5 6 月 2007 at 11:51 上午 #3435馬丁參加者
press release from UN Environment Programme:引用：Melting Ice-A Hot Topic? New UNEP Report Shows Just How Hot It's Getting Lives and Livelihoods of Hundreds of Millions if not Billions in Many Parts of the World Influenced by Ice and Snow Losses Linked to Climate Change World Environment Day 2007 Tromso/Nairobi, 4 June 2007 – The futures of hundreds of millions of people across the world will be affected by declines in snow cover, sea ice, glaciers, permafrost and lake ice a new and unique report launched to mark World Environment Day (WED) says.
Impacts are likely to include significant changes in the availability of water supplies for drinking and agriculture, rising sea levels affecting low lying coasts and islands and an increase in hazards such as subsidence of currently frozen land. An estimated 40 per cent of the world's population could be affected by loss of snow and glaciers on the mountains of Asia says the UN Environment Programme (UNEP) in the Global Outlook for Ice and Snow. Similar challenges are facing countries, communities, farmers and power generators in the Alps to the Andes and the Pyrenees, says the report. Melting ice and snow are also likely to increase hazards including avalanches and floods from the build up of potentially unstable glacial lakes. These can burst their ice and soil dams sending walls of water down valleys at speeds close to that of a modern anti-tank missile.
Rising temperatures and the thawing of frozen land or 'permafrost' is triggering the expansion of existing- and the emergence of new- water bodies in places like Siberia. These are bubbling methane into the atmosphere with emissions so forceful they can keep holes open on the lakes' icy surfaces even during sub zero winter months. Methane is a powerful global warming gas and new estimates indicate that the quantities emerging from these so called thermokast lakes is up to five times higher than had previously been supposed. Meanwhile less snow and sea ice are leading to more of the sun's heat being absorbed by the land and the polar oceans which in turn may speed up global climate change. These are among the 'feedbacks' which some experts fear could trigger even faster or more abrupt climatic changes with even wider-ranging impacts on people, economies and wildlife. Adaptation Some communities are already adapting to climate change. For example hunters in parts of Greenland are abandoning traditional dog sleds in favour of skiffs as a result of less predictable sea ice. A key railway line in China, built on permafrost, has been designed with special cooling technology to reduce the risks of subsidence. However the report acknowledges that many indigenous peoples lack the financial resources and technology needed to adapt. While, many parts of the world currently remain ill prepared for the likely pace of climatic change. Achim Steiner, UN Under-Secretary General and UNEP Executive Director, said today: "This report is about ice and snow and may to some people seem to address issues from remote and far away places. But the report underlines that fate of the world's snowy and icy places in a climatically challenged world should be cause for concern in every ministry, boardroom and living room across the world. Indeed the findings are as relevant to people living in the Tropics and temperate climes- and in cities from Berlin to Brasilia and Beijing to Boston- as they are for the people living in Arctic or in ice-capped mountain regions". "The report comes in 2007, a year in which climate change came in from the cold in terms of science, likely impacts and costs. Indeed the Intergovernmental Panel on Climate Change has concluded that the bill may be less than 0.1 per cent of global GDP a year. So overcoming the climate change challenge is the bargain of the century," he added. "The missing link is universal political action. Today's report should empower the public to take their leaders to task?should encourage them to ask how much hotter it has to get before we act on a fair and forward-looking emissions reduction deal in Bali this December," said Mr Steiner, who was speaking at the launch in Tromso. Helen Bjoernoey, the Minister of the Environment for Norway, said: " This report gives us an overall picture of the changes in snow and ice cover and the consequences for human beings and nature, not only in the polar and mountainous areas, but all over the world. To me it is particularly alarming to realize that climate change can be a reinforcing process-global warming results in further global warming". "As documented in the report, melting of ice and snow will in itself have severe consequences on nature and society.
But it will also reduce the reflection of sun beams from the surface of the Earth and in this way contribute to further global warming. Recent scientific findings indicate that these changes may occur at a faster rate than reflected in the IPCC 4th Assessment Report. So, there is reason for deep concern," she said. "The challenge of global climate change can only be met through global political action. Norway has adopted as an aim to limit the global temperature increase to a maximum of 2 degrees Celsius. And we will work for having this limit adopted as a framework for negotiations on future commitments under the UNFCCC. Norway is prepared to take its share in this global effort. We will work actively towards a positive result at this year's Bali meeting, which can pave the ground for adoption of an agreement on global emission reductions at the latest in 2009," said Ms Bjoernoey. The Global Outlook for Ice and Snow, involving UNEP and a network of some 70 of the world's best experts, has been compiled in part to support the International Polar Year (IPY) running from 2007 to 2008. The peer reviewed report builds on and in some areas extends the work of the Intergovernmental Panel on Climate Change (IPCC) whose fourth assessment reports were issued between February and May this year. The report also flags up areas in need of further scientific clarity which the IPY, a major international science initiative of the World Meteorological Organisation and the International Council for Science of which UNEP is a partner, aims to resolve. These include the likely fate of the Antarctica and Greenland ice sheets where 98 to 99 per cent of the world's freshwater ice on the Earth's surface is held.
