GEO011 Midterm 1
Climate: Average of many years worth of weather while the weather is the actual state of the atmosphere.
How is climate different from weather: Weather is the actual state of the atmosphere at a particular time. Highly variable and unpredictable
Why is Climate predictable?: It depends on relatively fixed features of the earth: Spherical shape, Shape of orbit around the sun, Tilted axis of rotation. Other important Factors that determine climate: Oceans, continent, Multi-layered atmosphere composed of greenhouse gases (GHGs).
Climate Change: Refers to significant and lasting changes in climate, particularly the increase in global average temperatures and sea-level rise due to human activities like burning fossil fuels, deforestation, and industrial processes.
How is sunlight related to latitude?: The amount of sunlight depends on latitude. Near the equator (low latitudes), the sun's rays are more direct, leading to warmer temperatures. Near the poles (high latitudes), the sun's rays are more spread out, resulting in cooler temperatures. Reasons why tropics are hot, and poles are cold.
Feature of seasonal contrast with latitude: Seasonal contrasts in temperature are more pronounced at higher latitudes due to the tilt of the Earth's axis, leading to varying angles of sunlight throughout the year. How hot (cold) the summer (winters) are. Tropics (mid-to-high latitudes) have low (high) seasonality.
Cause of seasons: Tilt of earth’s spin axis. Its orbit around the sun, leading to varying angles and durations of sunlight at different times of the year.
How and why do oceans influence seasonal contrast? Oceans warm (cool) slowly during summer (winter) coastal regions benefit from ocean’s moderating influence. Continental interiors respond quickly to seasonal changes why central plains have warm summers and cold winters compared to coastal locations.
How do oceans influence climate?: Water has a high capacity for storing heat much greater than that for land. Oceans warm (cool) slowly during summer (winter) coastal regions benefit from ocean’s moderating influence. Continental interiors respond quickly to seasonal changes why central plains have warm summers and cold winters compared to coastal locations.
Important warm currents and cold Currents: Gulf Stream: A warm Atlantic Ocean current that originates in the Gulf of Mexico and flows up the eastern coast of North America and northern Europe. Kuroshio: A warm current flowing northward off the eastern coast of Japan. California Current: A cold current flowing southward along the western coast of North America.
Climate in South California: “Mediterranean Climate”: Hot, dry summers & mild, relatively wet winters; Importance of latitude (~32oN) and ocean, including the cold California Current. Inland Temperatures (Riverside) similar, but larger seasonal cycle warmer summer temperatures by about 20oF.
Atmosphere layers and vertical temperature distribution in each layer: Thermosphere (640 km), Mesosphere (50 to 80 km), Stratosphere (50 km), Troposphere (8 to 17 km)
Where does weather occur? Troposphere
Where is the ozone layer? Stratosphere
Where is the ozone hole? Antarctica (Stratosphere)
How are CFCs related to the ozone hole? Chlorofluorocarbons (CFCs) accelerate destruction of ozone, reducing its abundance and ability to protect the planet from UV radiation.
General circulation of the atmosphere: 3 cells, Hadley, ferrel and polar.
Hadley cell: A key component of the general circulation of the atmosphere, it helps transport heat from the equatorial region to higher latitudes.
InterTropical Convergence Zone (ITCZ): A belt of low surface pressure that is centered near the equator but migrates north and south within the tropics as the seasons change.
Why are tropics rainy: Cold air holds less water vapor, so as rising tropical air cools, water condenses out as droplets that congeal and form towering cumulus clouds and rainfall-producing thunderstorms.
Where do most of the world's deserts exist?: Subtropical latitudes.
Why do deserts occur at the Subtropical latitudes? The air sinking in the subtropics is now quite dry because most of the water vapor was precipitated out of it when the air was rising. Furthermore, as air descends it gets compressed and warms.
