GEOL 0820 Ramsey Natural Disasters Spring, 2021 LECTURE #23: Mega Disasters – Climate Change Date: 19 April 2021 I. Final Exam • same access as the mid-term exams using Canvas o I will send a reminder email to your Pitt email account over the weekend o the exam will “open” at the start of the assigned time period: Wednesday, April 28th at 2:00pm and close at 3:15pm • same format as the mid-term exams o except a little longer (~75 questions) nd o material: 2 half of hurricanes, flooding (plus the video), wildfires, mega- disasters o weeks 11 – 14 II. Early Earth • was more similar to present-day Venus than what we have today o very high amounts of carbon dioxide (CO2) in the atmosphere and MUCH hotter temperatures Venus early Earth Earth today carbon dioxide (CO2) 96.5% 98% 0.04% nitrogen (N2) 3.4% 1.9% 78% oxygen (O2) ~ 0% ~ 0% 21% argon (Ar) 0.007% 0.1% 0.93% average temperature (°F) 872 550 61 * average pressure (bars) 92 60 1 * Earth would be at/below 32° F with no CO2 (more like Mars is now)! o so, where did all the CO2 go? . 80% is in rocks like limestone (CaCO3) and other organic material (oil/gas/coal) Plate Tectonics! . some dissolved into the oceans . some is in living plants (plants converted CO2 and produced O2) . other biologic uses of CO2 (bones, shells) III. Long Term Climate Change • Earth’s history shows large variations in climate o from the very early Earth with its large CO2 percentages o to much later in history . with extended periods of cooling/ice ages . to renewed periods of warming (e.g., time of the dinosaurs) Page 1/6 o so, how do we know all this? . we can examine changes in rock and fossil composition over time . for example: O2 isotope ratio in shells (think back to those early lectures!) 17 18 there are three isotopes of O2 (16O, O, O) - 16O is the most common evaporation from the oceans favors lighter isotopes therefore,16O and 17O get concentrated on land (as ice/snow) and 18O gets concentrated in the sea if the amount of 18O/16O is measured in shells, scientists know about the conditions of the water at the time they were formed - lower 18O meant warmer conditions - why do you think? o what are factors that lead to these changes? . Plate Tectonics if there is more continental land mass at the poles like Antarctica today - collects more snow - creates ice sheets leads to colder climates . N-S alignment of continents (like today) blocks the normal E-W flow of warm equatorial waters causes them to flow N or S (like the Gulf Stream) - leads to more evaporation and more snow and more cooling . external factors small changes in the Earth’s orbit changes in the sun’s energy output IV. CO2 and More Recent Climate Shifts • shorter term trends o melting of large ice masses on land and rising ocean temperatures . affect the ocean circulation patterns temperature over time Page 2/6 o El Niño / La Niña . cycles of warming and cooling in the Pacific Ocean . changes rainfall and temperature patterns in N. America and elsewhere example, increased hurricane formation and western wildfires in La Niña years o large volcanic eruptions (in more recent history) . particulates (ash and other gases) reflect incoming solar energy can cause years to decades of cooling o very large eruptions (in long-term Earth’s history) . causes extreme weather/climate/agricultural changes example: Toba super eruption 75,000 ago - reduced the total human population to < 10,000 people! • human influences (what we’re seeing now) o burning fossil fuels o land clearing (burning of vegetation) . adds ~ 6 gigatons of CO2 per year still a small influence compared to natural processes but could be enough to trigger more rapid changes (“tipping point”) th o 20 century . the rates of warming are faster than anything in geologic history . causes? changes in plate tectonics, Earth’s orbit, solar output? - no, all too slow no major volcanic eruptions therefore, change in the greenhouse gasses (us!) - most dramatic since 1977 . average of ~ 1° F (not noticeable to us) about ~ 40% of that due directly to man-made activities (emission of greenhouse gases) temperature change over the last 1000 years Page 3/6 temperature change over the last 140 years • what are greenhouse gases? o most common: . water vapor (H2O) . carbon dioxide (CO2) . methane (CH4) . nitrous oxide (N2O) . ozone (O3) . CFC’s o allow solar heat in but trap the radiant heat from the Earth from escaping . water vapor (H2O) responsible for ~ 75% of the greenhouse effect o commonly produce positive (sometimes leading to run-away) feedback loops . example, more warming more evaporation more H2O in the atmosphere more warming . another example, snow/ice cover: more warming less snow/ice less solar energy reflected & more absorbed by the ground more warming . CO2 receives the most attention (example, the Keeling curve) - small changes have a much larger impact - CO2 is the highest in the atmosphere in the past 800,000 years - only about 50% is removed by natural processes Keeling Curve Page 4/6 V. Next 100 years? • Intergovernmental Panel on Climate Change (IPCC) o 100’s of scientists meeting and reporting their findings on climate change o assess current models/predictions o report areas of uncertainty climate impacts and uncertainty (IPCC) o issue high-level findings, such as: . warming of climate is not in question . 90% of all warming since 1950 is due to human activity . all greenhouse gases are at their highest amount in the past 650,000 years . the probability that this is all from natural causes is < 5% . average world temperatures could rise from 1 to 6° F by 2100 > 60% chance of increased droughts, hurricanes, and extreme tides > 90% chance of more frequent heat waves and heavy rainfall a rise in sea level of between 7 – 23 inches levels now will continue to affect the climate for the next 1,000 years! estimated temperature rise by 2090 (relative to 1990) Page 5/6 VI. Mitigation Options? • changes in technology o carbon-free or carbon-neutral energy technologies for power plants, cars, etc. takes time (politics) o cap and trade . limit CO2 emissions through a market-based trading system . CO2 producers pay more for emissions credits . non-CO2 producers gain by selling credits o air scrubbing . possible but VERY expensive o fertilizing the oceans to grow algae (similar to massive tree planting) . they would take up CO2 . effects on the ocean’s biosphere unknown? o weathering of rocks . pulls CO2 out of atmosphere and makes carbonic acid . also very slow o geoengineering . inject large amounts of particles into the atmosphere to reflect solar energy similar to a volcanic eruption risks unknown? . carbon sequestration capturing CO2 and injecting it deep underground in a liquid form o all will take a long time and large cost to implement . unfortunately, this lowers the political will to act Page 6/6 .