Atmospheric CO2 Leaps into Uncharted Territory: 408 ppm

Even as it fades, the 2015-16 El Niño has given a big boost to the annual spring peak of carbon dioxide in the atmosphere. Preliminary CO2 data from Mauna Loa, Hawaii, for the week ending April 16 showed a concentration of 408.69 parts per million (ppm), according to NOAA. The weekly value analyzed by NOAA topped 405 ppm for the first time on March 26 (405.62 ppm), which was itself surpassed by 406.57 ppm on April 9. The one-day average concentration hit an eye-opening peak of 409.44 on April 9. That’s close to 4 ppm above any value recorded on Mauna Loa prior to this year.

“We are now witnessing the fastest growth rates of the entire record of CO2 measurements. This record-breaking growth is an expected consequence of the near record-breaking fossil fuel usage combined with the largest El Niño event in several decades.” said Ralph Keeling (Scripps Institution of Oceanography) in a Keeling Curve blog post on Wednesday. Keeling’s father, Charles David Keeling, launched the regular CO2 measurements at Mauna Loa in 1958. NOAA and Scripps now collaborate on the sampling, with slight differences in how they analyze and report the data. Scripps reported a daily value of 407.80 ppm on April 18 (see Figure 2).




Figure 1. A year’s worth of carbon dioxide concentrations measured at Mauna Loa, Hawaii, by NOAA from April 2015 through mid-April 2016. Daily averages are shown as black dots, and weekly averages as red lines. The labeled blue lines show monthly averages. Image credit: NOAA/ESRL Global Monitoring Division.


Carbon dioxide has been accumulating at an unsettling pace for some time now. Preliminary data for last year (2015) showed the biggest annual increase in CO2 concentrations of any year on record: 3.05 ppm. It was also the fourth consecutive year that CO2 levels increased by at least 2 ppm. This occurred for the first time in 1977 (just for that year) and was a rare event until the 2000s. From February 2015 to February 2016, the year-over-year increase in monthly values was 3.40 ppm, according to NOAA.

“Carbon dioxide levels are increasing faster than they have in hundreds of thousands of years,” said NOAA’s Pieter Tans in a March statement. “It’s explosive compared to natural processes.”


Figure 2. Two longer-term perspectives on CO2: the increase since 1958 measured at Mauna Loa (left), and the ups and downs produced by ice-age cycles over the last 800,000 years, as retrieved from polar ice cores. The increase of more than 120 parts per million since the mid-1800s (vertical line at far right of right-hand image) is larger than the typical difference between the frigid depths of ice ages (the dips in the right-hand image) and the relatively mild interglacial periods. Predictable variations in Earth’s orbit help trigger the onset and decline of ice ages. Image credit: Scripps Institution of Oceanography.


Fossil fuels, El Niño, and a touch of variability
The past month’s surge is not unexpected, but its strength is noteworthy. As fossil fuel burning pumps CO2 into the atmosphere, new highs in concentration have been achieved every spring at Mauna Loa since records began in 1958. The annual peaks and dips shown in the sawtoothed pattern in Figure 2 are a result of the seasonal cycle of vegetation growth in the Northern Hemisphere, which holds most of the world’s land areas. CO2 values normally top out in the second quarter of the year, as warming soils release CO2 but just before northern vegetation growth begins to take off. The global CO2 concentration then dips later in the year, as the increasingly lush summer vegetation absorbs huge amounts of CO2. These natural ups and downs occur on top of the inexorable year-by-year increase produced by human activity.

The tendency of a strong El Niño to foster drought and fire across much of the tropics cuts back on the ability of global vegetation to absorb CO2. This means that global CO2 levels tend to be higher during El Niño than they’d otherwise be (and lower during La Niña). The largest one-year jump in CO2 values in the Scripps data from Mauna Loa was the 3.7 ppm observed in 1998, at the tail end of our last “super” El Niño event.

Why such a spike this past month?
It’s not clear exactly what has led to such a big surge in CO2 concentrations at Mauna Loa during the past month. Industrial emissions don’t change quickly enough on a large enough scale to produce this big a spike. According to Keeling, “the levels last week were a bit higher, maybe by a part per million or two, than I would have projected even taking El Niño into account. I’m frankly not sure what is causing this, but I would not expect it reflects anything other than an unusual blob of air that temporarily settled over the central Pacific.”

