Monday, November 16, 2009

Paul, F. 2007. Glacier Changes in Alps observed by satellite.

Paul, F., A. Kääb, W. Haeberli (2007). "Recent glacier changes in the Alps observed by satellite: Consequences for future monitoring strategies." Global and Planetary Change 56: 111-122.

Mean glacier area loss per decade from 1985 to 1999 has accelerated by a factor of seven compared to 1950-1973.

Downwasting (stationary thinning) is a major source of glacier mass loss confirmed by mass balance measurements.

Larger valley glaciers have retreated over 2km from just a 1K temp increase since 1850.

Short intermittent periods of advance in the 20’s and 70’s.

Worldwide retreat signal of glaciers is dominated by large valley glaciers and large mountain glaciers while the smaller glaciers have largely been ignored.

Mountain glaciers reflect the decadal oscillations while the valley glaciers represent the mere secular trend.

Where does our study fall in the GCOS/GTOS system hierarchy?

Optical satellite imagery for glacier detection depends on a spectral channel in the middle infrared spectrum (1.5um) where snow and ice exhibit a very low reflection compared to clouds and most other natural surfaces except water which is black (Dozier 1989).

Good tool for rapid change analysis is false color composite images… see notes in small notebook. Perhaps animated GIFs

Need to use images from same time of year to avoid varying cast shadow zones which will disturb the visual analysis.

Advantage of TM3/5 ratio is that in very deep shadows ice is still mapped completely but lakes and all other water bodies are mapped as glaciers which requires more post-processing. It’s also better at reducing the interference of vegetation in shade but on Hood and Rainier it still seems like the TM4/5 ratio is applied efficiently so will stick to it.

From 1985 to 1989 Swiss glaciers lost 18% of their area compared to -1% from 1973 to 1985 which is a relative loss of 14% per decade! Small glaciers account for 44% of the total area loss since 1973 although they only covered 18% of the total area in 1973.

Non-uniform geometry changes (not related to active glacier retreat) can occur everywhere on a glacier.

Downwasting – Mass balance data from 10 glaciers showed a mass loss of 17m water equivalent from 1981 to 2003 corresponding to about -.8m per year which is 3x the long term mean value for the 20th century of -.27m per year.

Linear trends show an increase in speed of glacier mass loss showing that the glaciers were not able to primarily adjust to current climate conditions by dynamic retreat towards higher elevations with cooler temps resulting in an elevation lowering of the glacial surface,

It has also eliminated most firn reserves from previous years thus steadily lowering the ice flow velocity and creating many disintegration features in the glaciers such as hollows, tunnels, caves, etc. Are these observable or noticeable on Hood or Rainier?

Indicators of downwasting are growing rock outcrops, separation from tributaries, formation of pro-glacial lakes, and non-uniform geometry changes. Are these observable or noticeable on Hood or Rainier?

Thermokarst – When the water of a glacial lake rises above 0 and causes further melt of the glacier.

Great section on how devastating new rock outcrops are to glacial ice in this paper – New rock outcrops have lower albedo and thermal inertia so they heat up during the day and emit heat at night creating gaps between the rocks and ice that further grow by turbulent heat fluxes – splitting the ice apart from the accumulating area of the glacier causing it to quicly melt – Definitely include this in paper.

There has also been a gradual lowering of the glacier albedo in the past 20 years. – Long accumulating periods of fair-weather can accrue dust and soot and other aerosols. These can only be removed by heavy precipitation - think summer months in the pacific northwest and it’s positive feedback to glacial recession. There is also the unveling of dark firn bands from previous years that are getting even darker since precipitation mostly falls as snow at higher elevations.

Most of the Alps firn reserves from the 1970’s are gone and the glaciers would need large amounts of snow to gain some mass to redistribute to flow velocity.

Even fast reacting mountain glaciers have response times of several years so their actual shape is not yet in balance with current climatic conditions.

There is a transition from active retreat to downwasting which is hard to observe with remote sensing.

No comments: