WHAT'S HAPPENED TO THE SEASONS?

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From temperate England to tropical India, the cycle of the seasons is fundamental to life. But lately they seem to have changed their patterns, with profound consequences. John Parker reports ...

From INTELLIGENT LIFE Magazine, spring 2010
 
In the Indian state of Orissa, the black-headed oriole is the messenger of spring. It appears in the villages in January to greet the season’s start and flies away to the forest in March, signalling its end. Richard Mahapatra’s mother used the oriole’s fleeting appearance to teach her son about the natural rhythms of the world. “People like my mother remember six distinct seasons,” says Mahapatra, an environmental writer who now lives in New Delhi. After spring (basanta) and summer (grishma) came the rainy season (barsha). Between autumn (sarata) and winter (sisira) came a dewy period called hemanta. Each season lasted two months and the appearance of each was marked by religious festivals. “She had precise dates for their arrival and taught me how to look for signs of each.”

Damselflies gathered thickly a week before the rains began. Markers of the monsoon, they did not cluster at other times. The open-billed stork alighted on the tamarind tree on Akshaya Trutiya, a festival which usually fell in April or May and traditionally marked the start of the agricultural year. Farmers said that if you forgot the day, the bird would remind you, so predictable was its arrival. In the Mahapatra family’s garden, the nesting of bats in the peepal tree marked the onset of winter; when the tree flowered, it was midsummer.

Lately the heralds of the seasons have become unreliable. Damselflies swarm not only in the rainy season but in winter, the driest time of year. The stork no longer appears just on Akshaya Trutiya, but at other times, too. Villagers hear the song of the oriole in summer and the rainy season, not just spring. And this, Mahapatra says, is because spring is no longer a distinct season. Instead of six periods of equal length, Orissa now has two, a brief rainy season and a burning eight-month summer. Winter is a mild transition between the two, and spring, autumn and hemanta have been relegated to little-noticed interludes of a mere week or so.

“When I return home”, says Mahapatra, “my mother mourns the death of the seasons. Her memories of Orissa’s climate are alien to the generation I belong to. For me, my childhood Orissa is dying. The state now has a new and strange climate that nobody can understand or predict.”

 
MAHAPATRA'S experience is far from unusual. Round the world, people think the seasons are shrinking and shifting. Spring is starting earlier in most of northern Europe: in Britain the horse chestnut, ash and beech trees burst into leaf a week earlier in 2009 than in 2001. In Nepal everything is later.
Villagers say that margha (January/February) is becoming falgun (February/March) and falgun is becoming chaitra (March/April). Transitional seasons are dwindling to insignificance, notably in Orissa but also in Malawi, where the four rainy seasons are running into one another. Unseasonable storms are more frequent in Vietnam, meaning weather patterns seem to be changing the character of each season, as well as the annual cycle.

Worried about the impact of global warming, the British charity Oxfam asked thousands of farmers in a score of countries to recount their experience of climate change in the past two years. Many of the villagers talked not about global warming—a generalised increase in temperature—but disruptions to the natural cycle. Seasonal shifts, they said, were more disturbing than global warming.

“Originally, there were very distinct seasons and we were very sure when things would happen,” Julius Nkatachi, a 70-year-old farmer in Balaka, southern Malawi, told Oxfam. “Now the seasons are not distinct, especially the hot and cold seasons.” “I have noticed that the rains no longer have a particular pattern,” added 86-year-old Wilson Chiphale, also from Balaka. “Sometimes they come early when people have not prepared. Sometimes they end too soon and the maize wilts.”

Thousands of miles away, in north-eastern Nicaragua, Howard Fernández echoes such complaints: “The summer now is winter. April used to be summer but it rained the entire month. In wintertime it doesn’t rain.”  Meanwhile, in Nepal a villager says “there is no stability in the cold or summer seasons.” Much of the world seems to be experiencing climate change not as higher temperatures but as the decline or death of the seasons.

 
 
THE RHYTHM of the seasons is fundamental to mankind. “While the earth remaineth,” says the Book of Genesis, “seedtime and harvest, and cold and heat, and summer and winter, and day and night shall not cease.” Most Europeans and North Americans experience the seasonal beat as a four-four march, spring, summer, autumn and winter. But the seasons themselves have always been more variegated, a little less fixed in their categories than they seem—and that is especially true in the tropics, where distinctions between them are less sharp than in more temperate climes. And it seems likely that over the past few years the distinctions have eroded further, especially in the tropics. As Titania says in “A Midsummer Night’s Dream” (describing the effects of her squabble with Oberon):
 
The seasons alter…
           The spring, the summer
The childing autumn, angry winter change
 Their wonted liveries; and the mazéd world,
 By their increase, now knows not which is which.


