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Smoke is seen being discharged from a chimney in smog in Changchun city, northeast Chinas Jilin province, 8 November 2013.

Smoke billows from a smokestack in Changchun, in China's northeast.

PHOTOGRAPH BY IMAGINECHINA VIA ASSOCIATED PRESS

Brian Clark Howard

National Geographic

Published May 27, 2014

Carbon dioxide levels in the atmosphere crossed a significant threshold in April, just weeks after the White House released a major report on the impacts of climate change and just days before the Obama Administration is set to propose new restrictions on emissions from coal-fired power plants.

The concentration of CO₂, widely seen as the most important greenhouse gas, averaged more than 400 parts per million (ppm) for the entire month of April across the Northern Hemisphere, the first time scientists have seen levels that high and that widespread for an entire month.

The World Meteorological Organization (WMO) announced the new milestone on Monday.

CO₂ levels above 400 ppm were recorded for the first time in 2012 in the Arctic. On a few days in the spring of 2013 they exceeded that threshold at Mauna Loa, Hawaii, where measurements have been made since 1958.

But this is the first time scientists have seen a whole month over 400 ppm at monitoring stations across the Northern Hemisphere, says Gavin Schmidt, a climate scientist with NASA's Goddard Institute for Space Studies in New York City, who was not involved with the measurements.

"Four hundred ppm is not in and of itself particularly important physically," says Schmidt, "but it is emblematic of the fact that we are pushing the climate system into territory that is uncharted."

He notes that environmental groups have been talking up the 400-ppm threshold because "humans like big round numbers."

The 400-ppm level represents a 40 percent increase in carbon dioxide since the start of the industrial revolution, the WMO points out.

Significant Impact

The CO₂ concentration in the Northern Hemisphere is a bit ahead of that in the Southern Hemisphere because there are more industrial sources of emissions in the north. The Northern Hemisphere also has more land and vegetation, so it dominates the seasonal CO₂ cycle: The level in the atmosphere peaks around May, then falls as the northern growing season shifts into high gear and plants start drawing large amounts of CO₂ from the air.

That natural cycle creates zigzags in the atmospheric CO₂ trajectory. The steady, long-term rise comes from human emissions. The WMO predicts that by 2015 or 2016 the CO₂ level will average more than 400 ppm across the entire planet for the entire year. Last year the global annual average was around 395 ppm, according to the U.S. National Oceanic and Atmospheric Administration. Lately it's been rising two to three ppm a year.

Increasing CO₂ will cause more heat waves, droughts, and rising sea levels, said Michel Jarraud, Secretary-General of the World Meteorological Organization, in a statement.

"This should serve as yet another wake-up call about the constantly rising levels of greenhouse gases, which are driving climate change," Jarraud added. "If we are to preserve our planet for future generations, we need urgent action to curb new emissions of these heat-trapping gases."

Schmidt says carbon dioxide levels are higher now than they have been for at least 800,000 years—the age of the oldest ice scientists have been able to retrieve from cores drilled into the Antarctic ice sheet. Bubbles of ancient air trapped in those cores prove that as ice ages have come and gone over the past 800,000 years, the CO₂ concentration has varied from about 180 to 280 ppm. Based on other evidence, scientists consider it likely that CO₂ has not been above 400 ppm for millions of years.

Within a few years, says Schmidt, a level as low as 400 ppm will be a distant memory.

In the meantime, almost 200 governments around the world have agreed to try to work out a deal by the end of 2015 to limit the global average temperature increase to two degrees Celsius (3.6 degrees Fahrenheit) above the average of preindustrial times. Temperatures have already risen about 0.8 degrees Celsius (1.4 degrees Fahrenheit).

In April the United Nation's international panel of climate experts warned that carbon dioxide levels would need to be kept below 450 ppm to keep the temperature rise below two degrees. If the current emission trends continue, that threshold will be passed in two to three decades.