Where are the jet streams? Fast-flowing air currents found in the upper atmosphere, influencing weather patterns. The subtropical jet is located above near the convergence of the Hadley and Ferrel cells, and the polar jet is located above the Polar Front (convergence of Ferrel and Polar cells)
How will climate change affect the location of the polar jet stream and the subtropical dry zones? Altering precipitation patterns and increasing drought risks. Shift Poleward
What is the implication of climate change affecting the location of the polar jet stream and the subtropical dry zones migration? Allows the dry subtropical zones to penetrate farther into mid-latitude regions such as Europe and the U.S. during the summer season.
Greenhouse gases (GHGs): Gases in the atmosphere caused by human and natural causes, they absorb heat and warm the atmosphere around them. Gases in Earth’s atmosphere that absorb longwave radiation including the radiation emitted from Earth’s surface.
Are GHGs abundant gases in our atmosphere? Not all gases are greenhouse gases; nitrogen and oxygen—the most abundant gases in the atmosphere—aren’t greenhouse gases.
List of few GHGs: H2O, CO2, CH4, N2O
Lifetime periods of GHGs (CO2, CH4 and N2O): CO2 and CH4 - about a decade, N2O - 100 years
Primary sources of anthropogenic GHGs: Human activities: fossil fuel combustion, agriculture, and industrial processes.
Global warming potential (GWP): A measure of how much a given mass of greenhouse gas is estimated to contribute to global warming relative to the same amount of carbon dioxide.
Evidence of world warming: Independent temperature data from the atmosphere, the ground, and the ocean subsurface, combined with evidence such as melting snow, ice and permafrost, rising sea levels, and observed changes in plant and animal behavior make it clear that Earth is warming noticeably.
How much has global average surface temperature increased over the 20th century? Global average surface temperatures have risen over the 20th century, with significant warming observed since the mid-20th century: Global temperature has increased by nearly 1.0°C (1.8°F) since 1880. The rate of warming in recent decades has increased by 50% relative to the longer-term trend. This is ~25% of the estimated change in global temperature during the last Ice Age, when NYC was covered by an ice sheet 0.5 km thick. Rate of warming accelerating: 0.10°C/decade over the 20th century; 0.15°C/decade in past few decades.
Pre Industrial atmospheric CO2 level and how much has atmospheric CO2 increased since preindustrial times?: Has increased 1 degree celsius, pre industrial CO2 level was 280 ppm (now 400 ppm) 40% increase
Are the changes of CO2 and temperature large relative to past CO2 and temperature variations over the geologic record? If not, then what’s the big deal?: Global CO2 records have been higher, but the rapidity of CO2 increase from anthropogenic factors makes Anthropocene dangerous
IPCC (Intergovernmental Panel on Climate): Established in 1988 to evaluate the risk of human-induced climate change, and its periodic assessment reports are the authoritative source for accurate information.
What are some of their climate projections for the late 21st century? Cold days and nights will be warmer and less frequent. Hot days and nights will be more frequent. Extent of permafrost will decline. Ocean acidification will increase as the atmosphere accumulates CO2. ocean acidification will increase with CO2. Global sea levels will rise and continue for centuries.
How does the IPCC account for uncertainty? AR5 presents conclusions in terms of the likelihood of particular outcomes, expressed as a probability based on the quality, volume and consistency of the evidence of extent of expert agreement.
Water vapor feedback: Adding CO2 to the atmosphere tends to warm the atmosphere. The initial warming causes more surface water to evaporate, increasing the atmospheric water vapor content. Since water vapor is a greenhouse gas, the atmosphere will then tend to warm even more. Positive feedback loop, because it amplifies the original change.
Ice albedo feedback: Melting ice reduces Earth's albedo (reflectivity), leading to more solar absorption and further warming - Positive feedback.
Positive feedback: Amplifies initial change. Clouds (Fewer low clouds, more high clouds), Permafrost Carbon, Ocean Circualtion, Wildfire, Soil Respiration, Vegetatio Stress, Methane Clathrate, Glacier Melt.