Seasonal change is a product of the tilt of the Earth. The Earth’s axis is inclined at 23.4 degrees from the vertical and the planet spins around the sun at this angle, a bit like a top about to fall over. This means the sun’s rays strike different parts of the Earth at different angles of incidence at different times of year—and it is that angle of incidence which matters. The more oblique the angle, the greater the area over which rays of solar energy are spread, and dissipated. So the amount of solar energy per square metre is reduced in those places where the sun’s rays strike the Earth a glancing blow.

On June 21st the sun’s rays beat down perpendicularly upon the Tropic of Cancer. This is the summer solstice, the height of summer in the northern hemisphere with high temperatures and many hours of daylight. At that time, the southern hemisphere is tilted farthest away from the sun, so its rays strike the Earth at their most oblique angle. Where the angle is 30 degrees (as it is in much of South America and Australia), the sunlight is spread over twice as much land as it is when the sun is directly overhead. So each acre gets half as much solar energy. This is midwinter in the southern hemisphere.

As the Earth circles the sun, the angle at which the sun’s rays touch the most temperate zones changes from almost 60 degrees to roughly 30 degrees. The amount of heat and the length of daylight varies accordingly. These zones—roughly between the tropics and the polar regions—experience the shifting angles of incidence as a cycle of four seasons. But at the poles themselves, the angle of incidence varies from oblique to nothing at all (that is, the poles are in shadow). The Earth’s tilt means solar rays never touch the Antarctic during the northern summer, while the Arctic is always showing its face to the sun. So the poles experience only two seasons, polar day (spring and summer) and night (autumn and winter).

Near the equator, the angle of incidence hovers at or near 90 degrees throughout the year. Temperatures are much more consistent than elsewhere and hours of daylight vary hardly at all. There are still seasons but here they are dominated not by the sun but other things, such as the monsoon, proximity to the sea and the presence of a rainforest or desert; temperate seasons are influenced by such things too, but to a lesser extent.

In the tropics the year does not necessarily break down neatly into quarters and traditional calendars often don’t divide it up into four, unlike Vivaldi. In fact, if the composer had been an elder of the Walabunna people, who live north of Uluru (Ayers Rock) in the centre of Australia, he would have written only two seasons, since they are one of many tribes to divide the year into dry and rainy periods (or yurluurrp and wantangka). Six hundred miles to the north the Wardaman people use four seasons, the nearby Jawoyn six, while the Yanyuwa people on the coast have five. Orissa’s seasons reflect an ancient Hindu calendar from the first century BC, which also divided the year into six. The system was religious in origin, being first set out in an astrological work called the “Vedanga Jyotisha”, associated with the Vedas, India’s earliest sacred texts.

Calendars based on several seasons reflect the rhythms of the natural    environment. The D’harawal people who live at Botany Bay, in the area of modern Sydney, traditionally divided the year into six according to the behaviour of plants and animals. January to February was gadalung marool, the time of the kangaroo—the kangaroos’ birth season when it was forbidden to eat them (now it is peak barbecue season in Australia). August was tugarah gunya’marri, the time between the flowering of the acacia trees and the lyrebird building his mounds.

Tim Entwistle, the director of the Botanic Gardens Trust in Sydney, thinks the more complex aboriginal systems describe Australia’s actual biological cycle more accurately than the four seasons brought by the British. He suggests adding a season by truncating winter and dividing the extended spring in two: “sprinter”—August and September, peak flowering season—and “sprummer”, a period of later flowering in October and November when the weather fluctuates more widely. The idea has yet to catch on.

 
IT MIGHT seem odd that climate change should have anything to do with changes in seasonality. The greenhouse effect does not alter the angle at which sunlight strikes the Earth. It does not lengthen or abbreviate hours of daylight. Since these things play a big role in generating seasonal change, there is no obvious reason why global warming should make any difference at all. But seasons are not defined only by the number of hours of daylight or whether the sun is directly overhead at midday. Spring in the northern hemisphere begins when the first leaves appear on the rowan or sycamore, when the first swallows arrive, when frogs spawn, bluebells flower or blackbirds begin to feed their young. Moreover, plants and animals respond to the returning warmth of spring, or the encroaching cold of winter, by putting out or losing their leaves, by nesting, hibernating or migrating. And if local temperatures are rising just at the time when plants are setting themselves to flower, or when birds are preparing to migrate or nest, then plants and animals will change the timing of  their behaviour.

