Oranges, Apples and Greenhouse Gases

Introduction

Modern global warming has been the subject of debate since the early 1900’s. A great place to start to find out more about the history of the discovery of global warming can be found on the American Institute of Physics site, here. These days the scientific evidence has established that the combustion of fossil fuels by humans is the main cause for the observed increase in greenhouse gas concentration in the Earth’s atmosphere. The lack of progress in the mitigation of these gases is essentially caused by some refusing to “believe” that the natural balance could possibly be upset by the activity of humans, and/or the belief that national economies cannot possibly afford solutions that are needed to prevent climate breakdown from occurring.  Essentially, a climate solution is dependent upon understanding why modern global warming is occurring and what will REALLY happen if no solution is put in place. A good place to start is with a thought experiment to explore the role of carbon dioxide as greenhouse gas. 

A thought experiment 

Oranges and apples are both fruit.  If we take a large box and fill it with 1 million oranges and remove 416 oranges and replace them with green apples, we still will have a box of 1 million pieces of fruit.  In this thought experiment, the apples now represent 416 pieces of fruit in a total of 1 million pieces of fruit.  This can be expressed as the apples representing 416 parts per million or in shorthand, 416 ppm.  So even though the apples and oranges are both fruit their characteristics are very different.  You can only make apple pies out of the apples and orange drinks out of the oranges. 

This thought experiment can be applied to the role of 416 ppm of carbon dioxide in the Earth’s atmosphere, where carbon dioxide represents the apples, and the combined total of nitrogen and oxygen molecules represent the oranges.  As much as apples are different to oranges, carbon dioxide is very different to both nitrogen and oxygen.  Even though the concentration of carbon dioxide is so very much smaller than nitrogen and oxygen its unique molecular properties allow it to absorb infrared radiation and importantly, retransmit it. Nitrogen and oxygen do not do this.  

The Greenhouse effect 

However, nitrogen and oxygen do have an important role in allowing most of the Sun’s radiated energy to pass through the Earth’s atmosphere and interact with the Earth’s surface (trees, sea, rivers, rocks, snow, pastures, creatures etc.). This interaction occurs in many ways and results in the production of infrared energy formed during electronic decay processes that occur in many of the elements which absorb Sun’s energy after it passes through the window afforded by nitrogen and oxygen in the atmosphere.

Because carbon dioxide exists in the atmosphere and absorbs infrared energy radiated back up from the Earth’s surface, it radiates that energy in ALL directions.  Some of this energy goes back into space and some is directed back towards the surface which warms the Earth. This effect is called the Greenhouse Effect.  It is a natural phenomenon which over the life of the planet has evolved, often through harsh conditions to the much milder climate conditions the Earth now has in these modern times. If there was no Greenhouse Effect, then the Earth would be on average approximately -30°C colder than it is today.

Carbon is great - in the right amount

It is this amazing property of carbon dioxide that causes this to happen, and it is for this reason that carbon dioxide is called a Greenhouse Gas.  There are other gases which also behave the same way, which will be highlighted later, but it is important to note that if the carbon dioxide concentration increases, for whatever reason, then the warming effect is enhanced, and the Earth becomes warmer. If it is reduced, then the Earth becomes colder.

The evidence

The scientific evidence to date indicates that since the late 1700’s the Earth’s average temperature has increased and over the last 10 years or so, this increase has become faster. This increase in temperature has been attributed to an increase in the concentration of carbon dioxide in the atmosphere that has occurred, also since the late 1700’s, which has enhanced the Greenhouse Effect and, so caused a positive imbalance in the Earth/Sun energy budget which has caused the warming. 

The Earth’s climate is dependent on the energy budget and with global warming, changes in climate are expected such as prolonged drought periods, extreme heat burden, warming seas, extreme weather events, land ice and glacier reductions, rising sea levels, coastal erosion, changes in ocean currents as well ecosystem changes and eco-disasters etc. 

Since much of the infrared energy is absorbed by the oceans, increased evaporation will cause a lot more water to move into the atmosphere which can cause devastating flood effects.   More water in the atmosphere amplifies the Greenhouse Effect since water can also absorb infrared energy. 

The energy budget is also controlled by natural orbital cycles of the Earth as it moves around the Sun.  These cycles are collectively called Milankovitch Cycles and are very important.  Prior to the late 1700’s, back to at least 1 million years ago, ice core studies showed that the concentration of the carbon dioxide varied between approximately 180 and 280 ppm with carbon dioxide acting as the thermostat to set a global temperature dependent on those limits.  The current carbon dioxide concentration is way over the upper limit of 280 ppm. 

Back in 1896, the Nobel Prize winner Svante Arrhenius, made a prediction that doubling the carbon dioxide concentration would increase the average global temperature by 5 to 6°C. Since that time, an argument has raged about what would cause the carbon dioxide concentration to increase. 

Remember we are talking here about modern climate change not what happened back in meso- or paleo- times.  The carbon isotopic evidence from ice core studies such as those conducted by Rubino et al. (2013) and by the CSIRO from their air archive since 1978, shows conclusively that the carbon dioxide concentration is increasing because of the use of fossil fuel combustion which started back in the late 1700’s and has continued unabated since that time.  It is important to note that carbon dioxide produced by modern volcanic emissions represents less than 1% of that produced by humans from fossil fuel combustion.

As mentioned earlier, there are other gases which can also enhance the Greenhouse Effect. These gases are all present in the atmosphere at concentrations much less than carbon dioxide but their effect cannot be ignored since their ability to absorb and re-transmit infrared energy can many times that of carbon dioxide.  For example, methane has a concentration of about 2 ppm, but its effect is 27 to 30 times, over 100 years, more powerful than that of carbon dioxide. This means, relative to carbon dioxide, methane has Global Warming Potential (GPW) of 27-30 over 100 years.   

Although carbon dioxide and methane are naturally occurring,  large volumes of carbon dioxide are produced by the burning of fossil fuels and extra methane is released when it escapes during the production of coal, oil and/or natural gas. The latter is called a fugitive emission. Another naturally occurring greenhouse gas is nitrous oxide (GPW=273) which arises from agricultural activities as of course does methane. Human made gases, called halocarbons, which are used for refrigeration, have GPW’s in the 1000’s but thankfully are very low in concentration so far and must be kept that way. 

Conclusion 

So, the Greenhouse Effect is natural.  It is enhanced if the concentration of greenhouse gases in the atmosphere increases.  The reason for the current increase in the concentration of carbon dioxide and methane in the atmosphere is the burning and/or production of fossil fuels.  There is no other large, modern source for the carbon that is warming the planet.