Chapter 7 The Issue of Global Warming Developing the Case of Human Responsibility Key Points Greenhouse gases maintain the temperature on Earth at a level for live. Human activities increase the amount of GHGs in the atmosphere. Increased GHGs may lead to warming of the atmosphere and climate change. Increased GHGs may alter weather patterns, shift biomes and increase sea levels. Feedback mechanisms are very comples and changes may lead to positive or negative results. Governments & individuals can act to reduce GHG emissions. There is still much controversy & varying preceptions about global warming. Short Term Objective 1. Describe the functioning of the atmospheric system in terms of the energy balance between solar and long-wave radiation. (ν): The number of waves that pass a fixed point per second Wavelength, Amplitude, Peak & Valley Peak Peak Valley Valley What do you know already Make a list of causes of climatic change. Burning fossil fuels Volcanic activity & astroid impacts Changes in Earth’s orbit Progression of the equinoxes Milankovitch Cycles Sun spot activity What are the percentages? Questions???? The Earth’s atmosphere is an example of an open system What does this mean and why is it important? The Greenhouse effect is natural and important to the earth. Why? N Albedo may affect the energy balanceS between short and long term radiation What is albedo? Use figures from the table to describe how the albedo of the atmosphere can change the amount of solar radiation arriving at the ground surface. Use figures from the table above to describe how the albedo of the ground surface can change the amount of long wave radiation emitted by the earth If the Greenhouse effect is natural then what’s the problem? Climate changes all the time but what has happened recently? The problem is that the rate of change seems to have risen rapidly since the Industrial Revolution. Hence it is sometimes called the Enhanced Greenhouse Effect. Why? The causes of climate change 1. Increasing levels of Greenhouse Gases in the atmosphere Climate Change is not a new thing! The worlds climate has been changing over the last 18,000 years, sometimes getting hotter and sometimes colder as you can see from the graph below. Paleoclimate Cycles During most of Earth history, global temp. was 8-10°C warmer than today, but there have been a few long periods of sustained globally cold periods. ice ages: 2500 Myr, 700 Myr, 300 Myr and 42 Myr Even over short periods there are fairly large fluctuations Proof of Global Warming? What do you think? Does it matter whether the causes of global warming are natural or human? How do the causes of global warming impact the way we mediate the problem? How to Change Global Climate The ways in which global climate may be influenced include: •changes in Earth’s orbit •variable solar output •changes in ocean circulation patterns •albedo (reflectivity) effects •greenhouse effect Is climate change natural or human induced (anthropogenic)? There are 3 main natural events that scientists believe affect the worlds climate: 1. Variation in solar output 2. Variation in the earths orbit 3. Volcanic eruptions and cosmic causes 1: Variations in Solar Output The sun’s output is not constant; it also varies. A variety of cycles have been detected, most are short term. The most obvious is due to the 11-year sun spot activity cycle. The effect of sunspots is to blast more solar radiation towards the earth Some scientists have suggested that around 20% of 20th Century warming may be because of solar output variation However a study in 2006 showed no major increase in solar output since mid 1970s Sun Spot Activity: Q & A What are sunspots? How are they linked with the amount of solar radiation the earth receives? Describe the pattern of sunspot activity. What is the link between sunspot activity and global temperature anomalies? 2: Variations in the Earth’s Orbit Milankovitch Cycles A Serbian physicist working at the beginning of the 20th century. He identified 3 variations in the Earth’s orbit around the Sun Link Milutin Milankovitch 1879 - 1958 Eccentricity of Earth’s orbit 18_2.swf Every 100,000 yrs the Earths orbit changes from spherical to elliptical, changing solar input Obliquity of the Earth’s Axis The Earth’s axis is tilted at 23.5o, this changes over a 41,000 yrcycle between 22o & 24.5o, affecting solar input, especially in higher latitudes. Wobbly Axis! The Earth’s axis wobbles, so which way the hemispheres are facing to the sun when closest to the sun varies over 21,0000 yrs. Affecting solar input. Milankovitch Cycles Many scientists argue that the Milankovitch cycle may have been just enough to trigger a major global climate change, but that climate feedback mechanisms are needed to sustain it. Feedback effects are those that can amplify a change and make it bigger (positive) or smaller (negative). An e.g. of positive feedback is snow and ice cover. Small increase in snow and ice raises surface Aledo reflecting more solar energy back into space. Resulting in further cooling An e.g. of negative feedback s cloud cover. As GW occurs, more evaporation occurs