Volcanic contribution to decadal changes in tropospheric temperature

Abstract

Despite continued growth in atmospheric levels of greenhouse gases, globalmean surface and tropospheric temperatures show slower warming since 1998 1−5 . Possible explanations for this "warming hiatus" include internal climate variability 3,4,6,7 , external cooling influences 1,2,4,8−11 , and observational errors 12,13 . One contributory factor to the relatively muted surface warming -early 21st century volcanic forcing -has been examined in several modelling studies 1,2,4,8 . Here we present the first analysis of the impact of recent volcanic forcing on tropospheric temperature, and the first observational assessment of the significance of early 21st century volcanic signals. We identify statistically significant signals in the correlations between stratospheric aerosol optical depth and satellite-based estimates of both tropospheric temperature and short-wave fluxes at the top of the atmosphere. We show that climate model simulations without early 21st century volcanic forcing overestimate the tropospheric warming observed since 1998. In two simulations with more realistic volcanic forcing following the 1991 Pinatubo eruption, differences between modelled and observed tropospheric temperature trends over 1998 to 2012 are decreased by up to 15%, with large uncertainties in the size of the effect. Reducing these uncertainties will require better observational understanding of eruption-specific differences in volcanic aerosol properties, and improved representation of these differences in model simulations. B. D. Santer et al. 3Our analysis uses satellite measurements of changes in the temperature of the lower troposphere (TLT) made by Microwave Sounding Units (MSU) on NOAA polarorbiting satellites 13,14 . Satellite TLT data have near-global, time-invariant spatial coverage; in contrast, global-mean trends estimated from surface thermometer records can be biased by spatially-and temporally non-random coverage changes 15 . We compare MSU TLT data to synthetic satellite temperatures 3 calculated from simulations Although our primary focus is on the recent "warming hiatus", we also examine volcanically-induced changes in warming rate following the eruptions of El Chichón (April 1982) and Pinatubo (June 1991). Both volcanic events increased stratospheric loadings of liquid-phase sulfate aerosols, leading to stratospheric warming and tropospheric cooling ( Supplementary Fig. 1) 17−19 . Stratospheric temperature recovers within 1-2 years after El Chichón and Pinatubo. Because of the large thermal inertia of the ocean, the recovery of tropospheric temperatures is slower (ca. 8-10 years) 20,21 .To analyze volcanic contributions to observed changes in warming rates, it is useful to reduce the amplitude of internal noise 20−22 . Our noise reduction strategy involves removing the temperature signal of the El Niño/Southern Oscillation (ENSO), a (Fig. 1C). After 1999, however, a "warming hiatus" is still apparent in the observed residual TLT time series, but the lower troposphere continues to warm in the CMIP-5 multi-mo...

Forecasting Global Warming

“…Various suggestions had been put forth to explain this apparent leveling off of ΔT, including climate influence of minor volcanoes Santer et al 2014;Solomon et al 2011), changes in ocean heat uptake (Balmaseda et al 2013;Meehl et al 2011), and strengthening of trade winds in the Pacific (England et al 2014). The major ENSO event of 1998, which led to a brief, rapid rise in ΔT due to suppression of the upwelling of cold water in the eastern Pacific, must be factored into any analysis of the hiatus.…”

The Role of Volcanic Activity in Climate and Global Change

“…The suggested mechanisms include natural variability associated with increased ocean heat uptake [120,123] and cooling forced by small volcanic eruptions [124][125][126][127]. The latter refers to eruptions of Kasatochi in August of 2008, Sarychev in June 2009 and Nabro in June 2011.…”

“…More accurate calculations using global models gave estimates ranging from 0.07 K [124,127] to 0.02 K [125]. Therefore, despite that these signals could be detected using a rectified statistical technique [126], it is unlikely that small volcanic eruptions of the twenty-first century could be a primary cause of the climate hiatus. p0280…”

Debunking the climate hiatus

“…The evidence for a difference in trends is further weakened when temporal dependency is accounted for. The third approach uses the method of subsampling (Politis et al 1999;Rajaratnam et al 2014) to determine how the current 16-year trend during 1998-2013 compares against all the previous 16-year trends observed between 1950 and 1997. A p-value of 0.3939 is obtained and evidence for the hiatus is further weakened.…”