The protesters are near the top of the building. Two are holding yellow signs saying "This is real climate action."
The protesters are in jump suits and have secured themselves using ropes. They have also positioned a solar panel about two metres long on the ledge with them.
Because Tim Groser seems to think that Climate Change Ministers are meant to make it happen, rather than prevent it. pic.twitter.com/ZqiUrUmHyp
One of the protesters has spoken to the Herald from the ledge about showing what "real climate action looks like".
"We have come to offer the Government a gift of solar panels, which are working - we are just about to start hooking up now, to charge our phones and stuff like that. We also want to show that this is what real climate action looks like, and we hope that the Government takes action like us," said Greenpeace protester Johno Smith.
Mr Smith, 32, said he could not reveal how the group scaled Parliament.
"We descended down to the ledge about 6.30am, so we have been up here for a little bit. But it's not too chilly today though."
The protesters were all trained and knew what they were doing, Mr Smith said. His own day job was as a self-employed contract climber - climbing trees and doing light installations, and rescuing the odd cat for the SPCA.
"This is actually the second time Greenpeace have been on this ledge. They did pretty much the same action about 17 or 18 years ago, and no Government has really done too much about it so we are here to restate the facts."
The group were communicating with security and were on good terms, and had been told a coffee might be possible later in the day.
"We are only going to stay up here for the day...we know what we are in for in terms of convictions, but we believe what we are doing and what we are highlighting is much more important."
In April Mr Smith was part of the Greenpeace group who boarded an oil rig in the middle of the Pacific Ocean.
He spoke to the Herald then about the reasoning behind his actions.
"I decided I had to take a stand because I don't think Shell have the right to go into the Arctic and cause the potential damage that may happen up there."
"I just hope that other people are inspired to stand up for what they believe in...stand up for what's morally right and have a voice."
Communicating from the ledge
The rooftop activists were using the solar panels to power their phone and communicate with people worldwide.
In a New Zealand first, the Parliament House activists were live streaming the protest using the application Periscope.
They were also holding a "Reddit on the Roof" session which allows people to ask them questions via online discussion forum Reddit.Visit the Greenpeace NZ twitter page for links to take part.
One of the protesters has posted on Reddit as JeffHclimber.
He said the Greenpeace activists wanted to let the Government know climate change was "actually kind of a big deal".
"If people want to know why we're doing this...you may think NZ's pretty and green, but it's actually one of the worst in the world at climate action thanks to a government that's doing next to nothing to cut pollution," he wrote.
"Instead it's handing over taxpayer money to oil giants so they can drill our seas for oil."
Trespass notices issued
A police spokesman said police were supporting parliamentary security staff, who had issued the four protestors trespass notices.
He refused to answer a question about any consequences for the protestors if they ignored those trespass notices.
"We are not going to speculate," he said.
Protesters to stay on roof all day
The environmental group says the message refers to what it says is the "Government's failure to act on climate change, which has seen pollution increase and New Zealand miss out on creating thousands of clean energy jobs."
"The most important thing about this morning is that everybody is safe. They're trained, they're professional, they know what they're doing," Mr Argent said.
The protesters will charge their phones throughout the day using the solar panels, a Greenpeace worker said.
Action was a 'last resort'
Mr Argent said the action was a "last resort" and came after his lobbying of the Government failed to result in meaningful action on climate change.
"It is to send a message to the Government that we want a real climate action plan now."
Greenpeace says government figures show by 2020, emissions will be 30 per cent more than 1990.
Security breach 'alarming'
Maori Party co-leader Marama Fox said the major breach of security was alarming.
"The fact that security was breached is something I am very concerned about.
"This is a very orchestrated campaign. They arrived early this morning, they have utilised the scaffolding that's there for the current maintenance programme we have around the Parliament buildings."
Mr Carter said he did not expect the scaffolding would pose any risk of a security breach.
"It's certainly a breach of security. We facilitate lawful protest here everyday, this is an unlawful protest and now it is a matter for the police to sort out."
Mr Carter said he did not believe proceedings at Parliament today would be disrupted by the protesters' actions.
He understood police were allowing them to stay, until they chose to come down, he said.
At that stage police would take "appropriate action".
"I'd prefer them not to be there in the first place, I'd rather they weren't there all day, but if the police propose that's the best action, that's a matter for the police to decide.
At some stage they will get cold and hungry I have no doubt.
Parliamentary Service tightened security in October following a terror-related attack on Canada's parliament in Ottawa.
The number of entrances for MPs, staff and the public was reduced to two, and security monitoring of the entrances increased.
The changes were a temporary measure, and were relaxed again after a few months, though some entrances to Parliemant now required people to pass through two security doors.
Those measures were designed to prevent access to the inside of the building, not the exterior where Greenpeace protestors are now holed up.
Other activists are watching the protest from outside of Parliament's grounds. Approached for comment, one said Greenpeace spokespeople would be making a statement shortly.
Security are visible through windows behind the group, as well as on the roof.
Coming to the defence of Greenpeace
Green Party MP Gareth Hughes, a former Greenpeace activist, defended the protest.
Greenpeace activist and Kiwi actress Lucy Lawless said she was unaware of today's protest, but supported messages about climate change.
"It's all hands to the pump, everyone's protesting in their own way trying to bring awareness to this because it's tremendously serious."
