NINE
MAGIC GATES, EL NIÑO AND LA NIÑA

Global warming’s effect on Earth’s climate is a bit like a finger on a light switch. Nothing happens for a while but, if you increase the pressure, at a certain point a sudden change occurs, and conditions flick from one state to another.

Climatologist Julia Cole refers to the leaps made by climate as ‘magic gates’, and she argues that since temperatures began rising rapidly in the 1970s our planet has seen two such events—in 1976 and 1998.

The idea that Earth passed through a climatic magic gate in 1976 originated on the faraway coral atoll of Maiana in the Pacific nation of Kiribati. In fact it originated specifically in one of the oldest corals ever found—a 155-year-old Porites—that lived and grew there. When researchers drilled a section out of this coral they discovered a detailed record of climate change extending back to 1840.

The magic gate of 1976 could be seen in a sudden and sustained increase in sea surface temperature of 0.6°C, and a decline in the ocean’s salinity (salt level) of 0.8 per cent.

Between 1945 and 1955 the temperature of the surface of the tropical Pacific commonly dipped below 19.2°C, but after the magic gate opened in 1976 it has rarely been below 25°C. ‘The western tropical Pacific is the warmest area in the global ocean and is a great regulator of climate,’ says Martin Hoerling, a climate researcher. It controls most tropical rainfall and the position of the Jet Stream, the powerful current of air high in the atmosphere whose winds bring snow and rain to North America.

In 1977 National Geographic ran a feature on the crazy weather of the previous year, which included unprecedented mild conditions in Alaska and blizzards in the lower forty-eight states of America. The immediate cause was a shift in the Jet Stream, but changes occurred as far afield as southern Australia and the Galápagos Islands which lie in the Pacific Ocean on the equator a thousand kilometres off the South American coast. The changes there affected evolution.

Charles Darwin visited the Galápagos Islands in the 1830s. He used its finches to illustrate his theory of evolution by natural selection. He could do this because the isolation of the islands had allowed its plants, birds and animals to develop under different circumstances. Since then the region has been a mecca for biologists, who established research stations to monitor its living creatures.

Scientists studying birds watched helplessly as the 1977 drought all but exterminated a species of native finch on one of the islands. Of the population of 1300 that existed before the drought, only 180 survived, and these were all individuals with the largest beaks, which enabled them to feed by cracking tough seeds.

Of those 180 survivors, 150 were males. When the rains finally came the male finches found themselves facing tough competition for mates. Again, it was those with the biggest beaks that won out. With this double whammy, a measurable shift in the beak size occurred on the island population. Since they had 150 years’ worth of beak measurements to look back on, biologists felt they were witnessing the evolution of a new species.

The 1998 magic gate is tied up with the El Niño–La Niña cycle, a two- to eight-year-long cycle that brings extreme climatic events to much of the world.

The name El Niño, which in Spanish refers to the Christ child, was coined by Peruvian fishermen who noticed that a warm current often visited their fishing-grounds at Christmas. La Niña means the girl child and refers to a cooling period in the ocean off South America.

During the La Niña phase, winds blow westwards across the Pacific, pushing the warm surface water towards the coast of Australia and the islands lying to its north. With the warm waters shifted westwards, the cold Humboldt Current is able to surface off the Pacific coast of South America, carrying with it nutrients that feed the most prolific fishery in the world, the anchovetta.

The El Niño part of the cycle begins with a weakening of tropical winds, allowing the warm surface water to flow back eastwards, overwhelming the Humboldt and releasing humidity into the atmosphere which brings floods to the normally arid Peruvian deserts. Cooler water now upwells in the far western Pacific. It does not evaporate as readily as warm water, and so drought strikes Australia and southeast Asia.

When an El Niño is extreme enough, it can devastate two-thirds of the globe with droughts, floods and other extreme weather.

The 1997–98 El Niño year has been immortalised by the World Wide Fund for Nature (now the WWF) as ‘the year the world caught fire’. Drought had a stranglehold on a large part of the planet. Fires burned on every continent, but it was in the normally wet rainforests of southeast Asia that they reached their peak. There over 10 million hectares burned, of which half was ancient rainforest. On the island of Borneo 5 million hectares were lost—an area almost the size of the Netherlands.

