The climate book, p.13
The Climate Book, page 13
This natural global pattern of biodiversity on land reflects processes that have operated over many millions of years – but most of us now live in places where biodiversity loss has been driven by three waves of human-caused change.
The first wave of human-caused change occurred far back in prehistory – at the time of our first contact with many species around the world. Our hunting helped to wipe out many large species of mammals and birds (the megafaunal extinction), while the rats and cats we spread to countless islands killed off many bird species which, evolving in a predator-free environment, had become flightless.
Settled agriculture began to replace nomadic lifestyles around 10,000 years ago, beginning the second wave of change. We started deliberately reshaping ecosystems to better meet our needs for food and materials, transforming the world into an easier place for us to live. The resulting agricultural landscapes were typically a complex patchwork of different crops (often changing each year), fallow, grazing land and more natural areas. This heterogeneity, and the fact that only a small fraction of the landscape’s biomass was harvested, enabled many species to persist alongside humans. Many Indigenous peoples around the world still manage their land like this today, and moves towards more nature-friendly agriculture typically adopt many of the same features.
From the mid-eighteenth century, linked revolutions in farming and manufacturing ushered in the third wave of human-caused change: ecosystem management turned into ecosystem domination. The resulting population boom required more land for farming and more wood for construction and fuel, driving more deforestation. We now use fossil fuels to power almost every sector of our economies, producing CO2 far more quickly than ecosystems can absorb it. Our imprint on around 75 per cent of land is visible even from space, and many regions face multiple intense threats (Fig. 1). Most obviously, we farm over 30 per cent of land, increasingly intensively; an area equal to the whole of North America and South America combined is used just to produce livestock.
The impacts of these threats to nature depend very much on where you look. In the few regions with no history of settled agriculture, hunting is often still the main driver of biodiversity loss, so the impacts echo the first wave’s megafaunal extinction. For example, in remote parts of many tropical rainforests, wild-meat hunting has largely or totally removed the large mammals; poaching likewise threatens the large mammals in many legally protected areas. Where subsistence farming is widespread, the impacts are more like they were during the second wave: there is a local pulse of biodiversity loss when natural ecosystems are converted to simpler agricultural ones, but the resulting landscapes – a complex, changing jumble, kept free of agrochemicals – can maintain moderate levels of biodiversity.
The number of severe threats to biodiversity around the world
Figure 1: Throughout the world’s lands and oceans 16 driver variables of biodiversity change – including climate change, human use, human population, and pollution – are mapped by number and intensity in 2020.
In places where the third wave is well underway – the darker regions in Fig. 1 – the fabric of life gets worn so thin that it can fall to pieces. Intensively farmed land is so structurally simple that there are very few niches for wild species. Harvesting so much of the ecosystem’s biomass leaves too little behind to support complex food webs: global vegetation biomass and tree cover are both now only around half of what they would naturally be, and the world’s cattle easily outweigh the more than 5,000 species of wild mammals put together. Meanwhile, agrochemicals make most farmland (and many of the waterways into which they drain) a harsh environment which most species cannot survive: ironically, the species best adapted to pesticides are the pests themselves, whereas thousands of species that could have contributed to natural pest control, pollination and soil fertility are often devastated. These include many wasp species whose larvae literally eat pests alive; the bees, flies, beetles, moths and butterflies that most crop species need for pollination; and the earthworms and many insects such as springtails that recycle nutrients from dead plants to fertilize the soil. Although intensive farming has increased agricultural production enormously, almost all of nature’s other benefits to people have declined globally over the last fifty years.
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The newest threat to nature is human-caused climate change. Its impacts have, so far, been small by comparison, but we can already see species trying to escape warmer temperatures. High-latitude species are being found further and further towards the poles, boreal forests are starting to expand into what used to be tundra, and mountain species are being found at ever higher altitudes. In the last fifteen years, human-caused climate change claimed its first known victim: the Bramble Cay mosaic-tailed rat (Melomys rubicola). Found only on a tiny low-lying island at the northern tip of Australia’s Great Barrier Reef, and last seen in 2009, this rodent probably succumbed to repeated flooding as the sea level rose and storms became more frequent.
Although climate change is not yet driving anything like as much biodiversity loss as humanity’s land use, the alarm bells are ringing. High regional biodiversity only arose where the climate was stable; unless global warming can be slowed very soon, it is sure to cause many more casualties. Mountaintop species will see their niches simply disappear. In flatter areas, rapid warming will mean that species have to move across the landscape in order to track their preferred climates: not all will be able to keep up. Crops will also need to move into more temperate areas that were previously wild, driving additional waves of habitat loss, and many currently productive regions will become too arid for reliable farming. This means it will not only be nature that has to move rapidly, but many millions of people too. Biodiversity loss may even form a vicious circle with climate change: ecosystems that have lost biodiversity store less carbon and are less able to cope with extreme weather events and other climate change.
