The Little Ice Age
1. Evidence of Little Ice Age
Modern Scientific data
o Temperature records
o Ice cores
o Ice delivered debris on ocean floor
o Tree rings
o Wide rings show warm summers
o Narrow rings cold summers
Historical observations
o Glacial action
o Movement of glaciers in Alps and Scandinavia
o Mer de Glace at Chamonix at foot of Mont Blanc
 Exorcism of glacier
o Reports of harsh winters
o Europe and North American colonies
 Thames River and New York Harbor frozen during winters
o Orange groves in China killed
o Eskimos kayaking as far south as Scotland
o Sea Ice in North Atlantic
o Snow on Ethiopian's mountains
Investigations of newspapers and journals
Investigation of clouds in paintings of time
2. Causes For The Little Ice Age:
o
o
1. Solar Activity:
- The sun experienced an extended quiet period in which its intensity fell by as much as 1/4
of a percent. This leads to less radiant heat emitted from the sun to neighboring bodies,
therefore a cooling occurs.
- Decrease in observable sunspots were noted. Amount of sunspots is correlated to the
activeness of the sun-more sunspots means more emission of radiant heat from the sun.
During this declined period of sunspots, people have connected it to Maunder Minimum, who
proposed this idea of sunspot and solar activity correlation.
2. Volcanic Activity:
- During the Little Ice Age, records show that this was a period of numerous volcanic
eruptions.
- As volcanoes erupt they spit particles and gases into the air, an event leading to the aerosol
effect.
- Aerosol effect reduces the amount of incoming solar heat by relecting it back into space.
This increases the earth's albedo. A higher albedo coincides with lower temperatures-a cooling
if you will.
- An example of this idea can be seen in the eruption of Tambora. This eruption produced so
much gases and particles that it lowered earth's temperature enough that it robbed Europe of
a summer the following year (The year without a summer).
3. Surface Albedo:
-Continued low temperatures, for whatever reason, produced snow and ice.
- More snow and ice equals more reflective surfaces to deny sun's radiant energy from
reaching teh earth's surface leading to additional cooling. Again staging a situation for the
formation of more snow and ice.
- A positive feedback mechanism.
4. Milankovitch Theory:
- Eccentricity. The degree of roundness of the earth's spherical shape.
- Tilt. Stronger tilt leads to a more varied seasonal climate.
- Precession of Equinox. Position of the earth on its elliptical path around the sun.
- During the Little Ice Age (LIA), all these factors were thought to have been situated in a
fashion that allowed for such a prolonged period of cooling.
- This theory is met with scepticism in that some of the cycles mentioned (eccentricity, tilt
and precession of equinox) require more time than what was allowed by the LIA period.
5. Ocean-Atmosphere Conveyor System:
-Occurs only in the N. Atlantic ocean-atmosphere domain.
- Warm tropical Gulf Stream ocean currnts and winds are conveyed up to the north to meet
cold Arctic waters and air.
- Within this area you have atmospheric lows and highs:
atm. lo: Forces air away from air mass center due to correolis effect. Outward tending winds
will force ocean currents to diverge from the center as well.
atm. hi: Opposite of atmospheric lo.
- It is these divergent tendencies of the N. Atlantic that keeps the Gulf Stream powered. If an
atm. hi replaced an atm. lo currents would converge, thus weakening the Gulf Stream which
was thought to possibly have occured during the LIA.
- Lack of warm winds and currents reaching the north would not warm the cold climate of the
north possibly producing snow and ice.
- This idea holds very sceptical because this event was localized, whereas the LIA was a global
scale event.
MEDIEVAL CLIMATE ANOMALY
Little Ice Age (LIA; ca. 1350-1850 AD)
The variation caused by the sunspot cycle to solar output is relatively small, on the order of
0.1% of the solar constant (a peak-to-trough range of 1.3 W.m−2 compared to 1366 W.m−2 for
the average solar constant).[5][6] Sunspots were rarely observed during the Maunder
Minimum in the second part of the 17th century (approximately from 1645 to 1715). This
coincides with the middle (and coldest) part of a period of cooling known as theLittle Ice Age.
Recently, total solar irradiance (TSI) has been reconstructed from a composite of several 10Be
records measured in polar ice for the past 9300 years (Steinhilber et al., 2008, 2009). The
composite is mainly based on the 10Be record from the GRIP ice core, Greenland. As system
effects mostly influence the signal on short time-scales, 40-year averages have been built from
the 10Be records.