Many of the burned forests will never recover on a time scale meaningful to human beings. The impact on Borneo’s unique fauna will probably never be fully known.

As greenhouse gases build up in the atmosphere we will experience persistent El Niño-like conditions.

Severe El Niño events can permanently alter the climate. The 1998 event released enough heat energy to spike the global temperature by around 0.3°C. Since then the waters of the central western Pacific have frequently reached 30°C, while the Jet Stream has shifted towards the North Pole. The new climatic regime also seems prone to generating more extreme El Niños.

Researchers wishing to document the response of nature to climate change often turn to the jottings of birdwatchers, fishermen and other nature watchers. Some of these records are very long—one English family recorded the date they heard the first frog and toad croaks on their estate every year between 1736 and 1947.

Prior to 1950 there is little evidence of any trend in these records, but over the last 55 years, right around the globe, a very strong pattern has emerged. Species have shifted towards the Poles by an average of around six kilometres per decade. They have retreated up mountainsides at the rate of 6.1 metres per decade. And spring activity has advanced by 2.3 days per decade.

These trends accord with the scale and direction of temperature increases brought about by greenhouse gas emissions and have been hailed as a global ‘fingerprint of climate change’. Such trends are so rapid and decisive it’s as if the researchers had caught CO₂ in the act of driving nature Polewards with a lash.

Tiny marine organisms called copepods, for example, have been detected up to 1000 kilometres from their usual habitat. Thirty-five non-migratory species of Northern Hemisphere butterflies have flown northward, some by as much as 240 kilometres, while at the same time becoming extinct in the south. Even tropical species are on the move, with Costa Rica’s lowland birds extending 18.9 kilometres northward over a twenty-year period.

With so many species relocating, it’s inevitable that human changes to the environment will block their way.

Edith’s checkerspot butterfly has a distinctive subspecies which inhabits northern Mexico and southern California. Increased temperatures in spring have caused the plant that its caterpillars feed on—a type of snapdragon—to wilt early, starving the larvae so they cannot pupate. The butterflies might have migrated to the north if the urban sprawl of San Diego didn’t stand in their path. With only 20 per cent of their original habitat now able to support them, these butterflies may not be around next century.

The early onset of spring activity is a key clue to climate change. In the bird world the common murre, a Northern Hemisphere seabird, has begun to lay its eggs on average twenty-four days earlier each decade over the period its nesting has been studied. In Europe, numerous plant species have been budding and flowering 1.4 to 3.1 days earlier per decade, while their relatives in North America have been doing so 1.2 to two days earlier. European butterflies are appearing 2.8 to 3.2 days earlier per decade, while migrating birds are arriving in Europe 1.3 to 4.4 days earlier per decade.

As some species shift rapidly in response to climate change, others are left behind. A key food item might arrive too late to be of use to a predator, or move too far north for that predator to use it.

The caterpillars of the European winter moth eat only young oak leaves. But oaks and moths have different cues to tell them when spring has arrived. Warming weather causes the moth’s eggs to hatch, but the oaks count the short cold days of winter as their guide for when to put out their leaves.

Spring is warmer than it was twenty-five years ago, but the number of cold days in winter hasn’t changed. As a result, the winter moths now hatch up to three weeks before the oaks bear their first leaves. Because the caterpillars can survive only two to three days without food, there are now far fewer of them. Those that do survive generally grow faster because there is less competition for food, meaning the birds have less time to find them.

In this illustration, it seems likely that natural selection will act upon the moth to alter the timing of its hatching, but this will occur only through the mass deaths of early hatching caterpillars, and for several decades at least we can expect the species to be rare.

Will the birds, spiders and insects that eat the moths survive? If they can’t it’s another example of how all around the world climate change is tearing apart the delicate web of life.

Over the past few decades, breeding newts have been entering European ponds earlier, while frogs have not. This means that the newt tadpoles are well grown when those of the frogs hatch from their eggs. This allows the newts to eat large numbers of the frogs’ young, which is having an impact on frog numbers.

Some reptiles face far more direct threats from global warming, for the sex of their young is determined by the temperature at which the eggs are incubated. For the North American painted turtle higher temperatures mean fewer males are born. If winter temperatures were to rise even slightly above their present high level, the creatures may find themselves with an all-female population.

