Average global levels of carbon dioxide stayed above 400 parts per million, or ppm, through all of March 2015 — the first time that has happened for an entire month since record-keeping first began, according to data released this week by the National Oceanic and Atmospheric Administration (NOAA).
“This marks the fact that humans burning fossil fuels have caused global carbon dioxide concentrations to rise more than 120ppm since pre-industrial times,” Pieter Tans, lead scientist of NOAA’s greenhouse gas network, told The Guardian on Wednesday. “Half of that rise has occurred since 1980.”
The burning of oil, gas and coal for energy releases “greenhouse” gases such as carbon dioxide and methane, which warm the planet by absorbing and redirecting outgoing solar radiation that would otherwise escape back into space. These gases have caused the Earth’s temperature to rise over the past century to levels that cannot be explained by natural variability.
Responsible for 63 percent of the warming attributable to all greenhouse gases, carbon dioxide is the “single most important greenhouse gas emitted by human activities,” according to the World Meteorological Organization.
Levels of carbon dioxide go up and down with the seasons, reaching their highest levels in May and then going back down as plants absorb the gas. But on a year-to-year basis, excess carbon dioxide is piling up in the atmosphere at a rate exponentially faster than anything the planet has ever seen before.
‘The beginning of the danger zone’
In May 2013, atmospheric levels of carbon dioxide topped a daily average of 400 ppm for the first time in human history. Some parts of the planet were consistently above the mark for most of last summer, and the entirety of the Northern Hemisphere hit the threshold in May 2014.
Average levels of the greenhouse gas haven’t been this high since between 800,000 and 15 million years ago, according to Climate Central.
But carbon dioxide levels aren’t just higher; they’re also increasing at a record pace — an astounding 100 times faster than the rate of natural rises in the past.
While the 400 ppm mark is a somewhat arbitrary figure — there’s little difference, for example, between the effects of a 395 ppm reading and those of a 405 ppm reading — it serves as a marker with both symbolic and scientific significance, representing a level of carbon dioxide that many scientists associate with a path towards certain irreversible and catastrophic climate impacts.
“It’s the level that climate scientists have identified as the beginning of the danger zone,” Princeton University Prof. Michael Oppenheimer told The Washington Post. “It means we’re probably getting to the point where we’re looking at the ‘safe zone’ in the rearview mirror, even as we’re stepping on the gas.”
Crossing this threshold “[reminds] us that carbon dioxide continues to increase in the atmosphere, and at faster rates virtually every decade” — a trend that “is consistent with rising fossil fuel emissions,” according to NOAA.
Temperatures have also been warming in line with the rising emissions. The world hit a record for the hottest year in 2014 and the trend continued with this winter being the warmest on record. In fact, 14 of the 15 hottest years on record have all occurred in the new millennium — and bear in mind, there have only been 14 years in the new millennium.
These changes are shifting Earth into a “new state” that is becoming less hospitable to human life, according to a groundbreaking report published earlier this year in the journal Science. Human activities are destabilizing the global environment and causing irreversible damage to the biosphere, the report said, warning of “serious, potentially disastrous consequences for society.”
‘Time is running out’
Carbon emissions actually stabilized in 2014 for the first time in over 40 years, due in large part to the widespread adoption of cheaper renewable technologies around the globe. Stabilizing the rate of emissions is not enough to avert global warming, however. NOAA data show that the average growth rate of carbon dioxide concentration in the atmosphere from 2012 to 2014 was 2.25 ppm per year, the highest ever recorded over three consecutive years.
This uncharted territory is something humans will have to navigate for quite some time: since carbon dioxide remains in the atmosphere for hundreds of years, the effects of today’s greenhouse gas emissions will be felt for generations to come. Even if all human carbon emissions stopped immediately, it would still take many centuries, likely much longer, to clear it out of the atmosphere.
“Elimination of about 80 percent of fossil fuel emissions would essentially stop the rise in carbon dioxide in the atmosphere, but concentrations of carbon dioxide would not start decreasing until even further reductions are made and then it would only do so slowly,” said James Butler, director of NOAA’s Global Monitoring Division.
It’s not too late to take action, scientists say, but if we continue on our current trajectory we will pass the point of no return. Reaching the 400 ppm milestone “should serve as yet another wakeup call about the constantly rising levels of greenhouse gases which are driving climate change,” said Michel Jarraud, Secretary-General of the World Meteorological Organization
“If we are to preserve our planet for future generations, we need urgent action to curb new emissions of these heat trapping gases,” Jarraud warned. “Time is running out.”
Yet even as the dire consequences of global warming unfold before us, public opinion about climate change still lags behind the science. Most conservative Republicans don’t think climate change is happening at all, and 70 percent don’t agree that humans are the cause. However, among scientists who have expressed a position on the issue, 97 percent agree that not only is climate change happening, but humans are the ones causing it.