Natural Heritage Trends: Scotland 2001
Global Pressures Affecting Future Change
Chapter 16 identifies trends and projections in air pollution impacts. As emissions of airborne pollutants have been reduced in recent years, and with further reductions planned, threats to the natural heritage have receded. The area of damage due to the acidification of soils is projected to decrease in Scotland by 12% between 1995/97 and 2010; the area of damage due to the acidification of fresh waters is projected to decrease by 67%; and the area of peatlands damaged through eutrophication from airborne nutrient nitrogen is projected to decrease by 37%. Ground-level ozone damage to semi-natural vegetation is also projected to decline, with a reduction in exceedance of about 20% over the coming decade.
Chapter 17 documents changes in the Scottish climate. During the 20th century, precipitation over land increased in the high latitudes of the northern hemisphere. Within Scotland, the wettest decade on record occurred during the 1990s, especially in the west. Cloud cover has increased. Days with bright sunshine have decreased in winter since the 1970s, particularly in the west. Although there has been little evidence of any increase in mean annual wind speed or maximum gust strength within Scotland, westerly air flows and the frequency of days with gales have both increased.
During the 20th century also, countries such as Scotland at latitudes north of 55° experienced temperature rises greater than the global average, with a warming of 0.8°C in Europe. Changes in minimum temperatures have a greater ecological effect than any other temperature change. Within Scotland, an overall decrease in the diurnal (day-night) temperature range has been most pronounced in spring. Spring temperatures rose by 0.5°C between 1960 and 2000. Coastal sea temperatures have increased by around 1°C since the 1970s, with warming most apparent in winter. Off-shore sea temperatures increased by 1-1.5°C. Minimum temperatures of oceanic waters during the 1990s were the highest recorded during the 20th century, matching near-surface air temperature trends for the northern hemisphere. Warming in Scotland is expected to continue to be greater in winter than in summer, with mean increases of between 1.5 and 5.8°C projected for the next century
Chapter 18 considers the consequences of climate change on habitats and species. By 1998, the growing season across the British Isles had become three weeks longer than it had been 1962, with earlier arrivals of migrant birds and earlier reproduction among some animals. The breeding distributions of a number of British bird and butterfly species extended northwards during the 20th century. Wetter winters and drier summers may have affected the structure of peatlands, with signs of more frequent and more extensive forms of peatland erosion. Heavier downpours of rain have caused rapid stream discharges, altering the physical structure of some riverbanks and floodplains, and in places washing out young fish and uprooting beds of freshwater pearl mussel.
Chapter 19 concludes with a synthesis of the state of the natural heritage in Scotland, with reference to Europe.