

Auckland Council research and evaluation unit scientist and author of the report Shanju Xie said emissions varied from year to year and it was not clear what emissions for 2016 and 2017 would look like.