Que. What is sea surface temperature rise? How does it affect the formation of tropical cyclones?
समुद्री सतह के तापमान में वृद्धि क्या है? यह उष्णकटिबंधीय चक्रवातों के निर्माण को कैसे प्रभावित करता है?
Structure of the Answer
(i) Introduction: Briefly define sea surface temperature and its rise in the Anthropocene.
(ii) Main Body: Explain the effects of sea surface temperature rise on tropical cyclone formation with detailed points under appropriate headings.
(iii) Conclusion: Summarize and highlight the potential future consequences if status quo in terms of rising global temperatures persists.
Introduction
According to Climate Copernicus, the average sea surface temperatures (SSTs) over the extrapolar ocean (60°S–60°N) have increased markedly since records began in 1850. Between the late 19th century (1880–1900) and the last five years (2019–2023), the average SST over the extrapolar ocean has increased by about 0.9°C. The increase from 1980 to 2023 has been around 0.6°C. This rise in SST is primarily attributed to global climate change, which significantly impacts marine ecosystems and weather patterns.
The increase in sea surface temperatures leads to multiple consequences, including marine heatwaves, disruption of oceanic food chains, changes in atmospheric circulation patterns, and ocean stratification. These effects can have severe implications for biodiversity, fisheries, and coastal communities, making it crucial to address the underlying causes of climate change and implement effective adaptation strategies to mitigate these impacts.
Since tropical cyclones are low-pressure centers with closed isobars and derive their energy from the latent heat of condensation, the formation, intensity, and frequency of tropical cyclones are impacted by rising SSTs, creating more powerful and destructive storms.
Mechanism of Sea Surface Temperature (SST) Rise and Cyclone Formation
(i) Source of Cyclone Energy: Tropical cyclones extract energy from warm ocean waters. An SST above 26.5°C is essential for the formation of these storms, as it facilitates the transfer of heat to the atmosphere.
(ii) Enhanced Evaporation and Moisture: With higher SSTs, the rate of evaporation increases, leading to more water vapour in the atmosphere. This moisture-rich air intensifies cyclone activity by fueling storm clouds.
(iii) Latent Heat Amplification: The energy released during condensation of this moisture (latent heat) powers the cyclone, leading to stronger and more sustained winds. The warmer the SST, the greater the amount of latent heat released.
(iv) Lower Pressure Systems Formation: Warm SSTs contribute to the creation of low-pressure systems, a fundamental requirement for cyclone formation. The temperature gradient between the sea and the atmosphere becomes more pronounced, triggering atmospheric instability.
(v) Tropical Cyclogenesis Support: Sea surface temperature rise creates favourable conditions for tropical cyclogenesis (the development of tropical cyclones), leading to increased storm occurrences, especially in vulnerable regions like the Bay of Bengal and the Caribbean.
Effects of SST Rise on Cyclone Intensity and Frequency
(i) Increased Cyclone Intensity: Higher SSTs provide more energy to tropical storms, which manifest in higher wind speeds and lower central pressures, leading to severe tropical cyclones (Categories 4 and 5). For instance, Cyclone Amphan in 2020 rapidly intensified due to abnormally warm Bay of Bengal waters.
(ii) More Frequent Extreme Cyclones: While overall cyclone frequency may not rise significantly, the number of intense cyclones is expected to increase due to warmer oceans. Studies show that the frequency of Category 4 and 5 storms has increased globally in recent decades.
(iii) Rapid Intensification: Cyclones tend to intensify faster in warmer seas. This phenomenon, termed “rapid intensification,” has been observed in storms like Hurricane Harvey (2017), which gained strength quickly before landfall due to high SSTs.
(iv) Extended Cyclone Seasons: Traditionally, cyclone seasons are confined to certain months. However, as SSTs rise, cyclones are occurring outside their usual periods. This extends the cyclone season and reduces the time between storm occurrences.
(v) Geographical Shifts in Cyclone Tracks: Rising SSTs are linked to the poleward shift of tropical cyclone tracks. This shift could expose new areas—previously unaffected—to severe storms, increasing risks to human settlements and infrastructure. Regions like Arabian Sea are increasingly witnessing tropical cyclones.
(vi) Rising SST and Cyclone Unpredictability: The rise in Sea Surface Temperatures (SST) increases the unpredictability of tropical cyclones, impacting their intensity, frequency, and trajectory. This complicates forecasting, leading to greater challenges in disaster preparedness, coastal planning, and managing the associated risks.
Long-term Implications of SST Rise and Future Climate Projections
(i) Exacerbation of Climate Change Effects: The rise in SST is both a consequence of and a contributor to climate change. As global temperatures rise, SSTs will continue to increase, fueling stronger cyclones and triggering feedback loops that worsen climatic events.
(ii) Displacement and Economic Costs: Coastal communities are at higher risk due to stronger cyclones resulting from rising SSTs. Storm surges, flooding, and wind damage cause displacement and economic losses. For example, Hurricane Katrina in 2005 caused over $125 billion in damages, largely driven by warmer waters in the Gulf of Mexico.
(iii) Warming Oceans and Storm Surges: Rising SSTs also contribute to the height and intensity of storm surges, which result from cyclone winds pushing seawater inland. Higher SSTs lead to warmer upper ocean layers, which in turn drive larger, more destructive surges.
(iv) Potential for Superstorms: Climate models suggest the likelihood of more frequent “superstorms” as SSTs continue to rise. These storms could have devastating effects, especially in densely populated regions. Hurricane Irma in 2017 is an example of a superstorm fueled by unusually warm Atlantic waters.
(v) Adaptation and Mitigation Strategies: To combat the impacts of rising SSTs, countries must invest in both climate adaptation and mitigation strategies. Enhanced early warning systems, improved coastal defences, and international efforts to reduce greenhouse gas emissions are essential to minimising the risks associated with stronger cyclones.
Conclusion
The rise in sea surface temperature due to global warming significantly impacts the formation, frequency, and intensity of tropical cyclones. This phenomenon, driven by anthropogenic climate change, has grave implications for global weather patterns, economic stability, and human security. As tropical cyclones grow stronger and more frequent, addressing climate change and investing in disaster preparedness become imperative for vulnerable nations.
