CO Levels At 2000 Year Low, Humans Credited
Carbon monoxide, CO, is a trace gas that is important in atmospheric chemistry. It indirectly influences climate and has significant effects on methane and ozone levels. CO is a byproduct of combustion—particularly the incomplete burning of fossil fuels and biomass—and conventional wisdom says that humans, with their tendency to set things on fire, should be responsible for releasing much of the gas into the atmosphere. Little is known about the abundance and sources of CO prior to the industrial age, or about the importance of anthropogenic activities have had. A new study in the journal Science presents a 650-year-long record of CO atmospheric concentration using samples from Antarctic ice cores. Reconstructed past CO variability and its causes have come up with a shocking fact: CO levels are at a 2,000 year low. Apparently, humans actually prevent wildfire, reducing the release of carbon monoxide and, consequently, CO2.
According to the EPA, carbon monoxide is an odorless, colorless toxic gas. Because it is impossible to see, taste or smell, CO can kill people before they detect its presence. At lower levels of exposure, CO causes mild effects that are often mistaken for the flu. These symptoms include headaches, dizziness, disorientation, nausea and fatigue. The effects of CO exposure can vary greatly from person to person depending on age, overall health and the concentration and length of exposure. Fortunately, carbon monoxide is a minor constituent of Earth's atmosphere.
Carbon monoxide plays a key role in the chemistry of the troposphere, largely determining the oxidation potential of the atmosphere through its interaction with hydroxyl radical (OH). CO also interacts with atmospheric methane, a gas whose preindustrial variability is the topic of continuing debate in scientific circles. The main sources of atmospheric CO include atmospheric oxidation of methane and non-methane hydrocarbons (NMHCs), biomass burning, and fossil fuel combustion. These sources account for about 90% of modern atmospheric CO. Unfortunately, there were no large-scale data on fires, apart from records kept by firefighting agencies in a few countries, until very recently.
In a report entitled “Large Variations in Southern Hemisphere Biomass Burning During the Last 650 Years,” Wang et al. present the first record of changes in two stable isotopes: carbon-13 (13C) and oxygen-18 (18O). From the relative abundance of these isotopes, the researchers estimated how much CO came from burning biomass. Working from small amounts of air trapped in ice, the tiny amount of CO in the air (35 to 55 parts per billion), and the even smaller amounts of heavy isotopes in the CO, Wang et al. were able to reconstruct historical variation in atmospheric CO levels. They describe their work at the beginning of the paper:
Stable isotopic ratios (δ13C and δ18O) in atmospheric CO help to resolve the relative contributions of these sources and thus to better estimate the global CO budget. To date, no isotopic ratios from CO in ice have been reported, and few CO mixing ratio measurements have been reported. Through use of a recently developed analytical technique, we present measurements of CO concentration ([CO]), δ13C, and δ18O from a South Pole ice core [89°57'S 17°36'W; 2800 m above sea level (asl)] and from the D47 ice core (67°23'S 154°03'E; 1550 m asl) in Antarctica (Fig. 1).
Fig 1. The 650-year records of CO concentration, δ13C, and δ18O from two ice cores: D47 ice core (diamonds) and South Pole ice core (squares). (A) [CO]. (B) δ13C. (C) δ18O. Error bars represent analytical uncertainties. The shaded area shows the timing of the Little Ice Age. Source Wang et al./Science.
As can be seen in the figure above, they found that the concentration of CO ([CO]) decreased by ∼25% from the mid-1300s to the 1600s, and then recovered completely by the late 1800s. Minimum values of [CO], δ13C, and δ18O roughly coincide with the Little Ice Age (circa 1500–1800), as defined in the Northern Hemisphere. The researchers used isotopic compositions to help distinguish combustion-derived CO (such as biomass burning) from noncombustion-derived CO (such as hydrocarbon oxidation).
C18O is particularly useful for this because of large differences in the oxygen isotopic composition between combustion and noncombustion sources of CO, with the δ18O signature from combustion sources being significantly enriched as compared with the δ18O signature from hydrocarbon oxidation. Depending on specific combustion conditions, the δ18O value for biomass burning–derived CO is generally between 15 and 22‰.
