Week 15 Notes TONIGHT (May 5) Term Papers Due Term Papers Due Climate Change (Chp 14) Climate Change (Chp 14) Review Review May 12 – Class begins at 6:30 PM Final Exam Final Exam Extra Credit papers due Extra Credit papers due May 18 (Mon) - Grades available

Final Exam 200 Points 200 Points 66 multiple choice questions (3 points each) 66 multiple choice questions (3 points each) ~ 22 questions from ~ 22 questions from Thunderstorms (Chp 10) Thunderstorms (Chp 10) Tropical Storm (Chp 11) Tropical Storm (Chp 11) Air Pollution (Chp 12) Air Pollution (Chp 12) Climate Classifications (Chp 13) Climate Classifications (Chp 13) Climate Change (Chp 14) Climate Change (Chp 14) ~ 44 questions - previous chapters ~ 44 questions - previous chapters Study previous exams !! Study previous exams !!

Climate Change

Climate Change vs. Climate Variability Climate variability: Climate variability: – Average value of a climate element (temperature) does not change, but fluctuates from observation to observation Climate change: Climate change: – Average value of the climate element changes over time (average temperature increasing or decreasing)

Climate Change Climate change is complicated Climate change is complicated Change impacts some areas more than others Change impacts some areas more than others Human perspective is relative Human perspective is relative - short lifetimes GCMs (Global Climate Models) may produce more than one outcome in the climate system GCMs (Global Climate Models) may produce more than one outcome in the climate system Recent realization that humans DO impact climate Recent realization that humans DO impact climate

Looking into the Past Use caution – Use caution – Alternative explanations other than climate change! Alternative explanations other than climate change! In 17th & 18th centuries, the river Thames in London froze in winter In 17th & 18th centuries, the river Thames in London froze in winter Much colder winters? Much colder winters? Or another explanation: River was able to freeze more readily back then? Or another explanation: River was able to freeze more readily back then? – Old London bridge acted to slow river flow down – Lack of embankments back then (river wider) – Lack of waste heat from industrial plants Weather records show winters back then were 1º C cooler Weather records show winters back then were 1º C cooler

Reconstructing Past Climates Instruments records Instruments records Proxy measurements Proxy measurements Tree rings Tree rings Ice cores Ice cores Plate tectonics (folding, faulting) and erosion complicates the picture Plate tectonics (folding, faulting) and erosion complicates the picture – Much of the record is confused or destroyed (90-99% eroded) – Little remains from first 90% of Earth’s lifetime Changes in arrangement of continents and oceans Changes in arrangement of continents and oceans

Ice Age Times in Earth’s history when ice covered a large part of the Earth’s surface Times in Earth’s history when ice covered a large part of the Earth’s surface First proposed by Swiss naturalist Louis Agassiz First proposed by Swiss naturalist Louis Agassiz “Erratics” – rocks found in unusual areas “Erratics” – rocks found in unusual areas Found blocks of granite transported 100 kilometers from Alps Found blocks of granite transported 100 kilometers from Alps

From 2.7 to 1.8 Billion Years Ago “Snowball Earth”: Widespread, global glaciation “Snowball Earth”: Widespread, global glaciation Evidence of glaciers in parts of Africa located near the Equator at the time Evidence of glaciers in parts of Africa located near the Equator at the time 3 discrete glaciations found in Wyoming between 2.5 and 2.2 billion years ago 3 discrete glaciations found in Wyoming between 2.5 and 2.2 billion years ago

Sudden Shift in Climate Catastrophic event caused increase in CO 2 Catastrophic event caused increase in CO 2 Earth remained free of ice caps for 1 billion years Earth remained free of ice caps for 1 billion years Snowball Earth appeared again – several ice ages observed following warm-up Snowball Earth appeared again – several ice ages observed following warm-up “Cambrian explosion” – after last ice age in this period, acceleration in evolution observed “Cambrian explosion” – after last ice age in this period, acceleration in evolution observed

The Big Five Five clearly established events of mass extinction Five clearly established events of mass extinction During last 600 million years, 99.9% of all previous species died During last 600 million years, 99.9% of all previous species died Now: 1 million species, 75% insects Now: 1 million species, 75% insects

100 Million Years Ago Warmest climate period supported by proxy data Warmest climate period supported by proxy data 6º C to 12º C warmer than present day 6º C to 12º C warmer than present day Configuration of continents played a role Configuration of continents played a role – Equatorial seaway Today Today – Circumpolar ocean current around Antarctica makes Antarctica colder than the Arctic

