Global Climate Change Brief

Extracted from two sources "Global Climate Change: The Brief", written by Tony Robalik in the spring of 2007; and "The College of Charleston Greenhouse Gas Audit, 1993-2001".

Global Climate Change

(from #1)

“The greenhouse effect” is a loaded phrase these days, and many arguments have erupted over it – but largely, I feel, as a result of a lack of understanding about what is meant by the term. This policy brief is meant to bridge the gap of understanding between the scientists who study the climate and the lay public (in other words, the rest of us) who need a functional understanding of the phenomenon. We need to know what it is, what it means for our future, and what steps we can take to secure a better future – for us, our children and grandchildren (and theirs), and for all the other living beings whose lives hang in the balance of our decisions.

“The greenhouse effect” is composed of two parts: the natural and the anthropogenic. The natural greenhouse effect helps to make the Earth habitable. It has been calculated that the atmosphere would be roughly 21°C (38°F) colder than it is without the effect of naturally occurring greenhouse gases (GHGs) (Houghton, 2004, p.16). Very basically, the greenhouse effect works in this way: incoming sunlight passes through the Earth’s atmosphere. Some is reflected into space by low-lying clouds and particles in the atmosphere (known as “aerosols” and the major components of LA’s famous smog blanket); and some is reflected into space by the ice caps on Greenland, Antarctica, and the Artic. The rest is absorbed by the land and then radiated back into the atmosphere and into space. If there were no GHGs in the atmosphere, all this energy would pass into space without interference and Earth would be a frigid 21°C (38°F) colder than it is now (on average). What GHGs do is absorb some of the energy being radiated from the surface of the Earth and re-radiate that energy in all directions – including back towards the surface. This tends to make the planet warmer, which is generally a good thing.

The most important greenhouse gas is water vapor – we all know how much hotter it feels on moist days than dry ones. The next most important is carbon dioxide (CO₂) which, after water vapor, is the most common greenhouse gas by volume in the atmosphere. The concentration of CO₂ in the atmosphere prior to the industrial revolution (about 1750) is estimated to have been about 280ppm (parts per million) (Houghton, 2004, p.31). This is the natural level of CO₂ thanks to the respiration of all the Earth’s animals, plants, and natural phenomena like volcanic eruptions. There are other greenhouse gases, of course, including methane, nitrous oxide, the chlorofluorocarbons (CFCs) and their replacements the HCFCs and the HFCs. While the latter two do not destroy the ozone like the CFCs, they have been discovered to have a warming effect much more powerful than CO₂, though fortunately they are present at much smaller levels (Houghton, 2004, pp.44-47).

The term the climate scientists use for the ability of these gases to warm the planet is “radiative forcing”. If something exhibits “positive radiative forcing”, that means it is causing the atmosphere to warm. “Negative radiative forcing” means just the opposite – it causes the atmosphere to cool. An example of the latter are the aerosols released from volcanic eruptions and the burning of some fossil fuels – these aerosols reflect sunlight back into space and can cause regional cooling effects. Scientists speak of these things as “forcing” the climate.

The industrial revolution changed things considerably. The concentration of CO₂ in the atmosphere has been measured at 379ppm as of 2005, an increase of roughly 35% since pre-industrial times (IPCC AR4, 2007). This wouldn’t be so worrying if not for evidence from ice core samples (in Antarctica, where the ice goes down for miles and can be read like tree rings) that the current atmospheric concentration of CO₂ is higher than it’s been for at least 650,000 years (see Figure 1).

Source: McInnes (2007). Rohde (2006a).

Figure 1. Atmospheric concentrations of CO₂ from 650,000 years ago to the present. This graph incorporates two different ice cores: one the “Vostok” ice core (with data only for the past 400,000 years) and the other the “EPICA” ice core. The left scale represents deuterium (so-called “heavy water”) levels, from which scientists can determine the temperature. The critical point to take home is that CO₂ levels have skyrocketed since the industrial revolution to levels not seen in the available record, and certainly not seen in human times.

