An atlas of megadroughts in Europe and in the Mediterranean Basin during the Common Era provides insights into climate variability.

Photochemically generated benzyl radicals react with C(60) producing radical and nonradical adducts Rn C(60) (R = C(6)H(5)CH(2)) with n = 1 to at least 15. The radical adducts with n = 3 and 5 are stable above 50 degrees C and have been identified by electron spin resonance (ESR) spectroscopy as the allylic R(3)C(60)(.) (3) and cyclopentadienyl R(5)C(60)(.) (5) radicals. The unpaired electrons are highly localized on the C(60) surface. The extraordinary stability of these radicals can be attributed to the steric protection of the surface radical sites by the surrounding benzyl substituents. Photochemically generated methyl radicals also add readily to C(60). Mass spectrometric analyses show the formation of (CH(3))nC(60) with n = 1 to at least 34.

The supposed role of climate change on societal reorganizations in Europe 1,2 and Asia 3,4 during the first half Common Era (CE) is difficult to prove without adequate annually resolved and absolutely dated climate proxy archives 5,6. Interpretation of concurrences between cooling in the 6 th century and pandemic 7,8 , rising and falling civilizations 1-6 , human migrations and political turmoil 8-13 lacks understanding of scalar and causal mechanisms. Here we use tree-ring chronologies from the Russian Altai and Austrian Alps to reconstruct summer temperatures over the past two millennia. In both regions, conditions during Roman and recent times were warmer than throughout the medieval period. Unprecedented, long-lasting and spatially synchronized cooling following a cluster of large volcanic eruptions in 536, 540 and 547 CE 14 , was likely sustained by ocean and sea-ice feedbacks 15,16 , superimposed on a solar minimum 17. This newly defined Late Antique Little Ice Age (LALIA, 536 to ~660 CE) exceeded the LIA in severity. Covering much of the Northern Hemisphere, it should be considered as an additional environmental factor contributing to the establishment of the Justinian plague 7,8 , transformation of the eastern Roman and collapse of the Sasanian Empire 1,2,5 , movements out of the Asian steppe and Arabian Peninsula 8,11,12 , spread of Slavic-speaking people 9,10 , and upheavals in China 13. Annually resolved and absolutely dated insight into late Holocene climate variability is crucial in order to distinguish anthropogenic from natural forced variation 18 , and to evaluate the performance of climate model simulations 19. Spatially well-distributed palaeoclimatic archives are also essential for answering questions surrounding possible relationships between climate variability and human history 5,6. However, around the world today, there are only 13 temperature sensitive tree-ring chronologies that span the entire CE (Table S1).

No abstract

Exactly dated tree-ring chronologies from ENSO-sensitive regions in subtropical North America and Indonesia together register the strongest ENSO signal yet detected in tree-ring data worldwide and have been used to reconstruct the winter Southern Oscillation index (SOI) from 1706 to 1977. This reconstruction explains 53% of the variance in the instrumental winter SOI during the boreal cool season (December-February) and was verified in the time, space, and frequency domains by comparisons with independent instrumental SOI and sea surface temperature (SST) data. The large-scale SST anomaly patterns associated with ENSO in the equatorial and North Pacific during the 1879-1977 calibration period are reproduced in detail by this reconstruction. Cross-spectral analyses indicate that the reconstruction reproduces over 70% of the instrumental winter SOI variance at periods between 3.5 and 5.6 yr, and over 88% in the 4-yr frequency band. Oscillatory modes of variance identified with singular spectrum analysis at ~3.5, 4.0, and 5.8 yr in both the instrumental and reconstructed series exhibit regimelike behavior over the 272-yr reconstruction. The tree-ring estimates also suggest a statistically significant increase in the interannual variability of winter SOI, more frequent cold events, and a slightly stronger sea level pressure gradient across the equatorial Pacific from the mid-nineteenth to twentieth centuries. Some of the variability in this reconstruction must be associated with background climate influences affecting the ENSO teleconnection to subtropical North America and may not arise solely from equatorial ENSO forcing. However, there is some limited independent support for the nineteenth to twentieth century changes in tropical Pacific climate identified in this reconstruction and, if substantiated, it will have important implications to the low-frequency dynamics of ENSO.

Climate field reconstructions from networks of tree-ring proxy data can be used to characterize regional-scale climate changes, reveal spatial anomaly patterns associated with atmospheric circulation changes, radiative forcing, and large-

We describe the development of a tree-ring chronology network in Nepal that is suitable for reconstructing temperaturerelated climate forcing over the past few hundred years. The network is composed of 32 tree-ring chronologies and is represented by five indigenous tree species. An empirical orthogonal function analysis of the chronologies over the common interval 1796-92 indicates the existence of coherent large-scale signals among the tree-ring chronologies that are hypothesized to reflect, in part, broad-scale climate forcing related to temperatures. A long monthly temperature record for Kathmandu is developed and used to test this hypothesis. In so doing, significant monthly and seasonal temperature responses are identified that provide guidance for the formal reconstruction of two temperature

Past global climate changes had strong regional expression. To elucidate their spatio-temporal pattern, we reconstructed past temperatures for seven continental-scale regions during the past one to two millennia. The most coherent feature in nearly all of the regional temperature reconstructions is a long-term cooling trend, which ended late in the nineteenth century. At multi-decadal to centennial scales, temperature variability shows distinctly different regional patterns, with more similarity within each hemisphere than between them. There were no globally synchronous multi-decadal warm or cold intervals that define a worldwide Medieval Warm Period or Little Ice Age, but all reconstructions show generally cold conditions between AD 1580 and 1880, punctuated in some regions by warm decades during the eighteenth century. The transition to these colder conditions occurred earlier in the Arctic, Europe and Asia than in North America or the Southern Hemisphere regions. Recent warming reversed the long-term cooling; during the period AD 1971-2000, the area-weighted average reconstructed temperature was higher than any other time in nearly 1,400 years