Climate Change: Global Warming and Global Dimming

Global warming is occurring and the climate is changing.  One does not need a scientist to confirm that fact.  Awareness of the local environment and perusal of news items should suffice.  The fact that something so momentous is taking place means there are money, power, and prestige on the table.  Everyone from politicians, to corporations, to scientists is determined to grab a piece of the action.

Of interest here is the role of the scientists and their ability to make predictions of the particulars of climate change.  A few are paid professionals whose job is to spend their careers trying to understand the weather and climate.  The majority are entrepreneurs who must acquire funds from some agency or other in order to do their work.  The way one gains this funding is to produce a string of publications that provide an aura of competence, and to confidently claim to program mangers that the issues are sufficiently understood that a model will make some prediction about where the changes we are making to our environment are taking us.  Proposals for funding are generally peer-reviewed in an attempt to validate the proposer’s confidence.  It is a system that often works just fine. 

There is a famous quote discussing the existence of “known unknowns” and “unknown unknowns.”  Climate change modeling is replete with occurrences of both.  There is, or at least should be, another famous quote about “always validate your models.”  Such validation is near impossible because of the known and unknown unknowns and the difficulty in conducting global experiments.  Even the data on “knowns” is difficult to assess.  This is not meant to discourage modeling efforts which are important, but to reign in the excessive confidence with which modeling results are presented in the popular media.  A good scientific paper must include estimates of the uncertainty involved in any conclusion.  A good newspaper article will blithely ignore any consideration of uncertainties.  Why complicate a good story?

The net result is that modeling claims are often proved to be false or inaccurate, providing ammunition for those who deny human-initiated climate change.

There is an even more troubling aspect of the assumption that the Earth’s climate can be accurately modeled.  There are those who claim that geoengineering schemes are sufficiently understood that they will allow us to solve our warming problem if we so desire.

This somewhat long introduction was prompted by two articles that discuss aspects of global climate change that are rarely discussed, but have the benefit of providing relatively near-term benefits to both human health and the stabilization of the global climate.  These articles also provide examples of the complexity of climate response to human activities, and serve as a warning to those who would use simple assumptions to conclude that human geoengineering can solve our problems.

Carbon dioxide is the largest pollutant we produce contributing to global warming, but it is not the most potent.  There are other pollutants that produce comparable effects but have the benefit of being more easily contained and eliminated.  That is the point made by David G.Victor, Charles F. Kennel, and Veerabhadran Ramanathan in a Foreign Affairs article [2012] A Climate Threat We Can Beat: What It Is and How to Deal with It. 

“At least 40 percent of current global warming can be blamed on four other types of pollutants: dark soot particles called black carbon, methane, lower atmospheric ozone, and industrial gases such as chlorofluorocarbons (CFCs) and hydrofluorocarbons (HFCs), which are used as coolants in refrigerators. Nearly all these pollutants have life spans of just a few weeks to a decade -- much shorter than that of carbon dioxide. But although their tenure is brief, they are potent warmers. Emitting just one ton of black carbon, for example, has the same immediate effect on warming as emitting 500-2,000 tons of carbon dioxide.”

Limiting these pollutants would not arouse the political and social angst that has hindered progress on carbon dioxide.  In fact, a program to address them would be a social and economic boon.

“A few hundred million tons of crops are lost to ozone smog every year; in India, air pollutants have decreased the production of rice by about ten million tons per year, compared with annual output in the 1980s. Globally, the inhalation of soot produced by cooking indoors already kills about two million people each year, mostly women and children living in extreme poverty. And because soot is dark, it traps heat from sunlight and thus speeds melting when it settles on mountain glaciers -- a direct threat to drinking-water supplies and agricultural lands that depend on glacier-fed river systems in China and India, such as the Ganges, the Indus, and the Yangtze.”

The technology for controlling these pollutants is already in hand.  What is required is the implementation of the appropriate policies.  There is much to be gained in pursuing the short-term goal of minimizing the four identified pollutants.

“Last year, the UNEP [United Nations Environment Program] summarized their work, highlighting the potential benefits of installing new cookstoves, building more efficient power plants [curbing emissions], and plugging the leaks that occur when natural gas is extracted from wells. The UNEP concluded that such steps would make it possible to cut 40 percent of global man-made methane emissions and almost 75 percent of global black carbon emissions by 2030. Those reductions could ultimately prevent as many as five million deaths every year and safeguard as many as 140 million tons of corn, rice, and soybeans every year -- the equivalent of four percent of annual global production.”

The authors then provided this startling assessment.

