Abstract: As the permafrost region warms, its large organic carbon pool will be increasingly vulnerable to decomposition, combustion, and hydrologic export. Models predict that some portion of this release will be offset by increased production of Arctic and boreal biomass; however, the lack of robust estimates of net carbon balance increases the risk of further overshooting international emissions targets. Precise empirical or model-based assessments of the critical factors driving carbon balance are unlikely in the near future, so to address this gap, we present estimates from 98 permafrost-region experts of the response of biomass, wildfire, and hydrologic carbon flux to climate change. Results suggest that contrary to model projections, total permafrost-region biomass could decrease due to water stress and disturbance, factors that are not adequately incorporated in current models. Assessments indicate that end-of-the-century organic carbon release from Arctic rivers and collapsing coastlines could increase by 75% while carbon loss via burning could increase four-fold. Experts identified water balance, shifts in vegetation community, and permafrost degradation as the key sources of uncertainty in predicting future system response. In combination with previous findings, results suggest the permafrost region will become a carbon source to the atmosphere by 2100 regardless of warming scenario but that 65%-85% of permafrost carbon release can still be avoided if human emissions are actively reduced.

Abstract: There has been considerable interest in a recently recognized and important sink in the global carbon pool, commonly referred to as “blue carbon”. The major goal of this study was to determine the historical reconstruction of mangrove expansion (Avicennia germinans) into salt marshes (Spartina alterniflora) and its effects on carbon sequestration and soil chemistry in wetland soils of the northwestern Gulf of Mexico. We used bulk stable isotopic, chemical biomarker analyses, and aerial imagery analysis to identify changes in OC wetland sources, and radiotracers (137Cs and 210Pb) for chronology. Soil cores were collected at two sites at Port Aransas, Texas (USA), Harbor Island and Mud Island. Stable isotopic values of δ13C and δ15N of all soil samples ranged from −26.8 to −15.6‰ and 1.8–10.4‰ and showed a significant trend of increasing depletion for each isotope from bottom to surface soils. The most depleted δ13C values were in surface soils at the Mud Island (Mangrove 2) location. Carbon sequestration rates were greater in mangroves and for the Mud Island Mangrove 1 and the Marsh 1 sites ranged from 253 to 270 and 101–125 g C m−2 yr−1, respectively. Lignin storage rates were also greater for mangrove sites and for the Mud Island Mangrove 1 and the Marsh 1 ranged from 19.5 to 20.1 and 16.5 to 12.8 g lignin m−2 yr−1, respectively. Τhe Λ8 and Λ6 values for all cores ranged from 0.5 to 21.5 and 0.4 to 16.5, respectively, and showed a significant increase from bottom to surface sediments. If regional changes in the Gulf of Mexico are to persist and much of the marsh vegetation was to be replaced by mangroves, there could be significant increases on the overall storage and sequestration of carbon in the coastal zone.

Abstract: Sea level rise is one of the climate change effects most amenable to adaptation planning as the impacts are familiar and the nature of the phenomenon is unambiguous. Yet, significant uncertainties remain. Using a normative framework of adaptive management and natural hazards planning, we examine how coastal communities in Florida are planning in the face of accelerating sea level rise through analysis of planning documents and interviews with planners. We clarify that communities are taking a low-regrets incremental approach with increasingly progressive measures motivated by confidence in planning intelligence and direct experience with impacts attributable to sea level rise.

Abstract: Here we summarize the motivation and issues surrounding the responses of ice sheets and sea level to past climate warming as part of the PALeo constraints on SEA level rise (PALSEA) working group. Papers in this special issue of Quaternary Science Reviews focus on the timescale of glaciations during the late Pliocene, the magnitude of ice-sheet fluctuations and volume leading up to and during the last glacial maximum, the timing and persistence of ice-sheet impacts on deglacial and future relative sea-level change, and relative sea-level change during peak interglacial climate. A more dynamic cryosphere is noted under both late Pliocene and last glacial cycle climate conditions, while relative sea-level changes during the last deglaciation appear to correspond closely with individual ice-sheet deglaciation. Lastly, relative sea-level change during peak interglacial conditions may have fluctuated by as much as a meter, although the sources of such variability (Greenland, Antarctica or elsewhere) remain elusive. (C) 2019 Elsevier Ltd. All rights reserved.

