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At both regional and national levels, there is an urgent need to develop a clear picture of how climate change will alter multiple environmental properties in the ocean. Specifically, what will such cumulative alterations mean for local biological productivity, ecosystem services, climate feedbacks, and related effects ranging from biodiversity to economics? Currently, a wide range of confounding issues, such as the plethora and complexity of information in the public domain, hinders accommodating climate change into future planning and development of ocean resource management strategies. This impediment is especially true at the regional level, for example, within national Exclusive Economic Zones (EEZs), where critical management decisions are made but for which substantial uncertainty clouds climate change projections and ecosystem impact assessments. Evaluating the susceptibility of a nation’s marine resources to climate change requires knowledge of the geographic and seasonal variations in environmental properties over an EEZ and the range, spatial patterns, and uncertainty of projected climate change in those properties (Boyd et al., 2007). Furthermore, information is needed on the climate sensitivity of the biological species or strains that comprise particular marine resources (Boyd et al., 2007; Nye et al., 2009) and/or contribute to food-web interactions, and also on potential implications for human resource exploitation patterns and intensity.

Considerable attention has been directed at understanding the conse-quences and impacts of long-term anthropogenic climate change. Discrete, climati-cally extreme events such as cyclones, floods, and heatwaves can also significantly affect regional environments and species, including humans. Climate change is expected to intensify these events and thus exacerbate their effects. Climatic extremes also occur in the ocean, and recent decades have seen many high-impact marine heatwaves (MHWs)—anomalously warm water events that may last many months and extend over thousands of square kilometers. A range of biological, economic, and political impacts have been associated with the more intense MHWs, and measuring the sever-ity of these phenomena is becoming more important. Progress in understanding and public awareness will be facilitated by consistent description of these events. Here, we propose a detailed categorization scheme for MHWs that builds on a recently published classification, combining elements from schemes that describe atmospheric heatwaves and hurricanes. Category I, II, III, and IV MHWs are defined based on the degree to which temperatures exceed the local climatology and illustrated for 10 MHWs. While there is a long-term increase in the occurrence frequency of all MHW categories, the largest trend is a 24% increase in the area of the ocean where strong (Category II) MHWs occur. Use of this scheme can help explain why biological impacts associated with different MHWs can vary widely and provides a consistent way to compare events. We also propose a simple naming convention based on geography and year that would further enhance scientific and public awareness of these marine events.

Alterations to the global water cycle are of concern as Earth’s climate changes. Although policymakers are mainly interested in changes to terrestrial rainfall—where, when, and how much it’s going to rain—the largest component of the global water cycle operates over the ocean where nearly all of Earth’s free water resides. Approximately 80% of Earth’s surface freshwater fluxes occur over the ocean; its surface salinity responds to changing evaporation and precipitation patterns by displaying salty or fresh anomalies. The salinity field integrates sporadic surface fluxes over time, and after accounting for ocean circulation and mixing, salinity changes resulting from long-term alterations to surface evaporation and precipitation are evident. Thus, ocean salinity measurements can provide insights into water-cycle operation and its long-term change. Although poor observational coverage and an incomplete view of the interaction of all water-cycle components limits our understanding, climate models are beginning to provide insights that are complementing observations. This new information suggests that the global water cycle is rapidly intensifying.

The modern industrialized and urbanized world, dubbed the "Anthropocene" by Paul Crutzen (2006), includes the past 250 years of multiple human impacts. Nobel Prize winner and atmospheric chemist Crutzen states: During the past 3 centuries human population increased tenfold to 6,000 million, growing by a factor of four during the past century alone. More than half of all accessible fresh water is used by mankind. Fisheries remove more than 25% of the primary production of the oceans in the upwelling regions and 35% in the temperature continental shelf regions. 30–50% of the world's land surface has been transformed by human action. Coastal wetlands have lost 50% of the world's mangroves. More nitrogen is now fixed synthetically and applied as fertilizers in agriculture than fixed naturally in all terrestrial ecosystems. Many of the world's rivers have been dammed or diverted.