When it comes to avoiding drastic warming and substantial sea-level rise, said Jarraud, "time is running out."

Follow Brian Clark Howard on Twitter and Google+.

28 comments
John  Doe
John Doe

It will be a pleasant respite for the planet when this stupidly destructive species is no longer a blight on the face of this wondrous world. It's just too bad we have to do so much damage to the rest of the natural evolution of the planet and all its inhabitants during our self-imposed extinction process! 

Still arguing over whether there's climate change and how destructive it's going to be for us? Lol...like arguing over whether the Titanic is sinking as the last lifeboats drift away... There are enough greenhouse gases in the permafrost that's about to melt to push us well over 1000 ppm, and it will happen within this century. Then, as all the crops fail and devastation sweeps the globe, have fun arguing over who gets the last scraps of food :)

Neil Aldrich
Neil Aldrich

we're screwed, but the earth will be fine ;)

Darke Tyger
Darke Tyger

Visualize PPM

A jar with 10,000 marbles. We talking about 3 marbles increasing to 4 marbles and this is going to radically alter the earth's climate? It has been as high as 20 marbles in deep time. and in "recent" history 3.4 marbles. Regardless, I do think politicians and alarmists are indeed losing their marbles over this.

Ray Del Colle
Ray Del Colle

The Natural Gas Lady can't connect the dots.  "We have warm years and cold years, but over the long run, global temperatures have gone up." http://clmtr.lt/c/HNs0cN

John Firmston
John Firmston

Short-term variation can be a distraction from the overall arc of climate change. That the world has warmed over the last century, is indisputable. Also changes in surface temperature may hide the fact the much of the added heat gets sequestered deep in the oceans.

Ray Del Colle
Ray Del Colle

The Natural Gas Lady can't connect the dots nor can she understand or handle the truth! I have the impression that things will get worse before they get better. "Don't be distracted by short-term variation. Over the last 130 years, the world has warmed nearly 1.5 degrees Fahrenheit." http://clmtr.lt/c/HNs0cN0cMJ

Daniel Tehrani
Daniel Tehrani

This is truly important information and I commend those who take it seriously. Yes, in the distant past--millions of years ago, such as during the Jurassic period (Jurassic Park-style)--Earth was very warm, with no icecaps as far as we know. Gradual climate change is normal and humans have been adapting to it throughout our history, but rapid climate change, like what's happening now, makes it hard to adapt.


Rapid climate change due to asteroid impact has actually been a cause of mass extinctions in earth's history--many scientists think that's what killed off the dinosaurs. Today's climate change probably isn't quite that rapid, but it's much faster than earth's natural climate rhythm which plods along over thousands and tens of thousands of years.


It's no small task to move millions of people due to sea level rise, drought, and storms like we're seeing now; agriculture, transport, all these systems that we rely on can't adapt to this rate of climate change without major damage and human suffering. It behooves us to drastically lower emissions to slow the rate of climate change and give ourselves, and all life, more time to adapt.  

andre stols
andre stols

This is one of the most frightening stories I have ever read in my 56 years of age- the world( and specially the Chinese) should take this threat seriously and educate the children about this from school level or else Humankind will seize to exist.


every single household can play their part and every government MUST apply strict laws.

KT Pittman
KT Pittman

Good article and it goes hand in hand with the recent article The Future of Food : A Five-Step Plan to Feed the World in this month's magazine (and internet). It isn't about who is right 100% and who is wrong, but more about sustainability and cooperation. That is, if any of us want to sustain our own lives on this planet any further.

Individually, people have to make that decision. So we can as a group effort, work together to make this work. Or destroy it, which we are doing whether you like it or not.

I wish more would educate themselves instead of using political media propaganda to fuel their ignorance.

