Description: Young people's burden: requirement of negative CO 2 emissions James Hansen, Makiko Sato, Pushker Kharecha, Karina von Schuckmann, David J. Beerling, Junji Cao, Shaun Marcott, Valerie Masson-Delmotte, Michael J. Prather, Eelco J. Rohling, Jeremy Shakun, Pete Smith, Andrew Lacis, Gary Russell, and Reto Ruedy Earth Syst. Dynam., 8, 577-616, https://doi.org/10.5194/esd-8-577-2017, 2017 Global temperature now exceeds +1.25 °C relative to 1880–1920, similar to warmth of the Eemian period. Keeping warming less than 1.5 °C or CO 2 below 350 ppm now requires extraction of CO 2 from the air. If rapid phaseout of fossil fuel emissions begins soon, most extraction can be via improved agricultural and forestry practices. In contrast, continued high emissions places a burden on young people of massive technological CO 2 extraction with large risks, high costs and uncertain feasibility.

Description: Atmospheric Torques and Earth's Rotation: What Drove the Millisecond-Level Length-of-Day Response to the 2015–16 El Niño? Sébastien B. Lambert, Steven L. Marcus, and Olivier de Viron Earth Syst. Dynam. Discuss., https//doi.org/10.5194/esd-2017-52,2017 Manuscript under review for ESD (discussion: open, 0 comments) We explain how the extreme 2015–16 El Niño event lengthened the day by 0.8 ms. The 2015–16 event was a Niño of different type compared to previous extreme events, so that we expected different mechanisms of coupling with the solid Earth. We showed that the atmospheric torque on the American topography, usually acting alone during classical Niños, was, in 2015–16, augmented by a friction torque over the Pacific ocean and inherent to the different nature of this particular event.

Description: Equatorial Atlantic interannual variability and its relation to dynamic and thermodynamic processes Julien Jouanno, Olga Hernandez, Emilia Sanchez-Gomez, and Bruno Deremble Earth Syst. Dynam. Discuss., https//doi.org/10.5194/esd-2017-58,2017 Manuscript under review for ESD (discussion: open, 0 comments) The contributions of the dynamic and thermodynamic forcing to the interannual variability of the Equatorial Atlantic sea surface temperature are investigated using a set of interannual regional simulations of the Tropical Atlantic Ocean. The ocean model is forced with an interactive atmospheric boundary layer, avoiding damping toward prescribed air-temperature as is usually the case in forced ocean models. The model successfully reproduces a large fraction ( R 2  = 0.55) of the observed interannual variability in the Equatorial Atlantic. In agreement with leading theories, our results confirm that the interannual variations of the dynamical forcing largely contributes to this variability. We show that mean and seasonal upper ocean temperature biases, commonly found in fully coupled models, strongly favor an unrealistic thermodynamic control of the Equatorial Atlantic interannual variability.

Description: A wind proxy based on migrating dunes at the Baltic coast: statistical analysis of the link between wind conditions and sand movement Svenja E. Bierstedt, Birgit Hünicke, Eduardo Zorita, and Juliane Ludwig Earth Syst. Dynam., 8, 639-652, https://doi.org/10.5194/esd-8-639-2017, 2017 We statistically analyse the relationship between the structure of migrating dunes in the southern Baltic and the driving wind conditions over the past 26 years, with the long-term aim of using migrating dunes as a proxy for past wind conditions at an interannual resolution.

Description: Drought identification in the eastern Baltic region using NDVI Egidijus Rimkus, Edvinas Stonevicius, Justinas Kilpys, Viktorija Maciulyte, and Donatas Valiukas Earth Syst. Dynam., 8, 627-637, https://doi.org/10.5194/esd-8-627-2017, 2017 Drought effect on vegetation in the eastern part of the Baltic Sea region was determined using satellite data. The impact of precipitation deficit on vegetation on arable land and in broadleaved and coniferous forests was analysed. The precipitation deficit in the first part of the growing season only has a significant impact on the vegetation on arable land, while this impact becomes more evident in all types of vegetation in the second half of the season.

Description: Flexible parameter-sparse global temperature time profiles that stabilise at 1.5 and 2.0  °C Chris Huntingford, Hui Yang, Anna Harper, Peter M. Cox, Nicola Gedney, Eleanor J. Burke, Jason A. Lowe, Garry Hayman, William J. Collins, Stephen M. Smith, and Edward Comyn-Platt Earth Syst. Dynam., 8, 617-626, https://doi.org/10.5194/esd-8-617-2017, 2017 Recent UNFCCC climate meetings have placed much emphasis on constraining global warming to remain below 2 °C. The 2015 Paris meeting went further and gave an aspiration to fulfil a 1.5 °C threshold. We provide a flexible set of algebraic global temperature profiles that stabilise to either target. This will potentially allow the climate research community to estimate local climatic implications for these temperature profiles, along with emissions trajectories to fulfil them.

