Soon after New Zealand passed a worrying climate change milestone, scientists have confirmed that atmospheric carbon dioxide levels have now also hit 400 parts per million (PPM) in Antarctica.
The South Pole was the last place on Earth to cross the mark - an amount not seen there for four million years and a grim symbol of the swift pace at which man-made pollution is warming the world.
The pole has shown the same, relentless upward trend in CO2 as the rest of world, but its remote location means it's the last to register the impacts of increasing emissions from fossil fuel consumption, the primary driver of greenhouse gas pollution.
The level was recorded for the first time in New Zealand just a few weeks ago at NIWA's Clean Air Monitoring Station at Baring Head, and in Australia shortly before in Cape Grim, Tasmania.
"The far Southern Hemisphere was the last place on earth where CO2 had not yet reached this mark," said Pieter Tans, the lead scientist of the National Oceanic and Atmospheric Administration (NOAA) Global Greenhouse Gas Reference Network.
"Global CO2 levels will not return to values below 400 ppm in our lifetimes, and almost certainly for much longer."
Over the course of the year, CO2 levels rise during fall and winter and decline during the Northern Hemisphere's summer as terrestrial plants consume CO2 during photosynthesis.
But plants only capture a fraction of annual CO2 emissions, so for every year since observations began in 1958, there has been more CO2 in the atmosphere than the year before.
Last year's global CO2 average reached 399 ppm, meaning that the global average in 2016 will almost certainly surpass 400 ppm.
The only question was whether the lowest month for 2016 will also remain above 400 ppm.
The annual rate of increase also appeared to be accelerating.
The annual growth rate of atmospheric carbon dioxide measured at NOAA's Mauna Loa Observatory in Hawaii jumped 3.05 ppm during 2015, the largest year-to-year increase in 56 years of monitoring.
Part of last year's jump was attributable to El Nino, the cyclical Pacific Ocean warming that produces extreme weather across the globe, causing terrestrial ecosystems to lose stored CO2 through wildfire, drought and heat waves.
Last year was the fourth consecutive year that CO2 grew more than 2 ppm - which set another record.
This year promises to be the fifth.
"We know from abundant and solid evidence that the CO2 increase is caused entirely by human activities," Dr Tans said.
"Since emissions from fossil fuel burning have been at a record high during the last several years, the rate of CO2 increase has also been at a record high.
"And we know some of it will remain in the atmosphere for thousands of years."
Under present projections, the sea level around New Zealand is expected to rise between 50cm and 100cm this century, leaving populations to adapt by either abandoning coasts and islands, changing infrastructure and coastal zones, or protecting areas with barriers or dykes.
Storms occurring on top of a higher sea level would affect public infrastructure such as roads, railways and stormwater systems, as well as private homes and other buildings.
Climate change was also expected to result in more large storms compounding the effects of sea level rise.
New Zealand - which just reported a 23% increase in greenhouse gas emissions between 1990 and 2014 - has pledged to slash its greenhouse gas emissions by 30% from 2005 levels and 11% from 1990 levels by 2030.