Mike Murphy
Mike Murphy

Just think of it this way. We are the reigning bug for now and whether we blow ourselves up, wipe out our resources or an asteroid hits the planet, the Earth will just start over. IMHO

Ray Del Colle
Ray Del Colle

"Carbon dioxide has increased about 40 percent in the atmosphere since the 1750s, due to pollution from dirty energy like coal, oil, and gas. The result is a warming climate." http://clmtr.lt/c/HNs0cd0cMJ

Rick Woodruff
Rick Woodruff

ok you state it has not been over 400 ppm for millions of years....so ok spit it out and tell all what the highest it has ever been and if you think we are doomed why was the planet not when it was basically ten fold and more in the past ?????

KENNETH LANE
KENNETH LANE

Nothing to see here, move along now, go home, never mind.  

Nicolas Marolda
Nicolas Marolda

Another case of the corrupt green lobby sponsoring media fear-mongering.

Justin Smith
Justin Smith

It would be nice if the current administration in the US would get their brain cells to working to building Non CO2 power plants FIRST! Then phase out the coal fired plants. 


But that is probably too intelligent of an idea to get past those in the current administration. 

Jack Wolf
Jack Wolf

Another stark warning about what's waiting just around the corner.  And, we are going to see changes regardless of future emissions.  However, if it's damned if you do and damned if you don't, then do.

Darke Tyger
Darke Tyger

@Daniel Tehrani 

Very important and rarely taught for obvious reasons these days.....  rapid climate change has happened before naturally and in all likelihood will again. Please read...

Sudden climate transitions during the Quaternary

http://www.esd.ornl.gov/projects/qen/transit.html

The time span of the past few million years has been punctuated by many rapid climate transitions, most of them on time scales of centuries to decades or even less. The most detailed information is available for the Younger Dryas-to-Holocene stepwise change around 11,500 years ago, which seems to have occurred over a few decades. The speed of this change is probably representative of similar but less well-studied climate transitions during the last few hundred thousand years. These include sudden cold events (Heinrich events/stadials), warm events (Interstadials) and the beginning and ending of long warm phases, such as the Eemian interglacial. Detailed analysis of terrestrial and marine records of climate change will, however, be necessary before we can say confidently on what timescale these events occurred; they almost certainly did not take longer than a few centuries.

Darke Tyger
Darke Tyger

@andre stols 

Are you aware natural rapid change is normal? and if every human being disappared tomorrow, it would still happen?  We are going to have to adapt to natural climate changes even if we never produced a single PPM of C02 again. Agreed?


 Sudden climate transitions during the Quaternary

http://www.esd.ornl.gov/projects/qen/transit.html

The time span of the past few million years has been punctuated by many rapid climate transitions, most of them on time scales of centuries to decades or even less. The most detailed information is available for the Younger Dryas-to-Holocene stepwise change around 11,500 years ago, which seems to have occurred over a few decades. The speed of this change is probably representative of similar but less well-studied climate transitions during the last few hundred thousand years. These include sudden cold events (Heinrich events/stadials), warm events (Interstadials) and the beginning and ending of long warm phases, such as the Eemian interglacial. Detailed analysis of terrestrial and marine records of climate change will, however, be necessary before we can say confidently on what timescale these events occurred; they almost certainly did not take longer than a few centuries.

Brian Deeley
Brian Deeley

@Rick Woodruff So that is what you got out of the article? what about the mention of rising seas, more droughts and heat waves? it also suggests that higher CO2 levels will effect the cycle of ice ages which they suggest regulate the levels of CO2. No ice ages = greenhouse effect.

John Patt
John Patt

@Nicolas Marolda Spouting illogical ad hominem attacks does not make your argument correct. Stop relying on weak emotional arguments, and let's deal with this rationally and analytically.

Brian Deeley
Brian Deeley

@Justin Smith OH and you don't think they haven't sponsored developing green energies and then have it shot down by congress? where have you been?

anne boad
anne boad

@Justin Smith Us is only nation in world to reduce emissions. Hard to believe, but apparently true.

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