BHOJ K. ACHARYA and BASUNDHARA CHETTRI
Global warming and climate change and its subsequent impact on biotic and abiotic components of the ecosystem have shaken the entire world. It is one of the greatest challenges being faced by scientists and policy planners around the globe. It is reported that the earth’s surface has warmed up by 0.6°C in the past 100 years, and with the current rate of emission of greenhouse gases, global air temperature is likely to increase by 1.5 to 4.5 °C by the end of the 21st century. Such changes in global temperatures have manifold effects ranging from glacial melt and sea level rise, unusual weather events such as floods and drought conditions, intense but short duration of rainfall, infestations of diseases, changes in agriculture patterns and various effects on flora and fauna.
The Himalaya is known as the Water Tower of Asia. It contains the greatest area of glaciers and permafrost outside the Polar Regions, hence, is also known as the Third Pole. The total amount of water flowing from the Himalayas to the plains, and then on to the Indian subcontinent is estimated to be about 8.6 million cubic meters per year. Himalayan glaciers are the source of ten of Asia’s largest rivers, and more than a billion people’s livelihoods depend on them. The Himalayan region is the most sensitive zone for global climate change. Studies have shown that the rate of increase in temperature across the Himalaya is three times the global average. Currently the temperature of Himalayas has been increasing by 0.06°C per year. According to the projection made by Intergovernmental Panel on Climate Change, average annual mean warming of the Asian land mass will be about 3°C by 2050 and about 5° C in the year 2080 with much higher rates towards the Tibetan Plateau.
More than a billion people directly depend on the Himalayas for survival. While Climate Change is global phenomenon and has a global effect, the immediate repercussions are local. In the Himalayas, it has adverse impact on ecosystems and habitats endangering the very existence of life not just in the Himalayan Mountains but in the plains downstream.
The Himalayan glaciers are melting due to global warming. Decreases in snow accumulation and glacial retreat might lead to acute water shortages in the future. Almost 67% of the glaciers in the Himalayas have retreated resulting in water scarcity in the Himalayas and for more people living downstream who depend on glaciers and snow as a source of fresh water. The high elevation lakes are also at higher risk of Glacial Lake Outburst Floods (GLOFs). GLOFs can have a devastating impact on people, livestock, forests, farms and infrastructure.
In addition to this, Himalayas have experienced various other impacts of climate change. The rapidly changing environmental conditions caused by climate change make plant species more vulnerable to diseases and pests, contributing to the degradation and fragmentation of forests. Climate change is altering the fragile ecosystems of the Himalayas causing upward movement of vegetation and wildlife. This change will upset the ecosystem balance and seriously endanger the survival of many plant and animal species. Climate change, besides the immediate impact on flora and fauna, has adverse impact on health, wellbeing and livelihoods of the people.
Over the years the impacts of climate change have been experienced in Sikkim Himalayas. Such impacts are noticed in the form of glacial melt, changes in sowing and harvesting season of crops, decreased productivity of crops with new invasive species and weeds, drying up of springs, shifts in geographical range of species, changes in species composition of the communities and threat of extinction of species. Some impacts of climate change on faunal components of Sikkim Himalayas are highlighted below.
Upward migration of species
With the emerging warming and climate change pattern, many species of animals are migrating towards higher elevation. Birds such as Blood Pheasant, Snow Pigeon, Ibisbill, Rusty-bellied Shortwing and White-winged Redstart have responded to climate change by shifting their lower as well as upper elevational range limits. Among snakes, Monocled Cobra Naja kaouthia, King Cobra Ophiophagus hannah, Himalayan Mountain Keelback Amphiesma platyceps and Worm Snake Trachischium guentheri have shifted their range upwards along the elevation gradient. Similarly, Snow Toad Scutiger sikkimensis and Common Toad Duttaphrynus himalayana among amphibians, and some mammals and many butterflies have shown upward elevational range shift in Sikkim Himalayas. Upward migration has reduced the range sizes and distribution limits of species. While some species might not get affected, the rate of effect differs among others so that all species in a community do not synchronize their shifting behavior. Asynchronous shift results in changed species assembly and community structure resulting in competition among species leading to extinctions. Lower elevation species moves upward along the elevation gradient but high elevation species have no space for upward movement and hence have to face extinction.
Altered breeding seasonality, breeding failure and population decline
Warmer temperature, alteration in habitats and changed climatic pattern may alter animal’s reproductive strategies. They start breeding earlier or later than their usual breeding season or produce lesser offsprings due to reduced reproductive rate resulting in population decline. Breeding activities such as habitat selection, nest building and even laying of eggs and emergence of hatchlings is supposedly impacted in many bird species in Sikkim Himalayas such as Ashy Drongo, Black Bulbul, Chestnut-crowned Laughingthrush, Grey-backed White-capped Water Redstart, White-collared Blackbird, Common Tailorbird, White-rumped Munia, Ruddy Shelduck and Ibisbill. This is attributed to unexpected weather events such as longer dry spells, altered plant phenology and insect emergence or may be heavy rainfall at the onset of breeding season.
Due to unusual rainfall event or early summer rain, some amphibians in Sikkim started breeding earlier than their actual breeding time. Bush frog Philautus sp., Duttaphrynus spp., Amolops spp. and Paa liebigii have advanced their breeding activities. The short and heavy episode of early rain followed by dry spells leads to drying of many streams before amphibians complete their metamorphosis. Such irregular rainfall pattern poses serious threat to both eggs and tadpoles; either they face the risk of being washed away by heavy rains or face desiccation before the completion of metamorphosis leading to mass mortality and population decline.
Skewed sex ratio
Temperature determines the sexes in most reptilian species, higher temperature favors female individuals. Due to climate induced changes, some snakes in Sikkim Himalayas have shown biased sex ratio. The number of female offsprings is more than the males. Such deviation of sex ratio from the normal can disrupt population dynamics of snake community.
Influx of exotic species and disappearance of some species
The hilly terrain of Sikkim forms natural continuum with the plains of North Bengal. Due to favorable temperature in the hills, movement of species from lowland to highland occurs thereby threatening the local diversity and endemicity. Such influx has been noticed in some snake and lizards. Influx of exotics might lead to disproportion in prey-predator relationship thereby disturbing the entire food chain. Similarly, some reptiles (such as turtles and tortoises) and amphibians have probably been disappeared from Sikkim due to drying of springs and streams in the lower elevation caused by climate change.
Wildlife encroachment on human habitations
Climate induced changes have directly or indirectly impacted the habitat and distribution limits and the food availability for wild animals. Due to shortage of food, wild animals wander around human habitations in search of eating materials. For example, one of the probable reasons for random movement of Himalayan Black Bear in villages and towns in recent years could be climate change. This species eats acorns and nuts of the previous year, and if the productivity of such nuts decreases due to unusual weather events, they wander around for other foods. Many other animals might have been the victim of such events.
Sikkim displays various signs of climate change impact on water sources, agriculture, forests, flora and fauna. While we have ample examples to prove that many species of plants and animals have responded to climate change but precise responses are not known. To understand and address the climatic effect on flora and fauna in the Himalayas widespread and long term monitoring studies is necessary.
[Dr Bhoj K. Acharya is Assistant Professor, Department of Zoology, Sikkim Govt. College, Tadong. E-mail: acharya2skm@gmail.com
Dr Basundhara Chettri, Assistant Professor, School of Policy Planning Studies, Sikkim University, Gnagtok. E-mail: basundharac@gmail.com]
