The Impact of Climate Change on Tropical Cyclone (essay)

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The work is a program in the International Earth Science Olympiad. Participants are required to carry out research in teams, decide their own topic, search for and analyse relevant information, and finally present a 12-minute-long presentation to the Olympiad Jury. After the presentation, I organized our speech draft into this essay.

THE IMPACT OF CLIMATE CHANGE ON TROPICAL CYCLONES

Fang Ziyan

1.Introduction

The tropical cyclone, one of the most devastating hazards, is a rapidly rotating low-pressure storm system. It is able to bring about strong winds, heavy precipitation, as well as secondary hazards such as landslides and mudflow, causing great damage to human society. In recent years, the tropical cyclone has witnessed a change in its global pattern, which researchers believe to be closely associated with climate change. According to the IPCC, anthropogenic climate change includes global warming caused by greenhouse effects and this warming is having an impact on the climate system.

The following essay will analyse the impacts that current climate change might impose on tropical cyclones, and put forward suggestions for responding to the changes and mitigating the risks.

2.Analysis of the Impacts of Climate Change on Tropical Cyclones

2.1 Frequency

The tropical cyclone (TC) frequency is likely to decline under climate change. An approximate 13% decrease in global TC numbers was found over the 1900-2012 period compared to the preindustrial baseline 1850-1900. An even larger drop of about 23 percent is witnessed since around 1950, around the time global temperatures began to noticeably rise. (Chand et al., 2022) Figure 2.1 illustrates the declining trend of global TC numbers.

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Figure 2.1 Global annual TC numbers from 1850-2000

(source: nature climate change)

According to Bengtsson et al (1996), one explanation for the reduction of TC frequency is that global warming has weakened tropical circulation, reducing upward mass flux, hence creating a less favourable condition for tropical cyclones to form. On the other hand, Emanuel et al (2008) claimed that the reduction of the TC frequency is closely associated with the increase in mid-troposphere saturation deficit due to global warming. That is to say, with global warming, the maximum humidity of air rises, making it harder to saturate within the specific height needed to form a tropical cyclone.

However, this conclusion of changes in tropical cyclone frequency can be challenged by the lack of long-term data, as the use of satellites to record cyclones started only from the 1970s. Furthermore, there are some researchers who argue that in the long-term, tropical cyclones may become more common as a result of climate change. For instance, a NOAA GFDL study using the high-resolution HiFLOR model predicts a 9% increase in storm frequency globally and a 23% increase in the Atlantic basin by the end of the 21st century.(Kieran Bhatia et al., 2018)

2.2 Intensity

It is widely agreed that the recent climate change would lead to an increase in the intensity of tropical cyclones. Climate projections suggest that with further warming in the coming decades, a greater proportion of Category 4 and 5 tropical cyclones will occur globally with more destructive wind speeds and more extreme precipitation rates (Figure 2.2)(Thomas Knutson et al., 2020).

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Figure 2.2 Tropical Cyclone Projects (2°C Global Warming)

In terms of precipitation, a higher temperature would result in more water evaporating and thus greater humidity in the air. Carrying more moisture, the tropical cyclone would be able to strengthen precipitation. There are models demonstrating that under the circumstances of a 2°C global warming scenario, the mean intensities of tropical cyclones are going to increase by 5% and near-storm rainfall rates to increase by 14%.(Potts & Laura, 2021) This might trigger more devastating landslides and flooding, as well as the wider spread of infection and mosquito-borne diseases because of larger areas of standing water.

Meanwhile, strong winds in tropical cyclones can lead to large waves on the sea called storm surges, the height of which is proportional to the wind speed. It is calculated that a global temperature increase of 2°C may result in a 5% increase in maximum wind speed, hence greater storm surges are more likely to be triggered, resulting in higher storm inundation level.5 This would also amplify the impact of its secondary hazards, such as more devastating tornadoes and greater damage to coastal ecology.

In short, with climate change, the intensity of tropical cyclones is likely to be strengthened, resulting in more serious primary and secondary hazards. Notably, human factors are also needed to be taken into account when evaluating the actual impact of tropical cyclones. In terms of exposure, the higher the population and asset density, the greater risk will be undertaken by the region. Meanwhile, the vulnerability of different areas will also impact their risk level. For instance, tropical cyclones are likely to impose more devastating impacts on those areas with poor design and construction of buildings, limited official recognition of risks and preparedness measures, and disregard for environmental management (UN-ISDR, 2009).

2.3 Location

It is observed that the latitude at which tropical cyclones attain their maximum intensity has been moving poleward. A reasonable explanation is that under global warming, the temperature required to form tropical cyclones moves closer to the poles. As it is shown in Figure 2.3, between 1982 and 2009, the average location of Northern hemisphere tropical storms moved north by 53km, whilst Southern hemisphere ones moved south by 62km, (Kossin et al., 2014) raising the potential that those storms could begin to bring greater damage to locations that may be less well-equipped to respond, especially those with great exposure and vulnerability.

Notably, the impacts of this change are not all negative. For instance, some locations may benefit from the much-needed precipitation brought by the cyclones, whilst others might enjoy the bumper harvest in fishing as tropical cyclones can stir up the waters of coastal estuaries and hence nutriment can be brought up to the shallow water from deeper areas.

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Figure 2.3 Poleward Migration of the latitude of LMI

3.What can we humans do?

Undoubtedly, the change in TC pattern under climate change is going to impose significant impacts on human societies. Ranson et al (2014) assessed research findings of future tropical cyclone damages under climate change, taking into account both monetary damages and unmonetized “loss potential” damages but excluding fatality. Their conclusion suggested that a 2.5 °C rise in the global surface air temperature would result in a 28% increase in TC damages in the WNP.

