In recent years, a study using a surface mass balance model, with fixed topography, concluded that the best estimate of the threshold in global temperature rise leading to a complete melting of the Greenland Ice Sheet was 3.1C (1.5-5.1C, 95% confidence interval). While this would take place over the course of many thousand years, it could ultimately raise sea levels by 3-7 meters. A new study in the journal Nature Climate Change suggests that this foreboding result could take place at a much lower temperature threshold. The study utilized a different approach than forcing a surface mass balance model, opting instead for a regional climate model coupled to an ice-sheet model. This approach incorporates several components that are important to accurately simulating long-term responses of the GIS to climate change, including albedo and elevation feedbacks. It is notable that simulations carried out in a complementary study by the same researchers yielded good results in simulating the last glacial-interglacial cycle, both supporting the results of this study and demonstrating the growing sophistication of regional models. Among the key take-aways of the study:
- The best estimate for the global mean temperature threshold for decline of the GIS is 1.6C, with a 95% credible interval of 0.8-3.2C. Above this threshold, the GIS would decline to 10% of its modern volume;
- The response time of the GIS to temperature increases, however, would be very long. For 2C regional summer warming, complete melting of the GIS would take 50,000 years, 4C warming would result in complete melting of the GIS in 8,000 years. However, a significant proportion of the ice would be lost within a few centuries;
- The GIS would continue to melt even if temperatures subsequently drop below the temperature threshold value, ensuring that sea-levels would continue to rise for thousands of years thereafter.
This would be an excellent reading for a science module in a climate change course, albeit a bit difficult for students without extensive scientific backgrounds. It would be interesting to seek to tease out the validity of the different methodological approaches utilized in this study and the previous one that found a much higher threshold for GIS melting. Moreover, it could stimulate some good discussion about the implications for operationalizing the precautionary principle, as well as whether the study’s findings should provide further impetus for engaging in geoengineering research.