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Class Notes for Lecture 7: Atmospheric Stability and Climate Change/Global Warming

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Class Notes for Lecture 7: Atmospheric Stability and Climate Change/Global Warming Sergio Ibanez ERTH 365 Class notes for Lecture 7: Atmospheric Stability and Climate Change/Global Warming Atmospheric vertical motion ● Important for energy and moisture transportation ● No Vertical movement = no precipitation, no clouds, and no mixing of pollutants away from ground level There are two types of vertical motion (Trigger Mechanism) ● Forced (dynamic) ○ Up over a hill ○ Warmer air over colder air ○ Horizontal convergence ● Buoyant (Thermal) ○ Air rises because it is less dense than its surroundings ○ Stability is important here Temperature changes with height (lapse rate) Two types ● Environmental Lapse Rate (ELR): Actual rate at which temperature is either increasing or decreasing at any given height ○ What you would measure with a weather balloon ● Parcel Lapse Rate ○ Temperature changes an air parcel when displaced vertically ○ Assume adiabatic process (i.e. no heat exchange occurs along parcel boundary) Sergio Ibanez ERTH 365 Temperature changes (usually decreases) with height Factors that influence ELR ● Heating or cooling of the lower atmosphere ● Advection of warm air or cold air at different levels ● New air mass Air parcels ● Rises and expands = cooling ○ AIr molecules further apart, few collisions > lowers the parcel of air ● Sinks and compresses = warming ○ Air molecules closer together, more collisions > warms the parcel of air Adiabatic if no heat exchange between the parcel and outside air Sergio Ibanez ERTH 365 Adiabatic Lapse Rates: ● Dry adiabatic rate if not saturated (RH < 100%) ○ Lapse rate = 5.5* F/1000 feet (constant) ○ 10* C/1000m ● Moist Adiabatic Rate if saturated (within cloud) ○ Heat from condensation offsets cooling ○ Lapse rate = ~3.3* F/1000 feet (variable) ○ ~6* C/1000m Stability in the atmosphere ● If the air is displaced from its original height ○ Stable - Returns to its original height ○ Unstable -Accelerates upward because it is buoyant ○ Neutral - stays at the level to which it was displaced Is a parcel warmer/colder than its environment? ● If colder (heavier) than stable ● If warmer (lighter) than unstable Absolute Stability ● Both dry and moist parcels are colder (heavier) than environment ● Return to original positions ● Reasons ○ Radiative surface of cooling at night ○ Advection of cold air near surface, warmer, aloft ○ Air moving over a cold surface ● Typically at night or cold winter days Absolute Instability ● Both dry and moist parcels are warmer (lighter) than environment ● Continue to rise ● Reasons ○ Surface heating ○ Warm advection Sergio Ibanez ERTH 365 ○ Cooling aloft ● Typically during the day or hot summer days Conditional Instability ● Dry (unsaturated) air is lifted ● Saturation occurs - releases latent heat and becomes warmer than surroundings ● Continues to rise as unstable air Cloud Development ● Clouds develop as an air parcel rises and cools below the dewpoint ● Usually a trigger or process is needed to initiate the rise of an air parcel ● Convection ○ Differential land surface heating creates area of high surface temperature ○ Air above warm land surface heats, forming a bubble or warm air that rises ○ Cloud base forms at level of free convection or cloud condensation level Section 2: Climate Change Looking at changes in the changes of the climate in the past present or future associated with natural or anthropogenic (human) factors Global Warming Warming of the 21 and 20 century associated with anthropogenic (human) factors Climate Change ● Is complicated ● Changes impact some areas more than others ● Human perspective is relative due to short lifetimes ● GCMs (Global Climate Models) Produce Multiple Outcomes Sergio Ibanez ERTH 365 To reconstruct past climates it is possible to use ● Instrument records ● Proxy measurements ○ Tree rings ○ Ice cores (oxygen isotopes) ● Plate tectonics (folding, faulting) and erosion complicates the picture ○ Record confused or destroyed (90 - 99% eroded) ○ Little remains from first 90% of earth’s lifetime ○ Changes in arrangement of continents and oceans In the 16th to 19th century ● Cooler period “little ice age” ○ Glaciers expanded ○ Cool summers and severe winters ○ Not a period of sustained cold The greenhouse effect ● Greenhouse gases ○ Transparent to incoming solar radiation ○ Efficiently absorb outgoing long wave radiation ○ Leads to warmer atmosphere ○ Carbon Dioxide is worst greenhouse gas\ Sergio Ibanez ERTH 365 Recent Warming ● Decrease in exceptionally cold temperatures ● Increase in exceptionally warm temperatures ● Minima have increased more rapidly than maxima ● Diurnal temperature decreased 0.08* C per decade ● Most pronounced warming Northern continents ● Marked cooling ○ Northwest Atlantic Ocean ○ Less in North Central Pacific ● Changes appear most clearly in winter IPCC ● Intergovernmental panel on climate change ● Established 1988 by WMO ● 194 nations are a part of it ● 3000+ climate scientists ● 2014 issued 5th assessment report summary IPCC 5th assessment report summary ● Warming of the climate system is unequivocal ● Most of Global Temperature is very likely anthropogenic ● It is likely that 1983 - 2013 was the warmest 30 year period for 1400 years ● There is high confidence that the sea level rise since the middle of the 19th century has been larger than the mean sea level rise of the prior two millenia ● Concentration of greenhouse gases in the atmosphere has increased to levels unprecedented on earth in 800,000 years ● Anthropogenic warming and sea level rise would continue for centuries ● Probability warming is only natural variation is less than 5% ● World Temperatures could probably rise between 2 and 15 F Sergio Ibanez ERTH 365 ● Sea levels will probably rise by 7 to 23 Key findings of IPCC 1.5C Report Impacts are already occurring and will be much worse at 2°C than previously projected. That means 2°C is no longer a safe goal to avoid the worst impacts of climate change. We can avoid much, but not all, of the loss and risk of climate change by limiting warming to 1.5°C Potential climate change impacts ● Health ○ Weather related mortality ○ Infectious disease ○ Air quality respiratory illnesses ● Agriculture ○ Crop Yields ○ Inflation demands ● Forest ○ Forest composition ○ Geographic range of forest ○ Forest health and productivity ● Water resources ○ Water supply ○ Water quality ○ Competition for water ● Coastal areas ○ Erosion of beaches ○ Inundation of coastal lands ○ Additional costs to protect coastal communities ● Species and natural ○ Loss of habitat and species ○ Cryosphere: diminishing glaciers ● Predictions for Bay Area ○ Decreased winter precipitation as jet stream moves north ○ Increased summer precipitation as water is warmer/more subtropical moisture ○ Weaker sea breezes due to warmer ocean temperatures results in hotter summer ○ Less snowpack in Sierra Nevada, leading to water shortages Sergio Ibanez ERTH 365 ● Feedback mechanisms ○ 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 Climate Change Deniers Out of 13,950 peer reviewed climate change articles between 1991 to 2012, 24 rejected the concept of global warming .
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