2. Weather and Climate Lecture 7 Climatic Change

3. Are we living in an ice age??

4. Introduction Climate: statistical properties of atmospheric variables: – Temp – Precipitation – Wind, etc – Relatively constant over a period of 35 years

5. Climate change A change in any statistical property of the atmosphere Can still occur without any change in annual average precipitation – Timing of heavy rainfall or drought – Snow as precipitation instead of rain, are all indicators of climatic change

6. Earth’s Past climates Present climate on earth highly ‘unusual’ – Today, Arctic sea mostly frozen, ice sheets over bulk of Antarctica – Throughout earth’s history, palaeoclimatic studies: Earth was predominantly warm throughout Punctuated with brief ice ages Warm periods lasted up to billions of years Ice ages lasted a hundred million years at the most Can be said that we are currently in an ice age

7. Reasons for climatic change Sunspot Activity – Dark regions which form on the photosphere of the sun – Diameters of about 10,000km, 1500 deg C cooler than surrounding – Form as a result of strong magnetic fields; peak every 11 years – Cause periods of less insolation and therefore less intensity and temperatures, therefore possible climate change

8. Reasons for climatic change Earth Geometry and Milankovitch cycles – Geometry of the earth varies through time – Amounts of insolation received as geometry varies will affect the amount of insolation, hence temperatures and therefore climate – 3 ways in which earth’s geometry varies, known as Milankovitch cycles

9. Milankovitch cycles Earth’s orbit around the sun changes from being near-circular to more elliptical on a cycle of about 1 million years The earth rolls or wobbles slightly on its axis on a cycle of 40,000 years Axis of the earth moves round slowly on a cycle of 20,000 years, affecting the distance of different areas from the sun on midsummer’s day

10. Milankovitch Cycles Cycles mainly change the distribution of energy over the earth’s surface Have a large effect on seasonality without changing the actual amount of energy within the season There must therefore be other factors at play in contributing to climate change

11. Plate Tectonics movement of plates M move land areas into different climatic regions if moved to the poles, or surrounding, encourages ice sheets to develop may therefore prevent warm ocean currents from reaching the poles, so snowfall is less inclined to melt and can accumulate to form ice sheets

12. climate models also show that without the Himalayas and the Tibetan Plateau, the Indian monsoon would not occur for almost 250 million years the earth’s climate was warm and wet, then about 40 million years ago, a marked cooling began coincided with major plate movements, including the merging of India with Asia that led to the uplift of the Tibetan Plateau

13. El Nino - El Nino Southern Oscillations (ENSOs) - occur once every 2 to 9 years, triggered by a reversal in the normal westward flow of the Trade winds and ocean currents that flow across the tropical Pacific from the Americas towards Asia - produces unseasonable weather throughout the globe

14. La Nina - like ENSOs, occur at irregular intervals, but roughly half as frequently as El Nino - brings about climatic effects opposite of El Nino - warmer, wetter weather in western Pacific - colder, drier conditions prevail in the tropical eastern Pacific

15. Volcanic Activity principally has a cooling effect on the earth’s climate volcanic ash in atmosphere leads to the alteration of the earth’s albedo (increases), and increase in reflected energy gases emitted may also react with ozone in upper atmosphere and destroy ozone; implications for global warming as ozone also reflects insolation

16. Deforestation - removal of trees and forests on a large scale can change the microclimate - less trees, more carbon dioxide (greenhouse gas), higher amounts of heat re-radiated after absorption of heat by carbon dioxide, higher temperatures - however, debatable

17. Pollution - burning of fossil fuels and emission of gases - absorb outgoing energy - overall warming effect on the earth, but debatable

18. Evidences for climate change The evidences for climate change stem from: - Glaciological Evidence - Geological Evidence - Biological Evidence

19. Evidences for climate change The following glaciological evidences suggest climatic change Retreat of Glaciers – Study of glacial retreat in Northern Hemisphere – Equated to the melting of glaciers – Reflection of a general rise in temperatures

20. Evidences for climate change Study of Ice cores and isotope analysis – Ice cores from Greenland and Antarctic icesheets, as well as Alpine glaciers – Oxygen isotope analysis: – At the end of the Pleistocene, temp over Greenland warmed about 9 deg C

21. Evidences for climate change In addition, study of the amount of carbon dioxide locked in ice cores also show climatic change – Past periods of high temperatures coincide with high carbon dioxide concentrations – Glacial periods with reduced carbon dioxide concentrations – Ice cores have shown different layers of different concentrations of carbon dioxide, hence suggesting climatic change

22. Evidences for climate change Geological Evidence is widely used to indicate past climate changes Drainage Patterns The extent and size of ancient drainage patterns and fluvial deposits in north Africa - cannot be explained by present climates - reflect past, wetter climates known as pluvials

23. Evidences for climatic change Sediment layers of streams and rivers – Size of material in sediment layers determined by capacity and competence of streams – Determined by speed and volume of discharge, in turn affected by climate – By examining the layering, or stratigraphy, some inference of periods of low and high precipitation episodes can be determined

24. Evidences for climatic change Biological Evidence like plant growth is strongly related to climate Fluctuations in: – Temperature, sunlight, precipitation – Will have an effect on vegetation type and growth – Scientists have used this information to study past climates

25. Evidences for climatic change Dendrochoronology – Involves the study of the annual growth of tree rings – Number of rings within the trunk tells the age, forming concentric rings – Relative spaces between each ring suggests how much the trunk has increased in size in a year

26. Evidences for climatic change Dendrochoronology – Width of each ring: Stressful conditions will retard the growth of these rings Favourable conditions, relatively think rings Cores from tree trunks which have lived for thousands of years: Variations in relative spaces between rings, suggesting changes in climate

27. Evidences for climatic change Pollen Analysis – Based on the idea that as climate changes, so will the dominant species of plants in the community – Study of peat layers where marshes and bogs are found: – Different species of pollen grains found in different layers of peat – Suggests a transition of one type of dominant plant species to another as a result of climate change