Figure 9

About every seven years, the Intergovernmental Panel on Climate Change (IPCC) assesses climate change research. One of the main responsibilities of the IPCC is to assess global climate and Earth system model projections of climate change both globally and regionally. These models are very complex because they couple land, atmosphere, ice, and ocean dynamics to simulate Earth's climate.

In the case of Earth system models, biological components such as land vegetation and marine phytoplankton are simulated to understand potential feedbacks between physical changes and photosynthetic organisms (Figure 9).

Simulating these biological components is critical to assess the potential impacts of climate change on living marine resources and fisheries.

Figure 10

Figure 11

Figure 12

The IPCC’s fifth assessment of projected global and regional ocean temperature change is based on global climate models that have relatively coarse (~100-km) ocean and atmosphere resolutions. These models are sometimes too coarse to resolve regional dynamics that might affect the uncertainty of climate change projections at regional to local scales.

In the Northwest Atlantic, particularly within the U.S. Northeast Continental Shelf, the global climate models assessed by the IPCC have a warm bias in sea surface temperature due to the Gulf Stream separating from the U.S. coast too far to the north of Cape Hatteras, North Carolina. Known as the “Gulf Stream separation problem,” this bias continues to exist in many global climate models that have an ocean component that is too coarse (~100-km) in horizontal resolution. Moreover, the coarse climate models cannot resolve the fine-scale bathymetry of the Shelf such as deep canyons, channels, and banks (i.e. Georges Bank). These topographic features impact the regional circulation of the Northwest Atlantic Shelf.

Saba et al. (2016) compared simulations and an atmospheric CO2 doubling response from four NOAA Geophysical Fluid Dynamics Laboratory (GFDL) global climate models of varying ocean and atmosphere resolution. The study found that the highest resolution climate model CM2.6 (~10-km ocean, ~50-km atmosphere) resolves Northwest Atlantic Shelf circulation and water mass distribution most accurately (Figure 10). The CO2 doubling response from this model shows bottom ocean temperature in the Northwest Atlantic Shelf, particularly in the Gulf of Maine, warms at a rate nearly two to three times as fast as the coarser models (Figure 11). This enhanced warming is accompanied by an increase in salinity due to a change in water mass distribution that is related to a retreat of the Labrador Current and a northerly shift of the Gulf Stream (Figure 12; Movie 2 and Movie 3). Both observations and the climate model demonstrate a robust relationship between a weakening Atlantic Meridional Overturning Circulation (AMOC) and an increase in the proportion of Warm-Temperate Slope Water entering the Northwest Atlantic Shelf. Therefore, prior climate change projections for the Northwest Atlantic Shelf may be far too conservative.