Abstract: Understanding public perceptions of climate change risks is a prerequisite for effective climate communication and adaptation. Many studies of climate risk perceptions have either analyzed a general operationalization of climate change risk or employed a case-study approach of specific adaptive processes. This study takes a different approach, examining attitudes toward 17 specific, climate-related coastal risks and cognitive, affective, and risk-specific predictors of risk perception. A survey of 558 undergraduates revealed that risks to the physical environment were a greater concern than economic or biological risks. Perceptions of greater physical environment risks were significantly associated with having more pro-environmental attitudes, being female, and being more Democratic-leaning. Perceptions of greater economic risks were significantly associated with having more negative environmental attitudes, being female, and being more Republican-leaning. Perceptions of greater biological risks were significantly associated with more positive environmental attitudes. The findings suggest that focusing on physical environment risks maybe more salient to this audience than communications about general climate change adaptation. The results demonstrate that climate change beliefs and risk perceptions are multifactorial and complex and are shaped by individuals' attitudes and basic beliefs. Climate risk communications need to apply this knowledge to better target cognitive and affective processes of specific audiences, rather than providing simple characterizations of risks.

Abstract: The IPCC 2013 Wetlands Supplement provided new guidance for countries on inclusion of wetlands in their National GHG Inventories. The United States has responded by including managed coastal wetlands for the first time in its 2017 GHG Inventory report along with an updated time series in the most recent 2018 submission and plans to update the time series on an annual basis as part of its yearly submission to the United Nations Framework Convention on Climate Change (UNFCCC). The United States followed IPCC Good Practice Guidance when reporting sources and sinks associated with managed coastal wetlands. Here we show that intact vegetated coastal wetlands are a net sink for GHGs. Despite robust regulation that has protected substantial stocks of carbon, the United States continues to lose coastal wetlands to development and the largest loss of wetlands to open water occurs around the Mississippi Delta due mostly to upstream changes in hydrology and sediment delivery, and oil and gas extraction. These processes create GHG emissions. By applying comprehensive Inventory reporting, scientists in the United States have identified opportunities for reducing GHG emissions through restoration of coastal wetlands that also provide many important societal co-benefits.

Abstract: Saltwater intrusion is a major hazard to coastal communities as it causes degradation of fresh water resources. The impact of rising sea level on the saltwater intrusion into coastal aquifers has been studied for decades, but how human activities affect the extent of saltwater intrusion is poorly understood. Human activities are known to influence groundwater availability indirectly by affecting precipitation patterns and directly by extracting groundwater and reducing recharge. In this paper the authors investigated the integrated impacts of human activities and rising sea level on aquifer recharge in Quintana Roo, Mexico, by incorporating anthropogenic impacts on groundwater recharge into an analytical saltwater intrusion model. The impact of human activities on groundwater extraction was firstly calculated; then, the resulting groundwater recharge was used in a Ghyben�Herzberg analytical model to determine the inland distance of saltwater intrusion. The analytical model tested six scenarios stemming from different combinations of human development patterns, hydrological settings, hydraulic conditions and rising sea level to obtain the range of possible inland movement of saltwater intrusion. Our results indicate that the groundwater recharge will decrease to 32.6 mm year−1 if human activities increase by 50 % more. With 1-m sea level rise, inland saltwater intrusion distance is estimated to be up to 150 and 1 km under head-controlled and flux-controlled scenarios, respectively. A sensitivity analysis of the model reveals that the large hydraulic conductivity of the Quintana Roo aquifer (0.26�68.8 m s−1) is the most important factor in determining saltwater intrusion distance. Therefore, in this aquifer, the response to human activities is greatly exceeded by natural hydrogeological conditions.

Abstract: Accelerated sea level rise was observed along the U.S. eastern seaboard south of Cape Hatteras during 2010-2015 with rates 5 times larger than the global average for the same time period. Simultaneously, sea levels decreased rapidly north of Cape Hatteras. In this study, we show that accelerated sea level rise recorded between Key West and Cape Hatteras was predominantly caused by a similar to 1 degrees C (0.2 degrees C/year) warming of the Florida Current during 2010-2015 that was linked to large-scale changes in the Atlantic Warm Pool. We also show that sea level decline north of Cape Hatteras was caused by an increase in atmospheric pressure combined with shifting wind patterns, with a small contribution from cooling of the water column over the continental shelf. Results presented here emphasize that planning and adaptation efforts may benefit from a more thorough assessment of sea level changes induced by regional processes. Plain Language Summary During 2010-2015, sea level rose rapidly along the U.S. East Coast between Key West and Cape Hatteras, causing extensive flooding to large urban areas such as Miami. Simultaneously, sea level was observed to decline north of Cape Hatteras at an accelerated rate. Here we investigate what caused the rapid sea level changes recorded during 2010-2015 at the U.S. East Coast. In this study, we show that sea level rise recorded between Key West and Cape Hatteras was mostly caused by the warming of waters carried by the Florida Current during 2010-2015, which can raise coastal sea level through thermal expansion of the water column. We also show that sea level decline north of Cape Hatteras was mostly caused by changes in atmospheric conditions, such as by an increase in atmospheric pressure, which affect sea level due to variations in the overall weight of the atmosphere over a certain location, and by changing wind conditions that can pile up, or push ocean water away from the coast.