Drivers of hiatus periods: volcanic eruptions, decadal variability and aerosols

The latest generation of climate model simulations are used to investigate decadal hiatus periods over the last 150 years. We find that the occurrence of hiatuses is related to a number of factors, including cooling after large volcanic eruptions and transitions to a negative phase of the Interdecadal Pacific Oscillation (IPO). In addition, while not strong enough by themselves to initiate a hiatus, the emission of anthropogenic aerosols can increase the likelihood of a hiatus occurring. We show that volcanic eruptions not only cause a direct cooling due to increased albedo, but can also initiate a La Niņa like state in the tropical Pacific, which may result in further cooling.

An examination of climate model projections based on two future warming scenarios indicates that hiatus decades are strongly linked to enhanced equatorial Pacific cooling and the shift to a negative phase of the IPO. In addition synthetic volcanic eruptions can cause hiatus decades to occur. The likelihood of a hiatus occurring into the future is found to be dependent on the rate of change of anthropogenic forcing, with larger volcanic eruptions and stronger shifts to a negative IPO needed to cause a hiatus under greater rates of warming. We find that there is little chance of a hiatus occurring after 2030 under a business-as-usual scenario, even in the event of a large volcanic eruption.