The Carstensz set of glaciers “at 4,884 meters above sea level is called Nemangkawi in the language of the Amume tribe, and deserves to be considered a tourism icon in Papua. Its peak is the highest in the entire Australia-Oceania region and deserves to be called one of the seven most beautiful positions in the world,” said the Indonesian Minister for Tourism Arief Yahyaaid recently (13 August 2015).
As part of the environmental assessment of 1997 for the expanding capacity of the Grasberg gold and copper processing centre to the north of the mining town of Tembagapura in West Papua, we led a team of Australian scientists to review available and conduct new studies on the tropical glaciers located approximately 6 km east of the Grasberg open pit. Nearly 20 years have now passed and it is interesting to revisit the results, conclusions and uncertainty analyses of that study in the light of relevant studies over the past 20 years.
The 1997 projects were partly a response to various local villagers and climbers reporting black spots on the surface of some glaciers and many people worrying over the rapid geophysical changes taking place in the mine zone.
In 1997, there was only limited historical information on the factors affecting the increase of the equilibrium line altitude and the spatial extent of the glacier field. On-site meteorological monitoring had only recently begun and was not sufficient to determine robust trends in temperatures, humidity, rainfall and other important variables such as radiation balances that are usually required for detailed glacier modelling.
Regional climate information showed warming trends of various magnitudes over the period 1960-1995; for some sites this had accelerated in the 1975-1996 period. Regional climate modelling by CSIRO showed surface dry bulb temperature increases of approximately 0.5° C for this shorter period. Projected climate changes for various global emission scenarios suggested that, even neglecting any sub-regional and second-order mining impacts, all of the glaciers would become isolated non-glaciated bodies by 2035-2105.
On the local scene, the emission rates of the mine were estimated at 300 MW of heat (mainly from the oil burning used to power the mine processing equipment and associated extraction facilities) and 370 g/s of total dust (mostly from the extraction of the ore). Airborne thermal imaging clearly showed the temperature signatures of various mine activities (e.g. roadways, stockpiles, water bodies, and mine process buildings) but the overall heat island due to mining activity dropped to less than 1° C within 300 m of the pit. Even discounting the dampening effects of the regular afternoon rain and mist that occurs throughout the year, the dust deposition rates at the nearest glaciers were predicted by dispersion modelling to be below 1 g/m2/day for fine particulates and less than twice this for total suspended particulates. These levels were well below any health or amenity guidelines and would be difficult to detect in such a moist environment.
The airborne imaging also determined the extent of the various glaciers for 27th January 1997 as a total of 3.3-3.7 km2, a slight decrease from the 4.0 km2 measured in 1994. The separation and shrinkage of the Meren glacier from the North Wall Firn were apparent and suggested that the remaining lifetime of that ice body would be very short.
The previous, limited sampling of the ice surfaces for the various glaciers had shown the presence of soot, regional dust and black carbon, pollen and fungi/bacteria but only allowed order-of-magnitude estimates of their effects on the thermal characteristics and highly localised melting of the darkened ice and snow.
Despite the various uncertainties in local conditions and the contributions from non-mine sources such as regional fires, the mining activity for the period 1995-2015 was not expected to accelerate the-then observed retreat of the various glaciers. Detailed modelling of the glaciers suggested the immediate demise of the Meren ice and a relatively short lifetime (60-120 years) for the Carstensz glacier. The future of the glaciers was predicted as almost entirely tied to the likely climatic change in the region.
The observed fate of the Meren glacier and the poor condition of the Carstensz glacier have since caused alarm, especially given the fate of other tropical glaciers in East Africa and the Andean mountains of Ecuador and Peru. In the past 18 years there have been several scientific advances, some sponsored or aided by Freeport Indonesia.
- The extraction and analysis of ice-core samples from the top of the Carstensz Glacier in 2011 and 2014 by a team from Ohio State University is allowing some glacier history to be reconstructed and its relationship with the nearby “warm western Pacific pool” to be established. Estimation of glacier extent from visible and infra-red satellite images has been conducted by various American researchers.
- Collation of paleoclimate information (such as mud cores, corals, tree rings and other biological markers) from various sources covering the West Pacific, “Third Pole”, Indonesian and Australasian regions, with some records going back more than 6500 years.
- Work on the impact of dark dust and algal growths on snow and ice by various teams, both by direct sampling and by drone surveys. A flurry of papers in the past five years has shown the complex processes involving dust aerosols and fine dust settling on ice and snow surfaces in the ablation zone. These have included controlled experiments seeding of small areas of inclined ice surfaces on a glacier with dust of various types and sizes. On a larger scale, many studies have looked at the enhanced heating or insulation provided by thicker layers of dust debris.
