British Birds Established 1907; incorporating 'The Zoologist', established 1843 Predictions of the effects of global climate change on Britain's birds Stephen Moss ABSTRACT Global climate change is no longer speculation, but reality. It will have unprecedented effects on Britain's weather and climate, and on habitats, ecosystems and the flora and fauna which comprise them, including birds. As a result, during the next century there are likely to be major changes in our avifauna: range extensions and contractions, rises and declines in populations, new colonists and extinctions as British breeding birds. Global warming will also affect patterns of migration, wintering and vagrancy, with long-distance migrants particularly at risk. In order to deal with the new challenges posed by climate change, our current conservation strategy will have to shift rapidly and radically. Whole ecosystems may have to be relocated or in some cases created from scratch, in order to deal with loss of habitat and changes in range. Whether or not this will ultimately prove successful it is still too early to say. [Brit. Birds 91: 307-325, August 1998] © British Birds Ltd 1998 307 308 Moss: The effects of global climate change Global climate change, as a result of mankind's profligate misuse of natural resources, is no longer mere speculation, but an objective, proven reality. In the carefully chosen words of the 1995 report of the Intergovernmental Panel on Climate Change (IPCC 1996): 'The balance of evidence now suggests that there is a discernible human influence on global climate.' The evidence for this is as follows: • Since the late nineteenth century, global surface temperatures have increased by 0.3°-0.6°C. • Nine out of ten of the hottest years on record, globally, have occurred since 1983. The top five have occurred since 1990. • The year 1997 was the warmest, globally, since records began in the late nineteenth century. • In England, the five warmest years since records began in 1659 have all been since 1975. This global rise in temperatures has been caused by the rapid increase in atmospheric concentration of the 'greenhouse gases', mainly carbon dioxide (C02), methane (CH4) and nitrous oxide (N20). These are released as a result of the burning of fossil fuels, and form a layer around the Earth's atmosphere. As the Sun's heat is reflected away from the Earth's surface, the gases prevent the heat escaping, leading to a rise in temperatures. Global warming—the future The IPCC has also forecast the likely progress of global climate change (IPCC 1996): • Over the next century, global average temperatures are predicted to rise by 1.5°-4°C, although as a result of the cooling effects of pollution this may reduce to 1°-3.5°C (all figures from 1990 baseline). • In the shorter term, by the year 2050, global average temperatures are predicted to rise by 0.5°-2°C. • In Britain, warming is predicted to continue at a rate of about 0.2°-0.3°C per decade—up to 1.6°C by the year 2050 (CCIRG 1996). If these predictions are correct, global warming will have an almost incalculable effect on the distribution, population and variety of birdlife, both globally and in Britain. Global warming in a historical context The World's climate is far from static. Major fluctuations have occurred in the past, as a result of which birds have had to adapt, often quite rapidly, to periods of climatic amelioration and deterioration. For example, about 3,000 years ago, during a spell of warming, Dalmatian Pelicans Pelecanus crispus thrived in the Somerset Levels (Burton 1995). More recently, a period of warming during the first half of the twentieth century enabled species such as Black Redstart Phoenicurus ochruros, Cetti's Warbler Cettia cetti, Golden Oriole Oriolus oriolus, European Serin Serinus serinus and Zitting Cisticola Cisticola juncidis to spread northwards across British Birds, vol. 91, no. 8, August 1998 309 Europe, and in the case of the first three, to colonise Britain (Burton 1995; Moss 1995). In contrast, a brief spell of cooling during the 1960s and early 1970s allowed Scandinavian species, including Common Goldeneye Bucephala clangula, Wood Sandpiper Tringa glareola and Snowy Owl Nyctea scandiaca, to colonise northeast Scotland, at least temporarily (Burton 1995). A longer-term trend towards wetter, cloudier summers was also implicated in the decline and eventual extinction of the Red-backed Shrike Lanius collurio as a British breeding bird (Peakall 1962). Using previous research by Alexander & Lack (1944), Parslow (1973) and others, Sharrock (1974a) showed that more species were breeding in Britain then than at any time since 1800, with a net gain of about five species per decade since 1949. So, even within our lifetimes, we have seen climate change affect the distribution of our breeding birds. There are, however, important differences from the current situation. Past climate change was fairly local, short-lived and gradual. For example, since