Low visibility affected both countries, but the similarity ends there. In parts of central and northern England, meteorologists issued routine fog warnings after temperatures fell overnight, allowing moisture to condense close to the ground. What caught attention was not the fog itself but its colour: a soft pink glow at dawn as low winter sunlight filtered through the mist.

The UK's Met Office explained that the phenomenon was the result of basic atmospheric physics rather than any unusual weather event. "Fog is essentially a cloud at ground level made up of tiny water droplets," a Met Office spokesperson said in comments reported this week. "When the sun is low on the horizon, its light travels through more of the atmosphere. Shorter wavelengths are scattered out, leaving the longer red wavelengths to dominate." When that filtered light passes through fog, it can give the mist a pink or rosy hue.

Scientists emphasised that the effect, while rare, carries no additional hazard beyond the normal risks associated with fog, such as reduced visibility for drivers. "It's important to note that pink fog is purely an optical effect," the Met Office said.

In Delhi, by contrast, winter fog has long ceased to be a visual curiosity. Each year, it combines with high concentrations of airborne pollutants to form thick smog that blankets the capital and surrounding regions, sharply reducing visibility and posing serious health risks. The problem is exacerbated by winter meteorology: cold, still air traps emissions close to the surface, preventing dispersal.

This week, air quality in Delhi once again reached what authorities classify as "severe" levels, with the Air Quality Index climbing far beyond thresholds considered safe. According to news reports, the Delhi Government responded by activating the highest level of its Graded Response Action Plan, restricting construction activity, limiting vehicle use and advising offices to reduce physical attendance to cut emissions and exposure.

Unlike the UK's pink fog, Delhi's winter haze is not just moisture in the air. It is a complex mix of fog droplets and fine particulate matter - especially PM2.5 - produced by vehicle exhaust, industrial activity, construction dust and seasonal agricultural burning in neighbouring states. These particles are small enough to penetrate deep into the lungs and bloodstream, increasing the risk of respiratory and cardiovascular illness.

India's Meteorological Department has repeatedly warned that dense to very dense fog is common across northern India during winter mornings, particularly when wind speeds are low. Under such conditions, pollutants accumulate rapidly, turning ordinary fog into toxic smog. Hospitals in the capital routinely report a surge in respiratory complaints during these periods, especially among children and the elderly.

Atmospheric scientists stress that while fog itself is a natural phenomenon in both countries, pollution fundamentally changes its impact. In Britain, fog typically consists of clean water droplets formed under calm, humid conditions. In Delhi, those droplets often act as carriers for pollutants, intensifying their effects and prolonging their presence.

Dr Claire Ryder, an associate professor at the University of Reading, said in comments reported by the British media that the pink fog observed this week depended on a precise balance of conditions. "You need the fog to occur at the exact sunrise or sunset time," she said. If the fog is too thick, the light is blocked altogether; if it is too thin, the sunrise colours are not sufficiently muted for the effect to appear.

Such delicately balanced conditions underline how unusual - and how limited - the British phenomenon is. In Delhi, by contrast, winter fog is persistent, predictable and increasingly severe. It is no longer treated as a meteorological curiosity but as a public health emergency that returns each year with near certainty.

There is also a policy dimension to the contrast. In the UK, fog warnings are primarily about road safety and transport disruption. In Delhi, similar warnings trigger emergency measures affecting industry, construction, transport and daily life for millions. Courts and regulators have repeatedly pressed authorities to act, while residents adjust routines - from school timings to outdoor exercise - around pollution alerts.

The comparison highlights a broader truth about weather and climate: similar atmospheric conditions can produce radically different outcomes depending on what humans put into the air. Fog in itself is neutral. What determines whether it becomes a hazard is the burden of pollution it carries.

For Delhi families, winter fog has become a symbol of chronic environmental stress, familiar, feared and hard to escape. For Britons this week, pink fog was a brief and unexpected spectacle, photographed at sunrise before clearing later in the morning.

Both are products of the same basic physics. Only one is a reminder of a deeper, unresolved crisis.