Negative feedback: Decreases initial change. Vegetation Feeedback, Planck (Radiative) Feedback, Lapse Rate (Temperature) Feedback, Low cloud feedback (Increased clouds), Ocean Heat Uptake, Aerosol feedback (from natural sources), Ice - Albedo (cooling) feedback. Carbon cycle feedback (some parts).
Net impact of feedback on Earth: Doubles the magnitude of the expected warming or cooling response to imposed changes and outweighs negative.
Albedo: Reflectivity of solar radiation back to space; the planetary albedo is about 1/3.
Natural factors that influence climate: The Sun. Volcanic eruptions. Earth’s orbit.
Anthropogenic factors that influence climate: nitrogen fertilizers, tropical deforestation and the burning of fossil fuels.
Industrial aerosols affect climate: These small particles (mostly sulfate and nitrate) are suspended in the atmosphere by industrial activity, such as coal combustion. The impact of aerosols are more regionally limited and more variable than well-mixed GHGs. Aerosols generally reflect solar radiation back to space, creating a regional cooling effect.
Volcanoes affect climate (Short time scale): Volcanic eruptions modify composition of the atmosphere by injecting small particles (aerosols) into the stratosphere. These particles reflect/absorb incoming sunlight that would otherwise warm Earth’s surface.
Difference in climate impacts between aerosols and GHGs: Aerosols reflect solar radiation back to space, creating a regional cooling effect. GHGs have a surface warming effect.
How do we know the increase in CO2 since preindustrial times is caused by human activity? Because fossil-fuel consumption is such an integral part of the global economy, utilization rates are reasonably well known.
How are carbon isotopes involved? What are the carbon isotopes? C-14: radioactive, seen in tree rings, decreasing. Increase in radiocarbon dead C-12 from fossil fuel burning. Decrease in ratio b/w C-13 and C-12 bad carbon heats troposphere, decreases atmospheric radioactivity, no natural sources.
Carbon cycle: The sum of the processes, including photosynthesis, decomposition, respiration, weathering, and sedimentation, by which carbon cycles between its major reservoirs
Importance of Carbon cycle: It regulates the Earth's temperature, makes up the food that sustains us, and provides energy that fuels our global economy.
Reservoirs of carbon in a carbon cycle: Atmosphere, ocean, and vegetation, soils, and detritus on land.
How have humans perturbed the carbon cycle?: Added burning coal to the carbon cycle increasing atmospheric carbon dioxide so more carbon dioxide produced than natural ratios.
Do all of our CO2 emissions stay in the atmosphere? If not, where do they go? No, 50% into oceans and forests, double the Co2 emitted
What do all of our CO2 emissions that stay in the atmosphere imply in terms of the magnitude of global warming/climate change? Double the CO2 emitted
Greenhouse effect: When gases have a warming influence on Earth’s surface because they absorb terrestrial radiation.
Greenhouse effect on atmospheric temperature (troposphere vs stratosphere)? Warms (Cools) the lower atmosphere in the troposphere (Stratosphere).
Greenhouse effect on atmospheric temperatures (Stratosphere)? Cool it.
Does the greenhouse effect occur naturally? How have humans perturbed it? Yes, but humans driven up atmospheric CO2 concentration with fossil fuel burning, deforestation, agricultural practices
Where is most of the GHG-induced heat going? Much of the warming due to increased greenhouse gas concentrations has gone into heating the oceans.
How does GHG-induced heat affect sea level? Cause sit to rise
What is ocean acidification? A reduction in the pH of the ocean over an extended period of time, caused primarily by uptake of carbon dioxide (CO2) from the atmosphere.
How does climate change affect O2 levels in the ocean? Less O2 dissolves into oceans, including the cold, dense polar oceans that sink to the deep sea and provide essential oxygen to organisms living at depth.
Why does climate change affect O2 levels in the ocean? Warming also reduces the tendency for this water to sink by making it less dense, further isolating the oxygen-depleted deep waters from oxygen-rich surface waters.
Climate “proxies”: tree rings, ice cores, corals, cave deposits, lake and ocean sediments, tree pollen, and historical records.
