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气候仪表板上的冰川
Glaciers on the Climate Dashboard

原始链接: https://climate.metoffice.cloud/glaciers.html

冰川是至关重要的天然水库，为人类提供了必要的季节性融水。自19世纪以来，冰川持续退缩，带来了严重的环境后果，包括威胁沿海社区的海平面上升。 冰川的健康状况由其“物质平衡”决定，即降雪积累与冰体流失之间的动态平衡。虽然冰川会随气温、降水和云量的变化而自然波动，但近几十年来呈现出明显的负面趋势。世界冰川监测局报告称，参考冰川已连续31年持续萎缩，自1976年以来累计损失了约20米的水当量。 科学家通过多种方法追踪这些变化，从物理标杆和雪坑测量，到先进的卫星雷达和重力测量。尽管冰川动态受地形和海水温度等复杂的局部因素影响，但政府间气候变化专门委员会（IPCC）的全球共识指出，观测到的冰川物质损失中，很大一部分是由人类活动驱动的。随着这些冰雪景观不断消失，理解它们对气候变化的响应，对于管理全球水资源和应对海平面上升依然至关重要。

近期关于英国气象局“气候仪表盘”的Hacker News讨论引发了人们对全球冰川快速消融的沉重讨论。 参与者分享了他们访问冰川湾和帕斯特泽冰川等地的个人见闻，强调了历史状况与今日融化景象之间的巨大反差。尽管一些评论者指出，20世纪初的冰川退缩（如格林内尔冰川所观察到的情况）部分是“小冰期”结束后的自然反应，但各方达成了一项强有力的共识，即当前的融化速度前所未有，且在很大程度上是由人类活动引起的气候变化所驱动的。 讨论迅速转向了关于气候政策的更广泛辩论，用户对政治上的不作为表示沮丧，特别提到了美国退出《巴黎协定》一事。虽然一些用户探讨了气候危机中集体责任与个人责任的问题，但整体基调反映出人们对这些自然景观不可逆转的丧失深感忧虑。该讨论帖还涉及了人们对测量冰层厚度的新技术产生的浓厚兴趣，以及对公众气候科学数据可视化方式的批判。
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原文

Why are glaciers important?

Glaciers are an important store of water. Their melt off during the dry season provides water for human use. Loss of glaciers could therefore lead to reduced seasonal water availability affecting the lives of many. If glaciers melt, as they have been doing over the past 30 years for which we have detailed measurements, the water ends up in the oceans, raising sea level, which can have impacts on coastal communities.

How have glaciers changed?

The balance between the accumulation of mass from snow falling on a glacier and ice loss, also knowns as the mass balance, controls how a glacier changes over time. Melting of the lower glacier can cause the terminus to retreat to higher and colder elevation. Increased snowfall can make the glacier advance downhill until it is halted by increased melting at the terminus. If the terminus is in the ocean, warmer water can melt the glacier, it then flows faster producing more icebergs. Glaciers are not only sensitive to changes in temperature and snow fall, but also to other elements like sea water temperature, humidity, cloudiness and whether precipitation falls as rain or snow.

There are thousands of glaciers world-wide and it is not practical to measure them all in detail. The World Glacier Monitoring Service monitors a set of reference glaciers across 19 mountain zones. The mass balance of these glaciers has been negative, i.e. they have been shrinking overall, for the past 31 years.

The cumulative loss of mass since 1976 amounts to around 20m of water equivalent. “Water equivalent” is the depth of water that we’d get on the glaciers if all the lost ice and snow were melted. Snow and ice can have very different densities depending on how compact the snow is, and how much air is trapped in the ice. Using “water equivalent” allows for consistency between measurements.

Longer records show that glaciers have been in long-term retreat since the 19th Century.

How is glacier mass balance measured?

Mass balance is measured using a variety of techniques. Ice loss can be measured using stakes driven deep into the surface of the glacier. As the ice melts, it reveals more of the stake allowing the ice loss to be quantified. Accumulation can be measured using stakes too, by digging pits that show how much fresh snow has accumulated, by probing through freshly fallen snow to the hard surface of ice beneath or even by analysing the annual layers of snow revealed by crevasses. Combinations of the different techniques provide information about mass gain and loss across the surface of a glacier.

Glaciers’ heights and shapes can be mapped from space, using radars, visible light sensors and other means. Large ice masses can also be monitored by dedicated scientific missions that measure the Earth’s gravitational field, such as GRACE.

Why have glaciers changed?

Glaciers respond to changes in temperature, the strength of sunlight reaching the glacier through changes in cloud cover and albedo, and precipitation. Rate of flow of glaciers can also be affected by a change in surface gradient. This may occur through downstream changes such as the loss of buttressing ice shelves, changes in basal lubrication due to meltwater, rainfall or infiltration of sea water. Each glacier is subject to a unique combination of the above-mentioned factors so there is variation in the mass balance between glaciers.

The IPCC AR5 concluded that “the robustness of the estimates of observed mass loss since the 1960s, the confidence we have in estimates of natural variations and internal variability from long-term glacier records, and our understanding of glacier response to climatic drivers provides robust evidence and, therefore, high confidence that a substantial part of the mass loss of glaciers is likely due to human influence.”

Find out more?

More detailed information is available from the World Glacier Monitoring Service.

Further scientific information and references:

Glaciers

WGMS

Glaciers

Zemp et al. (2019)

Sea Level

CSIRO

AVISO

CMEMS

Colorado

NASA

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