New Zealand scientists who contributed to an alarming global greenhouse gas stock-take say the figures don't bode well for meeting goals of the Paris Agreement on climate change quickly.
The latest World Meteorological Organisation's Greenhouse Gas Bulletin found abrupt changes in the atmosphere witnessed in the past 70 years were without precedent.
Globally averaged concentrations of CO2 reached 403.3 parts per million (ppm) last year up from 400ppm in 2015 because of a combination of human activities and a strong El Nino event.
Concentrations of CO2 were now 145 per cent of pre-industrial levels, according to the bulletin.
Rapidly increasing atmospheric levels of CO2 and other greenhouse gases have the potential to initiate unprecedented changes in climate systems, leading to "severe ecological and economic disruptions", the report said.
Its contributors included Dr Jocelyn Turnbull - radiocarbon science leader at GNS Science and one of 51 members of the WMO's greenhouse gas group - and GNS colleagues Dr Nancy Bertler and Dr Richard Levy.
Bertler and Levy provided context to the current CO2 concentrations and rate of change, or increases, through changes observed in the past.
Their work showed how current concentrations were last seen in the mid-Pliocene era, around three to five million years ago, when Greenland and West Antarctic ice sheets had collapsed.
At that point in our planet's history, even parts of the much larger East Antarctic Ice Sheet had retreated to cause global sea levels to be 10 to 20m higher than today, with global temperatures 2-3C warmer.
Levy also offered an outlook on higher-CO2 worlds - assuming concentrations of between 400ppm and 650ppm - that warned of temperatures 3-4C warmer and up to 40m of global sea level rise.
Concentrations higher than 1000ppm could spell an end to all of the planet's ice sheets.
They further showed how some extremely high resolution ice core records indicated past increases in CO2 varied and had different causes.
A slow increase of 10ppm over 1000 years at the end of the Last Glacial Maximum - the last period in the Earth's climate history when ice sheets were at their greatest extent - were due to changes in the Southern Ocean.
More abrupt changes, with an increase of between 10-15ppm over 100 to 200 years, were caused by complex interplay between the North Atlantic and Southern oceans.
But, Bertler pointed out, today's decade average was 2.2 ppm each year - making it 20 times as fast as the swiftest rates they observed in the past.
"Overall, it's not a good start to meet the Paris Agreement in a hurry."
Population growth, intensified agricultural practices, increases in land use and deforestation, industrialisation and associated energy use from fossil fuel sources had all contributed to increases in concentrations of greenhouse gases in the atmosphere since the industrial era, beginning in 1750.
Since 1990, there has been a 40 per cent increase in total radiative forcing - the warming effect on our climate - by all long-lived greenhouse gases, and a 2.5 per cent increase from 2015 to 2016 alone.
"Without rapid cuts in CO2 and other greenhouse gas emissions, we will be heading for dangerous temperature increases by the end of this century, well above the target set by the Paris climate change agreement," WMO Secretary-General Petteri Taalas said.
"Future generations will inherit a much more inhospitable planet."
CO2 remained in the atmosphere for hundreds of years and in the oceans for even longer.
"The laws of physics mean that we face a much hotter, more extreme climate in the future," Taalas said.
"There is currently no magic wand to remove this CO2 from the atmosphere."
New Zealand and climate change
• Under present projections, the sea level around New Zealand is expected to rise between 30cm and 100cm this century. Temperatures could also increase by several degrees by 2100.
• Climate change would bring more floods; worsen freshwater problems and put more pressure on rivers and lakes; acidify our oceans; put even more species at risk and bring problems from the rest of the world.
• Climate change is also expected to result in more large storms compounding the effects of sea-level rise.
• New Zealand, which reported a 23 per cent increase in greenhouse gas emissions between 1990 and 2014, has pledged to slash its greenhouse gas emissions by 30 per cent from 2005 levels and 11 per cent from 1990 levels by 2030.
•The new coalition Government has promised greater action from New Zealand, with a proposed new independent Climate Commission and Zero Carbon Act and goals for a carbon-neutral economy by 2050 and 100 per cent renewable energy by 2035.