2015, Schulte-Uebbing, Lena, Hansen, Gerrit, Hernández, Ariel Macaspac, Winter, Marten

IPCC Assessment Reports provide timely and accurate information on anthropogenic climate change to policy makers and the public. The reports are written by hundreds of scientists in a voluntary, collaborative effort. Growing amounts of literature and complex procedural and administrative requirements, however, make this effort a substantial management challenge next to a scientific one. During the 5th Assessment Cycle, IPCC Working Groups II and III initiated a program that recruited volunteer scientific assistants who provided technical and logistical support to author teams. In this paper we describe and analyze strengths and weaknesses of this ‘Chapter Scientist program’, based on an extensive survey among Chapter Scientists (CS) and interviews with other stakeholders. We conclude that the program was a useful innovation that that enabled authors to focus more on their core scientific tasks and that contributed to improving the quality of the assessment. We highly recommend similar programs for future scientific assessments. Key criteria for success that we identified are (a) involvement of early-career scientists as CS, (b) close integration of CS in the assessment process, (c) recruitment of CS through an open call to achieve transparency, and (d) provision of funds for such a program to support travel costs and compensation of CS.

2014, Sietz, D.

Global analyses of vulnerability reveal generic insights into the relation between socio-ecological systems and the stress impacting upon them including climate and market variability. They thus provide a valuable basis for better understanding and comparing the evolution of socio-ecological systems from a broad perspective. However, even when reflecting sub-national differences, global assessments necessarily aggregate regional variations in the underlying conditions of vulnerability. Refinements are therefore necessary to better accommodate context-specific processes and hence facilitate vulnerability reduction. This study presents a novel methodology to refining global insights into vulnerability at a regional scale. It is based on a spatially explicit link between broad patterns of vulnerability and modelled regional smallholder development. Its application in order to better represent the drylands of Northeast Brazil reveals specific facets of smallholders' vulnerability at the municipio level, reflecting non-linear dynamics. The results show that smallholders' vulnerability was widely exacerbated in the most vulnerable areas. One key mechanism causing such a vulnerability increase involved intensifying resource degradation and the related potential for impoverishment as modelled at the regional scale. In addition, by subsequently re-orienting their livelihoods towards off-farm activities, smallholders became more sensitive to fluctuations and competition in the labour market. In contrast to these critical trends, living and environmental conditions improved in only some areas, thus indicating a decrease in vulnerability. Altogether, in differentiating the heterogeneity of resource management and smallholders' livelihoods, the regional refinement presented in this study indicates necessary adjustments to generic strategies for vulnerability reduction gained at the global scale.

2015, Willeit, Matteo, Ganopolski, Andrey, Calov, Reinhard, Robinson, Alexander, Maslin, Mark

The Pliocene–Pleistocene Transition (PPT), from around 3.2 to 2.5 million years ago (Ma), represented a major shift in the climate system and was characterized by a gradual cooling trend and the appearance of large continental ice sheets over northern Eurasia and North America. Paleo evidence indicates that the PPT was accompanied and possibly caused by a decrease in atmospheric CO2, but the temporal resolution of CO2 reconstructions is low for this period of time and uncertainties remain large. Therefore, instead of applying existent CO2 reconstructions we solved an ‘inverse’ problem by finding a schematic CO2 concentration scenario that allows us to simulate the temporal evolution of key climate characteristics in agreement with paleoclimate records. To this end, we performed an ensemble of transient simulations with an Earth system model of intermediate complexity from which we derived a best guess transient CO2 scenario for the interval from 3.2 to 2.4 Ma that gives the best fit between the simulated and reconstructed benthic δ18O and global sea surface temperature evolution. Our data-constrained CO2 scenarios are consistent with recent CO2 reconstructions and suggest a gradual CO2 decline from 375–425 to 275–300 ppm, between 3.2 and 2.4 Ma. In addition to a gradual decline, the best fit to paleoclimate data requires the existence of pronounced CO2 variability coherent with the 41-kyr (1 kyr = 1000 years) obliquity cycle. In our simulations the long-term CO2 decline is accompanied by a relatively abrupt intensification of Northern Hemisphere glaciation at around 2.7 Ma. This is the result of a threshold behaviour of the ice sheets response to gradual CO2 decrease and orbital forcing. The simulated Northern Hemisphere ice sheets during the early Pleistocene glacial cycles reach a maximum volume equivalent to a sea level drop of about 40 m. Both ice volume and benthic δ18O are dominated by 41-kyr cyclicity. Our simulations suggest that before 2.7 Ma Greenland was ice free during summer insolation maxima and only partly ice covered during periods of minimum summer insolation. A fully glaciated Greenland comparable to its present-day ice volume is modelled only during glacial maxima after 2.7 Ma and more continuously after 2.5 Ma.