Similarities and differences in the response to climate warming of two ice caps in Iceland

The transient response to projected climate change of two ice caps in the central Icelandic highland was simulated with a vertically integrated ice-flow model coupled to a degree-day mass-balance model. The ice caps, Langjökull and Hofsjökull, are of similar size (area-900 km² and volume ∼ 200 km³) and located only ∼30km apart. The climate change simulations were started in 1990 from steady states corresponding to the average climate of 1981-2000 and driven with observed weather parameters until 2005. Thereafter, the forcing was according to a Nordic climate change scenario based on the IPCC B2 emission scenario. The simulations during the period 1990-2005 compare reasonably well with observations of mass-balance and glacier extent. Both ice caps are projected to essentially disappear during the next 100 to 200 years. Langjökull, which disappears within the next 150 years, shows larger mass-balance sensitivity to warming than the higher elevated Hofsjökull, where ice on the highest peaks may last over 200 years. A large proportion of the simulated runoff increase with respect to a 1981-2000 average has already taken place within the period 1990-2005. The runoff will increase further during the next 40-60 years and remain considerably higher than at present until the end of the 21st century.