Why are proxies useful? What do they tell us? Can be used to reconstruct climate for times prior to the establishment of a widespread instrumental atmospheric and oceanic data set.
Has Earth’s climate been very stable over geologic time intervals? No, glacial-interglacial cycle. Ex: 20,000 years ago glacial climate with ice sheets covering much of North America and Scandinavia. Prior to 2 million years ago no large ice sheets in the Northern Hemisphere. Prior to 34 million years ago no large ice sheets anywhere.
How are ice cores used to infer past climates? Scientists extract the gas from tiny bubbles in the ice core to measure the concentration of ancient air
What do paleoclimate data indicate about long-term temperature and CO2 variations? Three GHGs have been rising at dramatic rates for the last two centuries. CO2 increased by 40%; CH4 by 150%; N2O by 20%. Driven by fossil-fuel burning, deforestation and agriculture, the recent skyrocketing trends greatly exceed the natural fluctuations of the preceding hundreds of thousands of years From ice cores, the last interglacial had atmospheric CO2, CH4 and N2O levels close to pre-industrial.
Pleistocene: Glacial 2 million years ago until 10,000 years ago; fluctuations in sea level are the result of 40,000 and 100,000-year "glacial-interglacial" cycles of the last 2 million years
Last Glacial Maximum: 21,000 years ago
Holocene: Last 10,000 years-most recent interglacial period.
Eocene Optimum, 50 (53-49) million year ago alligators and sequoia forests were thriving above the Arctic circle.
Pliocene: 5.3 to 2.6 million years ago, was a time of global cooling
Anthropocene: Industrial Revolution to Present, unprecedented GHGs, human alteration of the atmosphere
Little Ice Age: 15th-19th centuries
Medieval Warm Period: 10th-13th centuries
Last interglacial: 125,000 years ago
Milankovitch cycles: etc: Changes in the shape earth's orbit and tilt that cause glacial periods and interglacial periods (eccentricity, tilt of Earth's spin axis, precession-wobble)
What orbital cycles are important for climate?: Orbital ellipticity, Precession (Wobble), Tilt
What are the orbital cycle periods?: Orbital ellipticity (100,000 year cycle), Precession: Wobble (19,000 and 23,000 year cycles), Tilt 41,000 year cycle)
Are the orbital cycle periods fast or slow processes (on human timescales)? Slow
Why is the last interglacial warm enough to melt the Greenland ice sheet? The Northern Hemisphere received 10% more solar radiation than it does today (not because the sun is brighter, but because Earth's orbit around the Sun was different than it is today). Due to slow changes in Earth's orbit around the sun, caused by gravitational tug of the Sun, moon, & the large planets ("Milankovitch Cycles").
How will climate change affect drought? The combination of decreased summer precipitation and increased evaporation due to warming surface temperatures is predicted to lead to a greater tendency for drought in many regions.
For the western U.S., how is drought related to tropical Pacific sea surface temperatures (SSTs)? These SST changes are associated with the enhanced North American drought (based on a calculation for the 1998–2002 period). The concentration of warming in the western tropical Pacific and Indian oceans is reminiscent of the east–west temperature contrast typical of La Niña events.
El Nino? An event where the trade winds in the eastern and central tropical Pacific are weaker than usual, there is less upwelling of cold subsurface ocean water in the eastern Pacific, and relatively warm water spreads out over much of the tropical Pacific ocean surface. During, the warmer tropical Pacific surface ocean waters influence the overlying atmosphere and alter the patterns of the extratropical jet streams of the northern and southern hemisphere and the general circulation of the atmosphere. The altered circulation of the atmosphere leads to changes in temperature and precipitation patterns in many regions across the globe.
La Nina? An event where the trade winds in the eastern and central tropical Pacific are stronger than usual, there is greater upwelling of relatively cold subsurface ocean water in the eastern Pacific, and that cold water spreads out over tropical Pacific ocean surface. During, the tropical Pacific ocean and atmosphere are in the opposite state as they are during an El Niño event and the influence on atmospheric circulation and global weather patterns is roughly, though not precisely, the opposite.
