1. Paleoclimatology

1. 1. Paleoclimatology Ron Sass Rice University

2. Various notable climate-related events in the History of the Earth * Major Ice ages (Well documented last 800,000 years) Snowball Earth/Varangian glaciation (Hadean and Paleoproterozoic; 700 to 600 million years BP)) Permian-Triassic extinction event (Permian-Triassic; 251 million years BP) Younger Dryas/The Big Freeze (~12,700 to 11,500 years BP) * Paleocene-Eocene Thermal Maximum (Paleocene-Eocene; 55.4 to 54.8 million years BP ) * Holocene climatic optimum (~9,000 to 5,000 years PB) * Climate changes of 535-536 (535-536 AD) * Medieval warm period (900-1300 AD) * Little ice age (1300-1800 AD) * Year Without a Summer (1816 AD)

3. Major Ice Ages

5. There have been at least four major ice ages in the Earth's past The Earth is approximately 4.6 billion years old. Life is approximately 3.6 billion years old. The earliest hypothesized ice age is believed to have occurred around 2.7 to 2.3 billion (109) years ago during the early Proterozoic Age. The earliest well-documented ice age, and probably the most severe of the last 1 billion years, occurred from 750 to 550 million years ago (the Cryogenian period) and it has been suggested that it produced a Snowball Earth in which permanent sea ice extended to or very near the equator. It has been suggested that the end of this ice age was responsible for the subsequent Cambrian Explosion, though this theory is recent and controversial. A minor ice age occurred from 460 to 430 million years ago, during the Late Ordovician Period. There were extensive polar ice caps at intervals from 350 to 260 million years ago, during the Carboniferous and early Permian Periods, associated with the Karoo Ice Age. Sediment records showing the fluctuating sequences of glacials and interglacials during the last several million years. The present ice age began 40 million years ago with the growth of an ice sheet in Antarctica, but intensified during the Pleistocene (starting around 3 million years ago) with the spread of ice sheets in the Northern Hemisphere. Since then, the world has seen cycles of glaciation with ice sheets advancing and retreating on 40,000- and 100,000-year time scales. The last glacial period ended about ten thousand years ago.

6. 700-600M yBP 460-430M yBP 350-260M yBP 160-130M yBP 40M-10,000 yBP

11. Controlling Factors Geologically short-term (<120,000 year) temperatures are believed to be driven by orbital factors (Milankovitch cycles). The arrangements of land masses on the Earth's surface are believed to reinforce these orbital forcing effects. Continental drift obviously affects the thermohaline circulation, which transfers heat between the equatorial regions and the poles, as does the extent of polar ice coverage. The timing of ice ages throughout geologic history is in part controlled by the position of the continental plates on the surface of the Earth. When landmasses are concentrated near the polar regions, there is an increased chance for snow and ice to accumulate. Small changes in solar energy can tip the balance between summers in which the winter snow mass completely melts and summers in which the winter snow persists until the following winter. See the web site Paleomap Project for images of the polar landmass distributions through time. Comparisons of plate tectonic continent reconstructions and paleoclimatic studies show that the Milankovitch cycles have the greatest effect during geologic eras when landmasses have been concentrated in polar regions, as is the case today. Today, Greenland, Antarctica, and the northern portions of Europe, Asia, and North America are situated such that a minor change in solar energy will tip the balance between year-round snow/ice preservation and complete summer melting. The presence of snow and ice is a well-understood positive feedback mechanism for climate. The Earth today is considered to be prone to ice age glaciations. Another proposed factor in long term temperature change is the Uplift-Weathering Hypothesis, where upthrusting mountain ranges expose minerals to weathering resulting in their chemical conversion to carbonates thereby removing CO2 from the atmosphere and cooling the earth. Others have proposed similar effects due to changes in average water table levels and consequent changes in sub-surface biological activity and pH levels. Over the very long term the energy output of the sun has gradually increased, on the order of 5% per billion (109) years, and will continue to do so until it reaches the end of its current phase of stellar evolution.

12. Ice Age 1. Suppose some additional polar ice forms as Sun’s energy input is lessened. 2. Light colored ice reflects back the Sun’s energy more efficiently than darker land. 3. Less exposed darker colored land absorbs less energy, more ice forms. 4. As more ice forms, less land is exposed. This reflects more heat, freezing more ice. 5. The altitude of the melting ice is increased so it becomes harder for older ice to melt. 6. If ice extends beyond 50° toward the equator, the process becomes irreversible. 7. If that is true, what starts the following warming period and the melting of the ice?

