Before he was nine years old, Charles Dickens had experienced six white Christmases. So it’s no surprise that the man credited with inventing some of the festive period’s best-loved traditions — most famously in A Christmas Carol — did so against a backdrop of snowy landscapes, frosted window panes and frozen lakes.

The winters of Dickens’s boyhood in the early 19th century were indeed exceptionally cold — which meteorologists speculate was due to the periodic global weather phenomenon we now know as La Nina.

Earlier this month, forecasters said that following an unusually warm October, November’s cold weather — some parts of the country had their first snowfall weeks ago — could lead to ‘a full La Nina event over the next few months’.

Sheep in the snow along the Newby Head pass in Gearstones this morning after a night of snow fall in the Yorkshire Dales

As a result, bookies are reporting an ‘avalanche’ of bets on a white Christmas.

Now, there would appear to be further evidence of the La Nina influence, with some areas of Britain facing up to 4in of snow and temperatures as low as -8c this week as a precursor of a month-long cold snap.

So what, you may ask, is a ‘full La Nina event’ — and, after a succession of grey, mild, wet winters, will it really bring with it the Dickensian wonderland of our childhood dreams?

The answer is . . . maybe.

We have all heard of the weather phenomenon known as El Nino, which describes the irregular but periodic warming of the surface waters of the tropical eastern Pacific Ocean.

El Nino — Spanish for ‘the little boy’ — was first noted several centuries ago. South American fishermen observed that warmer coastal waters occurring around the end or start of the year led to an explosion in the growth of plankton, and in the marine life — fish and shellfish — feeding on it. In gratitude, they christened this ‘El Nino’ because it coincided with festivities marking the birth of Jesus.

The northern most parts of the UK are already being hit by snow, as Ladbrokes cuts odds on a white Christmas for Glasgow

As so often in Nature, the pendulum swings both ways: El Nino’s warm currents are balanced by periods when the waters of the eastern Pacific are abnormally cold — a counter-phenomenon christened La Nina (‘the little girl’) by scientists.

Over the decades, experts have monitored the impact of these fluctuating oceanic temperatures on weather patterns and have attributed to them periods of drought, plunging temperatures, heavy rainfall and powerful storms in various parts of the globe.

British winters are usually quite mild because of the relatively warm seas around us and south-westerly winds bringing warm air from the south.

El Nino tends to bring wetter conditions to our shores, more violent storms and higher than average seasonal temperatures.

However, when La Nina is brewing — as is the case now — these warmer winds are blocked. As a result, bitter northerlies can come blasting in, bringing the kind of weather expected this week. They also create the potential for it to get a lot colder.

La Nina was blamed for the big freeze of winter 2010 and the coldest December on record, with lows of -13c, snow on the ground for weeks and blizzards that deposited 2ft drifts, bringing parts of the country to a standstill.

Compared with other countries, Britain got off lightly.

The north west is also earmarked for a snowy season this Christmas, as Manchester could follow the lead of Cumbria

There was disastrous flooding in Australia, with an ‘inland tsunami’ that forced hundreds of thousands of people living in Brisbane on the east coast to leave their homes. La Nina had pushed tropical rain that normally falls in the Pacific eastwards over Australia.

Meanwhile, storms wreaked havoc in the American Midwest. An unprecedented 875 tornadoes had already torn across the country before a monster twister in Missouri killed 116 people, making it the deadliest tornado since records began in 1950.

American weather experts blamed La Nina for pushing the jet stream — a river of cool air high in the atmosphere — northwards out of its customary seasonal position. This pulled warm, humid air up from the ground in the Midwest, enabling huge thunderstorms to form.

The shifted jet stream made it unseasonably warm in the northern U.S. and Alaska, accelerating the melting of glaciers, while southern American states baked in unusually hot and dry conditions.

Elsewhere, there were killer droughts in Peru and Ecuador, and parts of the Horn of Africa experienced their driest periods in 60 years, with ten million people needing food aid.

La Nina is not just about the weather but also its unexpected consequences.

The flu can originate in pugs, as well as poultry and birds, rapidly mutating into the form that affects humans

Most worryingly, it is feared that low winter temperatures may result in the development of a particularly powerful strain of flu virus — or worse, a flu pandemic — that could wreak havoc among the elderly and those of all ages with existing health problems.

The flu virus originates in animals — poultry, pigs and birds, for example — and can rapidly mutate into a form that infects humans.

A change in weather patterns may force migrating birds to alter their routes, flying over land rather than open water. If they rest near populated areas, the birds may come into contact with livestock that harbour their own flu viruses.

The mingling of wild and farm-animal flu viruses increases the chances of the microbes swapping parts of their DNA (a process called ‘recombination’) to create lethal new flu strains that could infect millions of us worldwide.

Climatologists at Columbia University in New York concluded that the last four global flu pandemics all occurred after periods of similar weather patterns to those caused by La Nina.

In 1918, so-called Spanish Flu killed an estimated 25 million people globally in its first six months and up to 100 million by December 1920; the Asian Flu of 1957 claimed one to two million lives; the Hong Kong Flu of 1968, one million; and swine flu, in 2009, more than half a million.

These pandemics proved particularly deadly because they all involved novel strains of the virus to which people had little inbuilt immunity.

Scientists also fear that the warmer, wetter conditions La Nina causes in parts of the world such as southern Africa, South-East Asia and northern South America will encourage mosquitoes to thrive — and, along with them, lethal infections such as Zika and the West Nile virus.

Adding to scientists’ concern is the fact that while El Nino rarely lasts longer than a year, La Nina can persist for two years or more.

The record is 33 months between 1973 and 1976, when Australia again bore the brunt, with floods hitting coastal areas of Queensland and New South Wales in January 1974. That year remains the wettest in Australian records.

Before the flu turns into the form that affects humans, it can originate in livestock including poultry

Of course, La Nina is not the only driver of our weather. There are competing influences, such as strong winter winds, that will contend with it.

These are determined by other factors, too. High-altitude winds in the faraway tropics particularly influence the pattern of high and low-pressure areas in the Atlantic. In turn, these can bring us mild but stormy weather in winter, rather than icy cold snaps.

Professor Adam Scaife, at the Met Office, says ‘La Nina on its own is not enough to make a very skilful forecast’ (though that may just be a weatherman wary of over-committing himself in what is still a notoriously inexact science).

For their part, bookmakers feel more confident about La Nina’s power to affect our lives. Responding to recent forecasts, Ladbrokes has cut the odds on a white Christmas to 2/1 for Glasgow, 3/1 for Newcastle, 5/1 for Manchester and 6/1 for London.

In the meantime, all we can do is turn up the central heating, pull on a thicker jumper and wait to see whether the Ice Girl cometh.