increasing cloud cover, which in turn may reflect more solar rays back into space diminishing effects of the warming. Also Tundra?? What effect does the tundra have in GW? 3. Volcanoes & Cosmic Collisions Major eruptions eject material into stratosphere. The sulphur dioxide forms a haze of sulphate aerosols, which reduces the amount of sunlight received at Earth’s surface The eruption of Tambora led to the year without a summer in 1816 as global temperatures dipped by 0.4-0.7 degrees C An asteroid smashing into the Yucatan peninsular is thought to have contributed to extinction of the dinosaurs. Unprecedented Global warming? What does this phrase mean? been seenwidespread before! Never “The observed warming of the atmosphere and ocean, together So is Global warming unprecedented? with ice mass loss, support the conclusion that it is unlikelyasthat global climate ofwarming the past in 50the yrspast. extremely Not unprecedented we have had periodschange of global be explained external forcing, very likely that it is can The IPCC* sums upwithout the current views on Globaland warming: not due to known natural causes alone” Anthropogenic Causes Seem To Be Confirmed! Facts Satellite observations since 1993 suggest an annual rise in sea level of 3.1mm, and a decline in Arctic sea ice of 2.7% per decade The level of CO2 in the atmosphere is far above the ‘natural’ level and continues to rise. Temperature rises have been recorded on all continents since 1970 11 of the 12 warmest years on record occurred between 1995 and 2006 Where do we get the long term evidence for climate change from? 1. Ice Cores • Best evidence for climate change comes from Greenland and Antarctic ice cores • Ice cores are a frozen record of past climates. Like a time capsule!! • Within these layers the ice contains air bubbles which contain carbon dioxide and oxygen isotopes. • From looking at the graph you can see clearly the periods of low concentrations of CO2 occur during glacial periods • High concentrations of CO2 link with warmer periods of time- like the Holocene interglacial we are going through now! How accurate and reliable are these sources of data? The sequences of sea level change links very closely with oxygen and CO2 isotope levels suggesting that this is a very reliable source! Where do we get the long term evidence for climate change from? 2. Pollen Analysis Pollen was extracted from sediment cores in peat bogs and lake beds. Pollen grains are preserved in waterlogged sediments. By analysing pollen we can see how ecosystems have changed in response to climate change. How accurate and reliable are these sources of data? 2. Pollen Analysis Not as reliable - as accurate pollen reconstructions rely on good preservation of pollen. Long pollen sequences are rare, and vegetation change may lag behind “climate change”. Where do we get the medium term evidence for climate change from? 1. Tree Rings (Dendrochronology) Many trees are sensitive to changes in temp, sunlight and precipitation In warm years trees have wide rings & vice versa Record can go back 10,000years+ How accurate and reliable are these sources of data? 1. Tree Rings (Dendrochronology) Good reliability – However, tree records only give localised records! Where do we get the medium term evidence for climate change from? 2. Paintings and written accounts London Frost Fair 1789 Bruegel Painting 1565 How accurate and reliable are these sources of data? Paintings are a good line of evidence Where do we get the medium term evidence for climate change from? The written word Dickensian Winters How accurate and reliable are these sources of data? The written word is also good evidence Where do we get the medium term evidence for climate change from? 2. Historical records How accurate and reliable are these sources of data? 2. Historical records Unreliable – These sources did not set out to record climate, and must be used with care. They are usually local, and difficult to generalise. Where do we get the medium term evidence for climate change from? 3. Glacier Retreat Glaciers change in response to climate change. We can look at old photos/maps/paintings to measure direct differences in glacial positions How accurate and reliable are these sources of data? 3. Glacier Retreat Reliable – Good records stretch back to around 1880, before this the record is patchy. Where do we get the short term evidence for climate change from? The last 128yrs of data suggest the Earth is 0.7 – 0.8 oC warmer 11 of the world’s hottest 12 years occurred in the decade 1995-2006 Global warming or natural? How accurate and reliable are these sources of data? Good evidence of the Link between CO2 & temperature Three possible effects of climate change. 1. Rise in Global Mean Temperature 2. Rise in Average Sea Level 3. Decline in Northern Hemisphere Snow |Cover Homework “An Inconvenient Truth” or “The Death of the Oceans” Watch it and fill in the sheets ready for discussion next lesson. Is the Carbon Anthropogenic (human) or Natural? Most scientists agree Anthropogenic causes are producing the enhanced greenhouse effect and leading to unprecident global warming.