Dr Shawn Vasoo, Clinical Director, National Centre for Infectious Diseases
Climate change has resulted in extreme weather events occurring globally and with increasing frequency and devastating effects. One example is a massive flood which occurred in Libya from 10 to 11 September 2023. This was precipitated by unprecedented rainfall and the collapse of two dams, resulting in at least 4,000 deaths and more than 10,000 people were reported missing as of 10 October. Libya usually receives about 200 millimetres of precipitation a year in many areas but on 10 September, the town of Derna where the dams collapsed received more than 100 millimetres in three hours.
Nearer to home, the government of Indonesia is relocating its capital from Jakarta to East Kalimantan, as Jakarta is sinking due to ground water extraction, and compounded by rising sea levels due to climate change.
In Singapore, the meteorological service reported several notable weather events in 2022: 2013-2022 being the warmest decade on record, 13 May 2022 being the warmest day in May on record at 36.7 degrees Celsius, and 2022 being the sixth wettest year since 1980.
These are just some of many examples of climate change and extreme weather events, facilitated by greenhouse gas emissions which result in global warming. Asia, being the most populous region in the world with multiple densely-packed cities, will be a region poised to be disproportionately affected.
Impact on Infectious Diseases
Climate change will affect the world on multiple fronts. Apart from climate-driven migration and food security, one major area is its impact on infectious diseases (IDs). Climate change is anticipated to impact IDs in four major ways:
1) An increased risk of novel IDs emerging and leading to epidemics and possibly pandemics
The COVID-19 pandemic brought into sharp focus how IDs can have a profound impact on human health, lives, and economies. While the link between COVID-19 and climate change is not well-defined, it is a zoonosis (i.e. a viral disease affecting humans which has an animal origin). Scientists have predicted that climate change will increase spillover events leading to epidemics from emerging IDs with a zoonotic origin such as SARS-CoV-2. This is because climate change will drive more interactions between humans and other animals harbouring novel or as yet unknown viruses, as we encroach into animal habitats brought on by increasing pressure for land-use changes, or as disease-carrying animals expand their habitats due to climate change.
2) A rise in vector-borne diseases
An example of a vector-borne disease that we are all familiar with is dengue, which is transmitted by infected mosquitoes carrying the dengue virus. With climate change, increased temperatures and heavy rainfall will drive a rise in the mosquito vector population and suitable breeding sites. Other mosquito-borne diseases such as Zika and Chikungunya may also resurge as a result, including those which are not currently endemic in Singapore may also emerge in the process.
3) A rise in water / food-borne diseases
While the interplay between climate change and food-borne diseases still needs to be further defined, it is clear that food security and production are closely intertwined with climate change. Water / food-borne diseases are caused by bacteria such as Escherichia coli (i.e. E. coli), and these bacteria can multiply more readily and better survive with increased temperatures. Combined with extreme weather and the contamination of water sources, this may have contributed to a 2018 E. coli outbreak across multiple states in the United States which was traced back to contaminated lettuce. This outbreak left 96 people hospitalised and five dead. Given that Singapore imports 90 per cent of its food and imported foods may arrive from multiple sources in very short time periods, there is a risk of such food and water borne pathogens being transported as well. Increasing rainfall, storms and floods also increase the risk for other diseases such as melioidosis (caused by a soil-borne bacteria), leptospirosis (a bacterial disease transmitted by skin contact with contaminated water), and diseases caused by the Vibrio species (a group of bacteria which may cause food-borne disease, or skin / soft tissue infection in individuals with poor immune systems, after broken-skin contact with seawater, when there is overgrowth of these organisms).
4) A rise in antimicrobial resistance
Increased temperatures accelerate bacterial multiplication and the transfer of resistance genes. Microplastics, which are very small bits of plastic debris pollutants in the environment due to the breakdown of larger plastics, have also been found to accelerate global warming via disrupting the resident bacteria in soil and oceans (i.e. the soil and marine 'microbiome'), which in turn increases the production of greenhouse gases. These microplastics also speed up the exchange of antimicrobial resistance (AMR) genes between bacteria. Due to harsher climatic conditions, and diminishing crop and farming yields, there may be increased pressure to use antibiotics in these industries, which in turn exacerbates the problem of AMR. Ultimately, these will lead to multi or even pandrug-resistant bacteria which can cause infections in humans during procedures such as surgery and chemotherapy to treat cancer, and which we do not have treatments for.
Managing Effects of Climate Change
The striking thing is that we would not have to leave Singapore to be impacted by these effects of climate change. The call to combat climate change is not an exercise in “crying wolf". The truth is that climate change has already impacted us, including its effect on IDs, and this will only grow with continued inaction. This begs the question – what can we do about climate change?
Multiple countries have committed to or are considering net zero emissions. Some of the more specific problems arising from climate change will require multidisciplinary and multilateral approaches across governments, industries and academia. Businesses need to take active steps to reduce their carbon footprint, and aim towards achieving net zero emissions.
At the individual level, we can all take practical steps such as taking climate change seriously and actively reducing our carbon footprint. Some ways to do so include:
1) Cut food waste, and consume more local produce
2) Recycle, upcycle and reduce unnecessary purchases
3) Being judicious about driving or flying to reduce transport emissions
4) Use energy-efficient appliances in your home, and reduce the energy usage at home and at work
5) Avoid single-use items and plastic bags
We may not get it right all the time, or all at once, but we can all make concerted efforts to do our part to tackle climate change.
The article was also published in Lianhe Zaobao on 6 February 2024.
