Rainfall in India in 2021 did not follow all the long-term patterns that have come to characterise it in recent decades. Instead, it was the 23rd highest since 1901 for the January 1 to December 21 period. The weather is determined by a system of interconnected parts. So it would not be surprising if a change in the pattern of rainfall had an impact on the pattern of temperature through 2021. Was India warmer than usual in 2021 in keeping with the trend of global warming? Here are three charts that show how the temperature in 2021 followed or did not follow its long-term trends.
When scientists speak of global warming and rising temperatures, they are speaking of long-term trends in temperature. Individual days or years can turn out to be cooler than earlier. Similarly, parts of the globe can follow somewhat different trends than the earth as a whole. The average maximum temperature in India, for example, had been rising from the 1980s consistently but dropped in the 2011-2020 decade, according to the gridded temperature dataset of the India Meteorological Department (IMD) analysed by HT. This last decade was still the second-warmest decade by maximum temperature after the 2001-2010 decade since 1951, the earliest year for which this data is available. The average minimum temperature in India, on the other hand, continued to rise even in the 2011-2020 decade, which was the second-warmest after the 1951-1960 decade.
How was 2021 in comparison? For the January 1-December 21 period, India’s average maximum temperature has followed the trend of the last few years and of the last decade. At 30.491 degrees Celsius, this is the 9th coolest year since 1951 by maximum temperature for this interval. 2020 was the coolest year for the January 1-December 21 interval. The average minimum temperature this year on the other hand falls somewhere near the middle of the distribution. Data for minimum temperature is available up to December 22. At an average of 19.129 degrees Celsius, it is the 40th highest or 32nd lowest since 1951. 2020 was the 10th hottest year by minimum temperature for the January 1-December 21 interval.
Not all trends in temperature are, however, a product of the climate crisis brought about by human activities. They can also be part of natural cycles. Temperatures are, therefore, also compared to a normal, which the IMD currently considers to be the average temperature in the 1980-2010 period. The 2021 maximum temperature is 0.46 degrees or 1.5% less than the 1980-2010 normal, while the minimum temperature is 0.02 degrees or 0.08% higher than normal.
As these annual averages suggest, a lesser than usual maximum temperature and a higher than the usual minimum temperature was the trend in most months. However, four months – February, March, July, and August – were at odds with the annual trend in maximum temperature and saw higher maximum temperatures than normal. The minimum temperature was lower than normal in five months: February, April, May, June, and August.
It is this pattern that suggests that rainfall had an impact on temperature. Clouds prevent the earth from receiving sunlight and decrease daytime or maximum temperature. At night, these clouds trap the heat that the earth is losing by radiating it back into the atmosphere and raise night-time or minimum temperature. Rainfall was much less than the Long Period Average (the average of rainfall in the 1961-2010 decade) for the month in February, March, April, and August. These months are also common to months of higher-than-normal maximum temperature and lower-than-normal minimum temperature. To be sure, rainfall is not the only factor that controls temperatures and it is not always the case that temperature will follow trends in rainfall. For example, while maximum temperature has tracked both positive and negative deviations in rainfall almost in step this year, minimum temperature has not.
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