End of the Mesozoic 248 to 65 Million Years Ago 248 to 65 Million Years Ago Sudden cooling observed Sudden cooling observed One of the “Big Five” One of the “Big Five” Dinosaurs extinct Dinosaurs extinct

Pleistocene 1.8 million to ~10,000 years ago 1.8 million to ~10,000 years ago Repeated ice ages – 32% of Earth covered by ice Repeated ice ages – 32% of Earth covered by ice – Evidence of 7 glacial periods – Each glacial period occurs every 100,000 years – Each glacial period had substantial fluctuations in climate – from extreme cold to near interglacial warmth. Fluctuation in climate dominated by cycles of 21,000, 41,000, and 100,000 years. Fluctuation in climate dominated by cycles of 21,000, 41,000, and 100,000 years. From sediment/ice core data – changes can be sudden! From sediment/ice core data – changes can be sudden!

End of Pleistocene Last ice age maxed out about 18,000 years ago Last ice age maxed out about 18,000 years ago – Ice sheet 3 kilometers thick as far south as Great Lakes – Total ice volume of ~ 90,000,000 km3 (30 million today) – Sea level lower by meters – Global average temperatures 5º C colder than now Dramatic warming started 15,000 years ago Dramatic warming started 15,000 years ago Rapid change in circulation pattern seen (dust) Rapid change in circulation pattern seen (dust) Conclusion: Climate is capable of sudden, large shifts Conclusion: Climate is capable of sudden, large shifts

Pleistocene

The Holocene Recent 10,000 years Recent 10,000 years Warm, stable interglacial period Warm, stable interglacial period Extraordinary quiet phase compared to earlier eras Extraordinary quiet phase compared to earlier eras

6,000 Years Ago Laurentide ice sheet disappeared Laurentide ice sheet disappeared Peak in post-glacial warming Peak in post-glacial warming Temperatures 2-3º C warmer than now Temperatures 2-3º C warmer than now Ancient trees found farther north than trees exist today Ancient trees found farther north than trees exist today

5,500 Years Ago Cooler and Drier conditions Cooler and Drier conditions Historical records can be used now Historical records can be used now Desiccation of Sahara – decline in rain 4,000 years ago Desiccation of Sahara – decline in rain 4,000 years ago Tree line retreats southward Tree line retreats southward Mountain glaciers growing Mountain glaciers growing

9 th and 10 th Centuries Warming in Europe and North Atlantic Warming in Europe and North Atlantic Vikings settle Greenland Vikings settle Greenland Limited geographical coverage of records makes it difficult to say global climate was warmer Limited geographical coverage of records makes it difficult to say global climate was warmer

16 th to 19 th Centuries Cooler period –”Little Ice Age” Cooler period –”Little Ice Age” – Firmer foundation of evidence – Best known example of climate variability in recorded history – Glaciers expanded – Cool summers, severe winters – Not a period of sustained cold – Concentrated in winter half

Since Late-19 th Century Global warming Global warming Evidence comes primarily from instruments Evidence comes primarily from instruments Annual global temperatures have risen 0.62º C Annual global temperatures have risen 0.62º C Warmest years in the record have all fallen in 1990s Warmest years in the record have all fallen in 1990s Warmest 20-year periods: , Warmest 20-year periods: , Slight cooling in-between these years Slight cooling in-between these years

Climate System Components

Climate Change Background  The earth has been in a warming trend for the past few centuries  Mainly due to the increase in greenhouse gas emissions  CO 2, CH 4, N 2 O, H 2 O  Atmosphere warmer because it can retain more heat (larger greenhouse effect)

The Greenhouse Effect Greenhouse gases: – Greenhouse gases are transparent to incoming solar radiation (short wave) radiation, but absorb outgoing long-wave radiation. Greenhouse gases act to warm the atmosphere The most abundant greenhouse gas is water vapor.

The Enhanced “Runaway” Greenhouse Effect Burning of fossil fuels increases greenhouse gas concentrations – Fossil fuels are coal, petroleum, natural gas Clearing of forests – Increases CO2 because plants remove CO2 from the air Enhanced greenhouse gases lead to a warmer climate.