- Of great interest are the Himalayan glacier controversies of the last five years (why do some retreat and others advance?). These have now been resolved and shown to be mainly due to the differing effects of dust debris on the glacier surfaces in Pakistan, India and Nepal. Such changes in albedo and surface melting depend on the dust characteristics, thickness, light scattering properties and the presence of biological matter, as well as the amount of black carbon from combustion sources.
- Quantification of black carbon emissions from diesel and oil-burning facilities (such as the power units supplying the mine) and of the impact of black carbon aerosols from local and distant sources upon the pristine regions of high altitude and remote mountaintops. Gas and particulate samples at other tropical glaciers have been interpreted as covering the period 20-5600 years before present and with much evidence of biomass burning.
- The construction of the worldwide 20th Century Reanalysis (weather reconstructions) database of surface and upper-level meteorological parameters at a resolution of 2.5 by 2.5 degrees and subsequent climate risk assessments for the agricultural and urban communities. These can give a 150 year history of regional conditions at the mine, glaciers and nearby oceans.
- New climate modes (patterns of behaviour) have been made available together with such reanalyses in the Climate Explorer tool. These “Messie modes” have been found to describe well the natural variability of fish resources in various oceans and may explain much of the fine-scale time variability of glacier and climate dynamics, with different modes being implicated on different continents.
The past climate history of the Carstensz region can now be readily compared to those in Ecuador, Kenya and Peru, using the 20th Century Reanalysis Project results. The influence of the globally important orthogonal climate modes (our G-set of ENSO, Modoki, Atlantic-ENSO, QBO, NAO, SAM, NPGO, AMO, PDO) on such extreme events can now be used to set any recent history in a longer-term context, facilitate disaster reduction planning and be the basis for a seasonal forecasting of site extreme meteorological events.
Satellite imagery has been very successful for many tropical glaciers. It is difficult for this often cloudy site but has given some coverage of glacier extent for the period 2000-2012, with a dominant downward trend being sometimes lessened by short-term natural variability. These studies show that the Meren Glacier disappeared completely sometime in the period February 1997 to March 2000. Ice-core sampling was urgently conducted over 2011-2014 as fears spread about the very functioning of the Carstensz Glacier itself.
Weather reconstructions and on-site observations can be used to give a long-term meteorological database for use in glacier modelling. The equilibrium line altitude can be well followed with time; a site-specific model is possible to examine the time series of glacier extent for the next 30 years and the time to demise.
As the snow fall on the Carstensz mountain becomes rarer and the erosion by increasingly frequent strong rain events increase, the demise of ice remnants is likely to accelerate, especially with the increasing presence of algae and other biogenic material. It is likely that there will be no glacial activity in West Papua after 2035, as the current predictions of climate for the next 50 years show an accelerating temperature increase at mountaintop level.
How can we react to such a situation? Climate adaptation measures for mountain-top mines have included short-term, seasonal and climate predictions of weather (and climate insurance pricing), as well as assessing the nature and extent of snow and ice characteristics of any nearby ice-fields. Weather forecasting at various timescales can be based on an explicit numerical model, climate mode likelihood (e.g. using quasi-orthogonal sea-state and ice-state “oscillations”), or validated climate models for the envisaged global and detailed regional emission scenarios. For disaster risk reduction, emphasis should be placed on the extreme events that affect production, infrastructure resilience, worker-safety, water quality and floods, transport and conservation land-use. These events include heatwaves, heat and cold stress, rapid corrosion, intense precipitation and drought. For mines close to a seaboard, sea-level rise, storm surge and tsunamis are very relevant to port design and conveyor placement as well as the security of near-shore water and waste storage areas.
From a technical viewpoint, particular emphasis should be given to any rapid changes in probability distributions and to such metrics as the 1 in 20 year return events. Measures have been introduced to characterise the state of the environment (e.g. climate metrics of change and rate of change) and of the readiness of resource organisations to embrace change, plan real options for corporate scenarios and reveal any unexpected interconnections, either at the sites of operation or throughout the supply chains for the mine and smelter. In the often-encountered situation of a multi-national workforce, there are challenges and opportunities presented by the rapidly changing cultural, political, and geophysical settings.
Various mitigation measures for the glacier surfaces (e.g. artificial snow, ice surface cleaning, cloud seeding) can be evaluated for cost and efficacy.