We’re familiar with carbon dioxide as a greenhouse gas, but it is more than just a greenhouse gas. It plays a number of different physiological roles within organisms. Current concentrations of CO2 in the atmosphere are 100 parts per million higher than at any period in the last one million years. This may play a role in some peculiar problems that affect us today.
For one, we’ve noticed a disturbing trend, where obesity increasingly affects not just humans, but all sorts of animals, including wild animals and lab rats fed a standardized diet.1 This would be suggestive of some sort of environmental factor that is affecting the health of a wide variety of lifeforms. We don’t know what it is that’s causing this, but different theories exist. Some candidates include epigenetic damage and exposure to endocrine disruptors.
One theory however, argues that exposure to carbon dioxide fools our body into believing that our energy consumption is higher than it actually is.2 As a result, our body increases its energy intake. Experiments have shown that long-term exposure to elevated carbon dioxide concentrations lead to a persistent state of acidosis in the body. It is suggested that an increased firing rate of specialized neurons in the hypothalamus leads to increased wakefulness and higher energy consumption. This fits observations that show time spent sleeping has decreased over the past century, even as our work burden has decreased.
We know that four out of five mass extinction periods can be linked to sudden rises in atmospheric carbon dioxide concentrations. In the ocean, acidification is thought to be a main factor in this, while temperature increases lead to mass extinctions both on land and in the ocean. However, what if carbon dioxide has a direct health effect on animals?
Studies suggest that elevated carbon dioxide concentrations can have detrimental effects on our health. One problem it appears to cause is oxidative stress, which is thought to underlie many of the health problems we face. Carbon dioxide exposure in an office environment at levels above 1000 parts per million leads to elevated levels of urinary 8-OHdG, compared to exposure at levels below 600 parts per million.3 The size of the effect is comparable to that of being a tobacco smoker. Other studies confirm that signs of oxidative stress begin to increase, long before concentrations of 1000 parts per million are reached.4
If carbon dioxide exposure leads to increased urinary 8-OHdG levels, this is very worrying, as 8-OHdG is commonly used as an indicator of a variety of health problems. Elevated levels are indicative of atherosclerosis risk, cancer risk and complications seen in diabetes.5 Elevated levels of this marker of oxidative stress are also found in male patients suffering from low fertility.6 It’s notable that human sperm counts are believed to have decreased by 50% during the 20th century.
In rooms that have elevated carbon dioxide levels due to poor ventilation, we tend to feel uncomfortable and suffer from symptoms such as poor breathing, dry eyes and wheezing. Such effects have been observed even in studies where subjects were never even exposed to levels above 1000 parts per million.7 Cognitive performance on tests requiring clear thinking also tends to decrease in such studies.
The question we have to ask ourselves is: What kind of future are we setting ourselves up for? Even our best case scenarios lead to levels above 500 parts per million, before 2100. Shell no longer believes that temperature increase will be kept below two degree Celsius, rather it predicts an increase of four degree Celsius, later rising to six degree Celsius.8
A rise in temperatures by six degree Celsius, also means an increase in atmospheric carbon dioxide levels to above 1000 parts per million. In such a world, humans are chronically exposed to high levels that are known to detrimentally affect our mental abilities. We would feel continually uncomfortable and unable to think clearly. If carbon dioxide is responsible for oxidative stress symptoms, a world with such high CO2 concentrations would be one where people age prematurely and chronic disease affects us at ever younger ages. It’s difficult to see how humans could ever survive on such a planet.
1 – Klimentidis Y, et al. “Canaries in the coal mine: a cross-species analysis of the plurality of obesity epidemics.” Proc R Soc B. linkurl:doi: 10.1098/rspb.2010.1890;http://rspb.royalsocietypublishing.org/content/early/2010/11/19/rspb.2010.1890.abstract
2 – http://www.nature.com/nutd/journal/v2/n3/full/nutd20122a.html
3 – http://www.mdpi.com/1660-4601/11/6/5586
4 – https://gra103.aca.ntu.edu.tw/gdoc/94/D89844003a.pdf?origin=publication_detail
5 – http://www.sciencedirect.com/science/article/pii/S0009898103004534
6 – http://www.sciencedirect.com/science/article/pii/S030121150200194X
7 – http://www.epa.gov/iaq/base/pdfs/indoorair20-247.pdf
8 – http://www.theguardian.com/environment/2015/may/17/shell-accused-of-strategy-risking-catastrophic-climate-change