7 weird ways CO2 is changing animals

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Increasing atmospheric greenhouse gases, such as carbon dioxide (CO2) and (CH4), not only change our climate systems but are also changing the ways animals live and behave. Here are 7 weird ways CO2 is changing the lives of some of the animals we love.


1. koalas and the leaves they eat

Koalas have a very specialised diet, feeding only on leaves from 7 different types of eucalypt species. Climate change may affect the distribution of these 7 species, either expanding or contracting, and therefore impacting on koala distribution.

However, research has shown that increasing atmospheric CO2 can change the chemistry of the eucalypt leaf. These leaves are already low in nutrients, such as nitrogen, and high in tannins and other toxins. Increasing atmospheric CO2 has been shown to lower the availability of nitrogen and increase the presence of toxins, also known as anti-nutrients. The change in leaf chemistry will have an impact on overall diet quality which will have consequences for the health and vitality of koalas.

further reading

DeGabriel, JL et al. 2009. The effects of plant defensive chemistry on nutrient availability predict reproductive success in a mammal. Ecology, 90: 711-719.

Lawler, IR et al. 1997. The effects of elevated CO2 atmospheres on the nutritional quality of Eucalyptus foliage and its interaction with soil nutrient and light availability. Oecologia 109: 59-68.


2. sea snails will struggle to jump

The conch snail escapes its potential predators by jumping or leaping away. Experiments have shown that with increasing CO2 the conch snail no longer jumps or takes longer to react to predators. Increasing CO2 impacts on their nervous system, slowing the snails down, and leaving them vulnerable to predation.

jumping snails and co2


further reading

Watson, S et al. 2013. Marine mollusc predator-escape behaviour altered by near-future carbon dioxide levels. Proceedings of the Royal Society B: Biological Sciences, 


3. baby clown fish and their brains

Scientists created experimental sea water with dissolved CO2 at levels expected by the end of the century. They found that the sense of smell in baby clown fish was highly affected. With their sense of smell distorted, the baby clown fish found it difficult to locate reefs and avoid them leaving them exposed to predators. CO2 disrupts a key brain receptor in fish which not only impacts on the sense of smell but also their ability to hear, turn and evade potential predators.

further reading

ABC News: Carbon Dioxide Affecting Fish Brains: study

baby clown fish



4. sharks turn from sprinters into marathon runners

The small-spotted catshark (Scyliorhinus canicula) is a common, bottom dwelling shark found throughout the Atlantic Ocean and Mediterranean Sea. Scientists from the University of Gothenburg borrowed 20 of these sharks and exposed them to seawater with varying levels of pH (increases in CO2 will lead to more acidic oceans with a lower pH value).

The scientists found that the metabolism of the sharks was similar in the control seawater versus a lower pH seawater. However, they noticed that the behaviour of the sharks changed dramatically during the night. Normally, during the night these sharks would swim for a few seconds or a minute at most, being sprinters. The experimental group turned into marathon runners, often swimming continuously for up to an hour.

The scientists suggested that the change in behaviour may have been caused by a change in the brain’s ion concentration or that the sharks were attempting to swim to better quality water.



An image of a small catshark being filmed in the experiment on altered pH in seawater.

further reading

Green L and Jutfelt F, 2014. Elevated carbon dioxide alters the plasma composition and behaviour of a shark. 


5. polar bears and snow geese

Polar bears strandard on icebergs have become the image of the adverse affects of climate change. While most of us know that climate change is decreasing Arctic ice and decreasing habitat for polar bears, less of us know that polar bears are dramatically changing their diets.

Traditionally, polar bears feed on seals and fish. However, as these food resources change or become scarce polar bears need to adapt their dietary preferences.

On the Cape Churchill peninsula, along the western shores of Hudson Bay, polar bears are arriving at the same time large numbers of summer breeding snow geese. The polar bears have taken advantage of this change of fortune, adapting their diet to now include this abundant resource. The sustainability of this situation, both for the polar bears and the snow geese, is questionable.

further reading

New York Times article: For Polar Bears, a Climate Change Twist


6. insects eat more soy

We have already seen how increasing CO2 can change leaf chemistry and how this may impact on koalas, but a different study has found that soybeans drop their defenses allowing insects to eat more of the leaves.

An experiment at the Soy FACE (Free Air Carbon Enrichment) research station, Illinois, USA, found that soybeans exposed to elevated atmospheric CO2 had leaves with lower nitrogen to carbohydrate contents (a similar finding to the eucalypt leaves in the koala experiment discussed above). Therefore, insects needed to consume more leaves to obtain the same amount of nitrogen. Compounding this effect, when plants face leaf predation they produce a hormone called jasmonic acid which alters the physiology of the plant to increase their defenses. However, this process was inhibited in the soybeans leaving them vulnerable to further predation. Consequently, insects, particularly the Japanese beetles, were living longer, having more breeding chances, and increasing the number of offspring.

Soy FACE (Mobile)


The Soy FACE experiment in Illinois, USA.

further reading

DeLucia EH et al. 2008. Insects take a bigger bite out of plants in a warmer, higher carbon dioxide world. PNAS, 105: 1781-1782.


7. a species extinction attributed to climate change

The next example is not so much of carbon dioxide changing the behaviour of a species, rather it is believed to be the first documented case of a species extinction due to climate change. In one way, the species could not adapt its behaviour to its changed circumstance and, unfortunately, is now believed to be extinct.

The Golden Toad (Bufo periglenes) once inhabited the mountaintop cloud forests of Central America. However, due to warming weather and drought conditions, the conditions that made the cloud forests possible have since disappeared. The change in moisture regime has altered species composition and the last time the Golden Toad was seen was in 1989.

Golden Toad


further reading

Pounds JA and Crump ML. 1994. Amphibian Declines and Climate Disturbance: The Case of the Golden Toad and the Harlequin Frog. Conservation Biology, 8: 72-85.