This is what seems to be happening across Europe. The study of the life cycles of animals and plants, and the ways in which they are influenced by the seasons, is called phenology and the father of modern phenology is Robert Marsham, an English gentleman farmer of the early 18th century. In 1736 Marsham started recording the dates on which 27 natural events first occurred on his estates at Stratton Strawless in Norfolk. They include the day when the first leaf budded on oak, beech and ash; the arrival of the first cuckoo, swallow and nightingale; the flowering of hawthorn and snowdrop; the croaking of the first frog and the first appearance of brimstone butterflies. Generations of his family maintained his “indications of spring” until 1958, providing an unprecedented historical record. Phenology owes a lot to such quiet dedication. Richard Fitter, a naturalist, kept records of the days on which 557 species of plants first flowered in Oxfordshire between 1954 and 1990.

 
Their account books make it clear that the first day of spring has been getting earlier in Britain. In the century from 1850 to 1950, the dates when buds appeared or insects emerged got very slightly earlier, with considerable fluctuations accord-ing to whether it was a warm or a cold year. From about 1960 the trend towards earlier springs accelerated. In 2001 the first oak leaves appeared on May 6th. In 2009 the date was April 20th, earlier than any point in the known record. Fitter found that 385 of his plants were flowering, on average, 4.5 days earlier in the 1990s than in the previous four decades. Some of Marsham’s indications of spring are now appearing three to four weeks earlier than when he was alive. The white dead-nettle now flowers 55 days early.

But are these results really representative, or just accidental products of localised hot spots? Two teams trawled through hundreds of thousands of records to find out. One, led by Annette Menzel of the Technical University of Munich and Tim Sparks of Britain’s Centre for Ecology & Hydrology (CEH), totted up every European finding they could lay their hands on and concluded that, between 1971 and 2000, 78% of plants and 75% of fruits turned to leaf or ripened earlier. Plants and insects, says Sparks, seem to have been more affected than birds. Another team, lead by Stephen Thackeray and Sarah Wanless, both of CEH, looked at an even wider range of species (including amphibians) in Britain. They confirmed that, between 1976 and 2005, 80% of the observations were of earlier seasonal events, that change seems to be accelerating and that species at the bottom of the food chain seem to be changing more than predators at the top. Overall, they reckon, spring in Britain is coming 11 days earlier than it did in the mid-1970s.

Changes to the timing of seasons have occurred in the tropics, too. Vietnamese farmers told Oxfam that 20 or 30 years ago a flood called the tieu man would inundate their fields in May or June. In 2007 the tieu man came in February; in 2008 in April—with dreadful effect. Farmers plant out rice seedlings in the flooded fields and in both years, a cold snap that followed the early floods destroyed the harvest.

The shift in the seasons seems to affect rainy periods especially. In the village of Kasese, in western Uganda, the head of the farmers’ co-operative told Oxfam that “until about 1988 the climate was OK. We had two rainy seasons and they were very reliable. Now the March to June season in particular isn’t reliable…Rain might stop in April.”

Tropical seasons are often disrupted in more dramatic ways. A Vietnamese fisherman says “normally, storms start in September or October but recently we have had storms in March or April. We have not been able to go out fishing.” A farmer in Malawi whose house was blown down by freakish winds said “wind and rain here is not a new thing, but it is changing. I’ve noticed the wind and rain here are getting more severe.” The strongest hurricanes—categories 3, 4 and 5 —used to be extremely rare in the southern Caribbean, but there have been several examples in the past decade. 

Some seasons have vanished altogether. In Kashmir there used to be a brief rainy season between winter and spring, called tsonth—three or four weeks of torrential downpours, bright sunshine and snow on the ground. But, says Rais Akhtar of the University of Kashmir, the state has not seen a tsonth for ten years. The first rainy season seems to have dried up in Uganda. In Ntchenachena, in northern Malawi, villagers used to describe four episodes of rain, each with their proper name and association with particular farming events. Since 2001, they say, the pattern can no longer be discerned.