A total meltdown of the Greenland ice sheet would trigger an estimated seven metre rise in sea levels. Even just a 20 per cent melting of Greenland and a five per cent melting of Antarctica would result in a four to five metre sea level rise. This is a possibility over the coming centuries if greenhouse gases are not reduced in the 21st century and this might happen sooner if warming air and warming seawater continue to destabilize parts of the ice sheets. The melting of these sheets in conjunction with those on mountain glaciers and ice caps, along with the thermal expansion of the oceans, have so far led to a sea level rise of just under 20 cm between 1870 and 2001?with sea levels rising by just over three millimetres annually between the early 1990s and 2006. Resolving just how much of the ice may melt has direct consequences for people living in low lying areas and islands. Based on today's population a one metre sea level rise would, without adaptation measures, expose some 145 million people to flooding with Asia most affected. Areas of concern include many small islands and populations living in the mega deltas of the Ganges-Brahmaputra, the Mekong and the Nile in Africa. Low lying Bangladesh is singled out as a country of particular concern. The overall economic costs to communities, livelihoods, industry and infrastructure could be nearly $950 billion under a one metre sea level rise scenario. Christian Lambrechts of UNEP's Division of Early Warning and Assessment said the new report was designed to support the IPY in other ways. "We hope that this Global Outlook will demonstrate that the planet's ice and snow is intimately connected to all life on Earth and not just those living or working in polar and mountain regions," he added. Joan Eamer of UNEP Grid-Arendal in southern Norway said: "The Global Outlook is unique in the sense that it brings together all the different forms of ice and snow that occur in the world?collectively known as the cryosphere- and links them to the climate, to nature and to people both now and in the future". Pal Prestud of CICERO?the Centre for International Climate and Environmental Research in Oslo and Chairman of the Steering Committee for the new report, added: "One issue that rings loudly throughout the report is the need for greater certainty with regards to that fate of ice sheets. There are signs that these are breaking up, not just slowly melting and to date we do not fully understand the processes behind this".
"We can state with confidence that sea level rise is increasing, but we lack the ability to predict how much the ice sheets will in the end contribute to this over the next 10 years let alone the next 50 years?all we can say is that their potential to dramatically increase sea levels is enormous and far above the current UN Intergovernmental Panel on Climate Change predictions," he added. Snow Seasonal snow cover is the main source of runoff in the dry season in many mountain regions?globally over a billion people depend on it for their water supplies for domestic, agricultural and industrial uses including in some cases hydro-electric power generation. Snow is also economically important for winter sports, agriculture and animal husbandry such as reindeer herding and survival of caribou. Snow that has melted and refrozen into ice can become too hard for these animals to graze for their key food source?lichens.
"There have been catastrophic declines in the Peary caribou on Arctic islands of North America and they are now considered endangered. The formation of ice layers, following rain during the winter..?has been identified as the chief cause of the declines," says the report. Satellite monitoring shows that, since the late 1960s, snow cover in the Northern Hemisphere has been decreasing by 1.3 per cent per decade. The Western United States, particularly in the spring in the Pacific North West, is among the regions seeing the biggest decrease. Here the 'depth' or quantity of water from snow melt has fallen by between 50 per cent and 75 per cent over recent decades. Melting of snow in the Rocky Mountains of British Columbia form the headwaters of the Columbia River. It supplies water for larges areas of western Canada and north-west United States including for important irrigation and hydroelectric schemes. The Global Outlook for Ice and Snow says that unchecked climate change will aggravate the changes. For example a 2 degree C temperature rise in the Cascade Range of mountains of the Pacific North West of the United States could "reduce temperate snow cover by over 20 per cent". Similar impacts are likely in the Andes, the Alps and the Pyrenees which in turn will decrease summer water run off. For every one degree C rise in temperature, the snow line is predicted to move up the mountains?by 120 metres in Chile for example and by 150 metres in the Alps. The report notes that the declines in snow will not be uniform with some climate models indicating reductions of snow of between 60 per cent and 80 per cent in middle latitudes like Europe by the end of the century?but increases in Siberia and the Canadian Arctic by the same time as a result of increased precipitation. Changes in patterns of snow are likely to impact on tourism and recreation including skiing and snowmobiling. "Other less widespread winter sports such as dog mushing, sledding and snowshoeing can be important to local economies and are impacted when snow arrives anomalously late, too little or not at all," says the report. Frozen Ground or Permafrost and the Increase in Methane Bubbling Lakes Permafrost or frozen ground is important for the stability of buildings and infrastructure. Subsidence is one manifestation of thawing permafrost. These soils also contain large quantities of ancient greenhouse gases which could be released into the atmosphere as a result of widespread thawing. "The upper part of permafrost in boreal and arctic ecosystems is estimated to contain around 750 to 950 gigatonnes of organic carbon," says the report. Currently there are around 750 gigatonnes of organic carbon in the atmosphere. Some models predict that permafrost could, by the end of the century, be thawing in "practically all areas south of the Brooks Range in Alaska and in most of a sub artic Canada. In Russia the most severe permafrost degradation is projected for northwest Siberia and the European north. Almost all permafrost along the southern coasts of Greenland will be thawing by the end of the 21st century". The area of permafrost in China is expected to decline by 30 per cent to 50 per cent during this century. Some countries are already adapting infrastructure to cope with projected permafrost thawing.
