Responses to a warming world
There is now credible evidence of the ecological impacts of climate change, from polar terrestrial to tropical marine environments. The responses of both flora and fauna span an array of ecosystems from the species to community levels. Many studies have shown that global climate change has extended growing seasons, changed distribution patterns and altered the ‘phenology’ of flowering, breeding and migration. Phenology, until recently a new term to me, is the study of plant and animal life cycle events and how these are influenced by seasonal variations in climate. Recently compiled evidence indicating advances in the phenology of insects, birds, amphibians and plants, provide the most compelling evidence yet of human induced climate change. However, although scientists claim that these studies provide unequivocal evidence of recent changes to species phenology, many people are sceptical that these changes are a consequence of human activity.
Dramatic variations in the Earths global climate patterns have been detected throughout its history, with a wide range of factors including light, temperature and atmospheric gases potentially accountable. During the past century, the Earth’s climate has warmed by approximately 0.6 oC, with two main periods of warming between 1910 and 1945 and from 1976 onwards. Furthermore, regional differences have been detected during the past 65-70yr years exclusively in the northern Hemisphere. This major source of variability known as the North Atlantic Oscillation (NAO), has contributed significantly to the recent wintertime warmth across Europe and also to cold conditions in the Northwest Atlantic.
However, it is the El Nino Southern Oscillation (ENSO) phenomenon that is responsible for the strongest climatic fluctuations. This phenomenon is characterized by variations in the temperature of the surface of the eastern Pacific Ocean – warming or cooling known as El Niño and La Niña respectively. The two variations are coupled: the warm oceanic phase El Niño, accompanies high air surface pressure in the west Pacific, while the cold phase, La Niña, accompanies low air surface pressure in the west Pacific. In popular usage, El Niño is Spanish for “the boy” and refers to the Christ child, because the periodic warming in the Pacific near South America is usually noticed around Christmas. This causes extreme weather such as floods, droughts and other weather disturbances in many regions of the world on average every five years.
Even so, it is the greenhouse effect that is at the centre of climate change debate. Personally, I think it is therefore important to understand how it affects our planets ecosystem. The term Greenhouse Effect is commonly used to describe the increase in the earth’s average temperature over the past 100 years. The sun heats up the earth by sending solar rays towards us. Some of these rays don’t get through, but those that do, warm the earth up. This causes the earth to radiate its own heat in the form of infra-red waves. Those which don’t escape past our atmosphere are absorbed by greenhouse gases. These gases warm the earth up to the temperatures we have today (yes, but its freezing I hear you say). Without this process, the earth would be some 3000C cooler and life on the planet would be very different.
Mankind however is producing too many greenhouse gases, meaning that they are absorbing more heat and warming the earth too much. One of the main greenhouse gases is carbon dioxide, which can be created by de-forestation, the use of fossil fuels such as coal and gas; and the daily use of fuel in our cars. All of the emissions increase the amount of carbon dioxide in the atmosphere and contributes to an increase in global warming (so the scientists advocate). The other side of the argument is that the earth has historical variations in climatic patterns, which is a consequence of natural variation, rather than the adverse effects of homo sapiens.
Climate change: The impact on birds in the UK
So, how do all these changes affect our wildlife and in particular our feathered friends in the UK? Well, flowers such as snowdrops are blooming earlier, and as many as 18 butterfly species have been emerging on average 3 days earlier due to the premature onset of spring. Birds have also been breeding consistently earlier over the past two to three decades, with laying dates becoming markedly earlier in the 1980’s and 90’s. For example, the Great tit has started breeding earlier by as much as nine days, because their laying date is strongly correlated with the appearance of the caterpillars of the winter moth Operophtera brumata. Thus, breeding is timed so that the young are in the nest, when the principle food of the nestlings is at its peak.
For some species, migration patterns are changing as well as timing. Arrival of summer migrants has become earlier and short-distance migrants may have delayed their departure to the wintering grounds. Indeed, an increasing number of short-distance (intra-European) migrants from continental breeding populations, such as blackcaps, are now spending the winter in the UK rather than moving to their more traditional wintering grounds in the Mediterranean.
An archetypal example of the effect of climatic change on the distribution of species, is the little egret. The little egret is a very elegant wading bird, with white plumage, a long, dagger-like bill for catching prey, and yellow feet which look as though they have been dipped in paint. I expect many of you would have seen them in increasing numbers on your local estuary. I was very lucky in that respect. As a student at Plymouth University in 2004, I conducted research on the ecology of little egrets on six tributaries of the Tamar estuary. The egret is a widespread species, occurring throughout the temperate and tropical latitudes in the Palearctic, African and Oriental regions and also in Australia. It is thought that winter mortality is an important factor affecting egret populations; therefore the majority of European little egrets move beyond southern Europe to winter in North Africa to avoid harsh conditions. However, since the 1950s an increasing number (approximately 10 % of the population) overwinters on the European side of the Mediterranean. Changes in their wintering behaviour have culminated in the egrets radiating northwards along the Atlantic coast of Europe, establishing populations in Spain and France throughout the 1960s. During the 80s, breeding little egrets colonised a 600 km section of coast in Brittany, establishing 16 colonies and a population of approximately 400 pairs.
In Britain, little egrets have undergone of the most dramatic changes in status of any avian species. In a little over four decades, their status has changed from a vagrant, to widespread and locally numerous non-breeding visitor. Following a large influx in 1989, the species has continued to be recorded in increasing numbers in Britain throughout the 1990s. Since then, an early-autumn invasion with a high proportion overwintering has become the norm. Whilst in 1996, the first successfully breeding pairs were recorded in Dorset and Cornwall respectively. Hence, the little egret demonstrates that adaptable, mobile species can readily shift their range and distribution: the greater dispersal ability of birds compared with most other flora and fauna, may allow them to track climate more rapidly, enabling them to colonise suitable habitats many kilometres from their previous range margins.
Regardless of all these factors, I am sure you will agree that climate change is a fascinating phenomenon that will affect all wildlife including ourselves in the future. However, the impacts of climate change are not just for the future. We’re already picking up a wide range of signals across the natural world that change is already with us. Spring is coming around 11 days earlier than 30 years ago. The RSPB has seen appalling breeding failures in some seabirds, due to food shortages caused by the changing ecology of warmer UK seas. We’re seeing early examples of range shifts, with the spread of little egrets and Dartford warblers helped by warmer average temperatures in southern England. As such, egrets may currently be occupying a vacant niche, but as numbers increase they may begin to compete for resources with native waders. Not just food for these majestic birds then, but food for thought about the impacts and actual cause of climate change for us all.