Volcanic eruptions contribute to climate variability, but quantifying these contributions has been limited by inconsistencies in the timing of atmospheric volcanic aerosol loading determined from ice cores and subsequent cooling from climate proxies such as tree rings. Here we resolve these inconsistencies and show that large eruptions in the tropics and high latitudes were primary drivers of interannual-to-decadal temperature variability in the Northern Hemisphere during the past 2,500 years. Our results are based on new records of atmospheric aerosol loading developed from high-resolution, multi-parameter measurements from an array of Greenland and Antarctic ice cores as well as distinctive age markers to constrain chronologies. Overall, cooling was proportional to the magnitude of volcanic forcing and persisted for up to ten years after some of the largest eruptive episodes. Our revised timescale more firmly implicates volcanic eruptions as catalysts in the major sixth-century pandemics, famines, and socioeconomic disruptions in Eurasia and Mesoamerica while allowing multi-millennium quantification of climate response to volcanic forcing.

International audienceSea ice and dust flux increased greatly in the Southern Ocean during the last glacial period. Palaeorecords provide contradictory evidence about marine productivity in this region, but beyond one glacial cycle, data were sparse. Here we present continuous chemical proxy data spanning the last eight glacial cycles (740,000 years) from the Dome C Antarctic ice core. These data constrain winter sea-ice extent in the Indian Ocean, Southern Ocean biogenic productivity and Patagonian climatic conditions. We found that maximum sea-ice extent is closely tied to Antarctic temperature on multi-millennial timescales, but less so on shorter timescales. Biological dimethylsulphide emissions south of the polar front seem to have changed little with climate, suggesting that sulphur compounds were not active in climate regulation. We observe large glacial–interglacial contrasts in iron deposition, which we infer reflects strongly changing Patagonian conditions. During glacial terminations, changes in Patagonia apparently preceded sea-ice reduction, indicating that multiple mechanisms may be responsible for different phases of CO2 increase during glacial terminations. We observe no changes in internal climatic feedbacks that could have caused the change in amplitude of Antarctic temperature variations observed 440,000 years ago

While global mean surface air temperature (SAT) has increased over recent decades, the rate 28 of regional warming has varied markedly 10 , with some of the most rapid SAT increases 29 recorded in the polar regions [11][12][13] . In Antarctica, the largest SAT increases have been 30 observed in the Antarctic Peninsula (AP) and especially on its west coast 1 : in particular, 31Vernadsky (formerly Faraday) station (Fig. 1) experienced an increase in annual mean SAT 32 of 2. 8° C between 1951 and 2000. 33 The AP is a challenging area for the attribution of the causes of climate change 34 because of the shortness of the in-situ records, the large inter-annual circulation variability 14 35 and the sensitivity to local interactions between the atmosphere, ocean and ice. In addition, 36 the atmospheric circulation of the AP and South Pacific are quite different between summer 37 (December -February) and the remainder of the year. 38Since the late 1970s the springtime loss of stratospheric ozone has contributed to the 39 warming of the AP, particularly during summer 7 . However, during the extended winter 40 period of March -September, when teleconnections between the tropics and high southern 41 latitudes are strongest 15 , tropical sea surface temperature (SST) anomalies in the Pacific and 42Atlantic Oceans 16 can strongly modulate the climate of the AP. The teleconnections are 43 further affected by the mid-latitude jet, which influences regional cyclonic activity and AP 44SATs. While the jet is strong for most of the year, during the summer it is weaker, there are 45 fewer cyclones, and tropical forcing plays little part in AP climate variability. 46The annual mean SAT records from six coastal stations located in the northern AP 47 (Fig. 1) show a warming through the second half of the Twentieth Century, followed by little 48 change or a decrease during the first part of the Twenty First Century 17 . We investigate the 49 3 differences in high and low latitude forcing on the climate of the AP during what we 50 henceforth term the 'warming' and 'cooling' periods, focussing particularly on the period 51 since 1979, since this marks the start of the availability of reliable, gridded atmospheric 52 analyses and fields of sea ice concentration (SIC). We use a stacked and normalized SAT 53 anomaly record (Fig. 2a) response to stratospheric ozone depletion and increasing greenhouse gas concentrations 5,18 . 68The trend in the SAM led to a greater flow of mild, north-westerly air onto the AP (Extended 69 Data Fig. 2a), with SAT on the northeastern side increasing most because of amplification 70 through the foehn effect 7 . This atmospheric circulation trend contributed to the large decrease 71 in SIC in summer (Extended Data Fig. 3a) and for the year as a whole (Fig. 3a). However, 72there was no significant trend in annual mean sea level pressure (SLP) across the AP during 73 4 the warming period (Fig. 3b). During the summer, tropical climate variability had little 74 influence on the AP SATs 15 and the trend in the...