A very different climate change impact was recently detected in Lake Tanganyika, Africa, one of the world’s oldest and deepest freshwater bodies. Located just south of the equator, it’s home to a host of unique species. Like most lakes, its waters are layered, with the warmest water on top. This can prevent the mixing of the oxygen-rich upper layers with the nutrient-rich ones below. Plants in the sunlit layers can be starved of nutrients, and those in the deeper layers can be starved of oxygen. In the past, this layering was seasonally broken down by the southeast monsoons, which stirred its waters and stimulated the spectacular variety of life it supports.

Since the mid-1970s, however, climate change has warmed its surface layers so much that the monsoons are no longer strong enough to mix the water. Inevitably, the plankton on which most lake life depends has now declined to less than one-third of its abundance of twenty-five years ago.

The spectacular spined snail, which is found only in the lake, has lost two-thirds of its habitat; today it lives only at depths of 100 metres or less, whereas twenty-five years ago it ventured three times as deep. These changes, scientists warn, threaten a collapse of the lake’s entire ecosystem.

All over the world the surfaces of lakes are warming, preventing the mixing of their waters and threatening the basis of their productivity.

Even remote rainforest is being affected by global warming.

In areas of the Amazon far distant from any direct human influence, the proportion of trees that make up the canopy is changing. Spurred on by increased CO₂ levels, fast-growing species are powering ahead, crowding out slower-growing plants. This diminishes the rainforest’s biodiversity, as the birds and animals that depend on the slower-growing species for food vanish, along with their resources.

One of the most important natural divisions on our planet is Wallace’s Line. To the west lies Asia with its tigers and elephants, while to the east is a region, centred on Australia, known as Meganesia, which has an ancient and distinctive flora and fauna, including many marsupials.

The richest habitat in all of Meganesia is the mountainous oak forests of New Guinea. During the oak-fruiting season, the rich humus of the forest floor is littered with large, shiny brown acorns. If you pick one up, you’ll most likely discover that it has been chewed, for these forests are home to more species of possum and giant rat than anywhere on Earth, and they love to snack on acorns.

Me with a baby giant woolly rat in the Nong River rainforests of central New Guinea in 1985. This creature’s habitat no longer exists.

In 1985, when I first saw these wondrous forests—in the Nong River Valley north of Telefomin near the centre of the island—they stretched before me into the blue distance, an unbroken stand of wilderness. I was the first mammalogist ever to work in that area, a rare privilege. It was home to many unusual species, some of which were unique to the region and unknown to science.

One such creature was a greyish, cat-sized possum with large brown eyes, small paws and a short tail, which the Telefol people (who sometimes journeyed into the valley to hunt) knew as matanim. Talking to hunters, I gathered it had a singular diet of fig leaves, fruit and the rotten wood of certain trees.

The Nong isn’t the easiest place in the world to reach, so in 2001 when I had the opportunity to return I jumped at it. You might imagine how excited I was, but even before the helicopter landed my spirits had plummeted. The entire valley, along with the surrounding peaks, had been transformed into a vast grove of vegetable tombstones.

Later, my old Telefol friends told me that during the last half of 1997 little or no rain fell, and the cloudless sky cast bitter frosts that killed the trees. By New Year, the remains of the forest had been baked to a crisp and its floor lay covered with dead leaves. When it came, the fire raced down through the valley and up onto the adjacent peaks. It burned for months, and even a year later it was likely to flare up from moss and dead plant matter buried deep underground.

These events had devastated the region, driving the wild animals from their haunts. The numbers of marsupial jaws kept by hunters as trophies showed that the environmental catastrophe had made the last untouched refuges accessible to humans. Strings of hundreds of jaws of the larger and rarer creatures such as tree-kangaroos, possums and giant rats hung from hearths, proof that even mediocre hunters had been assured of success.

Was there, hanging among those prizes, I wondered, the jawbones of the very last matanim on Earth?

It would take years of research to confirm the presence or absence of such a rare and elusive animal. But from what I saw on my visit in 2001, I think that its survival would have to be counted as a miracle.