The contribution from fossil fuel combustion is negligible before the 1900s according to historic CO2 emissions data. Simulations from the Model for Ozone and Related chemical Tracers (MOZART-4) show that fossil fuel combustion contributes only 2 to 3 ppbv to today’s CO budget in Antarctica. Thus, the main sources of CO were probably large variations in the degree of biomass burning in the Southern Hemisphere. When these findings are combined with previous work, an interesting history of biomass burning emerges, as depicted in the figure below.
Hypothesized causes of major long-term trends in global biomass burning.
In the figure, the amount of burning is based on a synthesis of sedimentary charcoal records (orange) and analyses of carbon monoxide trapped in Antarctic ice (green). The trend can be seen clearly: Biomass burning declined steadily from the 1300s through the 1600s, in parallel with cooling that occurred from the Medieval Warm Period to the Little Ice Age. Then, some combination of warming and human activity drove a rapid increase in biomass burning, which peaked in the late 1800s before abruptly declining to a historic low in the present.
The meaning of all of this is that humans are not the universal firebugs that some have made our species out to be. In an accompanying perspective article, Iain Colin Prentice, a Professor of Biology at Macquarie University in Sydney, Australia, provides an enlightening review of the new findings implications:
These findings challenge some of the myths that abound in the fire literature. None is more persistent than the perception that fires are caused mainly by human activities. People start fires, it has been reasoned; therefore, in earlier times, when there were fewer people, there must have been less burning. This faulty assumption underlies several attempts, some of which are cited by Wang et al., to reconstruct changes in the composition of the atmosphere during the industrial era. The evidence, however, shows the opposite. In southern Africa, for instance, researchers using remote-sensing observations have found a negative relationship between human population density and burned area, with fire decreasing as population increases. And despite the high media profile of “deforestation fires” in places like Indonesia and Brazil, research demonstrates that these fires are spatially restricted and subject to strong climate control; total biomass burning during recent decades has been lower than at any time during the past 650 years or even the past 2000 years.
Much of the wailing over slash & burn agricultural and tropical deforestation seems to be exaggerated, according to Prentice. Humans, at least in modern times, are a force for net wildfire prevention. Modern agriculture and land use patterns have resulted to the lowest biomass burning levels in the past 2,000 years. What save-the-earth-from-the-evil-humans eco-activist would have believed that? Evidently, science can still provide surprising answers to questions we assumed resolved long ago—another consensus position debunked.
Don't blame the humans, they help reduce wildfire.
Moreover, this work has implications for those trying to model Earth's climate mechanisms and, by doing so, predict future climate change. It turns out we didn't have a good understanding of preindustrial conditions as we thought. Wang et al. summarized their findings:
Previous modeling studies suggest that preindustrial biomass burning was much lower than today, with a reduction of up to 90%. This is the common assumption in climate model simulations. However, our results show that present-day CO from Southern Hemisphere biomass burning is lower than at any other time during the last 650 years. This is particularly relevant because assumptions on preindustrial [CO] are an important component for correctly estimating the radiative forcing of tropospheric ozone in preindustrial times. [CO] changes due to biomass burning also suggest that there were decadal and centennial scale variations in average concentrations of black carbon, which is another major atmospheric constituent produced with burning, leading to the unanswered question of its potential role in long-term climate variability.
As with all things scientific, the future impact of this work can be interpreted in different ways. The climate change catastrophists will undoubtedly say that rising global temperatures will lead to greater danger of wildfire and expanded biomass burning. But then, a warmer Earth is also a wetter Earth, so perhaps that judgment is also in error. It will be exciting to see what revelations the new year brings, and which conclusions of “settled science” have to be revised or discarded. All believers in consensus should remember, science never rests and no explanation is cast in stone.
New scientific findings once again show climate science's fundamental incompleteness, disprove climate change dogma and make a mockery of consensus. Every new revelation underscores the folly of trying to predict future climate based on supposition and wild guesses. Our understanding of the natural processes around us is filled with gaping holes, and the computer models that climate science relies on are not only lacking, they contain assumptions and relationships that are at odds with reality. It is no mystery why climate science has fallen into ill repute—it has labored mightily and produced a travesty.
Be safe, enjoy the interglacial and stay skeptical.