The Earth Story

North Sea oil platform

AIR!

Earth’s atmosphere recently crossed 400 ppm CO2 for the first time in millions of years and probably will not go back below that amount during any of our lifetimes. (http://tinyurl.com/bus4xpt). But did you know there’s something else changing in the atmosphere to go along with that CO2 rise?

It’s pictured in this graph. This gas is going down, decreasing in the atmosphere as CO2 goes up. That gas? Oxygen. Oxygen in the atmosphere is decreasing.

Be honest…did you just stop and take a deep breath? It really is kinda creepy to realize that the gas everyone is taught as a kid they need to survive is going down in the atmosphere.

Anyway, why is oxygen going down? The same reason that carbon is going up; burning of fossil fuels. When you burn coal or gas, you’re taking carbon and turning it into CO2, and occasionally some amount of H2O. These reactions need a source of oxygen to happen, and they get that oxygen from the atmosphere. Every time a gasoline engine is run or a power plant burns coal, it consumes the same gas that animal life uses to keep itself alive. In fact, oxygen is so much of a mirror for CO2 that the yearly cycles from the growth of plants in the northern hemisphere summer shows up on this graph as well.

There’s some good news though; the change in atmospheric oxygen is really small. I have to do a unit switch here…400 ppm of CO2 is equal to 0.04% CO2 in the atmosphere, while the atmosphere is over 20% oxygen. So, the decrease in oxygen is in effect a rounding error. It’s the change from 20.9% oxygen to 20.8% oxygen, give or take. Hopefully that helps everyone breathe a little easier.

Beyond just freaking people out by making them think we’re running out of air, there’s some cool science demonstrated here. First, the measurement of decreasing oxygen hasn’t been done for as long as the measurement of increasing CO2 because of the abundances of the gases. The change in atmospheric oxygen is a very tiny change in a big number, and those types of numbers are hard to measure precisely. It took until the 1990’s to really get an accurate measure of atmospheric oxygen.

Conversely, with CO2, researchers are measuring big changes in small numbers. Since those are easy to measure, that measurement has been done since 1960. It’s a lot easier to measure a 40% increase in atmospheric CO2 than it is to measure a 0.1% decrease in atmospheric oxygen. That’s actually why the units on this graph are so funky; “per meg” units are 1000 times smaller than “Per mille” units and 10000 smaller than “per cent” units.

Another interesting point; the decrease in oxygen content is actually quite a bit larger (on an absolute basis) than the increase in CO2. This makes sense too; not all of the CO2 released by man has gone into the atmosphere; about half has been taken up by the oceans. That burned carbon still removes oxygen from the atmosphere even if the CO2 molecule doesn’t immediately wind up in the atmosphere. Also, water vapor is produced by burning of hydrocarbons; the production of water removes oxygen from the atmosphere as well. Altogether, we’ve removed roughly 3 molecules of oxygen from the atmosphere for every 1 molecule of CO2 that has been generated by fossil fuel burning.

Finally, it’s worth noting what else this graph says. Occasionally people hypothesize that the source of the carbon in the atmosphere is something other than man’s burning of fossil fuels, something like volcanic emissions. Volcanoes do emit CO2, but they emit quite a bit less than man has through fossil fuel use, and that shows up in this plot. Volcanic CO2 emissions don’t remove oxygen from the atmosphere; the CO2 comes out of volcanoes already made as CO2. This plot is one of the fingerprints of fossil fuel use; burning fossil fuels doesn’t just emit CO2, it also takes oxygen with it, and no other source of CO2 does both.

-JBB

Image source: UCSD and the Keeling Curve http://explorations.ucsd.edu/files/Features/Keeling_Curve/page4.php

Discussion with Dr. Keeling: http://blogcritics.org/scitech/article/atmospheric-oxygen-levels-fall-as-carbon/

Southern California Methane Leak

In 2010, an explosion on an oil platform in the Gulf of Mexico left an open pipeline near the ocean floor gushing oil for months. A tiny bit of that oil made it to the surface and into nearby beaches, but because most of the leak was kilometers beneath the ocean’s surface, it was barely seen until a webcam was placed in the ocean near the recovery effort. Even though the oil wasn't making it to the surface, it still had the power to damage marine ecosystems, some of which have yet to recover.

Something similar is happening right now near Los Angeles.

In mid-October, a large natural gas leak formed at the Aliso Canyon Natural Gas Storage Facility, an underground reservoir that holds gas in the urban area. The gas leak has proven unstoppable since it formed, and it has caused the evacuation of several hundred families in the community.

