Anthropogenic Global Warming and Its Causes

By Clyde Spencer – Re-Blogged From

Unless you have been in cryogenic suspended animation for several decades, you are aware of the extreme polarization about the role that CO2, particularly from burning fossil fuels, assertedly plays in warming the planet. I will attempt to provide a fresh perspective on the issue below.

It seems that many people think of global circulation models (GCMs) as being a virtual reality, or at least some kind of scientific ‘truth.’ What is generally unappreciated is that the GCMs are, instead, complex and convoluted working hypotheses. As such, they are a part of the Scientific Method. However, they should be subject to careful scrutiny, evaluated against reality, and modified as appropriate to conform to reality. That is the essence of the Scientific Method! Any hypothesis that does not have utility as an explanation, or have reliable predictive powers, does not achieve the purpose of scientific theories.

The extant GCMs, while purporting to work from first principles, have widely varying predictions of future temperatures, and are generally contradictory in their predictions of future precipitation patterns. Projections fail to mimic the step-like behavior of past, recent temperature increases. They gave no prediction of the current plateau in average global temperatures, nor do they provide an acceptable explanation for the current temperature plateau. The only thing that they have in common is an upward trend, not unlike CO2, or even the general population growth. Clearly there are problems with the computer models! Apparently, basic assumptions about the relationships of feedback loops add an element of subjectivity that nullifies the goal of operating from first principles. There are other more technical criticisms of the GCMs, but I won’t go into them here. As long as all the modelers assume that CO2 is driving temperature increases, one can expect that the models are going to display that behavior because CO2 is increasing. If I were to buy a high-performance car, based on computer simulations of similar veracity, I’d ask for my money back.

Let’s assume, for the sake of argument, that anthropogenic carbon dioxide (CO2) is indeed a significant contributor to global warming. I will define “anthropogenic” as any production that is influenced by or created directly by humans from carbon sources that have been sequestered for short or long periods of time. The International Energy Agency (citing the US Dept. of Energy) claims that the burning of fossil fuels contributes more than 31 gigatons (Gt) annually to the atmosphere.1 However, fossil fuels used for transportation, heating, and power generation aren’t the only anthropogenic sources of CO2. The calcining of limestone to make cement (>3.8 Gt annually2) additionally produces more than 3 Gt of CO2 annually,3 of which approximately 2 Gt is CO2 produced from the chemical decomposition of limestone alone.4

To the extent that biomass is burned to supply heating and cooking, at a rate greater than it is replenished, there is a net contribution of CO2 to the atmosphere that is tied to population. If deforestation of old trees is accomplished by burning to make way for expanding agriculture, then there is a net contribution of CO2 again tied to the expanding population. Controlled burns of forest land and agricultural stubble are an additional anthropogenic contribution. Probably wildfires started by arsonists should be considered anthropogenic sources of CO2 also! Maybe we should also consider the CO2 resulting from smoking tobacco and marijuana for a thorough accounting! To be conservative, let’s assume that intentional biomass burning amounts to about 1 Gt annually.5

Additionally, CO2 released from fermentation of alcoholic beverages and the rising of leavened bread dough contribute in proportion to the population. The production of bio-ethanol produces CO2. CO2 is also an industrial byproduct of hydrogen production by steam reforming, and the synthesis of ammonia. Limestone is used to neutralize industrial-waste acid streams, and in so doing, CO2 is released. Steel can be produced without using fossil fuels for heat, but coke (derived from coal with the release of CO2) and limestone as a flux, are still important in purifying steel in the smelting process. Magnesium production directly produces CO2. While I don’t have good estimates on the industrial contributions, it probably would be reasonable to assume that it is at least 2 Gt annually.

However, a complete accounting of anthropogenic sources of CO2 needs to recognize the contribution of respiration, 24 hours a day, of some 7 billion humans and the animals that feed them (not to mention the methane that both produce). Humans alone produce nearly 3 Gt of CO2 annually6 just breathing. Some argue that this isn’t appropriate to consider. However, if an increasing population is producing more CO2 from metabolism, and if vegetation isn’t immediately converted back to oxygen and carbohydrates, then it needs to be accounted for! Agricultural land would largely be covered with vegetation even if there were no humans. The difference is that by planting cultivars, humans promptly convert that vegetation into CO2! Excluding respiration makes about as much sense as ignoring biomass burning. Animal respiration and digestive gases are usually allocated to natural sources. However, I would argue that, if the animals are domesticated, then the respired CO2 should be considered anthropogenic in the same sense that industrial fermentation is. Let’s assume that humans and their domesticated animals together contribute approximately 5 Gt of CO2 to the atmosphere annually. Landfills and sewage also create CO2 and methane of an additional undetermined amount! Farmland plowing is claimed to be a significant source of CO2; however, I have not seen what I would consider reliable estimates of the actual amount.

The above calculations and available estimates come to at least 41 Gt of anthropogenic CO2 annually. Conventional estimates of anthropogenic CO2 vary, but typical values are around 38 Gt annually,8 which doesn’t include respiration; therefore, my estimates (exclusive of respiration) are in line with conventional estimates.