But a sustainable future is still possible, if we are prepared to make more room for nature and to demand less from it. If we are to minimize the number of extinctions over the coming decades (we cannot stop them all) and avoid the worst impacts of warming, the regions with rich concentrations of unique species need to be cherished, their ecosystems restored and protected. Restoring high-carbon, high-biodiversity ecosystems is a true – and urgent – nature-based solution. /
2.20
Insects
Dave Goulson
I have been fascinated by insects all my life. When I was just five or six years old, I gathered yellow-and-black-striped caterpillars from weeds along the edge of my primary school playground, carried them home in my lunchbox and fed them until they eventually transformed into glorious red-and-black moths (you might recognize them as cinnabar moths). I was hooked and I have been fortunate enough to make a living out of my childhood passion for insects. For the last thirty years I have specialized in researching the ecology of bumblebees, the large, furry, stripy bees that drone clumsily among the flowers in our meadows and gardens throughout spring and summer. Their bumbling appearance is deceptive, for they are intellectual giants of the insect world, capable of astonishing feats of navigation and learning, and have complex and sometimes bloodthirsty social lives.
I first became interested in insects simply because I found them to be fascinating and beautiful, but I have long since learned that they are enormously important. Insects comprise the bulk of life on Earth; more than two thirds of the 1.5 million known species are insects. They are food for a great many larger animals, including most birds, bats, lizards, amphibians and fresh-water fish. Insects are also important biological control agents of crop pests, recyclers of all manner of organic matter from corpses to dung, leaves and tree trunks, and they help to keep the soil healthy. The majority of the world’s wild plant species depend on insects to pollinate them, as do three quarters of the crops we grow. Without insects, our world would grind to a halt; it cannot function without them.
Given the numerous vital roles that insects perform, we should be worried that many species are in rapid decline. For example, in the UK, butterfly populations have fallen by about 50 per cent since 1976. The biomass of flying insects on German nature reserves fell by an alarming 76 per cent between 1989 and 2016. In the Netherlands, caddis flies declined by 60 per cent between 2006 and 2017, and the biomass of moths by 61 per cent between 1997 and 2017. In North America, numbers of the monarch butterfly, famed for its annual migration between Mexico and Canada each year, are down about 80 per cent since the 1990s. A few insect species are bucking the trend, but most seem to be in trouble. Attempts to calculate an average rate of decline suggest that it might be in the range of 1–2 per cent per year – which may not sound like much, but it amounts to an insect apocalypse on the scale of a human lifetime. Worryingly, we do not know when these declines began as we have no data from before the 1970s – it is likely that we are now monitoring the tail of a much longer fall. We also have no idea what is happening to insects in the tropics, the great hotspots of insect biodiversity. Troublingly, the evidence for these population collapses is still too patchy – almost all the long-term studies of insect populations are from Europe and North America.
So what is driving these declines? In 1962, three years before I was born, Rachel Carson warned us in her book Silent Spring that we were doing terrible damage to our planet. She would weep to see how much worse it has become. Insect-rich wildlife habitats such as hay meadows, marshes, heathland and tropical rainforests have been bulldozed, burned or ploughed to destruction on a vast scale. Soils have been degraded and rivers choked with silt and polluted with industrial and agricultural chemicals or drained dry from overuse. The problems with pesticides and fertilizers that Carson highlighted have become far more acute, with an estimated 3 million tonnes of pesticides now going into the global environment every year. In the US, the weight of pesticides applied has increased by 150 per cent since Silent Spring was published, while at the same time new pesticides have been introduced that are much more toxic to insects than any that existed in Carson’s day. For example, the neonicotinoid insecticide imidacloprid is now the most widely used insecticide in the world, despite an EU-wide ban since 2018 brought on because of the harm it does to bees. Imidacloprid is about 7,000 times more toxic to bees than the insecticide DDT which was widely used in the 1960s and ’70s.
On top of all these pressures, wild insects now must cope with climate change, a phenomenon unrecognized in Carson’s time. Some insects, such as mosquitoes, will benefit from warmer temperatures and more rain, but most will not. My bumblebees are disappearing from the southern edges of their range, overheating in their furry coats as the climate warms. When climates changed in the past, they usually did so slowly, and wildlife existed in much larger populations, inhabiting extensive areas of intact habitat. Populations could easily shift towards the poles as it warmed, and back again when it cooled. Today, most insects persist in massively reduced populations inhabiting small fragments of surviving habitat. To move pole-wards they have to somehow cross tracts of hostile farmland and urban areas and hope to chance upon a patch of suitable habitat somewhere on the other side. Climate change is also bringing with it increased frequency of storms, droughts, floods and fires, all of them bound to severely impact already depleted populations. This may be the final straw for some.
