Recent progress in climate change research
In a paper published in Nature Communication (Cai et al. 2018a) we show that the extreme pIOD frequency is projected to increase linearly with the GMT but approaches a maximum as the GMT stabilises, in stark contrast to a continuous increase in the extreme El Niño frequency long after the GMT stabilisation.
Extreme positive Indian Ocean Dipole (pIOD) affects weather, agriculture, ecosystems, and public health worldwide, particularly when exacerbated by an extreme El Niño. The Paris Agreement aims to limit warming below 2 °C and ideally below 1.5 °C in global mean temperature (GMT), but how extreme pIOD will respond to this target is unclear.
The finding shows that the frequency increases linearly as the warming proceeds, and doubles at 1.5 °C warming from the pre-industrial level (statistically significant above the 90% confidence level), underscored by a strong intermodel agreement with 11 out of 13 models producing an increase. However, in sharp contrast to a continuous increase in extreme El Niño frequency long after GMT stabilisation, the extreme pIOD frequency peaks as the GMT stabilises. The contrasting response corresponds to a 50% reduction in frequency of an extreme El Niño preceded by an extreme pIOD from that projected under a business-as-usual scenario. The lack of further increase in the extreme pIOD frequency after the GMT stabilises highlights a reduction in climate extremes that the aspirational warming target can bring about.
Figure (a) GMT anomalies (black curve) and zonal temperature gradient anomalies at the equatorial Indian Ocean (red curve) referenced to the pre-industrial condition (1869–1899) and averaged over 31-year sliding windows from 1869 to 2099 period. Their 90% confidence intervals are indicated by grey and light orange shades, respectively. The value near the red circle indicates the average over the 31 years centred at 1.5 °C warming (light green-shaded zone). Figure (b) The same as (a), but for the extreme pIOD frequency (purple curve, events per century).