From 2 °C to 1.5 °C: How Ambitious Can Ireland Be?

The current climate policy of Ireland was set according to a 2 °C temperature rise target. Pursuing a 1.5 °C temperature increase limit requires ratcheting of decarbonisation ambition. A large ensemble of scenarios are generated with decreasing carbon budgets, and the challenges of not exceeding these carbon budgets are compared with the current 2 °C climate policy scenario. The results indicate that a national carbon budget compatible with a 1.5 °C target would need to be almost three times smaller than the carbon budget resulting from the current national climate policy. This budget is technically feasible, but extremely challenging with the current technology assumptions. A carbon budget which would be midway between 1.5 and 2 °C appears much more plausible. Cost effective decarbonisation rates are non-linear in the near-medium term, contrary to the current policy, and more ambitious carbon budget targets can only be achieved through much stronger near-term mitigation efforts than suggested by the current nationally determined contribution. Marginal Abatement Costs (MAC) increase exponentially with increasing ambition. Delayed action causes a step change increase in MAC as well as reduces the level of feasible decarbonisation ambition.