How will climate change affect record high temperatures/heat waves? More record highs and heat waves
Record low temperatures/cold snaps? Does not affect overall climate change; more record highs less record lows
How will extreme warm/cold events change with global warming? Stronger hurricanes, more stronger hurricanes, less hurricanes in general
How will climate change likely affect hurricanes?: A warmer ocean surface, all other things being equal, is likely to fuel more intense tropical cyclones, with stronger sustained winds. The combination of sea level rise and stronger tropical storms could pose a “double whammy” when it comes to damaging storm surges. Model simulations indicate a likely shift toward the strongest (Category 4 and 5) tropical cyclones over the next century, given projected climate changes.
Why is Hurricane Sandy so powerful?: It merged with an extra-tropical, wintertime cyclone. Climate change raised sea surface temperatures (SSTs) along the eastern coast of the U.S contributed to the unusual strength and flooding potential of the storm, and global sea level rise added roughly 30 cm (1 ft) to the coastal surge, leading to an estimated extra 65 square kilometres (25 square miles) of flooded area.
How has climate change affected the cryosphere (Arctic sea ice, mountain glaciers, ice sheets, etc.)?: Perennially frozen ground (permafrost) influences soil water content and vegetation over vast regions and is one of the cryosphere components most sensitive to atmospheric warming trends. Other regions of the cryosphere are also responding to climate change: the seasonal minimum sea-ice coverage of the Arctic Ocean is currently diminishing, and most mountain glaciers are shrinking.
How does climate change affecting the cryosphere, in turn, generally affect sea level?: If the ice sheets were to melt completely, sea level would rise by about 80 m (260 ft). Much of this storage is in the East Antarctic ice sheet, less likely to be affected by anthropogenic warming in the next few centuries; West Antarctica and Greenland melting would cause a modest, but devastating, 12 m (39 ft) of sea-level rise. In contrast, the expansion and contraction of sea ice (floating ice near the poles) has no effect on sea level, but can affect ocean circulation, local climate, and ecosystems.
What is a “simple” climate model based on?: It ignores the three-dimensional structure of Earth, atmosphere, and oceans, and simply focuses on the balance between incoming solar energy and outgoing terrestrial (heat) energy. It is the balance between these incoming and outgoing sources of energy that determines temperatures on Earth.
What does a “simple” climate model account for?: The greenhouse effect. Usually accomplished through a modification that represents the way heat is absorbed and emitted by the atmosphere. To account for feedback loops that can either amplify (positive feedback) or diminish (negative feedback) the impacts of any changes. In most climate models, the net impact of feedback roughly doubles the magnitude of the expected warming or cooling response to imposed changes.
What are General Circulation Models (GCMs)?: Complex models that calculate not only surface temperatures, but also other important climate variables, such as precipitation, atmospheric pressure, surface and upper level winds, ocean currents, temperatures, and salinity. This is accomplished by breaking the oceans and atmosphere into many small grid boxes, and by using the underlying physical, chemical, and biological relationships to calculate values for properties of each box and the interactions between different boxes.
Should GCMs be trusted? Why or why not?: Current climate models do a remarkably good job of reproducing key features of the actual climate such as the jet streams in the atmosphere, the seasonal band of rainfall and cloudiness that migrates north and south of the equator, and even the complex internal climate oscillation associated with the El Niño phenomenon. These models also closely reproduce.
What do climate models tell us about natural variations and the warming since the 1970s?: Thirteen different climate models indicate which portion of the annual average temperature variations over the last century can be attributed to natural forces alone. Natural forcing does not explain the warming since the 1970s. The expected warming from greenhouse gases alone is greater than that observed. When human forces, especially the buildup of atmospheric greenhouse gases and industrial aerosols, and natural forces are applied simultaneously to these same climate models, the general trends and many of the anomalies are reproduced.