clairetalksaboutclimate

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The world’s most deadly animal

For me, there’s nothing scarier than a spider. For some reason, those long legs and furry bodies creep me out like nothing else. 

My fear of spiders is most definitely irrational because in fact, the world’s most deadly animal is the tiny, unassuming mosquito. Every year, over 700 000 people around the world die from vector-borne diseases and in 2015, malaria was the cause of 438 000 deaths worldwide. Another worrying thought is that over half the world’s population live in areas where mosquitos are present. (Who., 2020). Obviously, mosquitos are a deadly animal. But will a changing climate impact their population and survival?

Scientists have found that there is a strong correlation between the level of temperature and atmospheric carbon dioxide (CO2), and the rate of mosquito speciation (modelled from the past 195 million years). With greater temperature and levels of CO2, mosquitos will evolve faster and their population will be increased and diversified (Tang et al., 2018).

Another concern that scientists had was that the rate of dengue fever is closely linked to mosquito density, which dependent on rainfall and temperature (dependent on the climate). Therefore, in a changing climate, we will see an increase in occurence of dengue fever (Li et al., 2019).

This leads to concerns about an increase in mosquito-transmitted diseases with a changing climate, especially because mosquitos can bring disease into completely new areas and also, return some previously-eradicated disease to regional areas, which may not have the public health infrastructure to deal with it.

References

Li, R., Xu, L., Bjørnstad, O., Liu, K., Song, T., Chen, A., Xu, B., Liu, Q. and Stenseth, N., 2019. Climate-driven variation in mosquito density predicts the spatiotemporal dynamics of dengue. Desalination and water treatment, [online] 116(February 26 2019), p.v-vi. Available at: <https://www.pnas.org/content/116/9/3624> [Accessed 1 April 2020].

Tang, C., Davis, K., Delmer, C., Yang, D. and Wills, M., 2018. Elevated atmospheric CO2 promoted speciation in mosquitoes (Diptera, Culicidae). Communications Biology, [online] 1(182), pp.154-154. Available at: <https://www.nature.com/articles/s42003-018-0191-7#citeas> [Accessed 1 April 2001].

Who, 2020. Mosquito-Borne Diseases. [online] World Health Organization. Available at: <https://www.who.int/neglected_diseases/vector_ecology/mosquito-borne-diseases/en/> [Accessed 1 April 2020].

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Flying foxes: FNQ’s canary in the coal mine

As a heatwave ripped through Cairns in November 2018, passersby may have noticed a rustling from the trees near the Cairns Library. This didn’t come from a breeze through the leaves but rather, the spectacled flying-fox roost madly flapping their wings as they tried to cool down in the unprecedented temperature conditions. 

Flying foxes struggle to cope with temperatures above 42°C and as temperatures hit a high of 42.6°C in Cairns, 23 000 spectacled flying foxes dropped dead from their roost, leaving hundreds of pups orphaned. 

Figure 1: Dead spectacled flying foxes cover the ground in the aftermath of the late November 2018 heatwave in Cairns, Australia

Like any animal that regulates homeostasis, bats have developed particular thermoregulatory behaviours to cope with heat stress. Wing-fanning (see Figure 2) forces convection and facilitates thermoregulation, whilst shade-seeking reduces the amount of direct sunlight exposure (Laburn & Mitchell 1975). When those two regulatory behaviours aren’t enough to maintain homeostasis, bats will facilitate evapotranspiration by panting and spreading saliva, although this also accelerates dehydration (Licht & Leitner 1967).

Figure 2: Flying foxes displaying wing fanning

But will these behaviours be enough to cope with the heat in a changing climate?

That type of event that Cairns experienced in 2018 has happened before. In January 2002, temperatures above 42°C killed <3500 bats in nine mixed-species colonies in New South Wales. Observations in one of the nine colonies recorded those same thermoregulatory behaviours and witnessed 5-6% of bat deaths due to hyperthermia (Welbergen, 2007). In comparison, those same behaviours were witnessed in Cairns, November 2018, however, approximately 33% of the spectacled flying fox population died from heat stress (Akst, 2019).

