Atmospheric carbon dioxide measurements taken at the summit of Mauna Loa have surpassed 415 parts per million for the first time in modern history in what scientists say is yet another jarring reminder of the effects of man-made climate change.

“Sobering” is how Josh Stanbro, head of Honolulu’s Office of Climate Change, Sustainability and Resiliency, described the news.

“It’s a whole new world we’re heading into,” he said. “Alarm bells are going off on Mauna Loa and we need to wake up.”

The measurement is courtesy of the Mauna Loa Observatory, which has recorded changes in the concentration of carbon dioxide in the Earth’s atmosphere since 1958.

The ever-climbing Keeling Curve, maintained by the Scripps Institution of Oceanography in La Jolla, Calif., was among the first scientific calculations to alert the world to the possibility of human contribution to the “greenhouse effect” and global warming.

Ice core records indicate that current carbon dioxide levels far exceed any present on Earth in the last 800,000 years, scientists say, and ocean measurements at Station ALOHA in the Pacific Ocean north of the islands recorded a similar rise in near-surface ocean carbon dioxide plus corresponding ocean acidification.

At the atmospheric baseline station atop Mauna Loa, the 415 parts per million reading was topped for the first time May 10. The May 14 reading was 415.26 parts per million.

In 2013, the measurement reached 400 parts per million the first time. Two years ago it surpassed 410 parts per million — nearly 100 parts per million more than its first reading 61 years ago.

“Every year it goes up like this we should be saying, ‘No, this shouldn’t be happening. It’s not normal. This increase is just not sustainable in terms of energy use and in terms of what we are doing to the planet,” said Ralph Keeling, director of the Scripps CO2 Program in a statement.

“We don’t know a planet like this, but the generations after us will have to live with the consequences of our actions. We must act now,” U.S. Sen. Mazie Hirono of Hawaii tweeted May 14 in response to the latest Keeling Curve record.

Victoria Keener, a climate scientist and research fellow at the East-West Center in Honolulu, said surpassing 415 parts per million is not a surprise.

“It’s like a slow time bomb that we’ve all been watching. We all knew it would happen. It’s just another milestone we failed to prevent,” she said.

Keener, lead principal investigator of the Pacific Regional Integrated Sciences &Assessments program, was the lead author of the Hawaii-Pacific Islands chapter in last year’s fourth U.S. National Climate Assessment report that examined the effects of climate change on the U.S. economy and communities.

The report concluded that Hawaii faces a future of extreme coastal flooding, warmer temperatures, extended periods of drought, dying coral reefs and hurricanes with greater intensity if humans don’t drastically reduce greenhouse gas emissions.

Keener said the Keeling Curve is a reminder that we’re running out of time and cannot afford to wait to take action on climate change.

“We need to implement aggressive policies even if they are not perfect,” she said.

The late Charles David Keeling of the Scripps Institution installed an infrared gas analyzer at Mauna Loa in March 1958, and on its first day of operation recorded an atmospheric carbon dioxide concentration of 313 parts per million.

Keeling chose Mauna Loa for the measurements because of its remote location and stability far above any pollution.

It wasn’t long before the project made two major discoveries: that carbon dioxide underwent a regular seasonal cycle, reflecting the seasonal growth and decay of plants in the northern hemisphere, and that it is rising over the long-term due to the burning of fossil fuels.

Unless serious efforts are made to reduce the dependence on fossil fuels, the planet is on the threshold of a new era of geologic history, one with a climate very different from those who came before us, according to the scientists at Scripps.

Chip Fletcher, University of Hawaii at Manoa earth sciences professor, added that the latest reading from Mauna Loa represents “yet another signal that humanity has failed future generations, continues to devastate global ecology, and relentlessly places profit before planet and before people.”