Understanding temperature anomalies

GS 1 | Geography

Global warming does not mean that each month or each year will be warmer than the previous month or the previous year. The global distribution of temperature anomalies is due to land-ocean-atmosphere processes that dynamically determine the weather and climate

The story so far: There was news recently that March 2023 was the second warmest March on record. The monthly report and the subsequent end-of-the-year annual summary by the U.S. National Oceanic and Atmospheric Administration (NOAA) serves as an excellent resource to contextualise the individual month’s ranking by temperature anomalies.

Why was March 2023 the second warmest?

v March 2023 was indeed the second warmest in the instrumental record. The warmest March occurred just a few years ago in 2016, when the biggest El Niño of the 21st century triggered a ‘mini’ global warming.

v January-to-March average temperature anomaly ranks 2023 as the fourth warmest such period on record.

v Why was March 2023 the second warmest and not the warmest?

Ø  Each year’s March can be warmer or cooler than the March of the year before. Natural climate variability, including events like El Niño, can temporarily spike temperatures.

Ø   Mark Twain says that “climate is what we expect and weather is what we get”. In India, we expect March to be the beginning of the scorching summer season. But a particular year’s March may be cooler due to some other climate factors, such as a La Niña, and especially when averaged over a region as large as India or even an Indian State.

Ø  A year is an ‘El Niño year’ if warmer water spreads in a band from west to east over the equatorial Pacific Ocean. In a ‘La Niña year’, cooler water spreads east to west in the same region.

Ø  Both phenomena have distinct and significant effects on the global climate. (Global mean temperatures themselves represent the increasing amount of additional energy we are trapping in the earth system and preventing its escape to space by, among other things, increasing the atmospheric concentration of heat-trapping greenhouse gases.)

Why is context important?

·      The monstrous warming to the west to north of India begins to tell the story of the weather anomalies that rendered a cooler March over Mumbai, excess pre-monsoon rains over the northwest, and scorching heatwaves in Kerala and Odisha.

§  The Arabian Sea has also warmed more than expected this March. We must watch carefully if this continues: it can favour a stronger monsoon but may also enhance cyclogenesis (i.e. birth of cyclonic circulation) over the Arabian Sea.

·      The global distribution of temperature anomalies is due to land-ocean-atmosphere processes that dynamically determine the weather and climate.

§  Global warming does not mean each month or each year will be warmer than the previous month or the previous year. Instead, a better place to begin would be by averaging the weather over a decade. Decade-to-decade warming clearly shows that humans are now ensuring each decade is warmer than the one before.

·      Reduced snowfall over the Eurasian landmass has historically tended to favour a stronger monsoon. As it happens, 2023 is expected to be an El Niño year, and El Niños tend to produce weaker monsoons. So this summer’s El Niño effect could be blunted by the lower snow cover over Eurasia.

Conclusion