Climate of the Gulf of Maine WITH potential changes and impacts
Gregory A. Zielinski, Maine State Climatologist (www.umaine.edu/maineclimate) and Research Associate Professor, Institute of Quaternary and Climate Studies, University of Maine, Orono, ME 04469, gzielinski@maine.edu
Major Considerations
¨ Changing climatic conditions will not necessarily produce the same type or magnitude of change in the Gulf of Maine region as may be occurring or will occur globally.
¨ The key: understanding the climate system of the Gulf of Maine through evaluation of past conditions and acquiring and monitoring conditions within the marine environment. Although global climatic change is important, understanding how that change is manifested at the regional level will be the key to postulating how the marine environment will be impacted.
¨ Temperature changes in Maine since 1895 (beginning of instrumental period) have been quite variable. Note that the decrease in Maine’s temperature over the last 107 years as presented by the New England Regional Assessment (NERA) is highly generalized. Temperature changes have varied spatially across the state during that time period with warming along the coast, but cooling in northern Maine.
¨ Precipitation generally decreases until the 1960s, but has slightly increased over the last 40 years. As was the case for temperature, the decreasing trend in Maine’s precipitation over the last 107 years from the NERA report is highly generalized.
¨ The number of extreme or record-setting events have occurred quite frequently over the last few decades, but it is important to realize that these events are based only on the ~100 years of the instrumental record, an extremely short period of time to evaluate the range of conditions in the Gulf of Maine climate system.
¨ Models used to predict climatic change at the regional level may not perform as well as those that are used to evaluate global climate. In particular, specific types of events that can have a major impact on conditions in the Gulf of Maine region are not reproduced very well with these models.
¨ Two different climate models were used to evaluate changing climatic conditions in New England until 2030 and then to 2100 given a yearly 1% increase in greenhouse gases. Both models showed increases in both annual and seasonal maximum and minimum temperature, and precipitation. However, the models varied by almost a factor of 2 for these parameters especially for the 2100 time period. The models also differed in the characteristics of the precipitation increase (that is the lack of or occurrence of severe drought conditions).
Climatic Controls
Latitudinal position relative to equator and pole
*Half-way between the two resulting in frequent clash of contrasting air masses
*Represented by position of polar front and jet stream (upper-air manifestation of the polar front)
*Winter: average position well south of Gulf of Maine
*Summer: average position just north of Gulf of Maine
Circulation systems
*Within the westerlies
*Much airflow comes off the continent
*Day to day conditions a function of shape of upper-air westerlies
*Zonal flow: Air flow across the continent primarily west to east
*Meridional flow: Air flow across the continent consists of series of troughs and ridges
Warm air underneath the ridge moves northward with cold air moving southward within the trough
*Important circulation features
*Icelandic Low: Subpolar low pressure area located northeast of Gulf of Maine
Brings polar maritime air from the northeast into the region
*Bermuda-Azores High: Subtropical high pressure system
Brings tropical maritime air from the southwest into the region
*Relationship between the two: North Atlantic Oscillation
*Difference in pressure between these two systems
*Especially critical to winter conditions along the eastern seaboard
*Produces two modes:
*Positive mode: Large difference in pressure between the two systems produces strong zonal flow
Strong positive mode seems to lead to warm conditions in the eastern U.S., while the negative mode often leads to colder temperatures across the northern tier of states
*Negative mode: Small difference in pressure between the two systems produces meridional flow as "blocking" high often forms over Greenland
Mode that helps produce winter storms along the coast given the high temperature contrast with the meridional flow pattern
*ENSO (El Niño-Southern Oscillation): Two end members of the oscillation are El Niño and La Niña
*El Niño is the movement of the warm pool of water in western South Pacific Ocean toward the eastern Pacific Ocean thereby deterring eastern trade wind progression
*Process affects global circulation patterns
*Implications for Gulf of Maine region: Primary affect is warmer winters with variable precipitation trends
*Wind shear in the equatorial region of the Atlantic Ocean will inhibit thunderstorm development that ultimately reduces the potential for hurricane development in the Atlantic Basin
HOWEVER, important to realize that the number of hurricanes that form in the Atlantic Basin have no bearing on the number of hurricanes that make landfall or that would move up the east coast into the Gulf of Maine
*La Niña is the opposite condition whereby the warm pool of water remains in the western South Pacific Ocean with an enhancement of the eastern trade winds
*Also has a major impact on global circulation patterns, but impact on the Gulf of Maine region shown to be quite variable from event to event
*More hurricanes in the Atlantic Basin form under La Niña conditions
*Under more neutral conditions, other factors play more prominent roles in dictating climatic conditions in the Gulf of Maine
*Pacific/North America (PNA) pattern
*Also a single number to describe circulation across the U.S.
