Expert range of sea-level rise forecasts for 2100 and 2300
A few points stand out here:

-- These values are higher than the "consensus" view from the Intergovernmental Panel on Climate Change. The IPCC projected an 0.5 to 1.0 meter rise by 2100 in the case of unchecked warming. This survey offers higher values, with a 1.5 meter rise possible at the upper end. Why the difference?

Some back story: There are a variety of approaches that scientists take to model sea-level rise. First are "process-based" models that try to capture all the various physical phenomena that can cause ocean levels to creep upward (such as shrinking ice sheets in Greenland and Antarctica, groundwater pumping, the expansion of water due to extra heat). The problem? It's difficult to capture all of these processes precisely, particularly those involving ice.

Alternatively, there are "semi-empirical" models that look at how sea levels have changed with temperature in the past and try to project that forward. These models tend to be far more accurate in reproducing past changes in sea-level, which is a plus. They also tend to project even higher sea-level rise in the future than the process models. But they also have drawbacks: What if the relationship between temperature and sea level changes in the future?

The IPCC didn't rule these "semi-empirical" models out entirely. It simply concluded that it can't assess their reliability. That's why it ended up assuming — cautiously — a lower range for sea-level rise.
Source: washingtonpost