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The Intergovernmental Panel on Climate Change's much-anticipated climate update found that New Zealand had a significant "adaptation deficit" in the face of human-influenced global warming of between 2C and 4C by 2100.
The UN organisation's analysis said the country was already witnessing climate change in the form of extreme weather events, and could expect more frequent and more intense storms and damage to coastal infrastructure and low-lying ecosystems as a result of rising oceans.
New Zealand scientists described the report as a wake-up call which should prompt New Zealand to "take its head out of the sand".
The Government welcomed the IPCC's release and said it put new emphasis on the importance of adapting to climate change.
The report is the work of 309 authors from 70 countries, who were supported by 436 contributing authors and 1729 experts and government reviewers. The team has pored over the content and wording of the final version for five days in Yokohama, Japan, ahead of its release this afternoon.
The report's authors said in a statement that that the effects of climate change were "already occurring on all continents and across the oceans".
"The world, in many cases, is ill-prepared for risks from a changing climate. The report also concludes that there are opportunities to respond to such risks, though the risks will be difficult to manage with high levels of warming."
Victoria University Associate Professor of Geography, Environment and Earth Sciences James Renwick said the report painted a very clear picture of what the future could hold for humanity if it failed to get on top of greenhouse gas emissions.
He said one of the biggest issues that New Zealand faced was sea level rise and its associated hazards.
"Every 10cm of rise triples the risk of a given inundation event, and we are expecting something like a metre of rise this century. That would make today's 1-in-100 year event a weekly occurrence by 2100.
"New Zealand has a great deal of valuable property and infrastructure close to the coast that will be increasingly at risk as time goes on."
The report's authors had "high confidence" that New Zealand would face more frequent and more intense flood damage before the end of the century
Victoria University Antarctic Centre head Tim Naish, who was a lead author for the IPCC's previous report, said that new analysis confirmed and strengthened the certainty around anthropogenic climate change.
He said extreme weather events would become more frequent as the wet regions in the west of New Zealand could expect more rainfall and the dry regions in Canterbury, the Far North and the East Cape became drier. This would have implications for water resources and primary industries such as agriculture and horticulture and could create challenges for hydro-electric power generation.
Dr Naish said: "This report is a wake up call for New Zealand to take its head out of the sand, to take a longer-term view - at least longer than an electoral cycle - and rise to the challenge of adaptation if we are to future-proof this country for coming generations."
Climate Change Minister Tim Groser said the report backed the view that adaptation was as important part of dealing with climate change that could not be ignored.
"While much of our focus is on getting international agreement on reducing emissions, some change can't be avoided so we must be prepared to adapt."
He noted that on top of the risks that this country faced, it could also benefit from reduced energy demand because of warmer winters and some regions could observe increases in spring pasture growth.
The report said planning for sea-level rise in Australia and New Zealand had evolved considerably over the last two decades, but its implementation remained "piecemeal".
The IPCC Working Group II's co-chairman Chris Field said countries and governments were beginning to adapt, but were mostly reacting to past events and not preparing for a changing future.
"Climate-change adaptation is not an exotic agenda that has never been tried. Governments, firms, and communities around the world are building experience with adaptation," he said.
"This experience forms a starting point for bolder, more ambitious adaptations that will be important as climate and society continue to change."
- Isaac Davison of the New Zealand Herald