Date : 12/10/2023
Relevance: GS Paper 1- Geography - Cyclone
Keywords: Cyclone-genesis potential, 'Warm Arctic, Cold Eurasian' (WACE) pattern, Climate adaptation, Climate variability, Resource planning
- In recent years, climate scientists have been scrutinizing the various climate-related trends and phenomena affecting the Indian subcontinent. These observations encompass a decreasing trend in monsoon rainfall over six decades, intensifying occurrences of extreme rainfall, droughts, heatwaves, and cyclones. Notably, global warming is frequently cited as the prime suspect behind these changes.
- However, there is a pressing question that often remains in the shadows of climate discussions: are these changes truly trends, or are they indicative of shifts or decadal cycles?
- Understanding the nature of these changes is crucial because it can profoundly influence resource planning, including water management, agriculture, and energy strategies.
Unpacking Climate Terminology
Climate scientists employ a range of terms to describe observed changes in climate variables. These terms include "trend," "anthropogenic trend," "secular trend," "decadal variability," and "shift." The choice of descriptor depends on the duration and nature of the observed behavior of a climate variable.
- Trend: A trend implies that a climate variable is consistently changing in one direction, such as a continuous increase in temperature. The term "anthropogenic trend" suggests that these changes are occurring within human lifetimes, although the specific timeframe for a variable to be considered a trend is not always clear.
- Secular Trend: This term is used when a variable has been increasing or decreasing for a certain period within a longer timeframe. For instance, a variable may exhibit a secular trend if it has been steadily increasing for 30 years within a 100-year period.
- Decadal Variability: Decadal variability refers to oscillations from a positive to a negative phase that occur over the span of decades. It is somewhat similar to the concept of a shift, but decadal variability is often cyclic in nature.
- Shift: A shift represents a rapid transition from one state to another, such as a sudden change in the amount of rainfall or temperature. It can be an irreversible jump or a temporary change that later reverts to a previous state.
The Challenge of Observing Long-term Changes
In the realm of climate science, researchers sometimes find it challenging to designate a specific descriptor for a variable's observed behavior without observing it over sufficiently long periods. This ambiguity underscores the need for comprehensive, long-term data and analysis.
The Nature of Cyclone Formation
- One critical aspect of climate change is the formation of cyclones. Cyclone-genesis, or cyclogenesis, serves as an indicator of the likelihood of cyclone formation. Various parameters influence cyclogenesis, including sea surface temperature, ocean heat content, changes in winds from the surface to the upper atmosphere (vertical shear), and the rotation of winds near the surface.
- When these conditions align, they create favorable conditions for cyclone development. However, the mechanisms behind why some seed conditions lead to cyclones while others do not remain incompletely understood.
- A recent study published in the journal Climate and Atmospheric Science reported a significant change in the potential for cyclones to form over the Arabian Sea during the late 1990s. Cyclone-genesis potential indicates the likelihood of cyclones forming, and it depends on multiple factors.
- The study notes that, since the 1990s, all the factors except wind rotation have favored a higher potential for cyclone formation. The critical question arises: why did this rapid increase occur around that specific time?
The 'Warm Arctic, Cold Eurasian' (WACE) Pattern
- The study points to a shift in the 'Warm Arctic, Cold Eurasian' (WACE) pattern coinciding with the sudden increase in cyclone-genesis potential over the Arabian Sea. The WACE pattern is characterized by warm surface temperatures in the Arctic and a significant area of cold surface temperatures over Eurasia. This pattern is associated with upper-level circulation changes that extend into the Indian Ocean sector.
The Complexity of Climate Change
- Notably, the time of the observed shift in cyclone-genesis potential aligns with other significant events. Global warming, which had been steadily increasing, experienced a slowdown around the same time, although this remains a topic of debate among scientists. Furthermore, a regime shift, similar to the one observed in the mid-1970s, is thought to have occurred in the same period.
