Orbital variations
- 2. Natural Causes of Climate Change: EARTH’S ORBITAL VARIATIONS Presented By: RimshaQureshi M.Phil Scholar, University of Peshawar
- 3. Climate: Mean Meteorological condition of a place for a longer period of time. Climate Change: refers to significant changes in global temperature, precipitation, wind patterns and other measures of climate that occur over several decades or longer. The seas are rising, the food we eat is threatened, ocean acidification is increasing, ecosystems are changing. While some species are adopting, for others, it’s not that EASY. Evidence suggest many of these extreme climate changes are connected to rising levels of Carbon dioxide and other Greenhouse Gases in the earth’s atmosphere – more often, the result of human activities.
- 4. Causes of Climate Change: Climate is influenced by a multitude of factors that operate at timescales ranging from hours to hundreds of millions of years. Many of the causes of Climate Change are external to the Earth system, others are a part of the Earth system but external to atmosphere, still others involve interactions between the atmosphere and other components of the Earth system. So it’s much easier to document the evidence of climate variability and past climate change than it is to determine their underlying mechanisms.
- 5. Natural Causes of Climate Change: Factors that can shape climate are called Climate Forcings or Forcing Mechanisms. These include processes such as: Variation in Solar radiation Variation in Earth’s Orbit Variation in the Albedo or Earth’s reflectivity Volcanic activity Tectonic activity Sea water composition Earthquakes Acid- Rains (Natural)
- 7. Earth’s Orbital Variations and Climate Change Slight variations in Earth’s motion lead to changes in the seasonal distribution of sunlight reaching the Earth’s surface and how it is distributed across the globe. Shifts and wobbles in the Earth’s orbit can trigger changes in climate such as the beginning and the end of ice ages. But orbital cycles are so gradual they are only noticeable over thousands of years – not decades or centuries. The three types of kinematic changes are: Variations in Earth’s eccentricity Changes in the angle of Earth’s axis of rotation Precession of Earth’s axis Together these produce Milankovitch cycles which affect climate and are notable for their correlation to glacial and interglacial periods.
- 8. Earth's Eccentricity The difference in shape between an ellipse and a perfect circle is termed as eccentricity.
- 9. Earth’s Eccentricity: The shape of Earth’s orbit around the Sun varies from nearly circular to elliptical(eccentric) with periodicities of 90,000 and100,000years.(413,000 years/ 405,000 years) When the orbital is highly elliptical, the amount of insolation received at perihelion would be on the order of 20 to 30 percent greater than at aphelion. Currently, a difference of only 3 percent (5 million km) exist between perihelion and aphelion. This difference in distance amounts to about a 6 percent increase in incoming solar radiation from July to January. Earth’s orbit is an ellipse with the Earth-Sun barycentre as one focus and a current eccentricity of 0.0167, since the value is close to zero, the centre of the orbit is close to the centre of the sun( relative to the size of the orbit).
- 12. Axial Tilt Axial Tilt is the angle between an object’s rotational axis and its orbital axis, or, equivalently, the angle between its equatorial plane and orbital plane.
- 13. Axial Tilt: Axial tilt also known as obliquity, oscillates between 22.1 and 24.5 degrees on a 41000-year cycle. Earth’s mean obliquity is currently 23°26’12.1’’(23.43668°) and is decreasing (@47“ per century). This obliquity causes one pole to be directed more toward the Sun on one side of the orbit and the other pole on the other side – the cause of the Seasons of the earth. Changes in the tilt of the Earth can lead to small but climatically important changes in the strength of the seasons. As the axial tilt increases, the seasonal contrast increase so that the winters are colder and the summers are warmer in both hemispheres. It is the cool summers that are thought to allow snow and ice to last from year-to-year in high latitudes, eventually building up into massive ice sheets. There are positive feedbacks in the climate system as well, because an Earth covered with more snow reflects more insolation, causing additional cooling.
- 15. Precession: The third cyclic change to Earth’s orbital geometry results from two combined phenomena: Earth’s axis of rotation wobbles, changing the direction of the axis with respect to the sun(axial precession) The orientation of Earth’s orbital ellipse rotates slowly (apsidal precession) These two processes create a 26,000 year cycle, called Precession of the equinoxes. Changes in axial precession alter the dates of perihelion and aphelion, and therefore increase the seasonal contrast in one hemisphere and decrease the seasonal contrast in the other hemisphere. If a hemisphere is pointed towards the sun at perihelion, that hemisphere will be pointing away at aphelion, and hence the seasons will be more extreme. Today Earth is closest to the Sun(perihelion) near the December solstice, whereas 9,000 years ago perihelion occurred near the June solstice.
- 18. These orbital variations cause changes in the latitudinal and seasonal distribution of solar radiation, which in turn drive a number of climatic variations. Orbital variations play major roles in pacing glacial-interglacial and monsoonal patterns
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