The result is a strange paradox: seasonal patterns seem to be more simplified and less predictable. Temperate transitional periods, like Orissa’s spring, autumn and hemanta, are dwindling into insignificance, and a varied pattern of six seasons is being replaced by a simpler one of wet and dry, hot and hotter. Yet at the same time, farmers find the seasons less reliable and more confusing. “I’ve lived near Mount Elgon [in eastern Uganda] all my life”, says Willington Wamayeye, the head of a coffee growers’ co-operative, “and I have never known the weather to be so unpredictable.” “I know I am supposed to sow by a certain time or date,” says Mohammed Iliasuddin, a farmer in Bangladesh. “That is what my forefathers have been doing. But then for several years the temperature and weather does not just seem right for what we have been doing traditionally. I do not know how to cope with the problems.”

 

LIVING THINGS adjust themselves to the heartbeat of the seasons. Some respond to lengthening daylight: marigolds will flower only when there are more than six and a half hours of light. Many creatures, from hummingbirds to badgers to skunks, are quickened by warmth or become torpid at low temperatures. All seem driven by a built-in biological calendar. If you keep a ground squirrel in the blaze of artificial light all year, it will still hibernate in winter. And this calendar can be stretched or squeezed by light and temperature.

In their book “Seasons of Life”, Russell Foster, a professor of neuroscience at Oxford University, and Leon Kreitzman, a science writer, describe the calendar and explain how organisms measure and respond to the length of periods of light (“photoperiod”), timing their mating or migration accordingly. In sheep, for example, photosensitive cells in the retina control the release of melatonin which influences the expression of two genes called Per and Cry in a part of the pituitary gland. These genes in turn regulate thyroid-stimulating hormones which play a role in mating and reproduction. Hence, light and seasons are linked to thyroid hormones and the link controls basic biological behaviour. As John Tyler Bonner, a biologist, once put it: “Organisms do not have life cycles, rather they are life cycles.”

So it is inevitable that because they affect light and warmth, the new changes to the seasons will alter the world profoundly, just as the traditional changing of the seasons has always done. 

In fact they are already doing so, in two main ways. First, because the changes make the climate more unpredictable, they affect the calendars of life, which need to be predictable to work properly. Second, says Tim Sparks, different parts of the food chain respond to seasonal shifts at different speeds and this disrupts the whole chain. To take a simple example, winter moth caterpillars and great tits have both evolved life cycles that synchronise with that of the oak tree. In spring caterpillars hatch just as the tender oak buds burst into leaf. Hatch too early, the caterpillars have nothing to eat. Hatch too late, and the leaves become indigestible because of higher levels of tannin. The great tits feed their young almost entirely on winter moth caterpillars—hundreds per brood every day—so they must time their hatching to coincide with the caterpillar feast.

Over millennia, the three species evolved together but in the past 20 years their links have worked loose. The oak trees, which respond to rising temperatures, now produce their leaf burst about ten days earlier than they used to. The caterpillars, which respond to dwindling days of frost, rather than temperature alone, are hatching 15 days early, overcompensating. And the great tits don’t know what to do. They spend their winters in Africa, migrating to Europe to nest. Before migration nothing in their immediate surroundings can tell them when to start their great flight. Yet somehow they seem to learn from experience at the feeding grounds in one spring that they must hurry their migration a little the next one. At least, some do. In one population, at Wytham Woods near Oxford, great tits are laying their eggs two weeks earlier, keeping pace with the caterpillars. In another, around Arnhem in Holland, the birds have advanced their breeding by less than a week, so they have got out of kilter with the caterpillars.

This is one of the simplest food chains, with just three links. Most chains have dozens or hundreds of connections, each stretched in different directions. Early-spring species seem to be changing the most, says Sparks; midsummer ones less. Grass is growing earlier; other crops are planted later but ripening more quickly. At every point, the chain can break.

 
Overall, though, one can make a few generalisations. First, growing seasons are getting longer in temperate climes. Britain’s growing season has increased by more than a day a year over the past 20 years, according to the Tyndall Centre for Climate Change Research at the University of East Anglia. Researchers from the Technical University of Munich say spring in northern Europe now starts six to eight days earlier than it did 30 years ago; autumn is delayed by three days so the growing season has been extended by a week and a half since the early 1960s. In the northern United States the increase is ten to 14 days, says the Climate Change Science Programme, which collates research by several federal agencies.

All that sounds promising. Longer summers ought to mean more offspring and bigger, better or different crops. And it sometimes does. Mark Diacono has started growing olives, almonds and apricots on 17 acres in east Devon, home of clotted cream. Hans Schultz of the Research Centre at Geisenheim, in the wine-growing Rheingau region of Germany, says that, with vines blossoming ten days earlier and ripening 12 days earlier than the 40-year average, red grapes will migrate northward. In 2040, he reckons, cabernet sauvignon will be growing where riesling is now.