*Represents the pattern of westerlies across the country going from zonal to meridional flow
*Looks at the pattern more from the western half of the country as it is derived from pressure differences among the Gulf of Alaska, Alberta (Canada), and the southeast U.S.
*Does not show the same level of prevalence over particular time periods like the NAO does
Storm tracks
*Almost all storm tracks converge on New England/Gulf of Maine region
*Specific patterns more prevalent during particular seasons
*Summer: Most storms travel to north of region, but trailing cold fronts can sweep across region
*Winter: Two primary tracks
*Alberta Clippers: low pressure systems move across Great Lakes region through New England
Weak to moderate storms, but can strengthen once in Gulf of Maine
*Coastal storms: Two possible tracks
One track takes storm through the St. Lawrence River valley while the other track is up the coastline
Ocean currents
*Cold Labrador Current
*Keeps coastal areas cooler in summer, warmer in winter
*Cool water responsible for frequent fog along Gulf of Maine coast, particularly during the summer when temperature contrast between land and water at a maximum
Implications for fishing industry through ability to leave port
*Warm Gulf Stream
*Proximity to the Gulf of Maine
*Helps to strengthen coastal storms as warm water provides energy for rapid deepening of storm
Extreme events
Nor’easters and hurricanes
Potential impacts (in general) on the Gulf of Maine
Temperature
*Persistent hotter temperatures increase ocean surface temperatures and temperatures in shallower zones
*Potential impacts on specific species (See the relationship between temperature and winter flounder in the New England Regional Assessment on the impact of future climatic change in New England (available on-line at www.necci.sr.unh.edu)
*Changes in sea level
*Persistent colder temperatures decrease ocean surface temperatures and temperatures in shallower zones
*Potentially greater periods of ice cover near shore and particularly in estuarine environment and bays
*Potential impacts on specific species
Precipitation
*Periods of wet conditions, both several days and extreme events, leading to increased runoff into estuarine and ocean waters
Brings various materials, pollutants, nutrients into these waters
*Periods of drought
*Runoff reduced which may lead to increased salinity
*Water entering marine environment may be concentrated in various compounds that normally would not be a pollutant or have an adverse impact on marine ecosystems
Severe storms
Nor’easters and hurricanes
*High waves affecting shallow ocean zones
*Direct impact on ability of fishing boats to leave port
*If increased number of these storms, then greater potential for impact on the fishing industry
Climatic Records
*Regional changes may not be the same as those observed globally
*New England Regional Assessment findings
*Caution in taking their conclusions on past climate as presented
*Place straight-line fit to trends in climatic data from 1895 to present
Maine temperature
*Average for the state
Straight-line fit produces a decrease in temperature over the last 107 years of 0.4˚F
However, this straight-line fit represents only 1% of the variability in the temperature record, not much of a representation!
*Closer evaluation by looking at climatic zones across the state
Using same procedure shows
*Northern has decreased by –1.2˚F
*Southern Interior decreased by 0.1˚F (essentially remained constant)
*Coastal increased by +1.1˚F
Other New England states adjacent to Gulf of Maine
*New Hampshire temperatures increased by 1.8˚F
*Massachusetts temperatures increased by 1.0˚F
Seasonal changes in precipitation
Maine showed no change in temperature trends at the seasonal level, but both New Hampshire and Massachusetts showed increasing temperatures in each season
Winter temperatures increased more than summer temperatures in those two states
Maine precipitation
Average for the state
*Using straight-line fit shows precipitation decreased by 12%
This straight-line fit represents only 8% of the variability in the precipitation record, a little better than that for the temperature record, but still, not much of a representation!
*Changes in precipitation across the state
*Northern has decreased by 19%
*Southern Interior decreased by 9%
*Coastal increased by 2%
Other New England states adjacent to Gulf of Maine
*New Hampshire precipitation decreased by 2.5%
*Massachusetts precipitation increased by 29.5%
Changes in circulation patterns as reflected in changes in indices
*Changes in NAO
*Negative mode more prevalent 1950s through 1970s, last 20 years, positive mode more prevalent
Snowy winters of 1950s-1970s!!
