Warming trends for the planet are typically depicted as the year-to-year changes in surface temperatures. In such global warming maps, India appears to be warming only slightly or even cooling in some regions. Headlines ensue claiming that India is spared from global warming.

Even as heatwaves become more frequent, more intense, and spread across larger areas, there is some wishful thinking that India is immune to global warming. While multiple temperature datasets indicate that India is generally warming less, or even cooling in some regions, when year-to-year change or annual temperature trends are considered, the debate over whether the country can escape the clear and unavoidable consequences of rising greenhouse gas emissions must be put to rest. Here is the simple science that should help end the confusion caused by depicting annual temperature trends.

Seasonal cycle: The Largest change

The seriously misleading conclusions drawn from annual mean temperature changes arise from India’s unique climate variability. For millennia, the seasonal reversal of the monsoon circulation along with the two inter-monsoon periods has been woven into India’s cultural life. The predominantly southwesterly winds during the summer monsoon are replaced by the northeasterly winds of the winter monsoon, even though the winter monsoon contributes only about 20 per cent of India’s total rainfall. Throughout the country’s history, various literature, both prose and poetry, has gleefully depicted the seasons.

During the summer monsoon—the main monsoon season—southwesterly winds sweep in from the Arabian Sea. The pre-monsoon season is the warmest for nearly all of India. In some regions, especially north-west and north-central India, temperatures can rise by as much as 20°C from the winter months to the pre-monsoon peak. Monsoon rains tend to cool most of India, and it is common for many Indians, even in peninsular India, to pull out wool sweaters during the monsoon. Pre-monsoon months are the heatwave season, and there is no doubt now that the heatwaves are beginning to cost many lives and livelihoods as well as hurt the Rabi crops across the country.

The pre-monsoon is also a transitional, inter-monsoon “bridge season” between the winter monsoon and the summer monsoon. During this period, winds are often weak and disorganised, adding to the misery of the already deadly heatwaves. Some regions, especially in peninsular India, receive substantial pre-monsoon showers, but many others must wait for the monsoon’s onset to find relief. As a result, the heatwave season can stretch into June across large parts of north-west and north-central India.

Just as the monsoon rainfall can be divided into homogeneous regions, temperature distributions can also be mapped onto homogeneous regions. Western Himalaya, north-west, central-north, north-east, and peninsular India, along with the western and eastern coasts, are approximately uniform in their seasonal temperature variations. Any global warming over India is better studied as seasonal changes over these homogeneous regions. Considering any climate variable into yearly averages over India can greatly diminish the seasonal change signals since the reversal of the monsoon circulation can cancel out the signals across seasons.

Hidden global warming signals

In the climate science community, internal variability or the natural seasonal changes are considered “noise” when it comes to extracting the global warming signal. The larger the seasonal cycle, the larger the “noise” and thus harder it is to elicit the global warming signal. Imagine that the global warming over some parts of India is approximately 1°C, whereas the winter-to-spring or pre-monsoon warming can be more than 20°C.

In cold regions such as the western Himalaya, winter temperature variability is so high that the global warming signal has not emerged yet. Temperature variabilities are relatively smaller during the pre-monsoon, and the warming signal is clearly detected over the same part of India. But the warming rates are a fraction of a degree Celsius per year. We must remember that these are warmings from one year’s per-monsoon to the same season in the following year. Thus, seasonal warming trends and not annual mean temperature trends must be the norm for India’s climate change analysis.

An additional complication for quantifying the warming trends over the homogeneous temperature regions is that not all temperature data agree with each other, even in seasonal warming trends. The India Meteorological Department (IMD) has been gathering temperature and rainfall data for well over a century and can be considered the most reliable for India’s temperature and rainfall change detections. Other temperature products tend to merge available instrumental data with climate models to produce the so-called reanalysis products. Reanalyses are datasets that combine historical observations with models to provide the best reconstructions of past atmospheric, ocean, and land-surface conditions. While the reanalysis products are immensely helpful for many process studies, they can be severely limited in their accuracy. For example, while the IMD data indicate that the October-November temperatures over western Himalaya and north-central India have not seen any significant change over the past four decades, multiple reanalysis products show significant warming over these regions. A detailed analysis of the seasonal trends is provided by scientists from IIT Kharagpur and IITM Pune that illustrates such details.

The tunnel vision on global warming should not distract from the significant seasonal impacts on all sectors from the natural modes of climate variability, even in the absence of global warming. Natural Modes of Climate Variability, such as El Niño and the Indian Ocean Dipole also create Havoc over India.

The relentless focus on global warming alone may or may not be appropriate for India to strategise solutions for its socioeconomic challenges. The yearly heatwave season, the two cyclone seasons, and the unpredictable monsoon chaos pose significant challenges for all sectors, from agriculture to water, energy, infrastructure, and health. India’s massive investments in weather and climate predictions, as well as national disaster management, have led to remarkable successes in saving lives and livelihoods.

The impacts of the natural modes of climate variability, such as El Niño, La Niña, the Atlantic Niño, and the Indian Ocean Dipole, add or subtract from the yearly march of heatwaves, monsoon active/break events, cyclones, wildfires, and winter storms. Many debates rage about whether global warming is adding or subtracting from the mean monsoon, the number and intensity of cyclones, heavy rains, landslides, floods, droughts, and such. These further emphasise the importance of focusing on seasonal cycles over India and totally discarding the temptations to average climate variability and change across seasons. The best way forward to go beyond the academic discussions on trends is to focus on modulations of the seasons and the impacts of seasonal changes on socioeconomic sectors, and remain steadfastly focused on food, water, energy, and health securities which can also transgress into national security issues.

Impact-based sectoral indicators

India has now reached nearly equal agricultural production in the Kharif and Rabi seasons. While the monsoon extremes can hammer the Kharif grain yields, unseasonal rains and heatwaves can destroy Rabi crops. Even the cities that receive metres of rain can face water shortages before the monsoon arrives. Air pollution remains a major concern throughout the year for much of India, but the heatwaves and the associated humidity increases can be deadly for many. Infectious diseases such as dengue and diarrheal diseases remain endemic and respond to natural climate modes as well.

Tracking the combined impacts of natural modes and the seasonal warmings from increased greenhouse gas emissions is the only clear strategy for India. Early warnings for anticipating disasters to prepare, respond, and recover effectively and efficiently are getting better, but they need to get down to neighbourhood scales to be fully protective. Decadal timescale predictions covering the next 1–10 years, bridging the gap between seasonal forecasts and long-term climate projections, are now operational in India, and they should also be downscaled to local scales for building resilience in each sector in each region. India’s long coastline, blue economy, and national security also need to be served by these early warnings and decadal predictions.

This is the best and likely the only way to avoid futile debates about whether India is somehow going to be saved from global warming. Weather-ready and climate-resilient India cannot afford to misjudge the severe challenges posed by the natural climate variability itself or the exacerbation of these disasters by global warming in each season.

Raghu Murtugudde is Emeritus Professor, University of Maryland; Visiting Professor, Kotak School of Sustainability, IIT Kanpur.