The dynamics of shallow-water coastal environments are controlled by external drivers—sea level rise, storms, and sediment and nutrient supplies—and by internal feedbacks. Interactions of biotic processes (vegetation growth, trophic dynamics) and abiotic drivers can lead to nonlinear responses to changing conditions and to the emergence of thresholds, hysteresis, and alternative stable states. We develop a conceptual framework for studying interactions between the dynamics of marshes and habitats in shallow coastal bays with unconsolidated sediments (seagrass, oyster reefs). Using examples primarily from the Virginia Coast Reserve Long Term Ecological Research site, we show that in the subtidal part of the landscape, two alternative stable states can exist—one dominated by seagrass up to a certain depth that represents a tipping point to the second, unvegetated stable state. The depth limit of the seagrass stable state is influenced by (1) the positive feedback of vegetation on reducing sediment suspension and improving the light environment for growth, (2) climate (e.g., temperature), and (3) water quality. Two stable states are also present in intertidal areas, with salt marshes lying above mean sea level and tidal flats below mean sea level. State transitions are driven by sediment availability, sea level rise, the relative strength of wind waves with respect to tidal currents, and the biotic feedback of vegetation on sediment stabilization and accretion. State-change dynamics in one system may propagate to adjacent systems, and this coupling may influence the landscape-scale response to environmental change. Seagrass meadows and oyster reefs affect adjacent marshes both positively (wave attenuation) and negatively (reduced sediment supply), and marsh-edge erosion could negatively influence the light environment for seagrass growth. Forecasting the resilience of coastal ecosystems and the landscape-scale response to environmental change in the next century requires an understanding of nonlinear dynamics, including the possibility of multiple stable states, the coupled evolution of adjacent systems, and potential early warning signs of thresholds of change.

The extent, duration, and seasonality of sea ice and glacial discharge strongly influence Antarctic marine ecosystems. Most organisms' life cycles in this region are attuned to ice seasonality. The annual retreat and melting of sea ice in the austral spring stratifies the upper ocean, triggering large phytoplankton blooms. The magnitude of the blooms is proportional to the winter extent of ice cover, which can act as a barrier to wind mixing. Antarctic krill, one of the most abundant metazoan populations on Earth, consume phytoplankton blooms dominated by large diatoms. Krill, in turn, support a large biomass of predators, including penguins, seals, and whales. Human activity has altered even these remote ecosystems. The western Antarctic Peninsula region has warmed by 7°C over the past 50 years, and sea ice duration has declined by almost 100 days since 1978, causing a decrease in phytoplankton productivity in the northern peninsula region. Besides climate change, Antarctic marine systems have been greatly altered by harvesting of the great whales and now krill. It is unclear to what extent the ecosystems we observe today differ from the pristine state.

Last year I traveled to Bangkok, Thailand, for the second Asia Pacific Adaptation Forum, which was called off at the last minute due to the city's worst flooding in the past 50 years. Bangkok, an urban center of great wealth in a relatively rich country, showed itself to be quite vulnerable to climate impacts. The flooding caused 815 deaths, massive displacements of population, and $45 billion in economic damage, including lasting damage to its automobile and electronics supply chains. Similarly, the landfall of Hurricane Katrina in New Orleans, Louisiana, in 2005 caused 1,836 deaths and $81 billion in damage. Thus, while it is certainly true that development can ameliorate some aspects of climate change vulnerability, we surely should not be fooled into thinking that development, sustainable or not, comprises the entire solution to the climate change adaptation challenge. At the very least, developing countries can find, and are finding, new development pathways that avoid some of the maladaptation that has already occurred in the developed world. Additionally, developing and developed countries alike can benefit from improving ecosystem management as an integral part of policies to help reduce vulnerability and increase resilience in the face of climate change.