*Positive mode also more prevalent 1900-1930
*Other time periods over last 150 years show fluctuating positive/negative modes
*Changes in PNA
Does not show the prevalence over decadal time scales like the NAO does
Extreme events
*Recent events
*2001 was the driest year on record for Maine
*October 1996 heavy rains with over 19 inches in southern Maine
*Hurricane Diane 1954 which produced greatest 24-hour rains in New England (18 inches in western Connecticut)
*Ice storm of 1998, although minimal direct impact on the Gulf of Maine
*Hurricane of 1938
*Several strong nor’easters, both snow producers ("Blizzard of ’78, April Fools snowstorm in Boston) and rain/extreme coastal damage storms (All Hallows Eve storm of 1991 [Perfect Storm])
*Suggestions that there have been an increase in the number and/or magnitude of extreme events
*One study indicates that the number of nor’easters along the eastern seaboard have not increased in number but have increased in magnitude: Based on coastal impact, not necessarily an independent measure of storm’s intensity
*This mechanism now exists (Zielinski, published in January 2002 issue of Bulletin of American Meteorological Society)
*CAUTION: The number of extreme events based on records that span the last 100 years, at the most, which is a very short record to look at the range of possibilities in the climate system
Future Implications
*Based on two different global circulation models (GCMs) as run for the New England *Regional Climate Assessment
*Looked at changes in annual maximum and minimum temperatures
*Changes in annual precipitation
*Changes in these same three parameters for each season: Winter (January- March), Spring (April-June), Summer (July-September), Autumn (October- December)
Be aware: these seasons differ from the usual seasons studied, that is, winter is usually December-February, spring is March-May and so forth
*Looked at two time periods: near-term (that is, present to 2030) and long-term (present to 2100)
*Guidelines used: a 1% increase per year in greenhouse gases
*CAUTION: Models can vary by a great deal as to their predicted outcomes and they are "models", not necessarily reality
Models also are not able to predict adequately, if at all, how the frequency and magnitude of extreme events may change in the future
*Two models used
*Canadian Model
*Temperature
*Predicted an increase in average minimum temperature of 1.8˚F (1˚C) by 2030 with a 9.5˚F (5.3˚C) increase by 2100
*Predicted an increase in average maximum temperature of 2.7˚F (1.5˚C) by 2030 with a 9˚F (5˚C) increase by 2100
Precipitation
*Predicted only a small overall increase in precipitation per year which produced an overall 10% increase by 2100
*Did include high fluctuations in precipitation such as the presence of drought periods like that in the mid-1960s or like we may be in right now!
*Hadley Model (United Kingdom)
*Temperature increases the same as the Canadian Model to 2030 (that is, a 1.8˚F (1˚C) increase in annual minimum temperature and a 2.7˚F (1.5˚C) increase in annual maximum temperature
*Temperature increases to 2100 were lower than the Canadian model
Annual minimum temperature increase was only 5.6˚F (3.1˚C), and annual maximum temperature was only 3.6˚F (2˚C)
*Predicted a continued increase in precipitation resulting in a 30% increase by 2100
Did not predict periods of drought as did the Canadian model
*Seasonality changes in these same parameters
*Both models show increases in temperature for each season with the Canadian model showing greater increases
Exception: Minimum temperatures in summer and autumn were similar for each model
*Both models show increases in precipitation for each season with the Hadley model showing greater increases
Exception: Spring precipitation increases are similar in each model
*Spatial changes
*Canadian model
Predicts higher temperatures inland compared to coastal regions which is opposite to the general trends over the last century
Shows no trend in precipitation increases across the region
*Hadley model
Shows no spatial trend in temperature
Shows a greater degree of heterogeneity in precipitation across the region, but no trend
*Potential impact from abrupt climatic changes
*The Earth’s climate system can shift climatic modes very quickly
*At times in the past, climate has shifted from near glacial conditions to near interglacial conditions in a matter of a few years
*This rapidity occurs when there are ice sheets in existence, nevertheless, these are very drastic changes
*However, during times when ice sheets do not exist, there still have been rapid shifts in climate on the order of decades: A time frame that can have a major impact on socioeconomic conditions within one’s lifetime and on the Gulf of Maine
*These changes have occurred in the past and they MAY happen again in the future, particularly those changes that have occurred over a few years
*Such rapid changes can not be adjusted to, thereby causing major problems
*Increased major storm activity may be a part of these abrupt changes, but the likelihood of this happening is not known
What needs to be done?
The key: understanding the climate system of the Gulf of Maine through evaluation of past conditions (climatic records/terrestrial environment and through geologic studies in the marine and estuarine environment) and acquiring and monitoring conditions within the marine environment (such as, GoMoos Project at UMaine). Although global climatic change is important, understanding how that change is manifested at the regional level will be the key to postulating how the marine environment will be impacted.