Cheney explained how
greenhouse gases, especially carbon dioxide, act as an insulating layer that
traps heat that would otherwise radiate away from earth. Levels of CO₂ have
increased from 280 parts per million (ppm) to more than 390 ppm today. (Here is
a chart showing annual average CO₂ since the 1950s. ftp://ftp.cmdl.noaa.gov/ccg/co2/trends/co2_annmean_mlo.txt) He
described the El Niño phenomenon, in which large, warmed areas of the Pacific
change the direction of the trade winds and dramatically alter weather
patterns. He cited a website, www.globalchange.gov, which has a
wealth of information about research and collaboration of 13 federal agencies
working on global warming. Here is just one summary page from that project. http://www.nasa.gov/content/nasa-supercomputer-generates-closer-look-at-future-climate-conditions-in-us/#.Uml6q3B4zKe
His talk focused on three
areas of impacts that are expected to affect Ipswich: terrestrial plant
communities; shellfish; and impacts along the shoreline.
- Impacts on plant communities: Models predict
that within just 20 years, southern forest communities will extend into
New England and the northern coniferous forests will disappear as a
dominant ecosystem in New England. Non-native and invasive plants will proliferate. Cheney cited a study comparing the plant community that Thoreau documented in Concord, MA (1852-58) to what was found there in recent years. Over ~150 years, average temperatures increased by 4.3° F; 27% of the species that Thoreau documented no longer grow there and 36% are now rare and may become locally extinct. Blooming is a week earlier, potentially impacting pollinators and other ecological relationships. Lilies, orchids, buttercups, violets, roses, dogwoods and mints are adversely affected, while “weedier” species such as mustards and invasives are more common. Here is an article on this topic by Arnold Arboretum: http://arnoldia.arboretum.harvard.edu/pdf/articles/1912.pdf
- Impacts on shellfish: The increase in carbon dioxide is not limited to the atmosphere. CO₂ also dissolves in ocean waters, causing the oceans to become more acidic. Recent research found that this impacts the ability of shellfish to form shells, but that the effects vary by species. Unfortunately for Ipswich, the soft-shelled clam is one of the shellfish that is most adversely impacted (along with oysters and bay scallops). There is a decrease in calcification of the shells, which makes them less dense and more buoyant. Here is a recent report on climate change impacts on the oceans. http://www.globalchange.gov/whats-new/agency-news/968-new-report-summarizes-climate-change-impacts-on-us-oceans-marine-resources
- Impacts on the shoreline and salt marsh: In the Boston area, sea level is rising at an average of 2.63 mm/year (about 1/10 inch). Over the coming decades, this will result in higher high tides and storm surges that will affect properties that used to be “safe.” He noted that six houses on Plum Island were demolished by the last nor’easter. “Superstorms” like Sandy are expected to become more common, especially affecting coastal areas.
- Cheney also discussed how sea level rise and the vertical growth of the salt marsh has been in balance for thousands of years, but now, sea levels are rising faster than salt marsh accretion. The dominant salt marsh grass, Spartina patens, cannot withstand the increased submergence in saltwater. Spartina alterniflora, the tougher salt marsh cordgrass that lines our tidal creeks, may take over some of the habitat, although there is also the possibility that invasives like Phragmites australis will dominate.
- There was also some discussion of the importance of our rivers, and the fact that all the rivers feeding Plum Island Sound – the Ipswich, Parker and Rowley – are highly depleted by excessive water withdrawals. This reduces their ability to transport the sediments that build the marsh. Though not part of his talk, the predicted impacts of global warming on rivers and public water supplies are dramatic, as well.
