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General Studies 1 >> World Geography

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TEMPERATURE ANOMALIES

TEMPERATURE ANOMALIES

 

1. Context

There was news recently that March 2023 was the second warmest March on record. The monthly report and the subsequent end­of­the­year annual summary by the U.S. National Oceanic and atmospheric administration (NOAA) serve as an excellent resource to contextualize the individual month’s ranking by temperature anomalies.

2. Temperature anomaly

Under normal circumstances, the temperature decreases from the equator towards the poles and each latitude has its own temperature. But other factors such as altitude, distribution of land and water, prevailing winds, ocean currents, etc. also affect the temperature of a place. As a result, there is a difference between the mean temperature of any place and the mean temperature of its parallel which is known as temperature anomaly or thermal anomaly.

3. Anomalies VS Temperature

  • In climate change studies, temperature anomalies are more important than absolute temperature. A temperature anomaly is a difference from an average, or baseline, temperature.
  • The baseline temperature is typically computed by averaging 30 or more years of temperature data.
  • A positive anomaly indicates the observed temperature was warmer than the baseline, while a negative anomaly indicates the observed temperature was cooler than the baseline.
  • When calculating an average of absolute temperatures, things like station location or elevation will have an effect on the data (ex. higher elevations tend to be cooler than lower elevations and urban areas tend to be warmer than rural areas).
  • However, when looking at anomalies, those factors are less critical. For example, a summer month over an area may be cooler than average, both at a mountain top and in a nearby valley, but the absolute temperatures will be quite different at the two locations.
  • Using anomalies also helps minimize problems when stations are added, removed, or missing from the monitoring network.

4. Why was March 2023 the second warmest? 

  • 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.
  • But the January­to­March average temperature anomaly ranks 2023 as the fourth warmest such period on record. This raises some obvious questions.
Image Source: The Hindu

5. Why was March 2023 the second warmest and not the warmest?

  • As seen, 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.
  • The old adage (often mistakenly attributed to Mark Twain) says that climate is what we expect and the 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.
  • 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. 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 heat­trapping greenhouse gases.)

6. Occurrence of Global distribution of temperature anomalies

  • 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-to­decade warming clearly shows that humans are now ensuring each decade is warmer than the one before.
  • As with the temperature, precipitation anomalies for March 2023 show the impact of a warm March over Eurasia in the form of below­normal precipitation.
  • We know that reduced snowfall over the Eurasian landmass has historically tended to favor 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.

7. Way forward

  • In sum, climate scientists need to provide the proper context when they compare and rank individual months against each other.
  • This will help the people at large better understand global warming as well as its cascading effects on the weather they experience every day.
  • All global warming is local; nobody lives in the global mean temperature. And the better people understand the impact of global warming in their backyard, the likelier they can be engaged in climate action.
For Prelims: National Oceanic and atmospheric administration (NOAA), El Niño effect, La Nina Effect, Temperature anomaly, Positive anomaly, Negative Anomaly, and Global Warming.
Source: The Hindu

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