Thread Rating:
  • 0 Vote(s) - 0 Average
  • 1
  • 2
  • 3
  • 4
  • 5
Greenhouse Gases - A Perspective
Carbon Dioxide and Other Greenhouse Gases

We’re always hearing about greenhouse gases and carbon dioxide (CO2) and how they are causing warming of the Earth that will be dangerous to life on the planet.
But is it all rhetoric?
What this post is about, is to try and put some perspective on the issue of carbon dioxide, and whether or not it is the big bad demon or not that alarmists are saying it is.

A “Normal” Climate

Our atmosphere is made up of molecules of which about 99% is radiatively inactive. Greenhouse gases make up the remaining 1%.  Under ideal “normal” circumstances suitable for life, the combined greenhouse gases increase the Earth’s temperature from a theoretical -19⁰C to an average of around +15⁰C i.e. 34⁰C of warming.

Typical estimates of the proportions of the greenhouse warming gases are around 78% water vapour, 20% carbon dioxide and around 2% from methane, nitrous oxide and other minor compounds. However estimates of the amount of water vapour can differ significantly from 60% less to 88% higher than 78%.
Source: “Climate: The Counter Consensus” by Prof. Robert M. Carter 2010

 What exactly are Greenhouse Gases?

Greenhouse gases absorb infra-red thermal radiation and hold the heat for a period of time in the atmosphere before being eventually re-absorbed back into the Earth or escapes into space.  It’s like a blanket that effectively keeps heat trapped near to the Earth.
The more important ones are water vapour, carbon dioxide, methane, nitrous oxide and ozone, in decreasing order of effectiveness mainly because of their concentrations.
Source: “Energy & Environment Vol 16 No 6 2005” by Jack Barrett

The Kyoto Protocol recognizes six greenhouse gases. The numbers in brackets are the IPCC’s estimate of the warming potential of each compound compared to carbon dioxide e.g. methane has 21 times warming effect than 1 part of carbon dioxide:
•CO2 – carbon dioxide(1)
•methane (21),
•nitrous oxide (310),
•hydroflurocarbons (140 to 1,700),
•perflurocarbons (6,500 to 9,200) and sulphur hexafluoride (23,00).

On the surface it makes CO2 look positively benign and might be the sort of thing a sceptic could say, except that the non-CO2 gases are only in very small percentages as to be almost negligible by comparison.  But you might notice the most prominent agent of water vapour is missing from the IPCC list. They say it is a “feedback” not a “forcing” agent and that it only lasts in the atmosphere for a few days as opposed to CO2, which they say lasts for more than 100 years. Therefore they don’t use it for the purpose of arguing the AGW – human caused warming case.

Feedback and Forcing Agents

It’s a given scientific fact that the Earth’s global temperatures throughout its history has ranged widely from hot to cold.   At any given time when the temperature was fairly steady, the atmosphere has been “balanced” i.e. the incoming energy from the sun was equalled by outgoing energy in some form from the Earth.  Then along came forcing or feedback agents to tip the balance and warm or cool the Earth respectively. The various cycles of warming and cooling has continued from the beginning, mostly due to how far the Earth orbits around the Sun.

Forcing Agents: These can be external e.g. the Sun, or internal e.g. material which absorbs heat such as aerosol dust from natural sources such as volcanoes or human sources such as aerosol spray cans, CO2 – carbon dioxide emissions and so on. According to the IPCC, CO2 is believed to account for the majority of the radiative forcing that keeps the greenhouse effect going.
See also :

Feedback Agents: These can change the effects of Forcing either positively and/or negatively. For example an increase in temperature causes more evaporation which causes higher temperatures, but at the same time creates more low clouds which reflect solar radiation back into space and rains to cause cooling.

An agreed scientific fact is that water vapour is not a forcing agent in its own right. It requires a rise in temperature to first create evaporation and more clouds. This causes an initial and temporary increase in temperature, but as the warm air rises, cooler air is sucked in from surrounding regions. It then it becomes a feedback agent. The tops of clouds reflect incoming energy from the sun. The warm vaporous air is cooled in the upper altitudes and condenses. Rainfall then cools the earth.  Cooler air under these clouds are drawn away to other warmer areas.

Water Vapour

Even though water vapour is the most dominant in its ability to absorb heat, the IPCC does not include it as a greenhouse gas as previously mentioned. So let’s look at why they should include it in their calculations. There is considerable overlap in absorption qualities between water vapour and other greenhouse gases. 

