Scientists at the Scripps Institution project that the powerful El Niño condition this year, along with rising emissions, will send concentrations of carbon dioxide, even accounting for annual ups and downs, beyond 400 parts per million shortly. Credit Scripps Institution of Oceanography
Is This the Last Year Below 400? [ppm of Co2]
Leader of Keeling Curve measurement says temporary bump from El Niño could push atmospheric CO2 levels above symbolic threshold for good
October 21, 2015 Ralph Keeling
The Mauna Loa CO2 record is a saw-tooth pattern, with CO2 concentrations typically falling from May through September, and rising over the rest of the year. This cycle is caused by the natural exchanges of CO2 with vegetation and soils. Each year, the values are higher than the year before, as CO2 continues to pile up in the atmosphere from fossil fuel burning. This year, as expected, we hit the annual low point back in September and CO2 concentrations are starting up again. The lowest point this year was well below 400 parts per million (ppm). The lowest daily minimum this year was 395.83 ppm and the average for the month of September, was around 397.1 ppm. By sometime in the next month or two, CO2 will again rise above 400 ppm. Will daily values at Mauna Loa ever fall below 400 ppm again in our lifetimes?
I’m prepared to project that they won’t, making the current values the last time the Mauna Loa record will produce numbers in the 300s…
The background for my forecast:
In recent years, CO2 has been increasing by around 2.2 ppm, per year. Barring anything unusual, we would therefore expect next year’s September value to be around 399.3 ppm, just barely below 400 ppm, and we’d expect the lowest daily minima to be around 398 ppm or so. But we seem now to be on the verge of the largest El Niño event since 1997. This is significant because CO2 tends to rise much faster during and just following El Niño events. From September 1997 to September 1998, for example, CO2 rose by a whopping 3.7 ppm. If this El Niño is comparable, the rise from September 2015 to September 2016 could easily be 4.4 ppm, allowing for an El Niño boost and allowing that fossil-fuel emissions rates globally are larger now than in 1998. Taking these factors into account, a reasonable forecast for next year’s September minimum is around 402 ppm, with the lowest daily minima also over 400 ppm. The El Niño growth spurt in atmospheric CO2 is mostly caused by drought in the tropics. Rainfall that normally falls over tropical landmasses shifts to the oceans during El Niño events. This slows the normal growth of tropical forests and increases forest fires. Indonesia suffered severe fires during the 1997 event and, from recent news, is already being hit hard this year. 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. 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.
By ANDREW C. REVKIN NY Times Oct. 22 2015
Climate scientists predict that the combination of El Niño impacts and rising emissions will cause atmospheric levels of heat-trapping CO2 to cross a threshold that won’t be revisited for a very long time. On Tuesday, a simple but sobering note predicting an imminent end to measurements of carbon dioxide in air lower than 400 parts per million was posted by the group at the Scripps Institution of Oceanography that has been carefully measuring the rising concentration of this greenhouse gas in the atmosphere since 1958.
The sawtoothed “Keeling Curve,” of these measurements, named for Charles David Keeling, the scientist who launched the project and ran it until his death in 2005, has become an icon of the Anthropocene, the proposed geological epoch created by humanity’s “great acceleration.” There’s no surprise in the 400 p.p.m. threshold being passed soon given continuing growth in emissions of the heat-trapping gas and its long lifetime once released. This landmark has been written about extensively here and elsewhere, and the annual surge and ebb of the gas has previously crossed that 400 p.p.m line temporarily (seasonal bursts of photosynthesis account for the sawtoothed ups and downs).
This time, partially because of the impact of El Niño on precipitation and thus plant growth, the scientists foresee an accelerated rise, but an insufficient seasonal surge of photosynthesis to draw levels lower. The long lifetime of the gas, once released, and the slow response of humans in trying to constrain emissions mean it’ll almost surely take generations, at least, before numbers below 400 are revisited on the way down.
The Scripps note is worth posting simply as an artifact of our age. It is written by Ralph Keeling, who took over after death of his father, the pioneering atmospheric scientist Charles David Keeling, in leading this simple but momentous observational effort. See my 2008 “ode to the value of monitoring” for a broader look at why seemingly boring observations of important parameters, from CO2 concentrations to stream flows, get too little respect, and funding. The climate historian Spencer Weart did a fine job of tracking the budget woes of the Keelings’ work. [see Ralph Keeling’s note above]