"Heavy rainfall is part of that story because the amount of moisture in the air, and hence the amount of rain, is related only to temperature. We probably wouldn't have had as much rain if it wasn't already warmer. Some of the rainfall rates I saw up here are pretty extreme for anywhere outside the tropics," he said.
Northland was a particularly interesting part of the country in terms of climate change due to the subtropical high pressure belt, a ring of high pressures above and below the tropics with little wind and low rainfall where most deserts were found.
As temperatures rose and the tropics expanded, the high pressure belt moved southwards. The edge of the belt was now over Northland in summer. As a result summers in Northland were likely to keep getting drier - but when there was rain it would "really belt down".
So far the northern part of New Zealand had warmed slightly - one degree over the past 100 years - compared with the rest of the country and the global average. That did not sound like much but in long-term averages one degree was "huge".
Warmer, more reliable summers sounded attractive, but a changing climate also meant changes to ecosystems and agriculture.
"Plants and animals feel small changes in climate very acutely so natural systems will move southwards. Tropical plants that can't grow here probably will be able to in another 50 years or so, and they're not all good news. They're not all pineapples," Prof Renwick said.
"Another big issue is pests and tropical diseases we don't have at present may come our way. I'm not sure that New Zealand will ever become a site for malaria but things that occur in northern Australia, Ross River virus for example, are already moving in our direction."
Climate change could worsen existing tensions, and lead to uncontrolled migration, in places like the Middle East and North Africa by making water scarcer and food production more difficult. New Zealand could also face increased migration if low-lying island nations such as Kiribati are covered by rising sea levels.
Prof Renwick was interested in the Kerikeri sculpture because new ways of communicating science and climate change were needed, including through the arts.
"Giving a lecture and showing graphs is fine up to a point but people need to connect to what you're saying," he said.
He got in touch with Mr Booth after hearing about the sculpture in a radio interview. While in the Bay he spoke at schools, a retirement village, a church hall and the Museum of Waitangi.
Mr Booth was invited to design the sculpture, called Te Haa o Te Ao (The Breath of the World), by Te Runanga o Ngati Rehia. If the required $250,000 can be raised it will be built next to State Highway 10 at the top of Bulls Gorge.
Mr Booth said Ngati Rehia's search for donors had been helped by Prof Renwick's involvement.
"The marriage of art and science has been a successful one since Da Vinci," he said.
"In the case of Te Haa o Te Ao, science enhances the credibility of the art, while the art gives visual expression to the science."
What Northlanders can do about climate change
One thing every Northlander can do to combat climate change is reduce their energy use - but government action is needed to really make a difference.
Victoria University's James Renwick said ways individuals could cut their energy use, and therefore greenhouse gas emissions, included better home insulation, flying less, and switching to an electric car or LED lights.
"But we can't rely only on that. What's required is widespread social change and that has to come from the highest levels of government. We need government policy that encourages society and business to move in the direction of zero-carbon," Prof Renwick said.
He urged Northlanders to write letters to their MPs, phone them up, and generally make some noise.
"It's an election year, it's a perfect time. If there's hundreds or thousands of people telling the government they want action, that would carry some weight."
Prof Renwick said switching from fossil fuels to a zero-carbon economy was often seen as a cost when it offered great opportunities for countries leading the change.
"There seems to be a vacuum of leadership in this. I see no reason why New Zealand shouldn't be at the forefront, but there's very little support from government or business to push it along. We seem to be content to be followers, to cruise along in the hope that someone will come up with a technological fix or sort it out for us."