Physical Geology 101 31. Climate Change (p. 502-510; 568-590) Weather and Climate Weather is not the same as climate. The weather refers to __________________________________ ___________________________________. This involves changes in: _______________________ _______________________ _______________________ _______________________ _______________________ Fluctuations in weather on the scale of hours, days, weeks, months, and years are totally natural. What well-known natural influences on global weather, affecting global temperatures and rainfall and causing billions of dollars in damage, are due to ocean current variations in the Pacific? ____________________ and ____________________ Over what time scale does this occur? _________________________ What is climate? _____________________________________________________________________ For example, the climate in equatorial areas is typically ____________________. The climate in areas between 20-30° latitude is typically ________________________, producing deserts. The regional climate of these areas may have a natural variability over the years, but there may also be major changes in climate over longer periods of time. For example, the climate may get much cooler, such as during an ice age, or it may get much hotter through a process called _____________________. Example of a region where climate has changed greatly in the past 30,000 years: _________________________ (used to have lush forests and high rainfall) Long term climate changes may result in a region turning to desert. This process is called: ______________________________ Ice Ages One of the obvious lines of evidence of global climate changes is the occurrence of ice ages in Earth's past. The ice ages point to the global climate having been much cooler, so that the entire planet was affected. Ice ages have occurred at least 5 times in Earth's history and may last around a million years. Examples of major ice ages: ______________________________ (~300 million years ago) – Karoo Ice Age ______________________________ (<1.6 million years ago) – Pleistocene Ice Age What is the evidence for an ice age 300 million years ago? ______________________ (glacial rocks) 1 Physical Geology 101 Over the past few million years, there have been numerous cycles of heating and cooling in global climate. How much do global mean temperatures need to drop for an ice age to occur? __________________________ During the past 1.6 million years- the Pleistocene and Holocene epochs, there have been global lows in temperatures on average every __________________ years. How many cycles of ice ages occurred during the last ice age? ______________ What name is the last ice age known by? ____________________________ Less extreme variations in global temperatures occurred in cycles of about ___________________ years during the ice age. When did the most recent ice age end? _______________ years ago. A period of warming in between ice ages is called an _________________________. The warmest point in the current interglacial period was between 7,000 and 6,000 years ago. Since then, it has been getting steadily WARMER or COOLER ? There have been short-term variations such as between 1300 and the mid-1800s, when glaciers around the world were advancing. This ~500 year period of cooling is referred to as the ___________________. Right now, we seem to be on a warming trend within a longer time-scale cooling trend. What regions were covered by ice sheets during the last ice age? ___________________, __________________, and _______________________ During an ice age, ice sheets expand in size but we never have the entire planet being covered in ice. Only the coldest regions in the northern and southern hemispheres were ice-covered. How thick were the Pleistocene ice sheets? _________________ How much of the Earth's surface did they cover? ___________ How much of the Earth's surface do ice sheets cover today? ____________ Changes in the size of ice sheets affect the climate in regions that are not covered in ice. As the ice sheets expand, warm and moist regions get shifted towards the equator. So the warm, moist Mediterranean climate got shifted southwards during the last ice age, into northern Africa. That’s why the Sahara Desert region used to be much wetter. Evidence for Ice Ages The study of ancient climates is called _________________________. There are several lines of GEOLOGICAL evidence for determining past climates: 2 Physical Geology 101 ________________________ - fossilized plants and animals can be related to specific types of climate that such species would have inhabited. Example: _______________________________ ________________________ - sedimentary rocks can often be linked to specific depositional environments, such as varve clays from glacial lake beds and tillite. ________________________ - ancient soils, also called __________________, have minerals in them that tell us of the chemical conditions in ancient air and water that can be related back to the temperature conditions. _____________________________ - we can study the isotope ratios of elements like oxygen in ancient sediment layers, corals, and ice cores drilled from deep in ice sheets to tell us about the composition of the ancient atmosphere. ________________________ - the distribution of recessional moraines can tell us about the extent of old ice sheets. (Example: ___________________________). Grooves on glacial pavements can tell us the directions that glaciers were moving towards. ________________________ - there were large lakes that formed far from the glaciers during the last ice age because of lower temperatures and less evaporation. Example: ________________________________ ________________________ formed along the edges of the ice sheets, dammed by glaciers. Example: _______________________________ This glacial lake broke through its ice dam many times, causing huge floods that washed over N. Idaho and E. Washington, forming the ____________________. The surface was stripped bare of topsoil, basalt was heavily eroded. As the lake drained, _____________________, up to 10m high, formed along the old lake bed. ________________________ - sea level was up to __________ lower during the last ice age because of all the water taken up by glaciers. This caused major changes in stream channels, and provided land bridges connecting areas of land that today are separated by water. This allowed many species of animals to migrate into new areas. Lowered sea level allowed many species of animals to migrate into new areas. A migration of humans into ____________________ from _____________ was possible during the last ice age because a land bridge extended across the Bering Strait between the two continents at that time. Causes of Global Climate Change What four types of geologic events may cause changes in global climate? 1. _____________________ 2. _____________________ - time scale over which climate is affected: ____________________ 3. _____________________ 4. _____________________ 3 Physical Geology 101 Global climate changes that resulted from the Chicxulub meteorite impact on the Yucatan Peninsula, Mexico, 65 million years ago resulted in the extinction of the dinosaurs. When we look at the variations in global temperatures, there is an obvious cyclicity that suggests some natural control on global climate variability over long time scales. This is related to changes in the Earth's rotation and revolution about the sun over long periods of time. First of all, the Earth does not have a perfectly circular and unchanging orbit about the Sun. Its orbit is slightly elliptical, and changes shape over a time scale of about _________________. This phenomenon is called ___________________. Also, the inclination of the Earth's tilt, currently 23.5° from vertical, oscillates back and forth between 21.5° and 24.5°, varying by about 1.5° every _________________. The direction the rotation axis faces also wobbles about over a time scale of ________________. This phenomenon is called ___________________. These three effects cause changes of up to 10% in how much of the Sun's energy strikes the Earth at a particular location. The changes are mathematically regular, and are known as: ______________________________________. Which phenomenon is responsible for global climate changes on the: 20,000 to 40,000 year time scale: 100,000 year time scale: PRECESSION PRECESSION or or ECCENTRICITY ? ECCENTRICITY ? Anthropogenic Influences on Climate Since the Industrial Revolution, human activities (also called ___________________________________) have resulted in a sharp increase in the amount of greenhouse gases emitted into the atmosphere. These are the substances that tend to cause an increases in temperatures at the surface because they absorb heat. Examples: ____________________, _____________________, ____________________________ The burning of fossil fuels like coal and petroleum has been a major cause of these increases. There are naturally occurring greenhouse gases in the atmosphere, such as water vapor and naturally occurring carbon dioxide and methane. These gases help keep the Earth's surface warm and habitable. But anthropogenic greenhouse gases appear to be upsetting the balance. In the past 100 years, global temperatures have risen by an average of _____°F (_____°C). Changes of just a few degrees are enough to cause major climate changes, so this is an alarming trend. For example, melting of glaciers would cause the Earth's ocean levels to rise by several meters or 10s of meters. Flooding of coastal areas would be devastating, and low-lying regions like Florida, Netherlands, Bangladesh, and the South Pacific islands could be eradicated. FINAL QUESTION: 4 Physical Geology 101 What is the projected temperature increase by 2100 if current trends continue? _______________ 5