Previous computer modelling studies have shown that for scenarios where atmospheric CO2 concentration is stabilised after an initial increase, the near-surface air temperature is rapidly near-stabilised but sizeable rates of sea-level rise can continue for more than 1000 years.
- This study shows that if CO2 concentration could be rapidly reduced following a projected increase, the thermal expansion component of sea-level rise is potentially reversible and could start to decrease on timescales of decades to a century-or-two following the onset of a decrease in concentration, depending when and how fast the CO2 concentration is reduced.
- Under emissions scenarios which are consistent with the Copenhagen Accord pledges, sea-level rise is not halted on multi-century timescales. The reversal of thermal expansion which was achieved under the idealised scenarios would appear to require geo-engineering options. The lowest emission scenario constructed for the pledges does, however, avoid about half of the projected median expansion over the combined 21st and 22nd centuries that is given by the highest emission (reference) pledges scenario.
- A preliminary “case study” has been made of total sea-level rise (including land ice melt), under example scenarios, which have increases in near-surface air temperature relative to pre-industrial values of around 1.5 or 2ºC by 2100. Over the 21st century, a small amount of median sea-level rise is avoided (~0.02m) for a scenario with a median temperature increase of 1.6ºC at 2100 following an overshoot, relative to that for a near-2ºC scenario. The rate of median sea-level rise, however, is notably smaller for the lower temperature scenario at the end of the century, indicating that subsequent avoided sea-level rise would be greater.
- Mitigation could also potentially reduce the likelihood of temperature thresholds being reached that might trigger a pathway to irreversible de-glaciation of the Greenland ice sheet and associated eventual sea-level rise.