Last Tuesday, carbon dioxide levels in the atmosphere scaled another psychologically important — and immensely worrying — peak, going past 410 parts per million (ppm). Atmospheric carbon dioxide concentrations are now at the highest levels they have been in at least 3 million years. More importantly, over the past couple of years, they have increased faster than probably ever before. While the rate of growth of CO2 in the atmosphere has shown regular ups and downs, the levels grew less than 1 ppm every year between 1959 — when one of the most important sites for taking these measurements, the Mauna Loa Observatory in Hawaii, started keeping records — and 1964.
There was a general quickening thereafter, but it still remained in the order of 1-2 ppm annually — until 2015, when the concentrations jumped by 3.03 ppm. The following year, they grew by 3.0 ppm. On May 10, 2013, scientists reported that during the 24-hour cycle ended the previous day, the average reading for an entire day at Mauna Loa had for the first time surpassed 400 ppm. At the end of September 2016, scientists announced that CO2 levels were likely to stay above 400 ppm “for the indefinite future”.
Levels measured at Mauna Loa have risen every year since 1959, going from 315.97 ppm that year to 400.83 in 2015, and 404.21 in 2016. The US National Oceanic and Atmospheric Administration (NOAA) noted in a release on March 10 this year that CO2 had risen by 2 ppm or greater for a record five years in a row, and “the rate of CO2 growth over the last decade is 100 to 200 times faster than what the Earth experienced during the transition from the last Ice Age”.
So why is an increased concentration of CO2 bad for the Earth? Simply put, CO2 is one of several gases that trap heat in the atmosphere, creating the “greenhouse effect” that keeps the Earth from getting too cold for life. But if the CO2 increases, extra heat is trapped in the atmosphere, and global average temperatures begin to rise. The more the CO2, the greater the atmosphere’s capacity to trap heat.
“Atmospheric CO2 is now higher than it has been for several million years, as measured in ice cores and ocean sediments,” Dr Pieter Tans, lead scientist of NOAA’s Global Greenhouse Gas Reference Network told The Indian Express in an email. “The current rate of increase is about 200 times faster than when CO2 increased by about 80 ppm from natural causes when the Earth climbed out of the last Ice Age, which occurred between 17,000 and 11,000 years ago. The rapid increase is no surprise. Emissions from the burning of coal, oil, natural gas, and from cement manufacture have been close to 10 billion metric tonnes of carbon (same as 37 billion metric tonnes CO2) per year.”
Determined efforts at climate change action have resulted, according to preliminary data for 2015 released last year by the Paris-based intergovernmental organisation International Energy Agency, in a “decoupling” of economic growth and emissions growth. The data suggest that even as electricity generated by renewables accounted for about 90% of new electricity generation, the global economy grew by more than 3%.
But scientists are cautious. “For the last several years, global emissions of fossil fuel CO2 appear to have levelled off. However, this happened while it is at a record high. As a direct result, the rate of atmospheric CO2 increase also remains at a record high. The main reason is that the extra CO2 cannot be removed from the ocean-atmosphere system for thousands of years,” Dr Tans said.
Also increasing CO2 concentration is vegetation. There is a roughly 7 ppm swing between the peak and trough values in a year, mainly because in winter in the northern hemisphere, the dormant vegetation doesn’t remove CO2 from the air. Similarly, a drought caused by a strong El Niño event could trigger a spike in CO2 levels. A minor comfort is that concentration levels could fall below the 410 ppm mark as daily measurements fluctuate — but if there is no drastic action, there could be no reversal. The concentration is not expected to fall below 400 ppm any time soon in any case.
The Paris Agreement, considered an achievement of global action in which all nations came together and vowed to keep global temperature rise to below 2 degrees Celsius above pre-industrial levels, also resolved to pursue efforts to limit temperature increase further to 1.5 degrees Celsius. Some scientists say that to do that, the upper limit for CO2 concentrations would have to be 450 ppm.
“The long residence time of emitted CO2 implies that emissions will have to decrease at a significantly more aggressive pace if the world would want a reasonable chance of keeping the temperature increase below 1.5 C. There is language in the Paris Agreement that emissions targets will likely have to be adjusted lower during future planned reviews of the progress,” Dr Tans said.