Methane is a particularly pernicious pollutant. It is transparent to light in the visible wavelengths and therefore it can’t be seen, and on its own it has no odor so it can’t be smelled. However, it is explosive when mixed with oxygen and so if a leak forms in someone’s home, that leak can remain undetected until it becomes explosive and potentially deadly.

To avoid this scenario, natural gas companies purchase methane and mix it with a chemical known as mercaptan in large storage facilities; that chemical provides the odor you’ve noticed if you’ve ever smelled a natural gas leak. The Aliso Canyon facility is this sort of storage facility.

The Los Angeles basin is one of the richest hydrocarbon reservoirs in the United States; in the early decades of the 20th century there were huge wells bored into the entire basin to extract oil and natural gas. The Aliso Canyon gas storage facility takes advantage of one of these oil fields; it is built atop a now-empty oil reservoir where the geology naturally held the oil in place until it was tapped. That sedimentary reservoir sits at a depth of about 2500 meters below the surface, beyond where anything other than drilling equipment can easily reach.

During normal operations, the facility receives delivery of natural gas from the surrounding area, mixes in the mercaptan, pumps the gas down to this natural geologic container, then pumps the gas out to ship throughout the Los Angeles basin. However, in early October, one of the pipes that pumps gas down into the reservoir ruptured, opening a flow path for gas to escape the pressurized reservoir below.

The gas has since been leaking from this broken pipe, working its way upwards through the ground from the leak site. Once it reaches the surface, it leaks into the air and since it is already mixed with the mercaptan, people in the area are hit by the gas odor. Residents have reported breathing and health problems associated with this leak since it began, but it is unknown how much of those health problems could be due to the odor or how much could be due to anything else. In high enough quantities it is an asphyxiant that denies your body oxygen, but in smaller quantities there are no known health effects. In fact, most people are regularly exposed to some methane, whether it is leaking out of the ground naturally or being released through some industrial operation. However, there are few studies regarding continuous exposure to methane over many months and natural gas leaking directly from the ground could have other trace components in it that would otherwise readily burn off; several studies have shown increased rates of respiratory illness in areas surrounding large natural gas operations with the exact cause of those illnesses still not constrained.

The amount of methane leaked already from this site is enormous. The volume being released from this pipe is estimated to be ~1/4 of the total methane emissions of the state of California, including all industrial and agricultural sources. It probably already shows up in satellite data, although I don’t have that available yet. Because human eyes can’t see it, the area’s population can’t see the plume, but infrared cameras can detect light wavelengths that do interact with methane. The Environmental Defense Fund flew a couple flights in December at this site using the appropriate cameras to image the plume. A still frame of that plume is shown in this post; more complete video is available over at our blog: http://tmblr.co/Zyv2Js1_rw5gK and http://tmblr.co/Zyv2Js1_s0Zuz.

In addition to the other issues, methane is also a potent greenhouse gas, much stronger than carbon dioxide. In small doses, like those released in the ocean or in swamps from decaying organic matter, methane can be used as an energy source by organisms, preventing it from reaching the atmosphere, but a huge plume like this is a direct pipeline of methane up to the atmosphere. The estimates of the California Air Resources Board suggest that this one leak is having the same climate impact as 7 million cars.

Because the ruptured pipe is deep underground, efforts to contain the leak so far have failed. Initial plans involved pumping heavy fluids down the pipe to block it, but methane is extremely low density and so even when fluids were pumped down, the gas was able to continue escaping upwards. The final plan is therefore going to require digging a relief well to reach the ruptured pipe and seal it at a different spot; this digging will take several more months to complete. Until then, this invisible geyser of methane will continue pouring into the skies near Los Angeles.

People directly affected by this leak are already filing lawsuits, and it is possible that an end result could be closure of this facility. However, storage facilities like this are common around the world; you literally can’t run an energy system using natural gas without a place to store the gas, and geologic storage is cheaper and more reliable than storing gas above ground. There’s a good chance you have a storage facility like this one within a short drive of wherever you live; in 2008 there were over 400 of them in the U.S. alone. Southern California Gas operates 4 of these facilities; the Aliso Canyon site is the largest.

