Signs Of Change

We live in times of change and the impact of climatic warming can already be seen in many marginal areas. Effects that appear to be directly attributable to climate change are most noticeable in polar and alpine regions with the retreat of glaciers and snow and ice cover regions (Fig. 12.1). Coastal erosion as a result of rising sea levels is also having a noticeable impact. Archaeological rescue excavations of ancient coastal settlement sites exposed by erosion are now numerous. Several Scottish coastal golf courses have had to be redesigned as sections have been totally removed by the advancing sea. A coastal Scottish National Nature Reserve (Tentsmuir) that had been growing steadily seawards for centuries is now in places retreating rapidly by as much as 200 m depth of dunes over the last 20 years, returning sections of the coastline to where they were in the 1920s (Fig. 12.2).

More positive changes include an increase in the number of plant species to be found on the summits of European mountains (see Section 10.7), and an earlier flowering of the vernal flora with an extension of the growing season into the autumn. Northern agriculture is also profiting from the passing of the Little Ice Age in both crop production and length of the grazing season. However, in many parts of the world deleterious changes are taking place which are being aggravated by increasing human disturbance. Desertification in arid grasslands is certainly influenced by increasing

Fig. 12.2 Coastal erosion at the Scottish National Nature Reserve, Tentsmuir, Fife.The line of concrete blocks were laid down as coastal defences on the high tide line in 1940. They became completely buried in this region of the reserve by accreting sand dunes that advanced 50-75 m seawards from the line of blocks. Large 8-12 m high dunes have been removed in the last 20 years and the coastline in this region is now where it is estimated to have been in the early 1920s (Crawford & Wishart, 1966).

Fig. 12.2 Coastal erosion at the Scottish National Nature Reserve, Tentsmuir, Fife.The line of concrete blocks were laid down as coastal defences on the high tide line in 1940. They became completely buried in this region of the reserve by accreting sand dunes that advanced 50-75 m seawards from the line of blocks. Large 8-12 m high dunes have been removed in the last 20 years and the coastline in this region is now where it is estimated to have been in the early 1920s (Crawford & Wishart, 1966).

drought, but what is perhaps more serious is that the innate ability of the vegetation to recover is hindered by the excessive trampling of livestock (see Section 11.1).

Drought may also be an increasing hazard for arctic plants. There are already reports of arctic berry-bearing plants such as cloudberry (Rubus chamaemorus; Fig. 9.18) and bog whortleberry (Vaccinium uliginosum) suffering from drought. Drought is also affecting trees in the non-coastal parts of Alaska (see Section 5.3.1). This contrasts with the more oceanic regions of the Arctic, such as the West Siberian Lowlands where the treeline is already depressed south of its temperature limitations. The rain belts are moving north in Russia and therefore paludification in arctic and subarctic regions with oceanic climates may be accelerated. The rate of bog growth due to increased precipitation will undoubtedly be augmented by the increased nitrogen content that these rains now carry northwards from the northern hemisphere's industrial regions (Section 5.3.1). These diverging scenarios of drought versus paludification make it impossible to generalize on the migration of high-latitude vegetation zones. Thus, model predictions of treeline advance based on temperature increase in the Arctic suggesting that by AD 2100 there will be a more than 500 km northward migration of the treeline, unless prevented by anthropogenic disturbance, is unlikely to be a general occurrence (Arctic Climate Impact Assessment report, Callaghan et al., 2005).

0 0

Post a comment