- The causes of such changes, whether shifts or decadal cycles remain only partially understood. These changes raise important questions for India and other regions affected by them. It is essential to determine whether the decrease in monsoon intensity, the increase in extreme rainfall events, and the rise in heatwaves are trends that will persist in the coming decades or part of longer processes that may reverse some of these effects.
Climate Change's Impact on Cyclone Formation
- Temperature Elevation: The temperature of both the ocean and the atmosphere plays a pivotal role in the genesis of tropical cyclones. These storms draw strength from the release of heat generated when ocean surface water evaporates and subsequently condenses into rainfall within the storm. In a warming climate, a warmer ocean leads to increased evaporation, which, in turn, means more moisture available in the atmosphere.
- Augmented Precipitation: A warmer atmosphere can accommodate a greater amount of moisture, resulting in increased rainfall. More rainfall leads to the release of more heat, ultimately fueling stronger winds within the cyclone. Recent studies have revealed that hurricane rainfall rates rise by at least 7% for every degree of warming.
- Intensification of Cyclones: A warming climate is anticipated to boost wind speeds, leading to a higher proportion of storms intensifying into formidable Category 4 or 5 hurricanes/ Cyclones.
- Sea-Level Surge: Elevated temperatures contribute to rising sea levels, increasing the depth of stormwater. As sea levels rise, the storm's inundation reaches further inland.
- Reduced Storm Speed: The velocity of a cyclone can significantly impact the total amount of rainfall at a particular location. Slower-moving storms offer a more extended timeframe for rainfall accumulation. Although studies indicate a slowdown in storm speed, the underlying mechanisms remain unclear.
- Fusion of Storms: In an increasingly warming world, the convergence of two sizable tropical storms over any of the world's oceans could result in the formation of a colossal super-cyclone.
Implication for India and the World
- Elevated Destruction: More powerful storms can inflict significantly greater harm to both people and economies. The impact of a Category 4 hurricane/ Cuclone, for instance, is estimated to be approximately 256 times more severe than that of a Category 1 hurricane.
- Unpredictable Predictions: The rapidly evolving nature of storms has rendered conventional forecasting methods unreliable. This unpredictability has had a direct impact on the ability to take adequate precautionary measures.
- Shifting Impact Zones: Recent research suggests that the areas where storms reach their maximum intensity are gradually shifting toward the Earth's poles. This shift holds significant implications for the primary areas affected by these storms.
- Rising Storm Frequency: The number of hurricanes forming each year may undergo alterations in the future. However, there is no universally accepted theory that comprehensively explains the current quantity of storms in the existing climate or forecasts how this might change in the future.
Resource Planning and Climate Adaptation
- The implications of these changes are profound, as they impact resource planning and climate adaptation efforts. The uncertainty surrounding climate risks at regional levels, including those related to sea-level rise, heavy rainfall, drought, heatwaves, and cyclones, complicates decision-making. Given the limited financial resources available, adapting to these climate risks poses substantial socioeconomic and political challenges.
The Need for a Comprehensive Approach
In light of these complex and interconnected factors, climate scientists face significant challenges. Instead of solely focusing on predictions for the year 2100 or narrow global warming targets, there is a pressing need to better understand the natural variability in specific regions. This is especially crucial because natural variability itself is influenced by global warming, as demonstrated by the study indicating that monsoon decadal cycles may be changing in duration.
The study highlighting the shift in cyclone-genesis potential over the Arabian Sea in the late 1990s serves as a compelling example of the complex interplay between climate patterns and regional climate phenomena. It underscores the importance of distinguishing between trends, shifts, and decadal cycles in climate research and their impact on resource planning and climate adaptation. As climate scientists grapple with these challenges, they must remain focused on understanding and addressing the natural variability in their own neighborhoods, taking into account the far-reaching effects of global warming. The future of climate adaptation and resource management depends on a comprehensive and nuanced understanding of these complex processes.
Source- The Hindu