Natural Environmental Change Professor Simon K. Haslett Centre for Excellence in Learning and Teaching 23 rd February 2010

Introduction Since 1988, the issue of human-induced climate change has become increasingly pertinent and has been grasped by the media and environmental pressure groups and used politically. However, there is a vast array of natural mechanisms that may be responsible for, or contribute to, this change. These mechanisms include: –Variations in the energy output from the sun –Astronomical variations –Variations in the composition and transmissivity of the atmosphere; and –Geomagnetism and climate This presentation aims to evaluate these natural mechanisms.

Mechanism 1: Variations in energy output from the sun Not seriously considered until 1970’s and 1980’s. ‘Solar constant’ of the pre-1960s used to describe the intensity of the solar beam. Pivovarova (1968) suggested solar output had decreased by 4% since The sun’s energy output may vary in two ways: –Sunspot activity –Diameter changes Solar activity may influence the variation of global temperature, but is not enough to account for the observed rising trend through the 20 th century.

Sunspot Activity Driven by the sun’s tides with predictable periodicities. Convect hot gases from the inside the sun to the surface of the photosphere. Generally, the more sunspots the greater solar radiation output. Cycle is 9-14 years, with an 11 year mean.

Sunspot Activity Duration of cycles important, short cycles = more radiation output. Considered to be a cause of the Medieval Warm Period. Since 1890, cycle has shortened from 11.7 to 9.7 years, and global temps have risen 0.6°C. Cycle slowed from 10.2 to 10.7 years and global temps fell, although greenhouse gases continued to rise. The 13 th century Norman Church, like many in the Bristol Channel area of southwest Britain, was inundated by coastal dune sands blown onshore during the Medieval Warm Period. Sand is seen here banked up away from the church walls to maintain access – many other churches were buried by blown sand during this period.

Diameter Changes Gilliland (1982) suggests the sun’s diameter changes and may influence climate. A smaller diameter sun radiates more concentrated energy. Therefore, smaller diameter periods relate to a warmer earth climate. 1% change in diameter = 1°C change on earth. The sun has been shrinking gradually for over 250 years, but less than 1%, and coincides with the global warming of this period.

Mechanism 2: Astronomical variations The orbital relationship between the earth and the sun is not constant. Three main orbital variations may affect earth’s climate i.e. Milankovitch Cycles. –Procession of the equinoxes (18-23 ka cyclicity). –Obliquity of the ecliptic (41 ka cyclicity). –Eccentricity of the orbit (100 ka cyclicity). Eccentricity influences the amount of solar radiation received, but precession and obliquity can only influence its distribution. All cycles act together to influence long-term climate.

Mechanism 2: Astronomical variations Milankovitch Cycles are perhaps evident in geological sequences, such as the alternating limestone and shale of the Lower Lias (House, 1985). White and Blue Lias (shale-limestone cycles), Lyme Regis, Dorset

Mechanism 3: Variations in the composition and transmissivity of the atmosphere Atmospheric aerosols affect transmissivity. High latitude ice cores can reveal ancient concentrations of atmospheric aerosols. Volcanic activity produces the most e.g. Mt. Pinatubo eruption. Aerosols emitted from a volcanic fumarole, the pale deposit is sulphur (Terceira island, Azores).

Volcanic Activity Eruptions introduce dust particles and aerosols into the stratosphere. These dust particles can circulate the globe in 20 days, becoming uniform by 6 months. Particles take 20 days to 1 year to fall 1km. Therefore, particles may be resident in atmosphere for many years. Dust veil and aerosols intercept incoming radiation, cooling the earth’s surface.

Mechanism 4: Geomagnetism and climate Wollin et al. (1973) demonstrated a link between climate and the intensity of the earth’s magnetic field. The mechanism is not known, but the weaker the magnetic field the warmer the climate. Satellite measurements since the 1970s show the magnetic field weakening by 1% per decade.

Summary A vast array of natural mechanisms may be responsible for climate change. Sunspot activity and changes in the sun’s diameter can influence prevailing temperatures. Variations in the earth’s distance and tilt from the sun can affect climate over time. Volcanoes are an important contributor to climatic variation. A relationship exists between the shape and strength of the magnetic field and weather and climate on Earth.

Further Reading Bradley, R.S. and Jones, P.D Records of explosive volcanic eruptions over the last 500 years. In: Bradley, R.S. and Jones, P.D. eds. Climate since AD Routledge, pp Chambers, F.M ‘Global warming’: New perspectives from palaeoecology and solar science. Geography, 83(360): Chambers, F.M., Ogle, M.I. and Blackford, J.J Palaeoenvironmental evidence for solar forcing of Holocene climate: linkages to solar science. Progress in Physical Geography, 23(2): House, M.R A new approach to an absolute timescale from measurements of orbital cycles and sedimentary microrhythms. Nature, 315: Gilliland, R.L Solar, volcanic, and CO 2 forcing of recent climatic changes. Climatic Change, 4(2): Pickering, K.T. & Owen, L.A An Introduction to Global Environmental Issues (2 nd Edition). Routledge, 512pp. (read pp , 70-73, 81, ). Pivovarova, Z.I The long-term variation of intensity of solar radiation according to observations of actinometric stations. Tr. Gl. Geofiz. Observ., 233: Rampino, M. and Self, S Historic eruptions of Tambora (1815), Krakatau (1883) and Agung (1963), their stratospheric aerosols and climatic impact. Quaternary Research, 18: Waple, A.M The sun-climate relationship in recent centuries: a review. Progress in Physical Geography, 23: Wollin, G., Kukla, G.J., Ericson, D.B., Ryan, W.B.F. and Wollin, J Magnetic Intensity and Climatic Changes Nature, 242:

This resource was created by the University of Wales, Newport and released as an open educational resource through the 'C-change in GEES' project exploring the open licensing of climate change and sustainability resources in the Geography, Earth and Environmental Sciences. The C-change in GEES project was funded by HEFCE as part of the JISC/HE Academy UKOER programme and coordinated by the GEES Subject Centre. This resource is licensed under the terms of the Attribution-Non-Commercial-Share Alike 2.0 UK: England & Wales license ( All images courtesy of Professor Simon Haslett. However the resource, where specified below, contains other 3 rd party materials under their own licenses. The licenses and attributions are outlined below: 1.The name of the University of Wales, Newport and its logos are unregistered trade marks of the University. The University reserves all rights to these items beyond their inclusion in these CC resources. 2.The JISC logo, the C-change logo and the logo of the Higher Education Academy Subject Centre for the Geography, Earth and Environmental Sciences are licensed under the terms of the Creative Commons Attribution -non-commercial-No Derivative Works 2.0 UK England & Wales license. All reproductions must comply with the terms of that license. AuthorProfessor Simon K. Haslett Research AssistantJonathan Wallen Institute - OwnerUniversity of Wales, Newport TitleNatural Environmental Change DescriptionAn brief introduction to natural causes of thermal environmental change. Date Created2010 Educational LevelHigher Keywords UKOER, GEESOER, earth sciences, environmental sciences, climate change, natural mechanism, global warming, sunspots, Milankovitch, volcano, geomagnetism, Medieval Warm Period Creative Commons LicenseAttribution-Non-Commercial-Share Alike 2.0 UK: England & Wales