Increasing CO₂ means increasing temperatures. As of 2005, global average temperature had increased by about 0.76°C from 1860, the time when accurate records were first kept (IPCC AR4, 2007). This may not seem like a lot, but bear in mind that this is global average temperature. Regional and local temperature increases vary dramatically, with the largest increases occurring at the poles. According to “NOAA Reports” (2007), 2006 was the warmest year on record, and the 10 warmest years on record have all occurred sine 1990, making the nineties the hottest decade since record keeping began.

What is clear from the above chart is that the current uptick in CO₂ concentrations is unprecedented going back at least seven ice ages and most certainly over all human history. At the very least, we are engaged in a very dangerous experiment. At the worst, we may create a climate that no human in history has yet experienced.

The Greenhouse Gases (GHGs)

(from #2) 

While it is unclear exactly what the impacts of a rapidly warming planet will be, it is clear that there will be significant changes. In fact the Intergovernmental Panel on Climate Change (IPCC) states that human emissions of greenhouses gases will continue to alter the atmosphere in ways that are expected to affect the climate. There are many gases that contribute, both directly and indirectly to the greenhouse effect. The most important of these gases have been identified (by the IPCC), and focused upon (by the international community through such methods as the Kyoto Protocol) as the emissions that should be reduced to curb the "enhanced greenhouse effect." The primary anthropogenic greenhouse gases are:

• Carbon dioxide CO₂

   

• Methane CH₄

   

• Nitrous oxide N₂O

   

• Halocarbons PFCs and HFCs

   

• Sulfur Hexaflouride SF₆

   

Carbon Dioxide (CO₂) – Carbon is a continually cycling element that moves between the atmosphere, ocean, land biota, marine biota, and mineral reserves. In the atmosphere, carbon exists primarily as carbon dioxide, which is a part of global biogeochemical cycling. The atmospheric concentration of CO₂ has increased by 31% since 1750 and has likely not been exceeded during the past 20 million years. About three quarters of anthropogenic CO₂ emissions are from burning fossil fuels, the other quarter from land-use changes, primarily deforestation.

Methane (CH₄) – Methane is produced primarily through anaerobic decomposition of organic matter in living systems. Anthropogenic releases of methane occur from use of fossil fuels, cattle, rice agriculture and landfill gas emissions. The atmospheric concentration of CH₄ has increased 151% since 1750 and continues to increase. The present concentration has not been exceeded during the past 420,000 years.

Nitrous Oxide (N₂O) – Nitrous Oxide is also produced with the combustion of fossil fuels, as well as in agriculture and some industrial processes. N₂O concentrations have increased 17% since 1750, and current concentrations of N₂O in the atmosphere have not been exceeded in the past thousand years.

Others: Hydrofluorocarbons, perfluorocarbons, and sulfur hexaflouride (HFC, PFC, SF₆) – Halocarbons are primarily produced for industrial processes. HFCs were introduced as replacements for ozone-depleting substances, primarily as refrigerants. HFCs and SF₆ are used in aluminum smelting, electric power distribution, and magnesium casting. These chemicals are powerful greenhouse gases and have very long atmospheric lifetimes. The atmospheric concentration of these gases is increasing (IPCC, 2001).

The five greenhouse gases trap the sun's energy to varying degrees, or global warming potentials (GWP). GWP allows all of the greenhouse gases to be converted to a common unit of carbon dioxide equivalents. The GWP of a gas is dependent on how it reacts with long-wave (infrared) radiation coming from the Earth and how long it remains in the atmosphere (Table 8.1). For example, one molecule of SF₆ warms the planet to a similar extent as 23,900 molecules of CO₂. Emissions are usually reported in Metric Tonnes Carbon Dioxide Equivalents (MTCDE). This value is the product of the weight of the gas in Metric tonnes and the GWP (for example, 1 metric tonne of CH₄ is 21 MTCDE). This unit allows for a quick comparison of different gases relative to the effect they have in the atmosphere. This toolkit will make all of these calculations and display emissions in MTCDE.

Source: Stern (2006), p.98.

Table 8.1. Characteristics of Kyoto Greenhouse Gases.