Current CO 2 : ~380 ppm Greenhouse Gases

Greenhouse Gases Warming Effectiveness Different gases vary in their ability to act as a greenhouse warmer. Different gases vary in their ability to act as a greenhouse warmer. GasConcentration (ppm)Greenhouse Warming Strength (W/m -2 ) Water Vapor3000~100 Carbon Dioxide353~50 Methane Nitrous oxide

Recent Warming Primarily a decrease in exceptionally cold temperatures Primarily a decrease in exceptionally cold temperatures Also increases in exceptionally warm temperatures Also increases in exceptionally warm temperatures – Night minimum temperatures have increased more rapidly than daytime maximum temperatures Diurnal temperature range has decreased 0.08º C per decade Diurnal temperature range has decreased 0.08º C per decade Most pronounced warming – northern continents Most pronounced warming – northern continents Marked cooling Marked cooling – NW Atlantic Ocean – Less in north central Pacific Changes appear most clearly in winter Changes appear most clearly in winter

Recent Warming

Mt. Pinatubo - Global Cooling Changing forcing changes the temperature (and water vapor, etc.)

Warming Measurements

Future projections of CO 2 Concentrations What happens in the future depends on how much more CO 2 we release into the atmosphere What happens in the future depends on how much more CO 2 we release into the atmosphere Even the low-emission scenarios result in greatly increased CO 2 concentrations by the year 2100 Even the low-emission scenarios result in greatly increased CO 2 concentrations by the year 2100 – Current Concentration: 380 ppm – Max scenario: 970 ppm – Min scenario: 550 ppm

Future Temperature Projections

GCM Forecasts

Notes on Temperature Projections Projected Warming (2000 – 2100) Projected Warming (2000 – 2100) – From ~2.5°F to ~10.5°F – Not all places will warm at the same rate Curves represent seven independent scenarios Curves represent seven independent scenarios Each bar on right represent range of warming produced by models of differing sensitivities for a specific scenario. Each bar on right represent range of warming produced by models of differing sensitivities for a specific scenario.

Potential Climate Change Impacts

“Median” Scenario Temperature Projections Land areas projected to warm more than oceans Land areas projected to warm more than oceans Greater warming at high latitudes Greater warming at high latitudes

Some areas are projected to become wetter, others drier with an overall increase projected Annual mean precipitation change: 2071 to 2100 Relative to 1990 “ Median” Scenario Precipitation Projections

Sea Level Projections

Main Climate Change Summary Higher temperatures – Higher temperatures – Especially on land Especially on land Polar Regions Polar Regions Hydrological cycle more intense Hydrological cycle more intense Storms have more “fuel,” so they can be more powerful, bringing more intense rainfalls Storms have more “fuel,” so they can be more powerful, bringing more intense rainfalls Sea levels rise Sea levels rise Oceans expand with extra heat Oceans expand with extra heat Melting of polar ice Melting of polar ice

Other Possible Changes As Poles warm quickly relative to the tropics… As Poles warm quickly relative to the tropics… – The jet stream will weaken and move north The storm track will also move north The storm track will also move north Latitude bands degrees should get drier Latitude bands degrees should get drier Rain events begin to replace snow events Rain events begin to replace snow events Reduction in the # of strong tornadoes in U.S. Reduction in the # of strong tornadoes in U.S. Tornado Alley migrates north Tornado Alley migrates north Atlantic hurricanes will more easily form and be generally stronger Atlantic hurricanes will more easily form and be generally stronger

Predictions For the Bay Area Decreased winter precipitation as jet stream moves north Decreased winter precipitation as jet stream moves north Increased summer precipitation as water is warmer/more subtropical moisture Increased summer precipitation as water is warmer/more subtropical moisture Weaker sea breezes due to warmer ocean temperatures results in hotter summers Weaker sea breezes due to warmer ocean temperatures results in hotter summers Less snowpack in Sierra Nevada, leading to water shortages Less snowpack in Sierra Nevada, leading to water shortages

Feedback Mechanisms Climate is linked with many physical processes Climate is linked with many physical processes – A change in part of the climate system may cause subsequent changes in other parts – Subsequent changes could support or act against the original change

Positive Feedback When the response in a second variable reinforces the change in the initial variable Example of positive feedback: – Global temperatures increase – Increase in temperature melts the ice and snow in the upper latitudes – Loss of ice and snow results in a lower albedo at the surface in the upper latitudes – Lower albedo leads to less reflection and more insolation – More insolation results in warmer temperatures

Negative Feedback When the response in a second variable lessens the change caused by the initial variable When the response in a second variable lessens the change caused by the initial variable Example of negative feedback: Example of negative feedback: – Global warming leads to more atmospheric water vapor – Increased water vapor leads to increased cloud cover – Increased cloud cover leads to a higher albedo – Higher albedo results in less insolation at the surface – Reduced insolation at the surface leads to cooling

Week 15 Notes Out of fairness, I have decided to give a general 24-hour extension to ALL students on their term papers. The very latest I will accept any paper is at 6 PM tomorrow (5/6) evening via only. No exceptions.