To face these threats and reduce possible losses, adaptation and mitigation methods are needed to be carried out against both tropical cyclones and climate change.

3.1 Response to the change in patterns of tropical cyclones

To prepare for higher-intensity cyclones, coastal countries should strengthen and improve their disaster management systems, especially those countries that have not experienced tropical cyclones but are at risk of being affected by them under climate change.

Governments concerned could carry out land use planning based on the changes of tropical cyclones. For instance, they can enforce building codes by stipulating maximum building height and density of buildings. Another option is to place less critical activities to these vulnerable areas, through programs including constructing parks, sports facilities, parks, and open grazing land.

Several mitigation methods could also be implemented to response to the intensified tropical cyclone, such as constructing hazard-resistant buildings and infrastructure to reduce the vulnerability and risks. Meanwhile, vegetation cover improvements, including planting trees in rows and coastal shelterbelt plantations, are also effective ways to break the wind force and reduce surface runoff discharge (increase the water infiltration capacity), hence mitigating the severe losses.

When attacked by tropical cyclones, some specific preparation methods are helpful to reduce the losses. The monitoring and prediction of tropical cyclones should be improved, and timely weather forecasts and warnings should be provided to the public. When cyclones arrive, residents should be evacuated into shelters nearby. After the cyclone, local authorities should implement immediate rescuing, and at the same time ensure water, food and healthcare provisions so as to prevent the spread of diseases.

For those areas that have not experienced tropical cyclones but are at risk of being affected by them under current climate change, public awareness programs must be implemented to familiarize the public with the causes and impacts of the hazard, and the ways in which the local population is vulnerable. Meanwhile, the explanation of warning systems and evacuation plans should also be publicized.

3.2 Measures to mitigate climate change

The influence of climate change on tropical cyclones has been notoriously difficult to separate from natural variability. However, an increasingly consistent picture is emerging that indicates human activities are probably influencing some aspects of these extreme weather events.5 Therefore, in order to reduce the risk level from the root, human beings should adopt several schemes to mitigate global warming.

There are methods on different scales to combat climate change. For instance, local authorities could lay down road or transport policies to reduce the use of fossil fuels. They can also encourage reuse and recycling so as to reduce possible rubbish burning. National efforts might also be helpful, such as investing in the research and development of renewable energy, or carrying out carbon capture storage projects. International efforts may have a larger impact on global emissions, including holding international environmental protection meetings just like the Kyoto Protocol(1997) and Paris Agreement(2015). Carbon permits can be handed out to countries, reducing emissions by providing economic incentives.

However, in reality, it might be hard for all stakeholders to reach a consensus on carrying out these climate change mitigations, as they may harm the interest of some groups and organizations. For example, some oil-exporting countries may be reluctant to stop trading in fossil fuels, and some high-latitude countries may be benefited from the melting of the Arctic Ocean as they can create new transport routes.

4.Conclusion

Tropical cyclones are a natural hazard with the ability to cause widespread damage. The growing phenomenon of climate change amplifies these devastating effects by increasing their intensity, but not their frequency. This will also trigger other serious disasters, such as storm surges, heavy precipitation, landslides and secondary succession, threatening human society and the surrounding ecological environment. Several measurements recommended on mitigating both tropical cyclones and climate change might be helpful to reduce the risk, the implementation of which would vary from region to region according to their specific characteristics.

Bibliography

Bengtsson, L., Botzet M., and Esch, M. “Will Greenhouse Gas-Induced Warming over the next 50 Years Lead to Higher Frequency and Greater Intensity of Hurricanes?” Tellus A: Dynamic Meteorology and Oceanography 48, no. 1 (1996): 57–73. https://doi.org/10.3402/tellusa.v48i1.11632

Chand Savin, Walsh Kevin, Camargo Suzana. et al. “Declining tropical cyclone frequency under global warming.” Natural Climate Change 12 (2022): 655–661. https://doi.org/10.1038/s41558-022-01388-4

Kieran Bhatia, Gabriel Vecchi, Hiroyuki Murakami, et al. “Projected Response of Tropical Cyclone Intensity and Intensification in a Global Climate Model.” Journal of Climate 31, no. 20 (2018): 8281–9303. https://doi.org/10.1175/JCLI-D-17-0898.1.

Korty Robert, Emanuel Kerry, and Scott Jeffery. “Tropical Cyclone–Induced Upper-Ocean Mixing and Climate: Application to Equable Climates.” Journal of Climate 21, no. 4 (2008): 638–654. https://doi.org/10.1175/2007JCLI1659.1

Kossin J., Emanuel K., and Vecchi G. “The poleward migration of the location of tropical cyclone maximum intensity.” Nature 509 (2014): 349–352. https://doi.org/10.1038/nature13278

Potts, Laura. 2021. “Intensity of tropical cyclones is probably increasing due to climate change.” High Meadows Environmental Institute, March 25, 2021. https://environment.princeton.edu/news/intensity-of-tropical-cyclones-is-probably-increasing-due-to-climate-change/.

Ranson Matthew, Kousky Carolyn, Ruth Matthias. et al. “Tropical and extratropical cyclone damages under climate change.” Climatic Change 127 (2014): 227–241. https://doi.org/10.1007/s10584-014-1255-4

Thomas Knutson, Suzana J. Camargo, Johnny C. L. Chan, et al. “Tropical Cyclones and Climate Change Assessment: Part II: Projected Response to Anthropogenic Warming.” Bulletin of the American Meteorological Society 101, no. 2 (2020): E303–E322. /https://doi.org/10.1175/BAMS-D-18-0194.1.

UNISDR. Making Disaster Risk Reduction Gender Sensitive: Policy and Practical Guidelines. United Nations, 2009. http://repo.floodalliance.net/jspui/44111/1124.