13. Differences in the insolation of the Earth by the Sun is influenced by solar cycles solar cycles governed by the time dependent geometric relationships between the Earth and the sun as influenced by the other planets. These cycles can be divided into the effects of orbital eccentricity, obliquity and precession of the equinoxes. In the Northern Hemisphere, peak summer insolation occurred about 9,000 years ago when the last of the large ice sheets melted. Since that time Northern Hemisphere summers have seen less solar radiation. Sun-Earth Radiative Equilibrium Sun-Earth Radiative Equilibrium S/4(1-a) S/4(1-a) sT4 sT4 17 http://deschutes.gso.uri.edu/~rutherfo/milankovitch.html

14. Milankovitch Variations

16. 180W 120 60 0 60 120 180E

18. Ice Age Carbon Budgets Red refers to the present time, green to the last glacial maximum T. J. Crowley, Global Biogeochemical Cycles, 9:377-389. 1995

20. Warm period, but still showed a polar ice cap

21. Cold period or ice age with massive continent having dry and windy interior. Note glaciation ice cap now strongly developed at south polar regions

22. Cold period or ice age. Large continental body extending from pole to pole interfering with ocean circulation.

23. Last series of ice ages began about 40 million years ago with the continents in much the same positions they are now.

24. The modern world is warm but has a continental structure very similar to that of 40 million years ago when the last ice age began.

25. Climate is affected by the increasing luminosity of the sun, by volcanic activity and by the changing composition of the Earth’s atmosphere.

26. Climate history since the end of the last ice age • 10,000 BC to 1000 BC General warming of the Earth • Since the last ice age there have been alternating periods of warmer and colder weather. • After a steady improvement from about 10,000BC, the warmest period of all was between 5000 and 3000 BC; temperatures were one to two °C above current levels. • Vegetation zones moved northwards and this period of climatic optimum coincided with the development and spread of agriculture across Europe. • 1000 BC to 1200 AD. A cooling then a warming from 800 AD (medieval warm period). • A general decline in temperatures and increased rainfall, reaching a low point between 900-300 BC, with an improvement noticeable by around 100 BC when wine vines spread further north, followed by a cool spell around 400 AD that lasted until about the year 0. • Then a warm period that was shorter and less intense than the first peak (perhaps one degree centigrade warmer than today) reached its height about 1200. • 1200 to 1850 The little ice age. • A steady decline in temperature followed 1200, reaching a long low between 1430-1850, the 'Little Ice Age', when temperatures were between one and two degrees centigrade lower than at present. • The main impact was severe winters, with summer temperatures not much different from today. • These climatic changes have been established through a multitude of different techniques; pollen records, isotope analysis, changes in lakes, glaciers and tree lines plus some historical records.

28. Holocene Climate Variation May Be Affected by Natural Oscillations in Ocean-Atmosphere Heat Transfer

31. Climate changes of 535–536 Refers to several remarkable aberrations in world climate which took place in the years 535 and 536. The Byzantine historian Procopius recorded of 536, "during this year a most dread portent took place. For the sun gave forth its light without brightness… and it seemed exceedingly like the sun in eclipse, for the beams it shed were not clear." Tree ring analysis by dendrochronologist Mike Baillie, of the Queen's University of Belfast, shows abnormally little growth in Irish oak in 536 and another sharp drop in 542, after a partial recovery. Similar patterns are recorded in tree rings from Sweden and Finland, in California's Sierra Nevada and in rings from Chilean Fitzroya trees. Further phenomena reported by a number of independent contemporary sources: * low temperatures, even snow during the summer * dark clouds, only a few hours of sunlight during the day * summarily, there were reports of almost night-like darkness at midday * floods in formerly dry regions * crop failures It has been conjectured that these changes were due to ashes or dust thrown into the air after the impact of a comet or meteorite, or after the eruption of a volcano (a phenomenon known as "volcanic winter"). A similar, lesser episode of climatic aberration was also observed in 1816, popularly known as the "Year Without a Summer", which has been connected to the explosion of the volcano Tambora in Sumbawa, Indonesia.