"If the Pope is coming out saying, 'This is real' - it's a matter of urgent global justice and it's about survival and having a viable planet for our children."
She said not enough was being done at policy level to address climate change.
"It's real, it's here and governments, especially our government, should be getting on with things."
Full security review ordered
Parliamentary Service has ordered a full review of security at the Parliamentary complex as a result of the breach by Greenpeace protestors this morning.
General manager David Stevenson said that for safety reasons, security staff would leave the protestors to come down from the buildings themselves, at which point they would be dealt with by police as trespassers.
"Parliament is the hub of our democracy and the forecourt is frequently the focus of celebrations and protests that reflect the mood of the nation," he said in a statement.
"This is a normal part of our democratic life. In contrast, trespassing in or on the buildings is totally inappropriate, regardless of the motivations of those involved.
"We are therefore taking this incident very seriously and will be looking for any lessons we can draw from it with regard to further tightening our security procedures."
Social media opinions split
Greenpeace's actions were garnering both support and criticism on social media this morning.
"Good to see Greenpeace acting like a bunch of massive t****, as usual. This is what people incapable of winning the argunment do [sic]," said Mark Chiddicks.
A user named MrCyn said: "As much as a I generally loathe Greenpeace, it is a legitimate concern and it is a unique, fairly undisruptive way of going about it."
Another said: "Installing solar panels. This has got to be the funniest protest I have ever seen. Can they do my house next?"
Recent Greenpeace action
April 2015: The Crossing Six Greenpeace activists, including one New Zealand, climb aboard an oil rig in the middle of the Pacific Ocean to protest against Arctic drilling.
March 2015: Stop Deep Sea Oil Greenpeace activists were among the 3,000 people who gathered outside a petroleum industry summit at Auckland's SkyCity.
Oct 2014: Polar bear protest Greenpeace took a fake polar bear around New Zealand to raise awareness about what's happening in the Arctic and the impacts of climate change around the world.
September 2013: Save the Arctic: Artic 30 The crew of Greenpeace ship took part in a peaceful protest at Gazprom's oil rig to call attention to the threat of oil drilling and climate change.
The impact of climate change
• A rise in sea level due to melting glaciers and thermal expansion of oceans
• High levels of greenhouse gases from melting permafrost and dying forests
• High risk of more extreme weather, including heat waves, droughts and floods
• Natural systems, including coral reefs, mangroves, arctic ecosystems, alpine ecosystems, tropical forests, will be threatened
The National-led Government's approach to climate change is for New Zealand to do its "fair share" while not penalising businesses and households.
It has a target of a 5 per cent reduction in greenhouse gases from 1990 levels before 2020, and 50 per cent below 1990 levels by 2050.
The plan to hit this target is through a mix of domestic emissions reductions, the storage of carbon in forests, the purchase of emission reductions units from other countries, and increasing renewable electricity generation.
The main policy tool for combating climate change is an emissions trading scheme (ETS), which requires some polluters to purchase carbon credits for each tonne of emissions.
Government is also looking at ways to reduce agriculture emissions - which are excluded from the ETS - by investing in the Global Research Alliance.
It is currently consulting on a new emissions target for the period beyond 2020 ahead of major climate talks in Paris in December.
A four-week consultation period that recently wrapped up, drawing more than 10,000 submissions, this week came under criticism by the New Zealand Association of Scientists, which was concerned about a lack of publicly available relevant information, a short submissions period and "minimal involvement" by key scientific institutions.
Parliamentary Commissioner for the Environment Dr Jan Wright described the discussion document which the Government used as a platform for its consultation as "disappointing", and in her own submission made an urgent call for a national forum to tackle the issue.
Dr Wright said New Zealand should be presenting an ambitious climate target backed by a robust plan, she said, and the country had "major opportunities" to reduce emissions through forestry, electricity and transport - "but they will not just happen of their own accord".
New Zealand is expected to be affected in a range of ways by present climate change projections, under which the mean temperature is expected to be 2C or higher by the end of the century - and even between 3C and 4C higher if no action is taken to curb the world's carbon emissions.
Within the same period, sea level is expected to rise between 50cm and 120cm.
A major report released by the Prime Minister's Chief Science Advisor, Sir Peter Gluckman, in 2013, outlined the changes over coming decades in wind, temperature, rainfall and seasonal extremes, and how they would impact industry and populations.
By the turn of the next century, Auckland would see 40 warm days above 25C each year, while in the South Island, frosts in coastal spots would be rare by 2050.
By the same time, there would be two or more extra weeks of drought annually for much of the North Island and eastern South Island.
There would be less rainfall in summer and autumn over the west of the North Island - but rates could increase by 5 per cent in winter and spring.
The picture was again different on the other side of the island; the Gisborne and Hawkes Bay regions stood to lose up to 10 per cent of its winter and spring rainfall.
Around the country, Kiwis could expect a climate 0.9C warmer by 2040, and 2.1C warmer by 2090, according to mid-range projections for average temperature rises.
This would bring general changes, including heavier and more frequent extreme rainfalls, stronger extreme winter winds and bigger changes in pH in cooler waters.
Extreme weather events, such as floods and droughts, would become more frequent, while higher sea levels, rising at 30mm a decade, would worsen the impact of storms at coastal centres.
Native species could battle to adapt to warmer temperatures, heightening the threat of pests and human diseases.