The variation caused by the sunspot cycle to solar output is relatively small, on the order of
0.1% of the solar constant (a peak-to-trough range of 1.3 W.m−2 compared to 1366 W.m−2 for
the average solar constant).[5][6] Sunspots were rarely observed during the Maunder
Minimum in the second part of the 17th century (approximately from 1645 to 1715). This
coincides with the middle (and coldest) part of a period of cooling known as theLittle Ice Age.
Figure 1: A) Zoom-in of the 9300-year long total solar irradiance (TSI) reconstruction (Steinhilber
et al., 2009) for the past 1200 years. The gray band is the 1σ uncertainty. Inset shows the group
sunspot number. MCA: Medieval climate anomaly; LIA: Little Ice Age. Capital letters mark grand
solar minima: O=Oort, W=Wolf, S=Spörer, M=Maunder, D=Dalton. B) Total global stratospheric
volcanic sulfate aerosol injection in teragram (Tg) (Gao et al., 2008).
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Comparing model simulations with proxy-based climate reconstructions offers the possibility
to explain mechanisms of climate
variability during key periods, such as the Medieval Climate Anomaly (MCA) and the Little Ice
Age (LIA). Discrepancies between both sources of information may also help to identify
possible deficiencies in our understanding of past climate, its modeling or its representation
by proxy records.
Current AOGCM millennial forced simulations do represent an overall warmer MCA and a
cooler LIA at global and hemispherical scales (e.g., González-Rouco et al., 2006; Ammann et
al., 2007) as a response to long-term changes in volcanic
activity and solar irradiance. The amplitude
of this response is dependent on the model sensitivity and on the specific set of forcing
reconstructions used to drive the simulations. Mann et al. (2009) show that in spite of
agreement in simulating global and hemispheric warming, the reconstructedpattern of MCALIA temperature change, and specifically the La Niña-like conditions in the eastern Pacific,
were not reproduced by forced simulations with the GISS-ER and the NCAR CSM1.4 climate
models. In this contribution, we will examine
the MCA-LIA transition in all available high complexity AOGCM transient simulations
of the last millennium.
Figure 2: Compilation of global and Iberian climate reconstructions over the last 2000 years. Global records include sun spot numbers
(Vaquero et al., 2002), solar irradiance (Bard et al., 2000) and temperature anomalies for the Northern Hemisphere (Jones and Mann,
2004). Iberian Peninsula records are aligned from west to east (see Fig. 1 for location) and include SST from marine cores offshore
Tagus River (Rodrigues et al., 2009), lake level of Estanya Lake (Morellón et al., in press), number of floods observed in Taravilla Lake
(Moreno et al., 2008), Rb/Al ratio from Zoñar Lake record (Martín-Puertas et al., 2010), number of detrital events per year recorded in
Montcortés Lake (Corella et al., in press) and coarse detrital grain fraction from off Minorca (Frigola, unpublished data).
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The climatic variations during the ‘Little Ice Age’ caused worldwide growth of glaciers, but the
evidence from Scandinavia and the European Alps is best documented (Grove, 1988; Lowell,
2000).
Estimates of Northern Hemisphere mean annual temperature for
the last millennium (Mann et al., 1999; Crowley and Lowery,
2000) do not show a marked LIA cooling, but rather a gradual
temperature decline during the first half of the last millennium.
It is also evident that there was significant regional temperature
variations during the LIA. Several temperature data sets obtained
from different archives (tree rings, corals, varved sediments, ice
cores, glaciers, historical records, etc.) show that some regions
were warm while others were cold, and vice versa. Most of the
reconstructed climatic changes have been linked to external forcing
factors (e.g., solar activity, volcanic eruptions) in combination
with internal ocean-atmosphere interactions (Crowley and Kim,
1996; Mann et al., 1998). Since these forcing factors, together
with ‘greenhouse’ gases, are suggested by the Third Assessment
IPCC Report, published in 2001, to play a role in future climatic
variations, it is important to obtain better records of climatic
change in the recent past and a better understanding of the relative
contribution of these forcing factors.
Until recently, and mainly based on evidence from western Europe
and the North Atlantic region, the conventional view of the climate development during the
last millennium has been that it
followed the simple sequence of a warm Mediaeval period, then
a cool ‘Little Ice Age’, followed by global warming. However,
climate reconstructions obtained recently have challenged this
rather simple sequence of climate development. The centralEngland temperature record going back to the late 1650s indicates
that the rapid glacier advance which is historically documented in
the early eighteenth century in western Norway may be explained
mainly by increased winter precipitation (mild and humid) due to
prevailing ‘positive NAO weather mode’ in the Ž rst half of the
eighteenth century. Lower summer temperatures alone cannot
explain such a signiŽ cant glacier advance over a few decades.
LIA ONLY TEMPERATURE?
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VOLCANISM AND LIA