To complicate things further, a generally unappreciated, significant source of CO2 is underground coal fires.8 An unknown number of smoldering fires in organic-rich shales are found throughout the world, also.9 Some of this CO2 can be assigned to anthropogenic origins, but there is a large number that are natural in origin, started by lightning or spontaneous combustion. One fire in Australia has been burning for 6,000 years.10 I have not explicitly taken these into account, and conventional Carbon Cycle accounting ignores them. An unknown amount of coal is consumed by fires in China, but estimates run as high as 200 Mt per year,11 and they possibly produce as much CO2 as all the cars in the USA! There are thousands of coal fires throughout the world and CO2 estimates run as high as 3% total new CO2 derived from them — nearly as high as for cement production!

The energy and fossil fuel use in industrial societies is a tangled web and sometimes it is difficult to decide where to assign sources. All things anthropogenic considered together, excepting fossil fuels, probably produce an amount equal to at least one-third the CO2 emissions from burning fossil fuels. These additional sources of anthropogenic CO2 are important because even if fossil fuels were eliminated tomorrow, if nothing is done to reign in the growth of population, these other sources will grow to become significant. Even in the absence of any fossil fuel combustion, should the world population triple, they would produce anthropogenic CO2 of at least 30 Gt annually – what is produced currently by all fossil fuel combustion! Assuming that CO2 is the problem claimed by many, we would be confronted with essentially the same problem that we currently are concerned about! Actually, it could be worse because warming oceans will be less effective at sequestering CO2. Is there really any wonder that the shape of the curve representing the CO2-concentration time-series resembles the population growth curve? The elephant in the room that few are willing to talk about is the runaway population growth since the beginning of the industrial revolution.

I have begged the question of the magnitude of the influence of anthropogenic CO2. Unless one can quantify all the influences on warming, it is impossible to assert confidently that the CO2 derived from fossil fuels is the major contributor to warming. Therefore, let’s return to the initial assumption that anthropogenic CO2 is the dominant agent responsible for 20th century warming.

Undeniably, physics predicts that CO2 will cause warming by absorbing infrared radiation radiated outward from Earth’s surface.12 The question is, “What proportion of measured warming is directly attributable to the atmospheric CO2 concentration?” To answer that, we have to look at all the processes that are known to, or could, influence warming.

Other factors that play a role in increasing temperatures, and thus changing the climate, include the following:

1) Compared to the heat supplied by the sun, the waste heat from our profligate use of energy is miniscule. However, it is sufficiently large to be calculable. Notably, it is concentrated in urban and industrial areas and contributes to the Urban Heat Island effect. It has the potential to upwardly bias recorded temperatures and falsely give the impression of greater warming than is actually taking place globally. Weather stations recording temperatures are neither random nor uniform in coverage; they are biased by being located where most people live. After all, who is going to be willing to pay for information in some remote corner of the world where few if any people live?

2) A decrease in cloudiness, particularly cloudiness in the mountains, may contribute to general warming and, especially, the retreat of glaciers. (There is anecdotal evidence that most alpine glacier retreat is impacted more by increased surface insolation than an increase in ambient global air temperatures.13) Decreased cloudiness not only has implications for surface insolation, but also implications for precipitation. It is well known that the energy exchanges within clouds are handled poorly (somewhat ad hoc) by the current GCMs, and probably always will be! The phase change from vapor to liquid is exothermic and the phase change from liquid to solid is also exothermic, but the amount of heat released is not the same. This is one of the complications encountered by GCMs because the clouds, in which these transformations occur, are much smaller than the grid-cell size used for all other calculations.14

3) A decrease in aerosol concentrations and/or type since the 1970s, when the first serious efforts to reduce air pollution began, may impact surface insolation as well as cloudiness by reducing nucleation particles.15

4) A dense network of condensation trails from commercial aircraft can accumulate, under favorable meteorological conditions, and noticeably dim sunlight over large areas. What is their effect on upwelling radiation at night? The IPCC states, “The level of scientific understanding of contrail RF [radiative forcing] is considered low, since important uncertainties remain in the determination of global values.”16

