Pieter Tans, lead scientist of NOAA’s Global Greenhouse Gas Reference Network, confirmed that the increase, reported previously by New Scientist, represented a record year-over-year growth for Mauna Loa. He also said that in addition to the stark rise in carbon dioxide levels over the past year, researchers have now observed four straight years of increases of more than 2 parts per million in the atmosphere.
“We’ve never seen that,” Tans said. “That’s unprecedented.”
Indeed, the average annual increase during 2015, of 3.05 parts per million of carbon dioxide at Mauna Loa, was also the highest in the record, according to NOAA — exceeding the previous record of 2.93 parts per million in 1998, which was also a strong El Nino year.
Pre-industrial levels of carbon dioxide were just 280 parts per million, rather than over 400 right now — and when the measurement record began at Mauna Loa in the late 1950s, were below 320 parts per million. So we have come a very long way, and very fast.
Tans said the reason is very clear: Rates of fossil fuel burning remain at historically high levels, releasing 10 billion metric tons of carbon into the atmosphere annually. “The emissions are at a record high, therefore the growth rate of atmospheric CO2 is also at a record high,” he said.
However, there also appears to be a role for the El Nino phenomenon in the records this year. “CO2 tends to rise much faster during and just following El Niño events,” wrote Ralph Keeling, director of the Scripps Institution of Oceanography carbon dioxide program and son of Charles David Keeling (after whom the iconic graph of rising greenhouse gas concentrations is named), last October. At the time, Keeling forecast that because of the current El Nino event, we would probably never see CO2 levels decline below 400 again “in our lifetimes.”
In that post, Keeling also explained why CO2 goes up so much during El Nino. It’s because of the way the phenomenon tends to drive droughts across the tropics, which in turn leads forests, like those in Indonesia, to lose carbon in wildfires — which happened at a massive scale in 2015. Drought also stunts forest growth, which leads to less carbon dioxide removal from the atmosphere, Keeling wrote.
“The loss of carbon from tropical forests in El Niño years is temporary as the forests tend to regrow in normal years, building back their biomass and sucking CO2 out of the air in the process,” Keeling concluded. “But the eventual recovery from this El Niño won’t bring us back below 400 ppm, because its impact will be dwarfed by the global consumption of fossil fuels, pushing CO2 levels ever higher.”
Of late, the growth rate for carbon dioxide concentrations in the atmosphere has been around 2.2 parts per million per year.
Greenhouse gas concentrations in the atmosphere fluctuate over the course of each year, forming a classic “saw-toothed curve” (seen above), due to the way that some parts of the Earth’s system (like trees and plants) pull more carbon out of the air during the northern hemisphere spring. That means that the level in February of this year, 404 parts per million as measured at Mauna Loa, will decline somewhat over the coming months. But overall, despite these fluctuations, the trend has been steadily upward.
“Why should people be troubled by that?” Tans said. “There is no scientific doubt that higher CO2 in the atmosphere causes the inner heat balance of the Earth to change … This will have impacts on the climate.”
He said the precise impacts can be difficult to pinpoint and predict, but they are unmistakable nonetheless.
“What is very certain is that we do have an impact on the Earth’s climate that is risky,” he said. “We have no other home.”