I was inspired to write this two-part series on soil by reading Kristin Ohlson’s recent book, The Soil Will Save Us. Part I focused on the management of minerals in the soil and suggested that increased use of seaweed-based fertilizers could improve our agricultural productivity as well as the quality of our diets. In Part II, I’ll explore Ms. Ohlson’s suggestion that improved soil management and farming practices could slow, stop, or even reverse global warming.
Before discussing how soil management could impact global warming, we need to start with an explanation of the overall carbon balance for the biosphere. By limiting the discussion to the biosphere, I am omitting carbon which exists deep underground and deep in the ocean, which effectively keeps it out of the carbon cycle. The approximate distribution of carbon in the biosphere in gigatons (billions of tons) is shown below.
Gigatons of Carbon
|Fossil Fuel Reserves||
When the Industrial Revolution began in the mid-1800s, the atmosphere contained 570 gigatons of carbon. Since then, through the combined effects of fossil fuel use, deforestation and (as we will explore further) soil degradation, we have added 270 gigatons, to reach the current level of 840. At present, humanity is releasing approximately 9 gigatons of carbon per year into the atmosphere, of which 4 gigatons are absorbed into the oceans, soil, and vegetation, resulting in a net increase of 5 gigatons per year in the atmosphere.
In order to maintain a climate similar to that in which human civilization evolved, we need to find a way to reduce the amount of carbon in the atmosphere to between 570 and 735 gigatons. So let’s take a look at the numbers in the table above and consider scenarios which might result in the removal of 150 to 200 gigatons of carbon from the atmosphere.
Fossil Fuel Reserves
Without the intervention of human beings, fossil fuel reserves are effectively excluded from the biosphere. When we burn fossil fuels, we add carbon to the biosphere which must then find a home in one of the other reservoirs listed above. If we have any hope of reducing the amount of carbon in the atmosphere, we need to transition to low and no carbon sources of energy and leave most of these reserves in the ground.
While it is certainly possible to increase the amount of vegetation on the earth to some degree, unless one assumes a significant drop in human population, it’s unlikely that this reservoir will grow by very much. Adding a significant amount of vegetation to the earth would require massive conversion of farmland to forest, which would dramatically reduce food supply.
The capacity of the upper ocean to absorb carbon from the atmosphere is already becoming limited as the concentration of dissolved carbon dioxide approaches saturation. Therefore, even if we wanted to induce significantly more carbon to dissolve in the oceans, we would not be able to. We really would not want this to happen, as it causes acidification of the oceans which is harmful to aquatic life.
Thus we are left with soil. The appeal of soil as a carbon reservoir stems from two factors. First, since it is already a rather large reservoir, an increase in carbon content of just 10% would absorb 150 gigatons of carbon from the air. Secondly, since we know that our land-use practices have significantly depleted the amount of carbon in our soils, increasing the amount by 10% seems within the realm of possibility.
As I reviewed in Part I, a healthy soil contains approximately 10% organic matter. (Organic matter is comprised of carbon containing molecules.) Prior to reading Ms. Ohlson’s book, my concept of the addition of organic matter to the soil was limited to either adding compost or plowing under cover crops. It turns out that I was missing a key mechanism, one that just might change the world.
During photosynthesis, plants absorb carbon dioxide from the air and water from the soil to produce glucose, a simple sugar. Plants use the sugar both as an energy source and as a raw material to make other more complex organic molecules to form stems, leaves, flowers, and fruits. In addition, plants “intentionally” allow up to 40% of the glucose they make to leach out of their roots and into the soil. By introducing sugar to nearby soil, the plants “recruit” a host of bacteria, fungi, insects, and earthworms whose assistance they need for health and growth. The glucose added to the soil by the plants provides the foundation for an entire underground food chain, the end result of which is a dark organic product typically referred to as humus. If left undisturbed, humus will remain in the ground for long periods of time. Unfortunately, at least on our farms, we don’t leave the ground undisturbed. We till it and till it and till it and till it. Each time we do so, we break up the humus and bring it to the surface where it is both eroded away and oxidized into to carbon dioxide and released into the atmosphere. The loss of carbon from the soil over the years has been a significant contributor to the increased level of carbon dioxide in our atmosphere.
I often write about problems for which the solutions are either complex or unknown. In this case, the answer is obvious: stop tilling the soil. Other than out of habit, the primary reason that farmers till a field prior to planting crops is to prevent other plants from shading seedlings. In a no-till approach, the farmer maintains cover crops, such as clover, in the fields and mows them prior to planting. This does not kill the cover crop but still allows sunlight to reach the seedlings while they become established. The no-till approach has been shown to raise yields, reduce erosion, and help the soil to maintain water content.
At present, 10% of farms in the U.S. and 7% globally are using a no-till approach, and these percentages are growing every year. While the United States Department of Agriculture has several programs in place to encourage it, conversion of farms to a no-till approach is hampered by the costs involved in replacing expensive equipment which they use for their current traditional approach, and by the reluctance of farmers to make such a significant change in their operations.