The CO2 absorption rate increases 1.5% in the absence of other greenhouse gases which causes temperature to rise. But when put together with other greenhouse gases its absorption rate drops down to 0.5%. In other words it’s much less effective in taking up heat.  Water vapour has about 5 times the ability to absorb heat as CO2, however the cooling effect mainly happens in the first 100m of the atmosphere, and gets less and less effective in comparison to CO2 as altitude increases.

Yet even if water vapour only lasts in the atmosphere for a few days, there is always rain happening somewhere on the planet every day. Cumulatively it must have at least some contributing cooling effect on a regional, if not global scale?  The eternal trade winds are a good example how cooler air is drawn into hotter areas such as the Tropics.  Further, with the water vapour in the higher altitudes being almost ineffective in absorbing heat,  it would be expected that more CO2 would have a greater effect on atmospheric warming. But this does not seem to be occurring in spite of the predictions of most GCMs. So the real question is whether water vapour is a more powerful forcing or cooling agent?  And if so, by how much?

The question of climate feedback systems is a highly complex subject. Scientists don’t yet know all the feedback systems that affect climate and maybe never will. It’s one of the reasons why computer modelling might be considered unreliable by some.  With all the uncertainty about feedback effects, not to mention outright scientific disagreements, it has to be wondered for example if this overlap of absorption rates has been built into the computer modelling on which the IPCC relies and which must give cause for some scepticism.
See also:

Health Effects of CO2
The level of CO2 in our atmosphere is at 0.03% which is about 300 ppm (parts per million). The level considered safe is 600 ppm for indoors.  In low concentrations e.g. less than 1% there is little noticeable effect. Inside a building without a fresh air supply then 1% (10,000 ppm) of CO2, some occupants might feel drowsy.

It usually needs to be over 2% or so before most people become aware of it without something to alert them e.g. some form of smell. An acid condition of the blood “acidosis” may form after several hours at that level. At 5% the breathing rate doubles and above that level it becomes toxic. Prolonged exposure creates various noticeable symptoms, which if left untreated can cause unconsciousness and even death.

However it should be understood that adding a given amount of CO2 to a contained space correspondingly reduces the amount of oxygen available. Any health issues as a result of exposure to CO2 could likely be as much due to a lack of oxygen as to the CO2.
Source: InspectAPedia article, “Toxicity of Carbon Dioxide Gas Exposure, CO2 Poisoning Symptoms, Carbon Dioxide Exposure Limits”.

How Much CO2 Is Up There?

Estimations about how much CO2 is present in the atmosphere are up to 780 Gt of total carbon.  About 7 Gt is estimated to be added each year from all sources, of which the IPCC argues about 3.5 Gt (half) is man-made.  Since pre-industrial times the total amount has risen from about 280 ppm – parts per million to 380 ppm.  You may remember the IPCC believes CO2 stays up there for about 100 years, but there are other scientific calculations based on carbon isotope evidence and a much shorter time that the CO2 stays up there i.e. five to 10 years. They suggest that only four to five percent – about 0.05 Gt  of the total 780 Gt is derived from fossil fuel burning.
Note: The whole paper is an interesting read but page 13 lists the scientists who have published shorter “residence” time of CO2 in the atmosphere.

But even if that is not true or even near it, if we use the IPCC figure of 3.5 Gt per year being added each year because of humans, it’s still only 0.45% of the total carbon count. (780 Gt divided by 3.5 Gt).  In other words, 99.55% of greenhouse gases has nothing to do with human CO2 emissions, and the remaining 0.45% just happens to be equivalent to the 0.1⁰C warming which other non-IPCC aligned scientists have come up with.
See also:

Yet despite how much water vapour dominates the greenhouse gases as a primary factor, and the IPCCs own estimations about how much CO2 is actually being added each year to the total atmospheric content, carbon dioxide still remains the centre of attention.  One of the reasons would have to be the continued focus of the IPCC on promoting AGW - Anthropogenic Global Warming instead of looking at the whole of the climatic systems. Until they are removed as the leading authority on climate change and the matter placed back into the hands of actual scientists, the matter will continue to be political.

By Russ Swan
Issues on Climate Change

Users browsing this thread: 1 Guest(s)