PNNL

Abstract

The Paris agreement focused global climate mitigation policy on limiting the global average temperature increase to 1.5C or 2C above pre-Industrial levels. As a consequence, the climate and impact science communities are increasingly framing projections of hazards and risk in terms of global warming levels (GWLs) as an alternative to emission scenarios. Here, for the first time, we describe projected changes in extreme sea levels (ESLs) for a wide range of GWLs driving sea level change at 2100, and for a large number of locations covering most of the world's coastlines. Our multi-method approach estimates that by 2100 approximately 50% of the 7,000+ locations considered along the world's coastlines will experience the present-day 100-yr ESL event at least once a year, even if global warming were to be limited to 1.5C. The tropics appear more sensitive to such frequency changes than the Northern high latitudes, the latter often avoiding such frequency change even under scenarios of warming that reach the upper end of current projections. The above central estimates are bound on the one hand by an optimistic view, by which not more than 10% of locations are projected to experience such a change at 1.5C or 2C, and, on the other hand, by a pessimistic outlook that projects the 100-fold change in frequency at more than 98% of the locations worldwide for warming of 1.5C. Unless one adopts a substantially risk prone attitude, therefore, our findings should heightened awareness of widespread sensitivity of ESL frequencies to the effects of increasing sea level, even for scenarios that strongly limit global warming.