Description: Modelling feedbacks between human and natural processes in the land system Derek T. Robinson, Alan Di Vittorio, Peter Alexander, Almut Arneth, C. Michael Barton, Daniel G. Brown, Albert Kettner, Carsten Lemmen, Brian C. O'Neill, Marco Janssen, Thomas A. M. Pugh, Sam S. Rabin, Mark Rounsevell, James P. Syvitski, Isaac Ullah, and Peter H. Verburg Earth Syst. Dynam. Discuss., https//doi.org/10.5194/esd-2017-68,2017 Manuscript under review for ESD (discussion: open, 0 comments) The unprecedented use of Earth's resources by humans, in combination with the increasing natural variability in natural processes over the past century, is affecting evolution of the Earth system. To better understand natural processes and their potential future trajectories requires improved integration with and quantification of human processes. Similarly, to mitigate risk and facilitate socio-economic development requires a better understanding of how the natural system (e.g., climate variability and change, extreme weather events, and processes affecting soil fertility) affects human processes. To capture and formalize our understanding of the interactions and feedback between human and natural systems a variety of modelling approaches are used. While integrated assessment models are widely recognized as supporting this goal and integrating representations of the human and natural system for global applications, an increasing diversity of models and corresponding research have focused on coupling models specializing in specific human (e.g., decision-making) or natural (e.g., erosion) processes at multiple scales. Domain experts develop these specialized models with a greater degree of detail, accuracy, and transparency, with many adopting open-science norms that use new technology for model sharing, coupling, and high performance computing. We highlight examples of four different approaches used to couple representations of the human and natural system, which vary in the processes represented and in the scale of their application. The examples illustrate how groups of researchers have attempted to overcome the lack of suitable frameworks for coupling human and natural systems to answer questions specific to feedbacks between human and natural systems. We draw from these examples broader lessons about system and model coupling and discuss the challenges associated with maintaining consistency across models and representing feedback between human and natural systems in coupled models.

Description: River logjams cause frequent large-scale forest die-off events in southwestern Amazonia Umberto Lombardo Earth Syst. Dynam., 8, 565-575, https://doi.org/10.5194/esd-8-565-2017, 2017 In lowland Bolivia, satellite images show rivers collapsing and the replacement of forest with savannah. This was first described in 1996 as the result of logjams (river dams created by fallen trees). I have investigated how the logjams form and affect the forest through remote sensing and fieldwork. Logjams occur nearly every year and propagate upriver until the river changes course. This region offers a unique opportunity to study how frequent forest die-off events affect biodiversity.

Description: Emission metrics for quantifying regional climate impacts of aviation Marianne T. Lund, Borgar Aamaas, Terje Berntsen, Lisa Bock, Ulrike Burkhardt, Jan S. Fuglestvedt, and Keith P. Shine Earth Syst. Dynam., 8, 547-563, https://doi.org/10.5194/esd-8-547-2017, 2017 This study examines the impacts of emissions from aviation in six source regions on global and regional temperatures. We consider the NO x -induced impacts on ozone and methane, aerosols and contrail-cirrus formation and calculate the global and regional emission metrics global warming potential (GWP), global temperature change potential (GTP) and absolute regional temperature change potential (ARTP). The GWPs and GTPs vary by a factor of 2–4 between source regions. We find the highest aviation aerosol metric values for South Asian emissions, while contrail-cirrus metrics are higher for Europe and North America, where contrail formation is prevalent, and South America plus Africa, where the optical depth is large once contrails form. The ARTP illustrate important differences in the latitudinal patterns of radiative forcing (RF) and temperature response: the temperature response in a given latitude band can be considerably stronger than suggested by the RF in that band, also emphasizing the importance of large-scale circulation impacts. To place our metrics in context, we quantify temperature change in four broad latitude bands following 1 year of emissions from present-day aviation, including CO 2 . Aviation over North America and Europe causes the largest net warming impact in all latitude bands, reflecting the higher air traffic activity in these regions. Contrail cirrus gives the largest warming contribution in the short term, but remain important at about 15 % of the CO 2 impact in several regions even after 100 years. Our results also illustrate both the short- and long-term impacts of CO 2 : while CO 2 becomes dominant on longer timescales, it also gives a notable warming contribution already 20 years after the emission. Our emission metrics can be further used to estimate regional temperature change under alternative aviation emission scenarios. A first evaluation of the ARTP in the context of aviation suggests that further work to account for vertical sensitivities in the relationship between RF and temperature response would be valuable for further use of the concept.

Description: Projected changes in crop yield mean and variability over West Africa in a world 1.5 K warmer than the pre-industrial Ben Parkes, Dimitri Defrance, Benjamin Sultan, Philippe Ciais, and Xuhui Wang Earth Syst. Dynam. Discuss., https//doi.org/10.5194/esd-2017-66,2017 Manuscript under review for ESD (discussion: open, 0 comments) We present an analysis of three crops in West Africa and their response to short term climate change in a world where temperatures are 1.5 K above the preindustrial levels. We show that the number of crop failures for all crops is due to increase in the future climate. We further show the difference in yield change across several West African countries and show that the yields are not expected to increase fast enough to prevent food shortages.