-JBB

Image credits: Earthworks, EDF https://flic.kr/p/BWWgYw http://bit.ly/1OXdbYZ

References/more info: http://1.usa.gov/1YQ0LqT http://1.usa.gov/1Ufax4D http://www.eia.gov/naturalgas/storage/basics/ http://www2.socalgas.com/safety/aliso-canyon/ http://reut.rs/1lLYQqQ http://bit.ly/1mKSMjh

The last time below 400?

In the late 1950s, professor Charles Keeling of UC San Diego/Scripps Institute established a technique for measuring the abundance of carbon dioxide in the Earth’s atmosphere. To begin understanding how CO2 varied across the world, they took measurements in several locations and selected Mauna Loa, a volcano in Hawaii with a peak that reaches high into the atmosphere and a substantial distance between it and developed continents as a location where they could measure a well-mixed, average sample of the atmosphere.

They began measuring CO2 abundances on Mauna Loa in 1958; at the time they measured about 310 parts per million of CO2 at that site. Within only a few years, that measurement demonstrated the main changes that happen in atmospheric CO2; a yearly variation of about 6 ppm on top of an annual increase of about 2 ppm.

The yearly variation reflects the growth of vegetation; the northern hemisphere has much more land area than the southern hemisphere so during northern hemisphere summer when trees are blooming and organisms are reproducing, CO2 drops, but all of that CO2 is re-released during northern hemisphere winter. The annual increase on top of it was comparable to the amount of CO2 released by humans through burning fossil fuels for energy and changing land use patterns.

This measurement has continued multiple times per day on Mauna Loa for nearly 50 years and during that time CO2 has marched relentlessly upwards due to human activities. In 2013, CO2 levels on Mauna Loa crossed 400 ppm for the first time; an increase of nearly 1/3 since Dr. Keeling’s first measurements and an even larger increase compared to the atmosphere prior to the industrial revolution and wholesale burning of fossil fuels.

The plot of these CO2 measurements over time is now known as the Keeling Curve in honor of its creator. In fact, today, Dr. Keeling’s work continues to be run out of Scripps Institute and the current head of that program is Dr. Ralph Keeling: Charles Keeling’s son.

Last week, Dr. Ralph Keeling proposed that we’re about to see another fascinating milestone on this plot; the last time it goes below 400 ppm.

CO2 is going up by about 2.2 ppm per year right now. It first reached 400 ppm during late winter in 2013 (http://on.fb.me/1LVRS9l), meaning by 2016, CO2 levels will have increased by over 6 ppm since that point. The yearly variation in CO2 levels is about 6 ppm, so that would put it right on schedule.

Furthermore, 2015 is showing the formation of a strong El Niño. The last strong El Niño, in 1998, was associated with a larger-than-normal jump in CO2 contents during the subsequent summer due to drought conditions in the tropics that reduced growth of plants during the summer. If that pattern, which is expected as the typical El Niño weather pattern, holds in 2016, CO2 will not drop as far as normal next summer and the daily averages may never cross below 400 again.

There is no official global significance to the number 400 ppm. The planet only recognizes that there is 2 more ppm CO2 in the atmosphere than there was last year and that CO2 acts to absorb more of the heat radiating away from the surface. 400 ppm is only a milestone number because of how we count numbers. That said, it’s disconcerting to realize there is now a good chance we have permanently crossed 400 ppm CO2.

Over the long term, geologic processes will work to push CO2 back down. When there is an atmospheric CO2 spike, the planet warms up and as a consequence the rate of weathering of rocks increases (chemical reactions happen faster when the temperature is higher). Weathering of rocks releases components like calcium and other nutrients for life, allowing life and ocean chemistry to gradually push CO2 contents back down. This process, however, takes tens of thousands to perhaps hundreds of thousands of years to happen.

The world will eventually get rid of the CO2 pulse released by humanity, but unless we either find a way to actively remove CO2 from the atmosphere, CO2 contents will never drop below 400 ppm in the lifetime of anyone reading this post.

CO2 tends to go up by about 1.5 ppm per month during northern hemisphere fall and as I’m writing this post CO2 contents are at just over 398 ppm. CO2 contents should cross 400 ppm in either late November or early December, and it is possible that will be the last time any human alive ever sees atmospheric CO2 below the 400 ppm mark. I’ll watch next summer to see if it drops below 400 again; if it does, then next summer will be all but guaranteed to be the final time below 400 due to the never-ending burning of fossil fuels.

-JBB

Image credit: Scripps https://scripps.ucsd.edu/programs/keelingcurve/

References: http://bit.ly/1WgyQ20 http://news.bbc.co.uk/2/hi/science/nature/7120770.stm