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All IPCC definitions taken from Climate Change 2007: The Physical Science Basis. Working Group I Contribution to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change, Annex I, Glossary, pp. 941-954. Cambridge University Press.

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At a glance - Is CO2 a pollutant?

Posted on 5 September 2023 by John Mason, BaerbelW

On February 14, 2023 we announced our Rebuttal Update Project. This included an ask for feedback about the added "At a glance" section in the updated basic rebuttal versions. This weekly blog post series highlights this new section of one of the updated basic rebuttal versions and serves as a "bump" for our ask. This week features "Is CO2 a pollutant?". More will follow in the upcoming weeks. Please follow the Further Reading link at the bottom to read the full rebuttal and to join the discussion in the comment thread there.

At a glance

If you look up the definition of pollution in a dictionary, you will soon realise it's rather subjective. There are many substances out there that are harmless at certain levels but harmful at others.

Carbon dioxide is well-mixed in our atmosphere. That's because when it is emitted, by any mechanism from a vehicle exhaust to a volcanic eruption, it stays in the air for many years. Unlike water, it does not condense and fall back out as rain. Turbulence does a splendid job of mixing it evenly into the air. But there are places on - and in - Earth where much higher concentrations of CO2 may be encountered.

The trouble with CO2 is that it cannot be seen and neither can it be smelt. In other words we cannot detect it from a safe distance.

In caves and mines, high concentrations of CO2 are a well-known hazard. They can result from things like rotting timber, oxidising coal and particularly by poor ventilation, where that mixing into the air fails to occur. Because CO2 is heavier than air, in poorly ventilated areas underground it may collect into pockets waiting for the unwary.

Miners or underground explorers breathing a higher than normal concentration of CO2 will experience gradually increasing ill effects. It depends on the concentration of the gas. For example the UK Health and Safety Executive has defined safe CO2 limits for the workplace. The limit for long-term exposure is 0.5% (5,000 ppm) but for shorter encounters it is 2%. Anything over that figure is regarded as a risk to human health. There have been many accidents and fatalities over the years caused by high concentrations of CO2 in underground workings and to a lesser extent in caves. Coal-miners refer to CO2 as black- or choke-damp in recognition of the hazard.

Possibly the worst CO2-related disaster was that of 21 August 1986 at Lake Nyos, in northwestern Cameroon in western Central Africa. The lake, only some 2 x 1 km in size but more than 200 m deep, is one of a number of flooded volcanic vents in a sporadically-active volcanic belt. Carbon dioxide-bearing springs are common in this area and some are present in the lake-bed.

Lake Nyos is typically stratified, meaning that normally its waters occur in distinct layers with different chemistry that do not normally mix. In something of a loaded gun scenario, the bottom layer used to become saturated with CO2 from those lake-bed springs. On 21st August 1986, something caused an overturning of the lake, meaning the deep CO2-saturated water headed for the surface. Like taking the top off a shaken-up pop bottle, a vast cloud of CO2 was instantly released and travelled out from the lake along the ground. At least 1,746 people and 3,500 livestock died instantly from asphyxiation.

Modern technology and international cooperation have since been successful in controlling the build-up of CO2 in lakes like Nyos. But clearly, in specific circumstances, CO2 is as deadly a pollutant as any other.

Please use this form to provide feedback about this new "At a glance" section. Read a more technical version below or dig deeper via the tabs above


Click for Further details

In case you'd like to explore more of our recently updated rebuttals, here are the links to all of them:

Myths with link to rebuttal Short URLs
Ice age predicted in the 1970s sks.to/1970s
It hasn't warmed since 1998 sks.to/1998
Antarctica is gaining ice sks.to/antarctica
CRU emails suggest conspiracy sks.to/climategate
What evidence is there for the hockey stick sks.to/hockey
CO2 lags temperature sks.to/lag
Climate's changed before sks.to/past
It's the sun sks.to/sun
Temperature records are unreliable sks.to/temp
The greenhouse effect and the 2nd law of thermodynamics sks.to/thermo
We're heading into an ice age sks.to/iceage
Positives and negatives of global warming sks.to/impacts
Global cooling - Is global warming still happening? sks.to/cooling
How reliable are climate models? sks.to/model
Can animals and plants adapt to global warming? sks.to/species
What's the link between cosmic rays and climate change? sks.to/cosmic
Is Al Gore's An Inconvenient Truth accurate? sks.to/gore
Are glaciers growing or retreating? sks.to/glacier
Ocean acidification: global warming's evil twin sks.to/acid
The human fingerprint in global warming sks.to/agw
Empirical evidence that humans are causing global warming sks.to/evidence
How do we know more CO2 is causing warming? sks.to/greenhouse
Explaining how the water vapor greenhouse effect works sks.to/vapor
The tricks employed by the flawed OISM Petition Project to cast doubt on the scientific consensus on climate change sks.to/OISM
Is extreme weather caused by global warming? sks.to/extreme
How substances in trace amounts can cause large effects sks.to/trace
How much is sea level rising? sks.to/sealevel
Is CO2 a pollutant? sks.to/pollutant

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