Given the potential value of soil as a carbon sink, we should try everything possible, including financial incentives, to convert farms all over the world to no-till practices. We can also improve our management of other lands as well. For example, grass lawns are much less efficient in adding organic content to soils compared to meadows. You can chip in to this process by converting part of your yard to a no-till natural area.
Who knows, maybe the soil really will save us.
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I am traveling this week, so this column has been written in a series of hotels and airplanes. As such, this week’s Common Science® is a bit less quantitative than usual. (Perhaps for some this will be a relief?)
If you’ve been following along with me for a while, you will have read quite a few columns on global warming and climate change with the view that significant problems will be visited upon us sooner than is commonly predicted, leaving me open to criticism to being alarmist. It is with my potentially alarmist lenses that I have been following a series of events and trends in the Arctic that I find to be both troubling and consistent with my concerns.
As you may know, the world is about 1 ºC warmer now than it was when the Industrial Revolution started in 1850. One degree may not sound like much, but the difference between the temperate climate of 1850 and the most recent ice age 15,000 years ago during which most of the Northern Hemisphere was covered in massive glaciers was only 4 °C. So 1 ºC really is sort of a big deal, and most climate scientists suggest that we will have added another degree by the end of this century.
The warming of the Earth has not been uniform, with the temperatures increasing to a greater degree in the far north and far south portions of the planet. This extra warming of the Arctic and Antarctic regions of the Earth is of great concern, since these regions of the world are home to many of the potentially self-reinforcing feedback loops which could accelerate global warming. Below are two examples.
Since ice is white, it reflects sunlight without absorbing much of its energy. As the Arctic has warmed, the area covered by sea ice has been reduced. Therefore, as time passes, more energy from the sun is absorbed since, rather than striking ice it strikes darker colored objects such as rocks, soil, or water which are efficient absorbers of energy. The increased absorption of energy from sunlight then causes more ice to melt, and so on. The extent of sea ice in the Arctic has been dropping steadily since the 1970s.
Methane is a much stronger green house gas than carbon dioxide, and there is a staggering amount of it currently sequestered in the Arctic, both within permafrost in the soil and as methane-water ice, known as methane hydrate, on the seafloor. (I wrote a previous two part series on methane hydrate (Part I, Part II) if you would like more details.) As the Arctic warms, methane is liberated from both of these reservoirs into the atmosphere, which warms the Arctic even more and releases more methane, and so on. Recent measurements in the Arctic show rapidly increasing rates of methane emissions. In fact, an internet search will yield a number of videos of methane bubbling out of the Arctic Sea.
As the Arctic warming continues, bad things are starting to happen.
Now I’ll move on to some philosophical introspection, which perhaps has been influenced by travel fatigue. The reactions that one has to events such as burning Arctic forests and mysterious methane blowout holes are, I believe, strongly influenced by one’s underlying opinion on the state of the world. Many people are untroubled when confronted with phenomena such as those that I have described above. In my experience, these untroubled people fall into one of three categories: disinterested people who would not read a column such as this, those whose faith leads them to the conclusion that humans have no influence on these types of things, and people who assume that human ingenuity will rise up to solve any problem.
Those who are troubled by such events, people like me, have a different view of the robustness of human civilization, as well as a fundamentally different relationship to time. I see a world in which the hubristic assumption has been made that the favorable and consistent environmental conditions of the last 15,000 years will go on forever and can support an ever increasing human population. With these assumptions in hand, we’ve not focused on being good shepherds of our key life support systems, our soils, air, and oceans, leaving us more vulnerable to disruptions than we should be.
It has also become increasingly clear to me that my sense of time puts me in the minority. If I see a trend that shows that we are going to have a problem in ten to twenty years, I feel a sense of urgency and am motivated to action. This turns out not to be common.
The flight attendant says I need to turn my laptop off now. I’ll be monitoring the developments in the Arctic and will update you as things unfold.
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Since personal obligations have kept me busy this week over Thanksgiving, I will not be publishing the conclusion of the “Sudden Cardiac Arrest” series until December 8th. This week, I am reprising a column from September, 2012, with this new introduction, which I hope will help to shed some light on two recent, but seemingly contradictory news stories. In 2013, carbon dioxide emissions in the United States were down by 3.7% compared to 2012. In stark contrast, gloggbal emissions, at a staggering 10 billion tons, were 2.1% higher than in 2012.
As I explained in “If We Mine it or Drill it, We’re Going to Burn It,” news stories which focus on carbon emissions are inherently misleading. Since the air in the atmosphere is all mixed together, it does not matter from which country the emissions originate. The parameter that truly matters is the rate at which we are extracting carbon, in the form of coal, oil, and natural gas, from below the ground.
The widespread utilization of hydraulic fracturing (fracking) combined with horizontal drilling in the U.S. has resulted in a significant increase in extraction of natural gas. Natural gas is difficult and expensive to export, so nearly all of this increased supply is being burned in domestic power plants to make electricity. As more electricity in the U.S. is being generated from natural gas, the amount produced by burning coal is decreasing. Generating an equivalent amount of electricity from natural gas rather than coal releases less carbon dioxide. Therefore, the shift towards natural gas for electricity production in the U.S. is the primary reason that carbon dioxide emissions from the U.S. have been reduced. As nice as this may sound, it doesn’t really matter.
