What is the High++ scenario?

The High++ scenario includes possible additional contributions to sea level rise from accelerated ice sheet dynamics.

In detail

The High++ scenario range takes on board the need to broaden our horizons on future sea level rise, and include possible additional contributions to sea level rise from accelerated ice sheet dynamics. These effects were not fully accounted for in the IPCC AR4 ranges. The upper end of the High++ scenario range is therefore providing a highly uncertain and very unlikely scenario for sea level rise. The use of such a scenario is for worst case and long term contingency planning rather than day-to-day investment decision making.