The American biologist Paul Ehrlich likened the loss of species from an ecological community to randomly popping out rivets from the wing of an aeroplane. Remove one or two and the plane will probably be fine. Remove ten, or twenty, or fifty, and at some point there will be a catastrophic failure and the plane will fall from the sky. Insects are the rivets that keep ecosystems functioning.
If we are to reverse insect declines, we need to act, and act now. We need to engender a society that values insects, both for what they do for us and for their own sake. The obvious place to start is with our children, encouraging environmental awareness from an early age. We need to green our urban areas. Imagine green cities filled with trees, vegetable gardens, ponds and wild flowers squeezed into every available space – in our gardens, parks, allotments, cemeteries, on road verges, railway cuttings and roundabouts – all free from pesticides and buzzing with life. We also need to transform our food system. The way we grow and transport our food has profound impacts on our own welfare, and on the environment, so it is surely worth investing in getting it right. There is an urgent need to overhaul the current system, which is failing us in multiple ways, being a major contributor to greenhouse gas emissions, poisoning and eroding vital soils, and wiping out the biodiversity on which food production depends. We need to work with nature, encouraging predatory insects and pollinators, and stop trying to control and kill. Alternative farming systems such as organic and biodynamic farming, permaculture and agroforestry all have much to offer. There is an appetite for change. We could have a vibrant nature-friendly farming sector, with more small farms employing many more people, focused on the sustainable production of healthy food, looking after soils and supporting biodiversity, and producing mainly fruits and vegetables rather than meat, but this needs support from policymakers and consumers.
It is not quite too late. Most insect species have not yet gone extinct, but many now exist in numbers that are a fraction of their former abundance, teetering on the edge of oblivion. The stripy cinnabar moths that I collected as a boy have since declined in number by 83 per cent, but there are still some left, and they could easily recover if we act now. We do not understand anywhere near enough to be able to predict how much resilience is left in our depleted ecosystems, or how close we are to tipping points beyond which collapse becomes inevitable. In Paul Ehrlich’s ‘rivets on a plane’ analogy, we may be close to the point where the wing falls off. /
2.21
Nature’s Calendar
Keith W. Larson
For many species, their geographic range is the same, year in, year out. However, for certain migratory species of birds, butterflies, whales, and many others, their so-called species range shifts with the seasons. These seasonal patterns of movement are usually driven by changes in weather, habitat conditions and food availability. Similarly, many plant and animal species undergo profound changes across the course of the year – a phenomenon known as phenology. Just like shifts in species range, these significant reoccurring events in the lives of plants and animals take place according to environmental cues such as changes in temperature, precipitation and day length.
A familiar example of phenology occurs in many plants: in the spring, new leaves grow, often followed by flowering; in the late summer, they produce fruit; finally, in the autumn, the leaves change colour and fall to the ground. In mammals, phenological changes can vary: for example, some species hibernate during cold months, while others change their coats of fur to match their surroundings. Because of the regularity of these seasonal events, phenology is sometimes described as ‘nature’s calendar’. The timing is important, because it allows individuals to synchronize breeding and avoid having unfavourable weather extremes coincide with key stages in their life cycle (for example, raising your young when there is little food due to winter conditions).
Even in tropical environments that appear to have relatively stable climates, pronounced rainy seasons lead to the predictable timing of flowering and fruiting in plants, influencing breeding patterns across a diversity of insects, mammals and birds. But seasonal changes do become more pronounced as you move higher in latitude from the tropics. In Sweden, the spring is when these changes are most spectacular. Birdwatchers gather to record the arrival of migratory birds such as the willow warbler and the pied flycatcher from their distant tropical wintering grounds; those who live in urban areas note the first flowering of the violet queen crocus in their gardens or the wood anemone blanketing the floors of beech woodlands. Squirrels and bears wake from hibernation to take advantage of spring warmth and the impending abundance of food. The mountain hare and the willow ptarmigan shed their snow-white coats to match their newly leafy surroundings.
Both species range and phenology are incredibly sensitive indicators of climate change, and researchers have turned to study them in a bid to detect the early fingerprints of change across ecosystems globally. As our planet warms, plant and animal species have few choices. They can either track the environmental conditions necessary for life, which generally means moving to higher latitudes and altitudes. Or they can change the timing of their phenological events, such as when plants develop leaves and flower earlier in the spring. If they lack the ability to move or to adjust their phenological clocks in the face of rapid climate or environmental change, they face local, regional or global extinction. The rate of change is crucial: if warming is too rapid, then species may fail to respond in time.
