GEOL 106 - LEC 7

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Geological Sciences and Geological Engineering
GEOL 106

11-11-22 9:06 PM Climate Change Chapter 11 Weather • short-term (days to weeks) atmospheric conditions (temperature/rainfall/etc) Climate • Long-term (years/decades/centuries) atmospheric conditions o Eg, tropical vs. temperature vs. arctic climates The ‘rock record’ tells us that there certainly has been climate change in the past Eg. look at Kingston Ontario • Covered in ice sheets 20,000 years ago • Covered in shallow tropical seas 500,000,000 years ago (ie. 500 million years) Why might climate change? 1. ‘natural’ causes • eg. Increased solar luminosity (sun getting brighter) The sun was 0.7 4 billion years ago and now it is 1.0 2. Anthropogenic Causes (Human induced) • burning coal/oil/gas © • perhaps adding carbon dioxide (co2) to the atmosphere and heating it Human induced Climate change • Specifically, enhanced global warming caused by human burning coal, oil and gas • Global warming exist??? YES • Green house gases heat out atmosphere H2O,CO2, CH4 (methane), NOx(nitrous oxides), 03 (ozone) o Without them, the average earth surface temperature would be -20*C (below freezing) But is there enhanced global marming? 1. have humans been changing the amounts of these greenhouse gases in the atmosphere? • We’ll look particularly at CO2 2. If so, is it leading to a warming of the atmosphere? 3. if 1 and 2 are both yes then what is the rate of change? So: we will look at the hazard posed by enhanced global warming as an example of climate change. How does the hazard of climate change differ from the other hazards we have discussed in the course? • Generally messier more complex and less-well understood So : is there enhanced global warming? • First question: is there an increase in atmosphere carbon dioxide (co2) due to human action) Global co2 emissions from human activity, 1800-2004 • But did all of that co2 remain in the atmosphere and did it cause warming • We need to look at the recent history od atmospheric co2 to determine if humans have affected it (recent=the last 2 million years) • How do we measure it in the past? o 1. Measure it directly day after day  we’ve only been doing this since the 1950’s  eg. Co2 concentration measured at Mauna Loam Hawaii  The ‘saw-tooth’ ups and downs are due to seasonal varaitions  Winter: tress dormant and co2 is not being extracted from atmosphere  Spring/summer: trees active suciking co2 out of atmosphere o 2. To go back farther in time, measure co2 in air bubbles trapped in ice sheets in Antarctic and Greenland Glaciers  this takes us back to over 400,000 years ago (we can count the annual ice layers as we go deeper) just like counting tree rings  eg. Greenhouse gases co2 methane and nitrous oxide is fairly straight in the graphs then it gradually increase rapidly Photosynthesis in plants • Carbon dioxide + water - sugar + oxygen So: A) todays level of atmospheric co2 is way higher then it has been for the last 400,000 years B) the dramatic rise in atmospheric co2 began with the Industrial Revoluiton Conclusion to first question -> is co2 in the atmospheric increasing due to human actions?? Almost certainly yes Second Question • Has the human induced atmospheric co2 increase led to an increase in atmospheric temperature? Answer probably • IPCC computer models predict an atmospheric temperature increase of somewhere between 1.8*C and 4.0*C by the year 2100 Third Question • How do we determine if the ratio of temperature increase since the Industrial increase since the industrial revolution has been unusually ( and potentially dangerous) rapid? o By looking back at the geological record of temp change (and there consequences) As an example we will look at the Younger Dryas Event about 12,000 years ago • Younger Dryas Event o We were warming up after the last glaciation, reaching temperatures near present values about 13,000 years ago  Suddenly (in as little as a few decades), Europe pluged back into sever cold ( the youger dryas event) .. what caused this sudden cooling? How do we determine global surface temperature in the past? • 1. Look at historical temperature readings (taken by humans) o since 1880 A.D. there appears to have been an increase of around 1*C o But maybe its not the increased co2 that has caused the warming. Need to consider all the factors that have changed that might have forced the temperature to increase (eg. Solar luminosity, etc).  Forcing factors -> no doubt that it: human produced greenhouse gases (like co2) dominate • 2. Look at ice cores and o to determine atmospheric temperatures from before humans were around:  look at oxygen isotopes in the ice cores  Ice is H20 : there is heavy 18 O and light 16 O  When it is warmer, more heavy 18 O evaporates from the sea  Thus the snow falling on ice sheers has a larger 18 O / 16 O ration when it is warmer  (look at Antarctic ice core data)  can also look at oxygen isotope ratio in fossil shells (CaCO3) in mud layers in lakes  can take us back 1 million years ago o When co2 is low the temperature is low wh
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