Global carbon dioxide levels in the atmosphere have surpassed 400 parts per million, and will almost certainly remain there indefinitely, according to new numbers from the Scripps carbon dioxide monitoring program at the Mauna Loa observatory in Hawaii.

The 400-level has long been considered a benchmark of irreversible damage to the environment.

"We're really in uncharted territory," said Ralph Keeling from the Scripps Institution of Oceanography, who directs the program. "It's too bad we're this deep into it already, but that's the fact."

The level has swung above 400 parts per million before, but this is the first time it will have stayed that high for all 12 months of the year.

While the year isn't over yet, the month of September almost always has the lowest levels, because it comes at a time when plentiful summer plants in the Northern Hemisphere slow down their carbon dioxide uptake and begin to die off in the fall.

Keeling said that sometimes October has a lower number, but it's only happened four times since 2002. He said it's unlikely that the number will dip below 400 parts per million this year.

And to make matters worse, we've surpassed that benchmark more quickly than anticipated, said Keeling.

"It was first in 2014 that we had a monthly value that was above the 400 level. So it only took a year and a half or two years to overwhelm that natural cycle," he said.

The number is also unlikely to decrease. Keeling said that even if we implement the best environmental policies tomorrow, it would take hundreds of years to stabilize and then lower the levels.

40% rise since Industrial Revolution

Carbon dioxide levels can seem an obscure concept, making it difficult for people to gauge what, exactly, is going on.

To put it into context, Danny Harvey, a professor in the department of geography at the University of Toronto, who teaches about climate change, explains that before the Industrial Revolution, carbon dioxide levels were around 280 parts per million.

"So that's about a 40 per cent increase, and way, way outside the range of the last million years," he explained.

This, coupled with temperature increases, puts the planet on track to become ice-free at some point in the future.

"It doesn't mean all the ice is going to melt in the next 100 or 1,000 years, but it does give you a perspective on just how big these changes are and the trajectory of where we're heading," he said.

University of Toronto scientist Danny Harvey says carbon dioxide levels have increased about 40 per cent since the Industrial Revolution. (Justin Sullivan/Getty)

Harvey said if we do nothing, we're on a clear path toward a climate that is between 1.5 and 4.0 degrees warmer, with carbon dioxide levels around 450 or 500 parts per million.

In order to stop that increase, the world would have to eliminate fossil fuel emissions completely by 2060.

'Status quo isn't on the table'

But this latest benchmark is just one of many that scientists have been warning about for years.

On Thursday, the Pembina Institute released a report saying that Canada is not on track to meet its 2020 or 2030 climate goals.

"Climate change is a more difficult policy problem than anything we've ever faced before," said Kathryn Harrison, a political science professor at the University of British Columbia who studies climate change policy.

The intangibility of the problem makes it a challenge to address.

"Left to their own devices, individuals will make rational decisions to use fossil fuels, because the benefits of driving your car to work — you get those," said Harrison. "While the costs of driving your car are spread among everybody across the planet and to future generations."

Harrison said that's where governments come in — she said leaders will have to be courageous in their plans.

"Because the option of staying the way things are now — it isn't available to us," she said. "The status quo isn't on the table, and I think that's a message that hasn't come through loud and clear."

Game not over yet

Harrison and Harvey both said that the costs of implementing policies that would reduce our greenhouse gas emissions would be about one or two per cent of the country's gross domestic product.

Harrison said this could include making cars on the road more efficient, tightening environmental rules for new construction projects, and phasing out fossil fuel extraction.

"Those things are not crazy and radical," she said.

Despite the glum news, Harvey said all isn't lost.

He said we're in a position now similar to a hockey team that's down a goal in the last two minutes of the third period.

"You might still win the game, but you have to pull your goalie, put your best players on the ice, and then maybe get that goal and then win in overtime."

He said if we want a chance of winning the so-called game and limiting warming as much as possible, then "we have to go flat out."