Estimation of Recent Climate Change in Irian Jaya by Numerical Modeling of its Tropical Glaciers^∗

Abstract

An attempt to estimate climatic change from the retreat of small mountain glaciers is made for the tropical Carstensz Glacier and Meren Glacier in Irian Jaya, Indonesia.

The central flowline of each glacier is modeled with a three-dimensionally parameterized numerical model. The measured net balance is increased by an amount sufficient to grow the modeled glacier to a steady-state length equal to the maximum Neoglacial extent, as determined from terminal moraines. The modeled glacier is then made to retreat by steadily decreasing the mass balance. The mass balance changes applied are of two types: either a shift of the net balance versus elevation curve on the balance axis (an accumulation change), or a shift on the elevation axis (a change in the equilibrium line altitude). While changes in the accumulation are the most likely form of year-to-year variation in the mass balance, a change in the equilibrium line altitude is considered to be the more important perturbation for secular changes in the length of the Mt. Jaya glaciers.

The results show that the present day equilibrium line altitude needs to be lowered by 96 m for the Carstenz Glacier to reach a steady state length equivalent to the actual Neoglacial extent, and that the observed retreat rate of the glacier can be well matched by increasing the equilibrium line altitude at a rate of about 80 m/century. The model matches known surface profiles of the glacier at various times and the measured surface velocities as well as the terminus retreat rate.

The increase of the equilibrium line altitude at a rate of 80 m/century can be considered, in a first approximation, to be due to an air temperature warming rate of 0.6°C/century. There can be no unique solution to the relationship between glacier net balance change and climatic change, but evidence from other sources of a general warming in tropical zones of 0.4 to 0.6°C for the last century supports the conclusion that the glacier retreat is due to increasing temperature.