32. Human history during the medieval warm period 800 AD-1200 AD • At the height of this 400 year warm period the tree line in central Europe was about 500 feet higher than today, vines grew in England as far north as the Severn and farming was possible on Dartmoor as high as 1,300 feet. Large parts of the uplands of southern Scotland were arable land and in 1280 the sheep farmers of Northumbria were complaining about the continual encroachment of arable fields on their upland pastures. • One of the most important effects of the milder climate was on the Viking voyages and settlements. Iceland was colonized from Norway in 874 at the beginning of the warmer period and Greenland from 986. Both of these societies were on the climatic margins of Europe and their existence was largely dictated by the weather. • The Greenland settlement flourished during the warm period with a population of about 3,000, almost 300 farms, sixteen churches and even a cathedral in the main village. But it remained a marginal and highly vulnerable society, dependent on the mild weather for its very existence.

33. The ‘Little Ice Age’ 1400-1850 in Greenland and Iceland • Greenland. The hay growing season gradually became shorter and shorter, yet the Viking settlers tried to retain their way of life based on cattle instead of shifting to the more readily available marine resources. As the climate deteriorated the Inuit moved further south and the Viking western settlement of Godthaab Fjord was destroyed by them shortly after 1350. The severer climate meant that pack ice remained in the seas around Greenland throughout the summer and contact with the rest of Europe was lost after 1408. The eastern settlement at Julianehaab died out, probably under Inuit attack, about 1500. • Iceland, too, became a much more marginal society under the impact of a worsening climate. Wheat growing died out (a one degree centigrade fall in annual temperatures in Iceland reduces the growing season by almost a third) and marine resources became overwhelmingly important in the economy. In the harsher climate the numbers that could be supported were much less and the population fell from about 77,000 at the height of the warm period around 1100 to 38,000 in the late eighteenth century.

34. The ‘Little Ice Age’ in Europe • The increasingly colder climate affected the rest of Europe too. The uplands of southern Scotland reverted to pasture and the growing o f vines for winemaking died out in England about 1400. • But the real impact of a much worse climate was felt after the middle of the sixteenth century - a series of severe winters and a period of much greater climatic instability began that was to last for almost three hundred years. • After 1580 the glaciers in the Alps, Iceland and Russia advanced, in many places by over a mile, and did not begin to retreat until after 1850. Between 1564 and 1814 the Thames froze in the winter at least twenty times, as did the Rhone three times between 1590 and 1603 and even the Guadalquivir at Seville froze in the winter of 1602-3. At Marseilles the sea froze in 1595 and in I684 there was pack ice off the coast of England. From the 1580’s the Denmark Strait between Iceland and Greenland was regularly blocked by pack ice even in summer. • Across Europe the lower temperatures reduced the growing season by about a month and lowered the height at which crops could be grown by about 600 feet, with consequent adjustments to the cultivation areas of nearly all crops. Outbreaks of even more severe weather within the overall pattern of a deteriorating climate could have devastating effects. For example, a series of cold mistral winds destroyed many of the olive groves of Provence between 1599 and 1603 and very heavy frosts around Valencia in the same period ruined many of the fruit trees.

35. The ‘Little Ice Age’ in Europe (continued) • The effects varied in different parts of Europe. There was no simple relationship between the temperature, the amount of rain and the size of the crop since the most important factor was how these influences were distributed through the seasons. The overall decline in temperature had its greatest impact in Scandinavia, where the reduced growing season made many areas extremely marginal for growing crops. • Further south a very cold winter might have some beneficial effects by killing a higher than normal number of pests. But even here the consequences of a deteriorating climate can be detected. In England there was a shift towards spring rather than autumn sown crops in order to try and avoid damage from a harsh winter. In the Netherlands, buckwheat, which is hardy and has a short growing season, but which was hardly grown in Europe before 1550, became increasingly important in the next hundred years. • Other evidence from the Netherlands suggests that a cold, late spring reduced grass growth so that pastures were late to develop, reducing dairy output, increasing prices and also leading to a slaughter of cattle the following year if the hay crop was not sufficient to provide enough feed till the new grass had grown. In other areas increased rain could be most damaging, especially in the winter, by reducing arable yields because of waterlogged soils. This long period of poor climate came at a time when European population was already at the limit that the agricultural system could support. The worsened growing conditions meant a significant reduction in food production leading to increased malnutrition, widespread famine and death. One consequence was a period of much greater internal instability within the European states, which was particularly acute in the early seventeenth century.

36. The Beginning

37. The End (for now)