The design of the Qinghai-Tibet railway already factors in the likely impact of a 2.6 degree C temperature rise by incorporating cooling techniques. "The impacts of climate changes on stability will also need to be considered in the design of the proposed China-Russia oil pipeline," says the report. Thermokast Lakes The report also flags up the curious case of lakes forming in places like Siberia as a result of the thawing of ice rich permafrost. Bubbles of methane, estimated to be up to 43,000 years-old, are being released to the atmosphere. In Siberia, the amounts of methane being released maybe five times higher than was previously supposed. "If significant permafrost warming and thawing occurs as projected, tens of thousands of teragrams of methane could be emitted from lakes?an amount that greatly exceeds the 4,850 teragrams of methane currently in the atmosphere," says the report. Sea Ice Sea ice is important in relation to ocean circulations such as the Gulf Stream and is also important for the food chain and also for wildlife such as polar bears and walruses as well as fisheries. The livelihoods and cultures of coastal Arctic indigenous people are inextricably linked with sea ice. Nearly four million people live in the Arctic including indigenous peoples. Impacts are already being felt. Hunters in Qeqertarsuaq, Western Greenland, are replacing dog teams with motor boats because of a lack of solid ice. Overall the extent of sea ice in the north has decreased by 2.5 per cent per decade in March and close to nine per cent in September over the past quarter century. At just over 10.5 per cent, the biggest decline has been in the Greenland Sea. In Antarctica the trend is less clear cut with a weak 'non-significant' overall increase in its extent, for example, in the Ross Sea of 4.8 per cent per decade but a decrease in, for example, the Bellingshausen Sea of 5.3 per cent per decade. Sea ice extent in both polar regions is expected to decline by a quarter by 2100 with the Arctic largely ice-free in the summer by the same date. But the report also points to possible abrupt changes or 'tipping points' that could bring an ice-free Arctic in the summer months forward by 60 years. The Northern Sea Route along the Siberian coast is currently navigable for 30 days but this could increase to 120 days during the century?a new economic opportunity for the region-but one, along with greater access to oil and gas fields and fisheries, that will require careful environmental management. Glaciers Many glaciers are already receding in response to climate change.
The report says that a three degree C rise in summer air temperatures could see the Alps lose about 80 per cent of their glacier cover. Heavily glaciated areas like Argentina and Chile's Patagonia region and the St Elias Mountains in Alaska could see the collapse of these ice bodies. The formation of lakes as a result of melting glacier and the risks of glacial lake outburst floods or GLOFs is also highlighted. Such lakes have potential to release up to 100 million cubic metres of water at speeds of up to 10,000 metres a second down vulnerable valleys.
Mountain regions at risk include the Himalayas, Tien Shan and the Pamirs of Tajikistan but also the Andes and the European Alps. In July 1998 a GLOF in the Shahimardan valley of Kyrgyzstan and Uzbekistan killed over 100 people. Another in August 2002 in the Shakhdara valley of the Tajik Pamir mountains claimed 23 lives. Meanwhile in Asia the lives of some 2.4 billion people?40 per cent of the current global population?are influenced by the summer meltwaters of glaciers in the Himalayas-Hindu Kush, Kunlun Shan, Pamir and Tien Shanan mountain regions. These glaciers could shrink by between just over 40 per and up to around 80 per cent by 2100 under current climate models with some mountain ranges completely devoid of glacial coverage. Rivers at risk include the Syr Darya, Amu Darya, Indus, Ganges, Brahmaputra, Yangtze and Huang He or Yellow river where some 1.3 billion people could be at increased risk of water shortages and many more at risk of losing irrigation water for crops as well as disruptions to industry and power generation. African glaciers have lost over 80 per cent of their area indicating major changes in climate and other phenomena such as rainfall. River and Lake Ice Freshwater ice is an important component of many river and lakes in the Northern Hemisphere including North America's Red River; Finland's Lake Kallavesi and Tornionjoki river and the Angara river in south east Siberia. Long term records indicate that rising air temperatures in the autumn and spring have produced a 10 to 15 day delay in 'freeze up' and a similar advance in break up.
Models indicate that continued climate change might change the timing and magnitude of spring melting affecting spring 'ice jam' flooding in communities. Climate change might actually reduce these dramatic events in the far north?but this could lead to the extensive wetlands on Arctic river deltas drying out and turning to shrubland. There is also concern over the impacts on fish and other biodiversity and links between transport and indigenous peoples. Currently many remote communities use frozen lakes and rivers as routes to traditional hunting, fishing and trapping areas or for accessing larger human settlements.
The Global Outlook for Ice and Snow