ALBERT

Description: In the future, Earth will be warmer, precipitation events will be more extreme, global mean sea level will rise, and many arid and semi-arid regions will be drier. Human modifications of landscapes will also occur at an accelerated rate as developed areas increase in size and population density. We now have gridded global forecasts, being continually improved, of the climatic and land-use changes (C&LUC) that are likely to occur in the coming decades. Aside from a few exceptions, however, consensus forecasts do not exist for how these C&LUC will likely impact Earth-surface processes and hazards. In some cases we have the tools to forecast the geomorphic responses to likely future C&LUC. Fully exploiting these models and utilizing these tools will require close collaboration among Earth-surface scientists and Earth-system modelers. This paper assesses the state-of-the-art tools and data that are being used or could be used to forecast changes in the state of Earth's surface as a result of likely future C&LUC. We also propose strategies for filling key knowledge gaps, emphasizing where additional basic research and/or collaboration across disciplines is necessary. The main body of the paper addresses cross-cutting issues, including the importance of nonlinear/threshold-dominated interactions among topography, vegetation, and sediment transport, as well as the importance of alternate stable states and extreme, rare events for understanding and forecasting Earth-surface response to C&LUC. Five supplements delve into different scales or process zones (global-scale assessments, and fluvial, aeolian, glacial/periglacial, and coastal process zones) in detail.

Description: Widely used sequence stratigraphic models predict that specific facies assemblages alternate in the stratigraphy of deep-sea fans, depending on the cyclic nature of sea-level variations. Our work tests this assumption through facies reconstruction of submarine fans that are growing in a small basin along the tectonically active Sicilian margin. Connected canyons have heads close to the coastline; they can be river connected or littoral cell–connected, the first receiving sediment from hyperpycnal flows, the latter intercepting shelf sediment dispersal pathways. Hyperpycnal flows directly discharge river-born sediment into the head of the river-connected canyon and originate a large turbidite fan. A drift formed by the longshore redistribution of sediment of a nearby delta introduces sediment to the head of the littoral cell–connected canyon, forming turbidity currents that flow within the canyon to reach the basin plain. However, since sediment failure and landslide processes are common in the slope part of the system, a mixed fan, consisting of both turbidites and mass-transport deposits, is formed. Disconnected canyons, with heads at the shelf edge far from the coastline, are fed by canyon head and levee-wedge failures, resulting in mass-transport or mixed fan deposition, the latter developing when the seafloor gradient or the lithology of the failed sediment allows turbidity current formation. Connected canyons form in areas with high uplift rates, where the shelf is narrow and steep and the shelf edge is at a relatively shallow depth. Disconnected canyons develop where there are lower uplift rates or subsidence, where the shelf is large and relatively gentle with a deeper shelf edge. It is deduced that the relative vertical movements of fault-bound blocks control whether canyons are connected to the coast at the present day. The role of tectonics in controlling the canyon feeding processes and the facies of submarine fan growth during highstand periods is therefore highlighted. A further view that arises from our paper is that in active margins, the slope portion of fan systems, through seafloor instability and variations in channel gradient, is a key factor in determining the final deep-sea fan facies, regardless of the distance between the coast and the canyon. The concomitant growth of turbidites, mass-transport deposits, and mixed fans demonstrates that models that predict changes in submarine fan facies on the basis of sea-level cycles do not necessarily apply to systems developed along tectonically active margins.

Description: While climate science debates are focused on the attainment of peak anthropogenic CO 2 emissions and policy tools to reduce peak temperatures, the human-energy-climate system can hold “rebound" surprises beyond this peak. Following the second industrial revolution, global per-capita CO 2 emissions ( c c ) experienced a punctuated growth of about 100% every 60 years, mainly attributable to technological development and its global spread. A model of the human-energy-climate system capable of reproducing past punctuated dynamics shows that rebounds in global CO 2 emissions emerge due to delays intrinsic to the diffusion of innovations. Such intrinsic delays in the adoption and spread of low-carbon emitting technologies, together with projected population growth, upset the warming target set by the Paris Agreement. To avoid rebounds and their negative climate effects, model calculations show that the diffusion of climate-friendly technologies must occur with lags one-order of magnitude shorter (i.e. ~ 6 years) than the characteristic time-scale of past punctuated growth in c c . Radically new strategies to globally implement technological advances at unprecedented rates are needed if current emission goals are to be achieved.