Nihar Gokhale writes: 400 parts per million (ppm) refers to the concentration of carbon dioxide in the Earth’s atmosphere. It is a level that has for long been considered a limit the world should not cross. On 10 May, an Australian monitoring station became the first in the southern hemisphere to record above 400ppm CO2.
In the last fortnight, the phrase ‘400 ppm’ has come up frequently in climate policy circles, and is accompanied part by alarmism, part quiet resignation.
400 parts per million (ppm) refers to the concentration of carbon dioxide in the Earth’s atmosphere. It is a level that has for long been considered a limit the world should not cross. It is now a limit we have breached.
On 10 May, an air monitoring station in Australia became the first in the southern hemisphere to record above 400 ppm CO2. This comes after other monitoring stations in the northern hemisphere showed such measures last year.
While the northern stations have shown brief periods of 400-plus readings during summers since 2012, scientists believe that this year is decisive – because it’s the first time the southern station showed such readings, and because they believe this is not a temporary blip – CO2 may never fall below 400 ppm.
WHY THE LATEST READING IS IMPORTANT
Last November, the world’s oldest CO2-monitoring station in Hawaii measured 400-plus ppm CO2. The American government-run National Ocean and Atmospheric Administration’s (NOAA) global average had passed that mark in March.
The northern hemisphere has a larger landmass and more vegetation, so seasonal cycles are sharper. Every year, there is a sharp rise in CO2 concentration during summer and winter.
But this is not so for the southern atmosphere. So, when the Cape Grim monitoring station in Tasmania, the Australian island, raised an alarm after breaching 400 ppm for the first time, it got everyone’s attention. Scientists at the station believe that the levels may not drop below 400 ppm, probably because there are no seasonal swings.
“Passing the 400 mark reminds me that we are on an inexorable march to 450 ppm and much higher levels. These were the targets for ‘stabilisation’ suggested not too long ago… It should be a psychological tripwire for everyone,” said NASA scientists Michael Gunson in a statement.
The high readings this year are worrying because they come after a record jump in CO2 readings in 2015. Carbon dioxide levels rose by 3 ppm in that year. This means that at the current rate we will reach the dangerous 460 ppm levels within 20 years.
While human-induced carbon emissions is the main culprit, so is the El Nino, a weather phenomenon that causes warming around the world. Drier weather means less vegetation and lesser conversion of CO2 into oxygen.
Unsurprisingly, 2016 is also slated to be the warmest year on record, with temperatures rising above 1 degree and just a little shy of the 1.5 degree mark.
WHAT DOES HIGH PPM DO?
400 parts per million means that in an air sample with moisture taken out, out of one million molecules, 400 were CO2.
CO2 traps the Sun’s heat in the Earth’s atmosphere – a phenomenon known as the greenhouse effect. More carbon dioxide means more heat is trapped, causing global warming and climate change.
“400 ppm is a level that the world should not cross. Yet, we’ve managed to breach it.”
Although not the worst possible CO2 level, 400 ppm is a tipping point. Like all climate tipping points, there isn’t an immediate catastrophe. It’s less a cliff, and more a slope that gets steeper as you descend.
More carbon also means polar ice will melt faster, raising sea levels sooner. Higher carbon dioxide concentrations also causes oceans to become acidic, hurting marine life.
HOW MUCH PPM IS SAFE?
Before the industrial revolution, the Earth had 280 ppm CO2. It has climbed sharply in the last few decades. CO2 levels have risen 24% since 1958, when the world’s oldest CO2 monitoring station at Hawaii opened.
Die-hard environmentalists want to go back to 280 ppm. Many others want it to fall to 350 ppm (giving the climate campaign 350.org both its name and its objective).
It is considered that 460 ppm can potentially cause global temperatures to rise by 3 degrees Celsius since the industrial days. Currently, we are 0.9C above that level, and the recently signed Paris Agreement on climate change wants it to remain within 2C, preferably below 1.5C.