the height of the last Ice Age, more than 15,000 years ago, global average temperatures have increased by only 5°- 7°C, an average of 1°C every 2,000-3,000 years. Today's climate change is very different It is global, long-lasting and happening faster than at any time in recorded history—as much as one hundred times the rate of 'natural' climate change.. This is likely to have dramatic consequences for habitats and ecosystems, and for the birds that depend on them. Even more worryingly, there is a growing body of evidence that global climate change is already having far-reaching effects on the World's ecosystems, involving species from taxa as diverse as amphibia, insects and flowering plants, and affecting ecosystems on every continent (Briggs 1997). Likely effects of global warming on Britain's weather and climate It is important to understand that the effects of climate change will not be spread evenly across the Earth's surface. Some areas will get much warmer than others, while a few places may even experience lower temperatures than before. Here in Britain, the Climate Change Impacts Review Group suggests that the following changes are likely to occur during the next century (CCIRG 1996): • Temperatures to rise, probably by more than the global average because of our relative proximity to the North Pole. • Milder, less-frosty winters. • A greater frequency of warm summers, with twice as many 'heat-wave days'. • A general increase in rainfall of about 10%, most of which will fall in northern and western Britain. • Winter rainfall to increase in southeast England, but summers to become much drier, with droughts and a rise in evaporation rates leading to near-desert conditions in some areas. • A higher incidence of 'extreme weather events', such as storms. 310 Moss: The effects of global climate change • Average wind speeds to increase, especially around the spring and autumn equinoxes. These predictions are based on the most likely consequences of global warming, and are therefore subject to a margin of error. For example, some scientists believe that warmer summers will result in more cloud-cover, and therefore higher summer rainfall. Others suggest that a weakening of the prevailing Atlantic weather patterns could result in a more continental-type climate, especially in southeast England. Recently, a far more catastrophic scenario has emerged: the 'Big Freeze', in which changes in ocean currents would lead to a weakening of the North Atlantic Drift, the current which gives northwest Europe its relatively mild winter climate. Should the North Atlantic Drift change course, Britain and Ireland could experience the kinds of winter temperatures to be expected at our northerly latitude—as low as minus 50°C (Pearce & Smith 1993). This is a possible, but unlikely, consequence of global warming, and for the purposes of this paper I propose to ignore it. The fact that it can be considered seriously shows, however, how unpredictable the consequences of global warming may be. Long-term effects of global warming on habitats and ecosystems The popular press tends to regard global warming as—to borrow the comment by Sellar & Yeatman (1930) on the Roman Conquest—'a Good Thing1, leading to Mediterranean conditions at South Coast holiday resorts, and bringing an end to winter freeze-ups. Birdwatchers and ornithologists may be tempted to agree, anticipating colonists from the south, such as Hoopoe Upupa epops, Black Kite Milvus migrans and Cattle Egret Bubulcus ibis. This is, however, a dangerous oversimplification. Global warming will set in motion a complex and unpredictable train of events which will affect all ecosystems, and the fauna and flora that comprise them. By upsetting the current balance (albeit a 'balance' already altered by Man's activities), no organism will be left untouched by its influence. Global warming is likely to have the following effects on habitats and ecosystems: • Changing the start and end dates, and length, of the growing season, and consequently altering the balance of plant life in any particular habitat (Huntley 1995). • Allowing plants to extend their ranges northward in latitude or higher in altitude, where they will compete with existing flora, to the detriment of habitats such as the specialised arctic-alpine ecosystem of the Scottish Highlands. • Causing the gradual disappearance of the dominant plant species, and its replacement with one more tolerant of the new conditions, such as Beech Fagus sylvatica replacing oak Quercus, scrub and carr replacing reedbeds, and Heather Calluna vulgaris replacing heath Erica (Briggs & Hossell 1995). • Allowing insects (both benevolent and 'pests') to extend their ranges, and, British Birds, vol. 91, no. 8, August 1998 311 by reducing winter mortality rates, to increase their populations. • Affecting the balance between predators and their prey, and between different species competing for similar resources, by favouring one species over another.