“These measures would also halve the global warming expected to occur between now and 2050....”

A second article by Veerabhadran Ramanathan, Jessica Seddon, and David G. Victor appeared in Foreign Affairs recently dealing with related topics: The Next Front on Climate Change: How to Avoid a Dimmer, Drier World.  Human activity also produces a number of atmospheric pollutants that that tend to counter the warming effects described above, but that doesn’t mean they don’t contribute to climate change.

“Until now, governments have focused on limiting the greenhouse gases that cause global warming and its attendant hazards, such as rising sea levels and stronger storms. But there is more to climate change than higher temperatures. Many of the activities that cause greenhouse gas emissions—burning coal for power, diesel for transport, and wood for cooking, for example—also yield ultra-small particles known as aerosols, which blanket vast areas in a haze that blocks and scatters sunlight. By reducing the solar energy that reaches the earth’s surface, aerosols reduce evaporation and slow the water cycle that governs where, when, and how much rain falls.”

These aerosol emissions are well-known, but most studies have focused on temperature changing effects.

“Darker aerosols, such as diesel soot and other kinds of black carbon, absorb sunlight and accelerate warming. But lighter aerosols, such as the sulfates and nitrates formed from coal, gasoline, and other fuel emissions, cool the planet by reflecting sunlight back into space. That explains, in part, why the world hasn’t seen more of a temperature increase from the greenhouse gases already present in the atmosphere.”

The cooling or “dimming” effects of this class of aerosols produces first local effects due to the concentration of sources associated with population and industrial distributions before they contribute to net global effects.  This means that local pollution can affect precipitation patterns in complex ways.

“Since the 1880s, when reliable record keeping began, global temperatures have increased by about 0.9 degrees Celsius. And as the planet has warmed, rainfall at latitudes above 45 degrees has generally increased. But twice since the mid-twentieth century, surges in aerosol emissions have significantly disrupted this pattern, reducing rainfall in a number of regions.”

“The first disruption was the result of the sulfur dioxide emissions produced by the massive combustion of coal and other fuels across Europe and North America in the mid-twentieth century, driven by rapid industrial growth after World War II. From the 1950s to the late 1980s, global emissions of sulfur dioxide (which in the atmosphere becomes sulfate, a reflective aerosol) nearly doubled, reducing the amount of sunlight reaching the earth’s surface by about two percent, on average. As a direct result of this dimming, average rainfall in the Northern Hemisphere declined by between three and four percent over the same period.”

Just as small global temperature effects can have major consequences, these seemingly small changes in average precipitation can produce significant effects.

“Indeed, there is strong evidence that sulfur dioxide emissions in the United States and western Europe contributed to the Sahelian megadroughts that began in the 1960s and continued through the 1990s, a period during which precipitation in the Sahel and some other parts of sub-Saharan Africa fell by between 25 and 50 percent relative to twentieth-century averages.”

Policy decisions made in the 1970s have reduced aerosol pollution and allowed average precipitation levels in North America and Europe to return to the earlier values.

The second aerosol-caused disruption is occurring in East Asia and South Asia.

“These regions, which have rapidly industrialized over the past four decades, have seen a two- to fourfold increase in sulfur dioxide and black carbon emissions since the 1970s. As a result, in 2010, China and India received somewhere between ten and 15 percent less sunlight than they did in 1970.”

This pollution did not go unnoticed by Mother Earth.

“As the wind has carried sulfates and black carbon over thousands of miles, the dimming effect has extended to the atmos­phere over the Indian Ocean, reducing the evaporation of seawater and thus weakening the monsoons that bring much-needed water to East Asia and South Asia every year. From 1950 to 2002, the most recent period for which estimates are available, there was a seven percent decrease in average annual rainfall over the Indo-Gangetic Plain, the fertile belt of land crossing eastern Pakistan, northern India, and Bangladesh that is home to more than one billion people, many of them dependent on rain-fed agriculture. Over the same period, summer monsoon rainfall in parts of northern China decreased by more than ten percent.”

As was the case with emissions of particulates that cause atmospheric heating, those that cause the cooling, or dimming, effect can be addressed with current technologies.  The main areas of concern are power generation, transportation, and energy consumption by the poor.

“With regard to electric power generation, most of the concern about aerosols centers on burning coal, which is responsible for more than 70 percent of the world’s sulfur dioxide emissions. Given its environmental and health impacts, conventional coal power is increasingly hard to justify.”