To understand why it doesn’t matter, one need look no further than Appalachia, the heart of the U.S. coal mining industry, rumors of whose death have been greatly exaggerated. Despite the loss of a portion of the electricity market, U.S. coal extraction is at an all-time high. Since coal is easy to transport, it is being shipped all over the world, particularly China and India, to generate electricity there.
The end result of the natural gas “boom” from fracking and the increase in coal exports is an increase in the extraction of underground carbon from the U.S. This is the story that matters about the U.S. contribution to carbon dioxide emissions and global warming. We are making it worse, not better.
For more detail and the underlying science, follow the link above to my previous column. If you have a comment or question use the interface below or send me an email to email@example.com://chapelboro.com/columns/common-science/extraction-emissions-matters/
STOCKHOLM – The Intergovernmental Panel on Climate Change uses the strongest words yet in its latest assessment on the state of the climate system.
The panel now says it’s “extremely likely” that human activity has been the dominant cause of global warming since 1950.
The last assessment in 2007 used the words, “very likely.” The full report comes out Monday.http://chapelboro.com/news/weather/landmark-climate-change-report-adopted/
Over the last several decades the media have consistently reported that global warming would result in more frequent and more powerful hurricanes. The graph below shows the data for total frequency of hurricanes in the Atlantic since 1944, as well as the number of strong hurricanes, defined as category three and above. While I have seen analyses of these data which have attempted to tease out an increasing trend, there has not been a noteworthy change in either the frequency or the strength of hurricanes during this period, despite rising air and water temperatures.
The lack of change in hurricane frequency and intensity is consistently referenced by climate change deniers as evidence that scientists have been wrong, biased, or participating in some massive conspiracy. The problem with both the news stories and the accusations of malfeasance is that there has never been a scientific consensus that global warming would result in either more frequent or stronger storms.
The inaccurate news coverage of the potential effects of global warming on hurricanes is another example of poor science reporting in the mainstream media. I believe that this failure stems from an unwillingness to spend the time and to commit sufficient news bandwidth to grapple with complex scientific issues. Fortunately here at Chapelboro.com, we can delve into these matters at a level of detail sufficient to understand what is really happening.
Given that one of the prerequisites for a hurricane is a water temperature of at least 79.7 °F, it is tempting to assume that warmer oceans would result in more and perhaps stronger storms. If water temperature were the only parameter which affected hurricanes, then this assumption might turn out to be correct. However, as is often the case with phenomena in nature, the situation is a bit more nuanced. Let’s consider the parameters other than water temperature which effect hurricanes and how these may be impacted by global warming.
In order for a tropical cyclone – the precursor to a hurricane – to get started, a mass of cold air must be positioned above an area of warm water. Furthermore, since the strength of the storm is dependent on the rate of condensation of water droplets in the upper atmosphere (which happens faster as the air gets colder) the initial strength of the storm is dependent on air temperature. Therefore, to the extent that global warming is increasing the temperature of the air above the ocean, both the probability of hurricanes forming and the expected storm strengths are directionally reduced.
Another key parameter in the formation of a tropical cyclone is the need for low wind shear, which sounds counter intuitive at first. In order for the circulating air flows of a cyclone to form and stabilize, the other air movement in the area must be limited; otherwise the cyclone never becomes “organized”. The research I have read on the potential impact of global warming on winds in the Atlantic is inconclusive. However, to the extent that warmer temperatures may result in stronger winds above the oceans (a reasonably likely scenario), the probability of hurricanes being formed would be reduced.
Despite not having a noticeable effect on frequency or strength, global warming is having two definite effects on hurricanes. The warming of the oceans does result in more days per year when the surface water temperature is at or above 79.7 °F, which is lengthening hurricane season. According to the Pew Center on Global Climate Change, the duration of hurricane season has grown by five days per decade since 1915. Therefore, in coming decades we should anticipate hurricanes starting in May and continuing through December. Global warming is also causing sea level rise from the thermal expansion of ocean water as well as the melting of the polar ice caps. Increases in the baseline level of the ocean reduce the amount of storm surge necessary to cause damage along the coast line, as evidenced recently in Manhattan by Superstorm Sandy.
I believe that part of the problem regarding news reports on the impact of global warming on hurricanes is that headlines about an impending series of superstorms create more of a splash than a thoughtful review of the slow steady lengthening of hurricane season and the number of inches that sea level is rising each decade. Perhaps a hurricane on Christmas will increase the buzz-worthiness of the actual science.
There is still no sign of Barry out over the Atlantic, so he must still be working away on Vilcom Circle. Have a comment or question? Use the interface below or send me an email to firstname.lastname@example.org://chapelboro.com/columns/common-science/hurricanes-part-iii-frequency-and-global-warming/