Influence of Human-Induced Climate Change on Hurricane Fiona

By Joanna Burris, for CALS500: Climate Science, Impacts, and Services, Assignment 2

Even before Hurricane Fiona’s landing in Atlantic Canada on September 24, 2022, news articles had already linked the major storm to climate change. The storm had ravaged the island nation of Puerto Rico a few short days before, leaving hundreds of thousands of people without water or power and causing significant flooding across the island (Diaz, 2022).  In Atlantic Canada, Fiona has been called a “pivotal” (Mulligan, 2022) and “historic” (Al-Hakim, 2022) storm, and “one of the largest and most dangerous ocean storms to ever hit the region” (Mulligan, 2022). But was the severe storm actually a result of climate change? And how do scientists know this to be the case?

Climate scientists have proven, without a doubt, that human behaviour has caused the Earth’s atmosphere to warm (IPCC, 2022, p. 4, A.1). The global average surface temperature in the decade from 2011 to 2020 was nearly 1.1°C warmer than the average temperature from 1850 to 1900 (IPCC, 2022, p. 5, A.1.2). Burning fossil fuels, such as oil, coal, and diesel, emits large concentrations of greenhouse gases (GHGs) into the atmosphere that, uncoincidentally, act as a greenhouse, warming the Earth beyond the level that the natural concentration of GHGs would have done in the same amount of time (IPCC, 2022, p. 5, A.1.3).

As the Earth’s global surface temperature has increased, the upper ocean temperature of the North Atlantic has increased markedly. Federal scientist Blair Greenan from the Bedford Institute of Oceanography explained for a CBC News article published shortly after the hurricane that sea water temperatures off the Maritime provinces have increased by 1.5°C in the last century (Tutton, 2022). Hurricanes form over tropical water and are fed by heat from the ocean’s surface (Emanuel & Gribkoff, 2020). As the hurricane accelerates, more warm water evaporates and energizes the storm (Emanuel & Gribkoff, 2020). 

So, was Hurricane Fiona more intense than it would have been without global warming? It’s very likely. Observed global climate data shows that a greater proportion of hurricanes (also called tropical cyclones) develop into “intense” storms than did four decades ago (Arias, 2021, p. 132, TS.4.3.1). Therefore, in 2022 there is a higher probability that any given tropical cyclone (including Fiona) would turn into a major storm than there would have been in 1980 because of increased ocean temperature. Warming surface water temperatures in the North Atlantic also cause tropical cyclones to stay stronger for longer (Waite & Siegel, 2022; Tutton, 2022). 

“Warm water shoots heat and moisture into storms like Fiona, giving them a longer duration, and, often, a wider path.”

Anya Waite, oceanographer and Dalhousie professor, in Tutton, 2022

In addition to storms themselves being stronger today than in the past, other intensifying variables mean the impacts of a given hurricane may be worse. For example, sea level rise – another outcome of human-induced climate change – can make coastal storms more damaging and increase the risk of flooding (Centre for Climate & Energy Solutions, n.d.).  

As further evidence of the connection between climate change and worsening tropical cyclones, scientists have used climate modelling to determine how much influence human GHG emissions have had on specific storms (Reed et al., 2022). The process of determining the extent to which a climate event is the result of a specific cause is called “attribution” (Hope et al., 2021, p. 204). Attribution studies have determined that human-induced warming resulted in more rainfall during hurricanes Irma, Maria, and Harvey in 2017, Florence in 2018, and Dorian in 2019 (Reed et al., 2022, p.2).

These results align with the latest IPCC report from 2021 which states that human-induced climate change increases heavy precipitation associated with tropical cyclones (IPCC, 2021, p. 9, A.3.4). A common attribution method is to use climate models to simulate the climate event without human interference. Called “counter-factual” simulations, these studies can then be compared to simulations under actual conditions to evaluate how humans influenced the climate event (Reed et al., 2022, p. 2; Hope et al., 2021, p. 205).

Looking ahead, what does this mean for future hurricanes in Atlantic Canada? While the total number of tropical cyclones is expected to stay the same or even decrease as a result of climate change, the proportion of storms that develop into major storms is anticipated to increase (Arias et al., 2021, p. 70, TS.2.3). Even if GHG emissions are dramatically reduced in the coming decades, past emissions have committed the global ocean to future warming (Bush et al., 2022, p. 29, 3.7.1), and therefore tropical cyclones will continue to intensify. Sea level rise is also projected to continue beyond the end of the century, both globally (IPCC, 2021, p. 22, Figure SPM.8d) and in the Maritimes (Greenan et al., 2019, p. 390, Figure 7.17a), which will result in more damaging storms and higher risk of flooding. 

References

Al-Hakim, A. (September 23, 2022).  Hurricane Fiona shows how climate change is fuelling severe weather events in Canada: Expert. Global News. https://globalnews.ca/news/9146319/hurricane-fiona-climate-change/#:~:text=Weather-,Hurricane%20Fiona%20shows%20how%20climate%20change%20is,weather%20events%20in%20Canada%3A%20expert&text=Hurricane%20Fiona’s%20strength%20signals%20an,to%20a%20climate%20change%20expert

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