that with a warming rate of 0.04° C yr–1

and no increase in precipitation, little glacier ice would be left by 2100, whereas if warming is restricted to 0.01° C yr–1

(4° C per century) and

precipitation increases by 10% per degree of warming, then ice losses will be restricted to 10 to 20% of the 1990 value. It must be emphasized that the results are far from certain, and that the actual response of glaciers will exhibit considerable regional variability.

In some regions, it is very likely that glaciers will largely disap- pear by the end of this century, whereas in others glacier cov- er will persist but in a reduced form for many centuries ahead (Kulkarni et al., 2007; Ye et al., 2008; Bhambri et al., 2009; Nicholson et al, 2009; Wang et al., 2009; Yang et al., 2009;

CASE STUDY Impacts of climate change on high-mountain glaciers in the Alps: Observations and results

from modeling studies Frank Paul, Dept. of Geography, University of Zurich, Switzerland

Alpine glaciers lost about one-third of their total area from 1850 until the 1970s, and almost one half was gone by the year 2000. Starting from the last glacier inventory of the 1970s, little change was observed in the area until 1985 (–1%), but then a strong decrease (–20%) until the year 2000 occurred. This area loss was accompanied by a strong loss of glacier mass of about –11 meters water equivalent (m w.e.) or –0.8 m w.e. per year. This is more than three times the reconstructed long-term mean mass loss from 1850 to the 1970s of about –0.25 m w.e. per year (e.g. Hoelzle et al., 2003). The strong glacier decline is most likely a response to the sudden increase in Alpine temper- ature of about 1º C in the 1980s, which has shifted the equilib- rium line altitude (ELA) by about 150 m upwards (precipitation has not changed much). This has reduced the accumulation area of most glaciers drastically and they react with an adjust- ment of their size to the new climatic conditions.

Simple models based on rules of thumb allow us to deter- mine the consequences of such step changes in climatic con- ditions on future glacier evolution over large regions. With an assumed steady-state accumulation area ratio (AAR0) of 0.6, it can be calculated that about 40% of the total glacier area

will disappear for a 150 m upward shift of the ELA. At cur- rent rates and considering the already lost glacier area since 1985, area loss will at least continue until 2015 and much longer for large glaciers with a response time of more than 30 years. In particular the large glaciers display strong evi- dence of down-wasting (e.g. collapse holes, disintegration) rather than retreat of the terminus. Based on current climate scenarios as published in the last IPCC report, it can be ex- pected that glacier decline will continue and most glaciers in the Alps will disappear by 2100. Because glaciers as well as their meltwater in summer plays an important economic role in the Alps (e.g. hydro-power, discharge regime, tourism, natural hazards), concern is growing that the currently ob- served and future glacier changes will have adverse effects on human welfare (Elsasser and Bürki, 2002). In consequence, several projects have recently started that should improve the modeling of future climate change impacts on glaciers and runoff. The output from regional climate models (RCMs) and their efficient coupling to the much higher resolution impact models (e.g. distributed mass balance or hydrologic models) is in the centre of the scientific investigations (e.g. Paul and Kotlarski, 2010).

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Caidong and Sorteberg, 2010; Federici et al., 2010; Kaser et al, 2010; Liu et al., 2010; Peduzzi et al., 2010; Shahgedanova et al., 2010; Shekhar et al., 2010).

Bahr et al. (2009) made a first-order estimate of the mini- mum future sea-level contribution from all glaciers and ice caps, based on the idea that most are currently out of equi- librium with current climate and still need to complete their adjustment to past climate changes. The delayed adjustment is equivalent to approximately 18 cm sea level rise (averaged over the entire globe) in the next couple of decades. This represents a lower bound, as global temperatures are almost certain to continue increasing over the next century, causing additional ice mass losses.