Between 1994-2007, 30 000 grey-headed flying foxes died due to extreme heat events (Akst, 2019). Evidently, heat stress isn’t a new phenomenon for bats. However, the late November 2018 heatwave was unprecedented, occurring during the bat’s birthing season. This meant that mothers and pups were especially vulnerable, leading to an unprecedented high mortality rate.

With climate change comes more abnormal and extreme temperatures. If Cairns experiences more heatwaves of similar timing and proportion to November 2018, the already-critically endangered spectacled flying fox populations won’t have much of a fighting chance in a changing climate.

References

Akst, Jef. Thousands of Australian Animals Die in Unprecedented Heatwave. The Scientist. [Online] January 17, 2019. The impact and implications of climate change for bats. Sherwin, Hayley A., Montgomery, W. Ian and Lundy, Mathieu G. 3, s.l. : The Mammal Society, 2013, Mammal Review, Vol. 43.

Justin A Welbergen, Stefan M Klose, Nicola Markus and Peggy Eby, 2007. Climate change and the effects of temperature extremes on Australian flying-foxesProc. R. Soc. B.275419–425

Laburn H.P & Mitchell D. 1975. Evaporative cooling as a thermoregulatory mechanism in the fruitbat, Rousettus aegyptiacus. Physiol. Zool. 21, 195–202. 

Licht P & Leitner P, Behavioral responses to high temperatures in three species of Californian bats. J. Mammal. 48, 1967a52–6.

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breaking news: water is wet

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Giving some context to the climate crisis

Climate change appears to be the issue of our time; dominating media headlines, scientific research, and political agendas. Whilst sea-level rise inundates Pacific Islands, Australia’s leaders crack inappropriate jokes about “water lapping at their doors” and young people have taken to the streets to express their anger at political inaction on climate (Figure 1). 

Figure 1: A student climate strike in Cairns, Australia

Meanwhile, spectacled flying foxes drop dead out of trees due to heatwaves (Figure 2), corals experience mass bleaching and tree kangaroos are going blind due to the impacts of the drought. 

Figure 2: Some of the 23 000 spectacled flying foxes that died during a heatwave in Cairns, 2018

The climate crisis is inherently unjust: those who’ve contributed the least to the issue, are suffering the most. 

So what’s the big deal with the climate: hasn’t it always been changing? Well, yes, it has. But ever since the Industrial Revolution, human activity has been accelerating this phenomenon: check out Graph 1 from NOAA. (IPCC, 2018)

Graph 1: Proxy Measurements of CO2 in the reconstruction of ice cores

Scientific consensus tells us that global warming has increased by 1°C in a post-industrial world, and on our current trajectory of greenhouse gas (GHG) emissions, there is high confidence that warming will reach 1.5°C between 2030 and 2052. (IPCC, 2018)

In 2018, the IPCC released a special report on the impacts of anthropogenic climate change, showing that many serious climate impacts will be omnipresent at 1.5°C. It also compared the ramifications of a 1.5°C vs 2°C warming. 

For instance, at two degrees of warming, coral reefs will be decimated (mostly - the percentage estimate is >99%), compared to 1.5 degrees of warming, where coral reefs would decline by 70-90%. (United Nations, 2020)

Figure 3: Mass coral bleaching on the Great Barrier Reef

Limiting global warming to 1.5°C will require a coordinated effort from all sectors in society, to transition to net zero emissions by 2050. (IPCC, 2018) Globally, we are not on track to achieve this, and both people and the environment are already suffering from the impacts of climate change. 

While society attempts to transition to a low carbon economy, this blog will be exploring some of the ways that species are attempting to adapt and cope with a changing climate. 

Stay tuned for another blog post next week 🐋

References:

IPCC (2018). Global Warming of 1.5°C. [online] Available at: https://www.ipcc.ch/site/assets/uploads/sites/2/2019/06/SR15_Headline-statements.pdf 

UN (2020). Climate Change. [online] Available at: https://www.un.org/en/sections/issues-depth/climate-change/ 

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