“Regulators in California and the European Union, meanwhile, have already pioneered policies that cut aerosol emissions from transportation. They have mandated cleaner fuels and combustion technologies, such as low-sulfur diesel and exhaust systems equipped with efficient particulate filters and catalytic converters. Officials elsewhere should follow their lead, and they should pair these regulations with rigorous compliance regimes, which are currently lacking in many countries.”

“Cutting aerosol emissions produced by burning dirty fuels in the world’s poorest households is another way to reduce global dimming. Just over one billion people, most of them in the developing world, rely on kerosene to light their homes, and three billion use solid fuels, such as crop residue and dung, for cooking and heating. Burning these fuels with traditional technologies generates aerosols that damage lungs along with the climate: the particulates emitted by biomass-based cooking and heating are responsible for about a third of the dimming in South Asia. Cleaner technologies for cooking, heating, and lighting, such as energy-efficient cookstoves and solar lanterns, are readily available, and making them universally accessible would offer huge health and environmental benefits to the world’s poor.”

Since these solar “dimming” aerosols act to counter the effect of increased greenhouse gases, eliminating them would require even greater efforts to inhibit the emission of atmosphere-warming pollutants such as carbon dioxide.

“Since aerosols have a short atmospheric life span, pursuing policies such as these could significantly reduce global dimming within ten or 20 years. That would dramatically limit the risk of droughts and irregular monsoons. It would also heat up the planet by reducing the atmosphere’s reflective aerosol ‘mask,’ however, so any effort to reduce global dimming must be accompanied by significant cuts to carbon dioxide and other greenhouse gas emissions.”

The success of these solar dimming aerosols has been recognized by a class of scientist and capitalists who would argue that it is cheaper, quicker, more efficient—and even safer—to purposely modify the earth’s climate by spraying large amounts of dimming aerosols into the atmosphere.  The atmospheric temperature would go down and we could continue spewing greenhouse gases into the air indefinitely.  What could be simpler?  What could possibly go wrong?

The issue of geoengineering the climate brings us back to where we began and the notion that climate modeling is beset by “known unknowns” and “unknown unknowns” and is most renowned for its incorrect predictions.  It is impossible to change the climate of the Earth without causing disruptions.  Lowering the atmospheric temperature would lower ocean evaporation and alter precipitation patterns.  Droughts and flooding would begin to occur in different locations, perhaps threatening the lives of billions of people.  Don’t listen to those people who would sell such geoengineering nonsense.

This source provides us with a chart of temperature over recent geologic history.

This data is derived from ice cores removed from glaciers.  The temperature is derived from the local temperature where the ice core was extracted.  Consider the temperature excursions that have occurred over the past 100,000 years.  They have been enormous—much larger than the potential human-generated changes that arise in current climate discussions.  In fact, plotting at this scale dampens really rapid changes that have occurred in recent geological history.  The chart is accompanied by these comments.

“On a shorter time scale, global temperatures fluctuate often and rapidly. Various records reveal numerous large, widespread, abrupt climate changes over the past 100,000 years. One of the more recent intriguing findings is the remarkable speed of these changes. Within the incredibly short time span (by geologic standards) of only a few decades or even a few years, global temperatures have fluctuated by as much as 15°F (8°C) or more.”

“For example, as Earth was emerging out of the last glacial cycle, the warming trend was interrupted 12,800 years ago when temperatures dropped dramatically in only several decades. A mere 1,300 years later, temperatures locally spiked as much as 20°F (11°C) within just several years. Sudden changes like this occurred at least 24 times during the past 100,000 years. In a relative sense, we are in a time of unusually stable temperatures today—how long will it last?”

Those who believe humans are causing irreversible climate change have plenty of scientific evidence to point to.  Those who choose not to believe also have plenty of geologic data to point to in arguing that the climate change we observe is probably natural.  It has become like religion and the existence of a God; it is an argument that no one can win.

Perhaps a better approach is to stare at the recent few tens of thousands of years on that chart and admit that humanity has been graced with the most benign climate period in history.  For whatever reason, this “stable” climate has allowed us the time to develop our civilization.  That civilization could be taken away from us in a human lifetime, either by our own actions or by the actions of Mother Earth.  We were lucky enough to stumble on the scene during an era with a relatively stable climate.

The best strategy when existing in a state of unstable equilibrium is to change nothing.  No matter what we believe about current climate change, the appropriate plan should be to get the planet back into the state it was in when we began to mess with it.  After we have accomplished that to the best of our abilities, then we should hold on tight and hope that we are provided a few more years of grace.

For the interested reader, here are a few more articles on climate change.

Putting Climate Change in Perspective

Geoengineering, Volcanoes, and Climate Change Experiments