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In January 2025, the India Meteorological Department (IMD) declared 2024 as the country’s warmest year on record, citing an annual mean surface temperature anomaly of +0.65°C above the long-term average. But a closer look revealed that the actual warming may have breached the 1°C mark — a threshold significant enough to trigger serious concern over rising extreme weather events and biodiversity loss.
How has this possible breach been understated? By quietly altering the benchmark against which warming is measured — the Long Period Average (LPA) — in IMD’s annual climate summary, the most authoritative document on the rate at which India is warming today. LPA represents the average temperature over a 30-year period and is central to assessing climate trends.
Each revision has increased the baseline temperature, effectively making the anomaly appear smaller than it might otherwise be.
Until the 2010 annual summary, IMD used the ‘1961–1990’ average as its LPA. By 2016 — then the warmest year on record — the LPA was changed to the ‘1971–2000’ average. It was updated again in 2019 to the ‘1981–2010’ average. And now, in its 2024 climate summary, the IMD used the average for the ‘1991–2020’ period.
The changes have major implications. Since India’s warming has accelerated particularly in the past two decades, moving the baseline forward means comparing current temperatures with a hotter average — thereby minimising the apparent change.
Consider this: In the 2010 climate summary press release, using the 1961-1990 LPA, the year 2010 recorded a mean temperature of 25.8°C — an anomaly of +0.93°C. When the LPA was revised in 2016 to the ‘1971–2000 average’, the anomaly for 2010 fell to +0.82°C.
In 2019, when LPA was revised to the ‘1981–2010 average’, the anomaly for 2010 fell +0.54°C. In the most recent summary, using the 1991–2020 LPA, the anomaly for 2010 has dropped further to just +0.39°C.
A simple calculation shows that the change in LPA has reduced the reported anomaly for 2010 by 0.54°C. If we apply this correction to 2024’s reported anomaly of +0.65°C, it suggests the actual deviation from the 1961–1990 LPA could be as high as +1.19°C.
Further complicating matters, IMD’s annual summaries do not disclose the actual recorded temperature for the year or the LPA temperature — only the anomaly. This lack of transparency makes it difficult to track trends or compare data across years, especially when the LPA keeps changing.
Some media reports quoting IMD Director-General Mrutyunjay Mohapatra, stated that the mean temperature for 2024 was 25.75°C. But this figure is lower than the 25.8°C recorded in 2010 — raising questions about whether 2024 was indeed the warmest year on record, or if the change in methodology is driving the narrative.
The confusion extends to 2016, now listed as the second warmest year. According to IMD statistics available on the central government's open access portal for socio-economic and environmental data, 2016 had a mean temperature of 26.2°C — roughly 0.45°C higher than 2024’s reported value.
Regardless of how warming is measured, its impacts are becoming increasingly visible. In 2024, India experienced extreme weather events on 322 out of 366 days, according to data from the interactive extreme weather atlas managed by the Centre for Science and Environment (CSE) and Down To Earth (DTE). This marked an increase from 318 days in 2023 and 314 days in 2022.
In percentage terms, nearly 88 per cent of the year saw extreme weather in one or more parts of the country, up from 87 per cent in 2023 and 86 per cent in 2022.
The trend has translated into substantial human and economic costs. Fatalities attributed to extreme weather reached 3,472 in 2024 — up from 3,287 in 2023 and 3,026 in 2022 — representing a 15 per cent rise over three years.
Agriculture has also suffered. Extreme weather events in 2024 affected at least 4.07 million hectares of cropped land, based on data from the CSE-DTE atlas. This is an 84 per cent increase over the 2.21 million hectares affected in 2023 and a 108 per cent increase from 1.96 million hectares in 2022.
Every region of the country has experienced more days with extreme weather events. Central India recorded the highest number in 2024, with 253 days — up from 218 days in 2022, a 16 per cent increase. The southern peninsula experienced 223 days of extreme weather, up 31 per cent from 2022.