Drivers of Climate Change and Variability on the Northeast Shelf
Deriving naturally and from human activities on a global scale, there are various components (Figure 1) that contribute to climate change and variability in the U.S. Northeast Shelf Large Marine Ecosystem (NES LME). These components can either warm or cool the climate depending on the source and direction of the forcing.
For example, changes in Earth's orbit that take place over tens of thousands of years lead to glacial and interglacial periods.
There are also natural swings in the Earth's climate that can be observed within local regions such as the U.S. NES LME. In the North Atlantic Ocean, large-scale climate oscillations can be associated with the North Atlantic Oscillation (NAO) and the Atlantic Multidecadal Oscillation (AMO) (Figure 4a). The position and strength of the Gulf Stream are also linked to the climate and oceanography of the U.S. NES LME (Figure 4b).
Other North Atlantic indices such as the Atlantic Meridional Overturning Circulation (AMOC) can also be associated with local impacts on the oceanography of the U.S. NES LME.
The major component of human activity that contributes to climate change is historical and continued emission of long-lived greenhouse gases. These gases comprise of carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O). Since the beginning of the post-industrial era in the year 1750, atmospheric concentrations of these gases have substantially increased due to human activities (Figure 5).
These long-lived greenhouse gases accumulate in the atmosphere over time and act as a blanket by trapping outgoing long-wave radiation (infrared) and thus can warm or cool Earth’s climate depending on their concentration. Because these gases have been continually accumulating in the atmosphere, the global mean surface temperature of the Earth averaged over land and water has risen almost 1°C and global sea level has risen by more than 0.15 meters (Figure 6). Globally, land temperature has warmed at a rate double that of the ocean. Over the past 10 years, sea surface temperature (SST) in the U.S. NES LME has warmed faster than any other NMFS management region (Figure 7). The year 2012 was observed to be the warmest on record for the NES with an annual mean SST of over 14°C (Figure 8; Movie 1). Although the unprecedented warm year of 2012 has not been attributed to either climate change or climate variability, the observed marine conditions in the NES can provide a context for the future mean state of this region.
The increase in atmospheric CO2 has had the largest contribution to the global warming. The primary human activities that are responsible for the rise in CO2 are fossil fuel use for transportation, building heating and cooling, cement manufacturing, and deforestation. Atmospheric methane (CH4) has increased due to agriculture, natural gas use, and landfills. Nitrous oxide has increased due to fertilizer and fossil fuel use.