Unfortunately, longer summers also often mean hotter ones and that can be a problem. Researchers from the Chinese Academy of Agricultural Sciences and the International Food Policy Research Institute in Washington, DC, found that a 1°C increase in temperatures in wheat-growing parts of China reduced yields by 3–10%. In general, says Sparks, horticultural crops such as tomatoes, onions and fruit are more sensitive to changing conditions than cereals and oilseeds, so they will be affected more, for better or worse. And a longer growing season helps not only crops but pests and diseases, including new species which can come into a region where plants have no resistance. This problem will be exacerbated if there are fewer cold winters like this year’s. Frost is nature’s disinfectant. Farmers in Britain are already complaining about increased losses in the fields as a result of more pigeons, rooks and field mice surviving warmer winters.

In tropical areas the more common pattern is for shorter, disrupted growing seasons. In Tete province, Mozambique, villagers cultivate maize on the fertile flood plain of the Zambezi river. Until the 1990s, they say, the rainy season would start in October and continue for three months. They sowed their maize just after the rains began and harvested it in March. Now the rainy season begins later, so the maize is sown later, shortening its growing period. The rain is also erratic, with mini-droughts between downpours, so the crop germinates when the rains start and shrivels up during the dry periods.

In poor tropical countries people are sensitive to seasonal change in a way long forgotten in the West. Robert Chambers of Sussex University has shown that the weight and health of mothers and children in Ghana and the Philippines varies hugely according to the season, plunging alarmingly just before harvest. When seasons alter, it is a matter of life and health in the tropics.

Some farmers adapt. Baluku Yofesi, the head of western Uganda’s Kasese co-operative, says, “because of the shortened rains you have to go for early-maturing varieties and people are now trying to select these.” But those who do best usually have a bit of spare money, land or access to technology. Not everyone has. Asked how people are coping where she lives, also in western Uganda, Florence Madamu throws up her hands in despair. “We’ve stopped even adopting seasonal planting”, she cries, “because it’s so useless. We used to plant in March and that’d be it. Now we plant again and again…The cassava no longer yields anything—there are flies that eat up the leaves. Bananas are attacked by mosaic [a virus]. The area no longer produces beans; we’ve tried and failed. The only crop that currently does well is sweet potato.”

And everywhere the ways of life associated with the traditional seasons are being strained. Oxfam’s researchers found that the authority of elders in the Miskito tribe in Nicaragua has been undermined because they decide when to plant and harvest—and their decisions have been mocked by the changing seasons. “The crop season has been moving from the traditional dates,” says Carlos Ling of Oxfam, “and this is very, very important. [It] affects your understanding of the whole Universe, not just your way of living. For people it’s very important to understand that on a particular date you plant the seeds in the ground and it is magical...[But] when certainties move, you feel a loss of control of your life.”

 
BACK IN Orissa, Richard Mahapatra’s family and friends are beset by similar doubts. Farmers used to trust a traditional weather-forecasting method called panjika. “The panjika never failed us,” says Haldar Nag, an Oriya poet. Everyone thought it was more accurate than the government’s weather forecast. But the system assumed Orissa would get 120 days of rain a year, and it now gets half that. “God knows what has happened—for more than a decade, the panjika has been unable to predict the weather.”

In villages in the west of the state the birds that helped people forecast the weather, such as the black-headed oriole or open-billed stork, are known as “wisdom birds”. “These birds have changed their character,” says Nag. The symbols of wisdom have become confused. “The peacock dances in anticipation of rain,” runs one of his poems, “but soon, to his surprise, the clouds fade away.”

Last year saw the worst monsoon for decades in Orissa, as in much of India. The state government declared yet another emergency. Villagers gaze uncomprehendingly at the peacocks’ lonely waltz. “The seasons have changed their nature,” Nag concludes sadly. “I think nature is finally paying us for our sins.”


FURTHER READIN
G:
Richard Mahapatra’s writings on Orissa are available at here.
 
Oxfam’s interviews are in “What Happened to the Seasons?” by Steve Jennings and John Magrath.
Seasons of Life” by Russell Foster and Leon Kreitzman is published by Profile Books.
 
The studies by Menzel & Sparks and Thackeray & Wanless are published by Global Change Biology.
 
 
(John Parker is the globalisation correspondent for The Economist. He wrote our cover story on wising up.)