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 17 th 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 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