Author Correction: Solar superstorm of AD 774 recorded subannually by Arctic tree rings.

The authors became aware of a mistake in the data displayed in Fig. 1 and Supplementary Table 2 of the original version of the Article. Specifically, the 14C production values were printed out in the code before the conversion between the omnidirectional fluence and the flux. As a consequence, the values of the 14C production in Fig. 1 and Supplementary Table 2 were too high by a factor of 4×π = 12.566.. As a result of this, a number of changes have been made to both the PDF and the HTML versions of the Article. A full list of these changes is available online.

Solar superstorm of AD 774 recorded subannually by Arctic tree rings.

Recently, a rapid increase in radiocarbon (14C) was observed in Japanese tree rings at AD 774/775. Various explanations for the anomaly have been offered, such as a supernova, a γ-ray burst, a cometary impact, or an exceptionally large Solar Particle Event (SPE). However, evidence of the origin and exact timing of the event remains incomplete. In particular, a key issue of latitudinal dependence of the 14C intensity has not been addressed yet. Here, we show that the event was most likely caused by the Sun and occurred during the spring of AD 774. Particularly, the event intensities from various locations show a strong correlation with the latitude, demonstrating a particle-induced 14C poleward increase, in accord with the solar origin of the event. Furthermore, both annual 14C data and carbon cycle modelling, and separate earlywood and latewood 14C measurements, confine the photosynthetic carbon fixation to around the midsummer.

Tree height strongly affects estimates of water-use efficiency responses to climate and CO2 using isotopes.

Various studies report substantial increases in intrinsic water-use efficiency (W i ), estimated using carbon isotopes in tree rings, suggesting trees are gaining increasingly more carbon per unit water lost due to increases in atmospheric CO2. Usually, reconstructions do not, however, correct for the effect of intrinsic developmental changes in W i as trees grow larger. Here we show, by comparing W i across varying tree sizes at one CO2 level, that ignoring such developmental effects can severely affect inferences of trees' W i . W i doubled or even tripled over a trees' lifespan in three broadleaf species due to changes in tree height and light availability alone, and there are also weak trends for Pine trees. Developmental trends in broadleaf species are as large as the trends previously assigned to CO2 and climate. Credible future tree ring isotope studies require explicit accounting for species-specific developmental effects before CO2 and climate effects are inferred.Intrinsic water-use efficiency (W i ) reconstructions using tree rings often disregard developmental changes in W i as trees age. Here, the authors compare W i across varying tree sizes at a fixed CO2 level and show that ignoring developmental changes impacts conclusions on trees' W i responses to CO2 or climate.

Biomass and carbon budget of European forests, 1971 to 1990.

In severely polluted areas, such as locally in Montshegorsk in northwestern Russia, all trees have died. However, measurements from Austria, Finland, France, Germany, Sweden, and Switzerland show a general increase of forest resources. The fertilization effects of pollutants override the adverse effects at least for the time being. Biomass was built up in the 1970s and 1980s in European forests. If there has been similar development in other continents, biomass accumulation in nontropical forests can account for a large proportion of the estimated mismatch between sinks and sources of atmospheric carbon dioxide.