An international report has stressed the need for changes never seen before, in all aspects of our society, to limit global warming to 1.5°C above pre-industrial averages.
The difference between 1.5°C and 2.0°C would change the impact of sea level rise, the survival of our coastal ecosystems and the availability of food and water resources, was also highlighted in the report.
One of the findings included the need to make deep reductions in methane and black carbon, both by 35 percent or more by 2050, compared to 2010 emissions.
The report from the Intergovernmental Panel on Climate Change (IPCC) was prepared following the adoption of the Paris Agreement in 2015.
Ninety-one authors and review editors from 40 different countries prepared the report.
"Limiting warming to 1.5 degrees is possible within the laws of chemistry and physics, but doing so would require unprecedented changes," said Jim Skea, co-chair of IPCC's Working Group III.
One of the lead authors, Associate Professor Bronwyn Hayward, from the University of Canterbury, said the hard-hitting review marked the end of magical thinking about climate change.
"The report is unequivocal, the climate is changing now.
"These changes are already affecting human well-being through extreme weather events and sea level rise, and risking far-reaching losses including coral reefs and Arctic sea ice," she said.
Dr Hayward said the report was politically charged, but it showed temperatures had already seen a rise of 1°C and our world is now warming at a rate of about 0.2°C per decade.
"This doesn't sound like much but if we carry on like this, effectively the world will be warmed 50 percent more than it has already experienced, between 2040 and 2050, and some regions will feel the effects of these changes even more severely and quickly," she said.
"Governments are looking at it to see how they've been getting on with meet their commitments to meet the Paris Climate Agreement. And the report is very clear: We're nowhere near where we need to be in terms of making commitments to cut greenhouse gasses to achieve that Paris agreement."
She said there would need to be significant cuts within the next 10 years.
Dr Hayward said the report presented New Zealand's government and the farming sector with difficult choices.
"We have some tremendous opportunities for reducing methane and nitrous oxide but the need for deep cuts in emissions raises far-reaching questions about stocking and land use."
She said we might expect significant shifts in terms of changing consumer behaviours towards more sustainable diets.
Why half a degree matters
Climatic Change Journal deputy editor Jim Salinger said the report shows the difference between the impacts of 1.5°C and 2°C is earth-shattering.
"For example, coral reefs would decline by 70 to 90 percent with global warming of 1.5°C, whereas more than 99 percent would be lost with two degrees.
Dr Salinger said species loss and extinction are projected to be significantly lower at 1.5°C of global warming compared to 2°C.
Dr Bronwyn Hayward said one of the significant differences will be the ability to reduce sea level rise by about 10cm by the end of the century.
"That would affect they estimate about 10 million people who are living in coastal communities.
"On top of that about 420 million people who might be affected by heat stress, once we get over two degrees," she said.
One of the New Zealand authors of the report said the findings dispelled any wishful thinking that climate change was under control.
The government's perspective
Minister for Climate Change James Shaw said the report was not great reading but the one glimmer of hope was the government's Zero Carbon Bill
"I'm comfortable the work we are doing, will ensure that where the zero carbon bill lands and the course of action we subsequently take, will be consistent with what this particular report suggests what countries need to do."
In addition, Mr Shaw said work on a nationwide adaptation plan and risk assessment for rising sea level rise would begin soon.
Ultimately, he believed New Zealand was ready to meet its responsibilities under the Paris Agreement.