A number of other sites around the globe also monitor CO2, with their measurements collated through a Global Greenhouse Gas Reference Network coordinated by NOAA. Readings from these sites can be several parts per million higher than those measured atop Mauna Loa, depending on local vegetation and circulation and each site’s proximity to major population centers. At the Harvard Forest site in central Massachusetts, daily CO2 concentrations have been hovering around 408-410 ppm over the last several weeks. This is “not particularly remarkable given the year and season,” said Harvard’s Steven Wofsy in an email.


Figure 3. Daily measurements of carbon dioxide collected atop Niwot Ridge, Colorado. The nighttime readings (red dots) typically run higher than daytime readings (green dots) due to the lack of photosynthesis at night. The Niwot Ridge values run slightly higher than the readings collected at the Mauna Loa site (dark line), which is located many hundreds of miles from any large land masses. Image credit: Courtesy Britton Stephens, NCAR.


Figure 4. Researchers work on a station near Niwot Ridge, Colorado, just west of Boulder, where carbon dioxide and other gases have been measured weekly for some 40 years. Image credit: UCAR/NCAR.


Another CO2 expert, Britton Stephens (National Center for Atmospheric Research), found little evidence of anything too dramatic in the last few weeks of data from a group of three dispersed stations in the U.S. West called Rocky RACCOON (Regional Atmospheric Continuous CO2 Network in the Rocky Mountains). “On that short time scale, nothing jumps out as unusual,” said Stephens. The CO2 values measured at several Colorado and Utah sites did show an uptick of several ppm from about April 14 to April 19, roughly a week after the highest values in Mauna Loa. According to Stephens, it’s possible that a large-scale “blob” of CO2 could have translated east from Hawaii to the central Rockies in that timespan.

The long-term outlook: unchanged
For those of us who have watched CO2 rise for years--the weekly values first passed 400 ppm in 2013--it is more than a bit unnerving to see daily and weekly numbers at Mauna Loa approaching the 410 ppm threshold. Some relief will come later this year, as the typical midyear dip begins. And the expected La Niña event may help tamp down the year-over-year increase in concentrations going into 2017.

Another bright spot: the Paris Agreement on Climate Change will become available for global leaders to sign on Friday (Earth Day). Leaders from 155 nations, including the U.S. and China, have signaled their intent to sign on the first day. That would be a record for any international agreement, and not a moment too soon. Major emission cuts in China may have already led to a decline in global emissions for 2015 (the data aren’t out yet), yet even the ambitious cuts in the voluntary national pledges of the Paris Agreement would not be enough in themselves to stave off the long-feared 2°C in global warming over pre-industrial levels.

That challenge comes into focus at the national level with the EPA’s 2014 inventory of U.S. emissions, released last week. It showed that total U.S. greenhouse emissions climbed 1.0% in 2014 following a 2.8% increase in 2013. Making matters worse, the EPA made a substantial upward revision to its estimates of U.S. methane emissions over the last few years, because research now shows that oil and gas operations were releasing significantly more methane than previously thought. Clearly, the substantial dip in U.S. emissions achieved during the late 2000s and early 2010s--variously attributed to high fuel prices, increased efficiency measures, and the transition from coal to natural gas--has ground to a halt. From this point on, each year in which U.S. emissions are climbing will make it that much harder for the nation to meet its Paris pledge: cutting U.S. emissions by 26-28% in 2025 compared to 2005 levels.


Figure 5. Probability of severe weather for Tuesday, April 26, 2016, as issued by NOAA/NWS Storm Prediction Center on Thursday, April 21. It's quite unusual to have probabilities as high as 30% outlined this far in advance of a severe weather threat. Image credit: NOAA/NWS/SPC.

Major severe weather threat taking shape for next week
We're monitoring the potential for one or more significant rounds of severe weather next week, most likely focused in southern Kansas, Oklahoma, and northern Texas. NOAA’s Storm Prediction Center (SPC) is already highlighting the risk of severe weather on Tuesday, Wednesday, and Thursday. The situation on Tuesday looks especially serious, as models are consistently agreeing that very rich low-level moisture and warm surface air will be juxtaposed with a powerful upper-level storm sweeping into the Great Plains from the Pacific. SPC began highlighting the risk of tornadoes on Tuesday in its Day 7 outlook issued on Wednesday--a very unusual step for SPC to take this far ahead of an event. The tornado threat is again mentioned in today’s Day 6 outlook, and the probabilities of severe weather have been raised (Figure 5], a sign of increasing forecaster confidence. Tuesday happens to be the 25th anniversary of the destructive central U.S. outbreak of April 26, 1991, which produced several violent tornadoes that killed at least 21 people, many of them residents of a devastated mobile home community in Andover, Kansas.

We’ll be back with an (upbeat!) Earth Day post on Friday.

Bob Henson