Transcript U3A-ClimChange07 7823KB Nov 06 2012

CLIMATE CHANGE
THE GREAT DEBATE
Session 7
SOLAR POWER
• The Sun is the primary driving force of
climate and sits in the centre of the
solar system that includes all the
planets
• Like all “yellow dwarfs” it generates its
energy by nuclear fusion of hydrogen
nuclei into helium
• A small amount of this energy reaches
Earth but this is enough to support our
natural requirements
SOLAR POWER
• It provides the energy to power
atmospheric and ocean currents
• It powers the cycles of evaporation and
condensation
• It provides the energy for
photosynthesis which is necessary to
support nearly all life forms on the
planet
• It provides a temperature regime that
makes most of the planet hospitable for
life
Photo of
Sun by
NASA
ENERGY VARIATIONS
• Until recently the energy output of the
Sun was thought to be constant but we
now know that is not the case and we
will look at the variations
• Even if it were constant, there are other
factors that influence the amount of
energy that reaches us and is absorbed
by the Earth’s surface and atmosphere
OTHER FACTORS
• The transparency of the atmosphere varies
due to changes in dust content and cloud
cover and the amount of heat it absorbs from
Earth radiation is controlled by its content of
greenhouse gases
• Ground surfaces reflect varying amounts of
solar energy depending on their nature.
Some are highly reflective such as fresh
snow while others tend to absorb most of the
energy such as smooth water surfaces
• Both are strongly influenced by biological
activities, including those of humans, so we
will look at them later in more detail
ORBITAL VARIATIONS
• The orbit of the Earth around the Sun
and the tilt of its axis cause strong
annual variations in our climate
• The orbital relationship between Earth
and Sun is also affected by the massive
outer planets and to a lesser extent by
our natural satellite – the Moon
• Regular climate cycles can be identified
by analysis of long term proxy records
such as ice cores and tree ring
sequences
SUN SPOTS
• When observed with a suitable filter the
Sun’s surface shows well defined areas
that are darker than their surroundings
because of their lower temperatures
• The largest may be tens of thousands
of kilometers across
• They are known as sun spots. Their
number is not constant but varies over
a 11-year cycle and is known as the
solar cycle
Lateral view
of sun spot
plasma
eruption on
22 September,
2011
Source:
NASA,
Solar
Dynamics
Observatory
SOLAR OR SCHWABE CYCLE
• The solar cycle has a significant effect
on the Earth’s climate because it
changes the Sun’s luminosity
• Solar activity minima are associated
with colder temperatures and maxima
with warmer temperature
• Longer than average solar cycles also
tend to be correlated with higher
temperatures
• The cycles have been observed since
the late Middle Ages
Dalton Minimum
Temperature changes from 1860 to 1990 are more
closely related to changes in sunspot cycle length
than to increasing levels of carbon dioxide
Variations in grain prices in Iceland from 1750 to 1850
compared with changes in sunspot activity during the
final phase of the Little Ice Age
IRREGULARITIES
• Sometimes the solar activity stops
entirely for several decades and few
sunspots are observed
• Not counting the Dalton Minimum, the
last time this happened was in the 17th
Century (Maunder Minimum) and at that
time some of the lowest temperatures
of the Little Ice Age were recorded
• Earlier minima have been identified
from tree ring records
Four solar minima occurred during the Little Ice Age
and one occurred during the Medieval Maximum.
Note: Temperature scale is incorrect
NASA PREDICTIONS
• Latest sunspot predictions released by
NASA indicate that another period of
minimum sunspot activity may be
commencing
• The current sunspot cycle (Cycle 24) is
shaping up to be the weakest for quite
some time and it has been suggested
that the downward trend will continue
for several decades. If so, we may be
facing another Little Ice Age
OTHER CYCLES
• Lunar Cycle - 18.6 years influences
precipitation
• Hale Cycle – 22 years. Due to reversal of
Sun’s magnetic field
• Bruckner Cycle – 35 years
• Gleissberg Cycle – 87 years
• DeVries-Suess Cycle – 210 years
• Dansgaard-Oeschger Cycle – 1500 ± 500
years
Longer cycles are probably due to interaction
between the Sun and the major planets
IDENTIFICATION OF CYCLES
• Longer cycles have been identified by
the analysis of proxy climate records
from ice cores in Greenland and tree
ring records from North America and
Europe
• Both of these sources provide annual
data on aspects of climate variation