Leading climate scientist James Hansen used a study published Tuesday to continue to hammer home the warning that humanity is nearing "the point of no return" when it comes to reversing or even mitigating the adverse effects of climate change.

The study, initially made public in draft form last July as a "discussion paper" so it could be circulated  ahead of the Paris climate talks, holds that multi-meter sea rise could happen within a matter of decades, rather than centuries as previous estimates suggested. Hansen argues the dramatic sea level rise could put the earth's coastal cities in grave peril while a sudden influx of population from those cities will bring discord and conflict to the rest of the world.

The study, co-authored by a team of 19 international climate scientists, was published this week in the peer-reviewed journal Atmospheric Chemistry and Physics.

Hansen dismissed criticisms that the somewhat unorthodox study had stretched the science and blurred the line between advocacy and research.

The conclusion that deep cuts in net emissions of carbon dioxide are required to avoid a global calamity is "a scientific conclusion," he said. "It's not advocacy. It's telling you what is needed."

The study uses models, paleoclimate data and modern observations to analyze the impact of ice shed from Antarctic ice shelves and Greenland. It concludes the feedbacks created by the intrusion of cold freshwater into the planet's oceans are already shutting down ocean circulation, leading to the formation of more powerful superstorms. The study also contends the real world has been responding much faster to the inundation of freshwater than the models anticipated.

The study's basic conclusions remain the same as the original, though the title was softened. The initial title of "Ice melt, sea level rise and superstorms: evidence from paleoclimate data, climate modeling, and modern observations that 2 °C global warming is highly dangerous" had the final phrase changed to "could be dangerous."

Hansen, the former director of NASA's Goddard Institute for Space Studies and currently the director of the Climate Science, Awareness and Solutions program at Columbia University Earth Institute, has been one of the foremost voices urging rapid and comprehensive action to slow greenhouse gas emissions. Hansen, 74, developed one of the world's first climate models 35 years ago and has produced prediction after prediction about rising global warming that proved to be correct.

"This is a tragic situation—because it is unnecessary. We could already be phasing out fossil fuel emissions if only we stopped allowing the fossil fuel industry to use the atmosphere as a free dumping ground for their waste," Hansen said in a video accompanying the study's publication, repeating previous statements he's made on instituting a carbon tax.

Hansen has been equally blunt about who's to blame for the planet's warming. He's been arrested several times at climate protests targeting the Keystone XL oil pipeline and other fossil fuel projects. He and 21 young people between the ages of 8 and 19 are currently suing the federal government for promoting "the use of fossil fuels, thus increasing the concentration of CO2 emissions in the atmosphere to unsafe levels and creating the dangerous climate change and ocean acidification that we face today."

In a conference call Monday, Hansen said that if scientists don't come out and say that drastic emissions cuts are needed, "then politicians will tell you what's needed and that will be based on the politics, rather than on science. So I don't see any reason not try to make the complete story clear rather than just drawing a line and saying, 'I'm not going to step beyond this.'"

The Paris Agreement, a treaty intended to slow global warming, limits fossil emissions and forest clearing in order to keep the planet from warming more than 2 degrees Celsius above pre-industrial times, and possibly to keep the rise below 1.5 degrees Celsius. Either ambitious target would require eliminating  additions of greenhouse gases to the atmosphere. But the paper's authors stress the 2 degree Celsius threshold would still lead to inexorable damage.

"If Greenland freshwater shuts down deepwater formation and cools the North Atlantic several degrees, the increased horizontal temperature gradient will drive superstorms stronger than any in modern times," Hansen said in the video. "All hell would break loose in the North Atlantic and neighboring lands."

The effects of ice melt on ocean circulation were not included in the latest assessment by the United Nations' Intergovernmental Panel on Climate Change (IPCC), meaning Hansen's predictions would occur much earlier and be less gradual than envisioned in the consensus reports of the IPCC.

Hansen's renewed calls for aggressive climate policy comes as the World Meteorological Organization confirmed that 2015 smashed temperature records, with global average surface temperature topping previous records by at least 0.76 degrees Celsius above the average temperatures from 1961-1990. This year is on pace to shatter even more records.  

"The alarming rate of change we are now witnessing in our climate as a result of greenhouse gas emissions is unprecedented in modern records," WMO Secretary-General Petteri Taalas said in a statement.