Projected sea surface temperatures over the 21st century: Changes in the mean, variability and extremes for large marine ecosystem regions of Northern Oceans

Abstract

Global climate models were used to assess changes in the mean, variability and extreme sea surface temperatures (SSTs) in northern oceans with a focus on large marine ecosystems (LMEs) adjacent to North America, Europe, and the Arctic Ocean. Results were obtained from 26 models in the Community Model Intercomparison Project Phase 5 (CMIP5) archive and 30 simulations from the National Center for Atmospheric Research Large Ensemble Community Project (CESM-LENS). All of the simulations used the observed greenhouse gas concentrations for 1976–2005 and the RCP8.5 “business as usual” scenario for greenhouse gases through the remainder of the 21st century. In general, differences between models are substantially larger than among the simulations in the CESM-LENS, indicating that the SST changes are more strongly affected by model formulation than internal climate variability. The annual SST trends over 1976–2099 in the 18 LMEs examined here are all positive ranging from 0.05 to 0.5°C decade–1. SST changes by the end of the 21st century are primarily due to a positive shift in the mean with only modest changes in the variability in most LMEs, resulting in a substantial increase in warm extremes and decrease in cold extremes. The shift in the mean is so large that in many regions SSTs during 2070–2099 will always be warmer than the warmest year during 1976–2005. The SST trends are generally stronger in summer than in winter, as greenhouse gas heating is integrated over a much shallower climatological mixed layer depth in summer than in winter, which amplifies the seasonal cycle of SST over the 21st century. In the Arctic, the mean SST and its variability increases substantially during summer, when it is ice free, but not during winter when a thin layer of ice reforms and SSTs remain near the freezing point.

Thermal plasticity is independent of environmental history in an intertidal seaweed

“…The fact that laboratory treatment temperatures also did not cause any differences in photosynthetic response may suggest that treatments may not have been extreme enough to generate responses. Considering that increases in mean sea surface temperatures are predicted to be driven by increases in short‐term extremes (Alexander et al, ), understanding ecophysiological responses to punctuated, anomalous events may be more important than predicting responses to increased, constant temperatures. The goal of this study, however, was not to study stress response, but rather to determine whether increases in near‐future mean temperatures would affect E. elongata , intertidal habitat builders, and whether different portions of the environmental mosaic within the intertidal habitat would be differentially affected based on their organisms' environmental history.…”

“…Thermal tolerance lies at the core of many processes in ecology, from ecophysiological mechanisms to macroecological patterns (Bartsch, Vogt, Pehlke, & Hanelt, 2013;Helmuth, Broitman, et al, 2006;Helmuth, Mieszkowska, Moore, & Hawkins, 2006;Hutchins, 1947;Somero, 2005;Vernberg, 1962). Over the next century, ocean surface temperatures are anticipated to raise up to 0.3°C per decade (Alexander et al, 2018). Temperature changes throughout this range are likely to engender changes in community structure and functioning (Schindler, 1990), including shifts in population dynamics and species abundances in temperate marine communities (Hale, Calosi, McNeill, Mieszkowska, & Widdicombe, 2011;Queirós et al, 2015).…”

It’s about time: A synthesis of changing phenology in the Gulf of Maine ecosystem

“…Similar metrics—the spring and fall thermal transition times, each defined as the day of year when a seasonally specific temperature threshold is surpassed for ≥8 consecutive days—have shifted more rapidly in the past decade, with the spring transition advancing two weeks since 2006, and fall transition occurring progressively later with the greatest changes since 2005 (Friedland et al, ; Thomas et al, ; seasonal updates available at Northeast Fisheries Science Center (NEFSC): http://www.nefsc.noaa.gov/ecosys/current-conditions). Analysis of 26 climate models in the CMIP5 ensemble using the “business as usual” (RCP 8.5) scenario shows warming trends of 0.4°C per decade until the end of this century, but the ensemble of models does not project this warming to further shift the annual cycle in the region (Alexander et al, ). In addition, changes in basin‐scale indices of natural climate variation, such as the NAO, Atlantic Multidecadal Oscillation (AMO), and Gulf Stream position, are likely amplifying regional warming and precipitation cycles, and have the potential to further affect seasonal shifts in the environment over the coming decades (Saba et al, ; Thomas et al, ).…”

“…Research on fine‐scale spatiotemporal oceanographic processes for the GoM has been limited due to the lack of a regional downscaled model. Future projections based on the ensemble of CMIP5 models show strong warming in all months, but strongest in summer (Alexander et al, ). Higher resolution models better resolve patterns in the regional Atlantic circulation and water mass distribution, and project much stronger (almost twice as fast) warming than the coarser resolution models (Saba et al, ).…”

Investigating the association between late spring Gulf of Mexico sea surface temperatures and U.S. Gulf Coast precipitation extremes with focus on Hurricane Harvey

“…Alexander et al () study SSTs in large marine ecosystems throughout the northern hemisphere and use climate model output to predict changes in SST. In the GoM, Alexander et al () indicate that the increase in SST could be in the range of 0.2 °C–0.4 °C per decade over the years 1976–2099.…”