Ocean impact on decadal Atlantic climate variability revealed by sea-level observations

Decadal variability is a notable feature of the Atlantic Ocean and the climate of the regions it influences. Prominently, this is manifested in the Atlantic Multidecadal Oscillation (AMO) in sea surface temperatures. Positive (negative) phases of the AMO coincide with warmer (colder) North Atlantic sea surface temperatures. The AMO is linked with decadal climate fluctuations, such as Indian and Sahel rainfall1, European summer precipitation2, Atlantic hurricanes3 and variations in global temperatures4. It is widely believed that ocean circulation drives the phase changes of the AMO by controlling ocean heat content5. However, there are no direct observations of ocean circulation of sufficient length to support this, leading to questions about whether the AMO is controlled from another source6. Here we provide observational evidence of the widely hypothesized link between ocean circulation and the AMO. We take a new approach, using sea level along the east coast of the United States to estimate ocean circulation on decadal timescales. We show that ocean circulation responds to the first mode of Atlantic atmospheric forcing, the North Atlantic Oscillation, through circulation changes between the subtropical and subpolar gyres—the intergyre region7. These circulation changes affect the decadal evolution of North Atlantic heat content and, consequently, the phases of the AMO. The Atlantic overturning circulation is declining8 and the AMO is moving to a negative phase. This may offer a brief respite from the persistent rise of global temperatures4, but in the coupled system we describe, there are compensating effects. In this case, the negative AMO is associated with a continued acceleration of sea-level rise along the northeast coast of the United States9, 10

Salinity and Simulated Herbivory Influence Spartina alterniflora Traits and Defense Strategy

Sea level rise is expected to push saline waters into previously fresher regions of estuaries, and higher salinities may expose oligohaline marshes to invertebrate herbivores typically constrained by salinity. The smooth cordgrass, Spartina alterniflora (syn. Sporobolus alterniflorus), can defend itself against herbivores in polyhaline marshes, however it is not known if S. alterniflora’s defense varies along the mesohaline to oligohaline marsh gradient in estuaries. I found that S. alterniflora from a mesohaline marsh is better defended than plants from an oligohaline marsh, supporting the optimal defense theory. Higher salinity treatments lowered carbon content, C:N, and new stem biomass production, traits associated with a tolerance strategy, suggesting that salinity may mediate the defense response of S. alterniflora. Further, simulated herbivory increased the nitrogen content and decreased C:N of S. alterniflora. This indicates that grazing may increase S. alterniflora susceptibility to future herbivory via improved forage quality. Simulated herbivory also decreased both belowground and new stem biomass production, highlighting a potential pathway in which herbivory can indirectly facilitate marsh loss, as S. alterniflora biomass is critical for vertical accretion and marsh stability under future sea level rise scenarios

Variations in the Difference between Mean Sea Level measured either side of Cape Hatteras and Their Relation to the North Atlantic Oscillation

We consider the extent to which the difference in mean sea level (MSL) measured on the North American Atlantic coast either side of Cape Hatteras varies as a consequence of dynamical changes in the ocean caused by fluctuations in the North Atlantic Oscillation (NAO). From analysis of tide gauge data, we know that changes in MSL-difference and NAO index are correlated on decadal to century timescales enabling a scale factor of MSL-difference change per unit change in NAO index to be estimated. Changes in trend in the NAO index have been small during the past few centuries (when measured using windows of order 60–120 years). Therefore, if the same scale factor applies through this period of time, the corresponding changes in trend in MSL-difference for the past few centuries should also have been small. It is suggested thereby that the sea level records for recent centuries obtained from salt marshes (adjusted for long-term vertical land movements) should have essentially the same NAO-driven trends south and north of Cape Hatteras, only differing due to contributions from other processes such as changes in the Meridional Overturning Circulation or ‘geophysical fingerprints’. The salt marsh data evidently support this interpretation within their uncertainties for the past few centuries, and perhaps even for the past millennium. Recommendations are made on how greater insight might be obtained by acquiring more measurements and by improved modelling of the sea level response to wind along the shelf

Robustness and uncertainties in global multivariate wind-wave climate projections

Understanding climate-driven impacts on the multivariate global wind-wave climate is paramount to effective offshore/coastal climate adaptation planning. However, the use of single-method ensembles and variations arising from different methodologies has resulted in unquantified uncertainty amongst existing global wave climate projections. Here, assessing the first coherent, community-driven, multi-method ensemble of global wave climate projections, we demonstrate widespread ocean regions with robust changes in annual mean significant wave height and mean wave period of 5–15% and shifts in mean wave direction of 5–15°, under a high-emission scenario. Approximately 50% of the world’s coastline is at risk from wave climate change, with ~40% revealing robust changes in at least two variables. Furthermore, we find that uncertainty in current projections is dominated by climate model-driven uncertainty, and that single-method modelling studies are unable to capture up to ~50% of the total associated uncertainty

Natural disasters and deterrence of economic innovation: a case of temporary job losses by Hurricane Sandy

Quantifying many natural disasters economically is a global concern. Even in the U.S., economic damages stemming from natural disasters are experienced annually. Unexpected natural disasters result in various economic and business management disruptions. Especially, complex inter-industrial and inter-regional connections in established economies may experience much larger impacts by a disaster, and hence, the economic and business losses need to count not only the direct, actual lost value of business during the disrupted period, but also the indirect, latent lost value that would not have occurred. In the U.S., severe economic damages generated by the two hurricanes that hit the Gulf of Mexico in August 2005 were recorded in the history; however, this hurricane-generated economic loss is still being experienced. Hurricane Sandy occurred in 2012 is recorded as one of the largest storms ever to mash American territory. The hurricane-caused disruptions of metro built environments and natural environmental systems demonstrated how fragile New York City (NYC) and Long Island areas are from hurricanes and storm surges. This promptly generated a new discussion of building coastal barriers surrounding the shorelines of the areas, expecting to minimize the destructive risk from a similar event in the future. An issue that was not seriously explored in this discussion is how to account for economic damages more extensively and accurately. Majority studies of estimating economic damages rely on governmental reports that mostly focus on the magnitude of building losses directly damaged or on speculations about future impacts on the area already damaged. However, when considering inter-industrial and inter-regional economic connections which are becoming more complicated, accounting for the indirectly connected ripple impacts is important in the market economies because recovery from economic damages requires an understanding of resilient paths of the lost business production. This study provides a procedure to estimate a type of interconnected economic damages based on the National Interstate Economic Model (NIEMO) and the temporarily lost jobs using Census data during the first 4 days caused by Hurricane Sandy. By tracing Sandy's moving path from Florida to New Hampshire, it was found that Sandy had brought another tragedy mainly to the NYC and Long Island areas, reaching $2.8 billion in 4 days with 99$10 billion losses according to the NIEMO analysis. Technological innovation that may support various mitigation and prevention policies would reduce the economic losses, expediting recovery to the normal status of U.S. economy