Central Idea

Studies have highlighted various climate phenomena in India, including declining monsoon rainfall, intensifying extreme weather events, droughts, heatwaves, and cyclones.
However, a critical question that demands attention is whether these changes represent long-term trends, abrupt shifts, or decadal cycles.
These distinctions hold significant implications for resource planning and management.

Understanding Climate Change Terminology

Trend: Refers to a continuous, prolonged change in climate variables, such as a steady temperature increase over time. The term “anthropogenic trend” implies changes occurring within human lifetimes.
Secular Trend: Indicates a variable’s continuous increase for a specific period within a more extended timeframe, like 30 years within a century.
Decadal Variability: Involves oscillations between positive and negative phases over tens of years, potentially resembling a shift.
Shift: Represents a rapid transition from one state to another, like a sudden change in rainfall patterns. An example is the shift in seasonal monsoon rainfall from above the long-period average (LPA) to below it.

A recent study in the journal Climate and Atmospheric Science identified a notable change in cyclone formation potential over the Arabian Sea in the late 1990s.
Cyclone-genesis potential depends on factors like sea surface temperature, ocean heat content, wind changes from the surface to upper atmosphere, and wind rotation. These factors have favored increased cyclone formation potential since the 1990s.
However, the crucial question is why this rapid increase occurred during this period. The study suggests that it coincided with a shift in the ‘Warm Arctic, Cold Eurasian’ (WACE) pattern rather than being a trend.

The WACE pattern involves warm surface temperatures over the Arctic and cold surface temperatures over Eurasia. It influences upper-level circulation changes that extend into the Indian Ocean sector.
Global warming experienced a slowdown during this period, and scientists have proposed the occurrence of a ‘regime shift,’ similar to one observed in the mid-1970s.

Regardless of whether these climate changes are shifts or decadal cycles, it is essential to understand their potential long-term effects on the monsoon, cyclone frequency, heatwaves, and extreme rainfall.
Accurate predictions are vital for planning and allocating resources to adapt to climate risks, such as sea-level rise, heavy rainfall, drought, heatwaves, and cyclones.
Climate scientists must focus on understanding natural variability in the local context, especially since this variability is influenced by global warming.
For example, the study indicates that the monsoon decadal cycle, previously lasting around 20 years, may now extend further, raising questions about the underlying causes.

Distinguishing between climate trends, shifts, and decadal cycles is essential for India’s adaptation strategies.
These distinctions affect how the country prepares for and responds to evolving climate patterns, and climate scientists must strive to unravel the complexities of natural variability to make informed predictions and policy recommendations.