5) An increase in surface water-vapor resulting from a) a world-wide program of dam building in the 20th Century, b) increased irrigation, and particularly, c) the invention of pivotal irrigation17, may be responsible for increased retention of heat at night and a decrease of temperatures in the day in arid rural areas. Massive amounts of water sequestered in deep aquifers under the Great Plains, and elsewhere, have been extracted and used for irrigation18. Microclimates change within irrigated fields, and in proximity to large reservoirs. Also, one of the by-products of internal combustion engines is water. (Hydrogen-powered cars would exacerbate this.) Water vapor has a much shorter residency (≈9 days)19 in the atmosphere than CO2, but a stronger ‘Greenhouse’ effect than CO2. It is replenished regularly – every commute cycle in cities and continuously at reservoirs! Furthermore, assuming prevailing winds transport the water vapor easterly at an average of 15 MPH, any individual ‘pulse’ can travel approximately 3,200 miles! Thus, there is the potential of water vapor evaporated in the western US influencing most of the country to the east. In places like Phoenix and Las Vegas, swimming pools and golf courses are ubiquitous where there were few 50 years ago. Also, one can now find water-misters at bus stops, gas stations, and backyard patios, driving up the relative humidity. In the 1950s, so-called ‘swamp coolers’ were common in the hot SW desert communities; one never sees them anymore because evaporative coolers aren’t as effective as they once were. The water vapor being generated over land that is naturally arid would help explain why average surface temperatures are rising faster than at the altitudes CO2 is supposed to be trapping outgoing thermal radiation. An examination of the Berkeley Earth project’s global high and low land-temperature data20 reveals that the low temperatures have been increasing steadily and for a longer period of time than the high temperatures. Furthermore, the lows have increased more than the highs during the 20th century. (See below) This is what is expected for a ‘Greenhouse’ effect, but it may be more than CO2 driving the increase!


6) Changes in land use, including urbanization and converting forests to agriculture, generally result in greater surface heating because of reduced albedo. Urban areas are not only local hotspots, but remote sensing research has demonstrated that the weather can be influenced for miles downwind of these hotspots.21

7) Albedo of snow and ice can be decreased not only by soot from combustion, but also by dust created from land that is plowed, and urban dirt such as tire and brake-lining dust, and abraded pavement. This can help explain warming in Winter, and glacier melting.22

The above are obvious contributors to temperature changes. Many of them are potentially related through feedback loops. Unfortunately, they aren’t well characterized. To the extent that they are ignored, and GCMs are tuned to get apparently good historical results based principally on CO2 trends, then the confidence in predictions is decreased precisely because we know that things have been left out! Individually, they may not be exceptionally important; however, in aggregate, they may be very important, particularly if they are components of incomplete feedback loops.

However, what is potentially a more severe problem in model building are the things that may be missing. One doesn’t know what they don’t know! As examples:

1) The sun is the most important source of heat for Earth. Satellite observations of a couple of sun spot cycles indicate that there is trivial variation in the sun’s Total Solar Irradiance (TSI) during those recent cycles.23 But, what if there are longer-term variations (>22 years) that haven’t been measured? Astronomers believe the sun was dimmer when the Earth was born and variations in observed sunspot cycles and radiogenic evidence strongly suggest that there are intermediate-term variations in solar activity that have not been characterized nor included in models.24 There is no satisfactory alternative explanation for the exceptionally cold weather during the Maunder Minimum, when there were no sunspots.

2) Even though the TSI changed relatively little during recent sunspot cycles, there is a significant increase in the shorter wavelengths at the peak of sunspot cycles. Might there be some unappreciated impact of increased UV beyond just creating more ozone? The IPCC states, “The effects of … shifts in the solar spectrum towards the ultraviolet (UV) range, at times of high solar activity, are largely unknown.”25

3) The Earth’s magnetic field strength has declined at least 10% during the same period of time that rising global temperatures have been observed;26 the decline appears to be accelerating, as measured by a recently launched satellite constellation.27 Is it coincidence? Or, might a weakening of the Earth’s magnetosphere allow more extraterrestrial high-energy particles to enter the atmosphere than previously, and heat the upper atmosphere? If one can’t dismiss the possibility because research hasn’t been done, then it raises a red flag about misplaced research efforts.

4) High-energy charged particles from coronal mass ejections spiral in at the magnetic poles. As they enter the upper atmosphere they produce the well-known auroras. However, the auroras are a result of ionization of the air and, consequently, heat is produced. Could the wandering of the poles over decades result in changes in the jet streams and then changes in weather at mid-latitudes?28

5) There is still controversy about whether cosmic rays might modulate cloud formation through ionization.29 This deserves more attention.

6) Recently, it has been found that bacteria apparently can play an important role in cloud formation and precipitation.30 Might the ubiquitous use of antibiotics for humans and livestock, and now routinely found in sewage, have some unintended consequences for bacteria that play previously unsuspected roles in precipitation?

In summary, there is much still unknown about weather and climate, and many of the things we are aware of are poorly characterized. There is disagreement about the sensitivity of temperature increases in the atmosphere resulting from increased CO2; that is the essence of my remarks above. There is disagreement about whether the water vapor feedback-loop is positive or negative! We know even less about what is called space weather. Even the fundamental Carbon Cycle has issues about accuracy and completeness. How much CO2 do the hidden, and largely unexplored, oceanic spreading centers — more than 80,000 Km in length — contribute to the dissolved CO2 in the oceans?31 How do we know that we are adequately accounting for diffuse volcanic CO2 emanating from the ground as is happening at Long Valley Caldera (Calif.)? Recent research strongly suggests that volcanism on land contributes much more CO2 than was formerly believed.32 If there is any sort of scientific consensus, it can only be a result of shared ignorance. There is an old joke that for the handyman who only owns a hammer, the solution to all problems looks like a nail. As long as there are still significant


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