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Climate Change. Lecture 6 March 4, 2010. Climate Change Assignment. Due next Thursday, March 11 2-3 paper on climate change and your assigned greenhouse gas Must use at least 3 sources and include Works Cited page Be prepared to discuss climate change in class
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Climate Change Lecture 6 March 4, 2010
Climate Change Assignment • Due next Thursday, March 11 • 2-3 paper on climate change and your assigned greenhouse gas • Must use at least 3 sources and include Works Cited page • Be prepared to discuss climate change in class • More detailed description up on website
Weather vs. Climate • The difference between weather and climate is a measure of time • Weather is the state of the atmosphere, land, and ocean conditions on a day to day basis. • Most people think of weather in terms of temperature, humidity, precipitation, cloudiness, visibility, wind, and atmospheric pressure • Climate is the average weather in a location over a long period of time (months, years, decades, etc) • Climate is what you expect, like a very hot summer. Weather is what you get, like a hot day with thunderstorms.
Weather and Climate • Both weather and climate are influenced by a variety of factors such as… • Astronomy (Earth’s tilt, rotation, distance from sun, and solar activity), terrain, location, humans • The Earth’s climate undergoes many natural changes and cycles
Why study climate? • Studying climate and a changing climate is important because it will affect people around the world • Rising global temperatures are expected to raise sea levels and change precipitation and other local climate conditions. • Changing regional climate could alter forests, crop yields, and water supplies. It could also affect human health, animals, and many types of ecosystems.
Global Climate Controls • Earth’s orbit and tilt • Land/sea distribution • Sun’s strength (long-term) • Earth’s albedo • ENSO • Greenhouse Gas Effect
Earth’s Orbit and Tilt • Orbit (Eccentricity) • How close is Earth’s orbit to circular? • Governs max. and min. distance from the sun • Orbit naturally fluctuates over 100s of thousands of years • Tilt (Obliquity) • Increased tilt increases seasonality • Tilt naturally fluctuates over tens of thousands of years
Land/Sea Distribution • Continents drift and shift over time (plate tectonics) • Pangaea: supercontinent that existed about 250 million years ago • Affects ocean currents, wind patterns, etc • Continents are still moving today and will continue to shift
Strength of the Sun • Sun goes through natural cycles of increasing and decreasing strength • These cycles are tens of thousands of years long • Sunspots follow a 11 year cycle (affects incoming radiation) • More output from sun warmer Earth http://science.howstuffworks.com/sun.htm/printable
Albedo • The Earth actually reflects much of the sunlight it receives • Light that in reflected back to space does not warm the Earth • The percent of sunlight the earth reflects is called the albedo • Changing this albedo changes the amount of energy from the sun that is absorbed by the Earth! (thus changing the climate)
What changes the albedo? • Increase in snow and ice cover • Increase in areas covered by sand • Deforestation • Increased cloud coverage and thickness • Volcanic eruptions (releases ash and small particles into atmosphere) • Changes in land cover (vegetation vs asphalt, etc)
ENSO • El Niño Southern Oscillation • Defined together as a periodic change in the atmosphere and ocean of the tropical Pacific region • El Niño and La Niña are the oceanic aspects of the phenomenon and the Southern Oscillation is the atmosphere aspect
ENSO • El Niño and La Niña events are defined as warming or cooling of surface waters of the tropical central and eastern Pacific Ocean • Southern Oscillation is defined by the sign of the pressure difference between Tahiti and Darwin, Australia • The oscillation does not have a specific period, but occurs every three to eight years
ENSO Classification • A warming or cooling of at least 0.5 C (0.9°F) averaged over the east-central tropical Pacific Ocean • When this temperature anomaly persists for five months or longer, it is called an El Niño or La Niña episode
El Niño • El Niño occurs during a time of suppressed trade winds (winds moving from the east to the west) at the equator • Causes a pool of warm water to collect in the eastern Pacific near S. America (water there is normally cool) • Changes global wind patterns and temperature, altering weather on global scale
Greenhouse Effect • The atmosphere itself absorbs almost none of the sun’s incoming radiation • The Earth’s surface absorbs part of the sun’s energy and warms • Greenhouse gases in the atmosphere act to trap in some of the longwave radiation leaving the Earth. • Without greenhouse gases, ALL of the energy radiated by the surface would escape to space
Greenhouse Effect • The radiative equilibrium temperature of the earth with no atmosphere is 0°F ➔ Adding greenhouse gases increased the radiativeequilibrium temperature to 59°F • Main greenhouse gases: Carbon dioxide, water vapor, methane • More greenhouse gases = more energy kept at the Earth’s surface = warmer average temperatures • We MUST have greenhouse gases in order to survive but we don’t want too many because we will overheat
Climate Change • Climate change is a change in the statistical distribution of weather over periods of times that range from decades to millions of year • Can happen in a variety of ways and variety of places (specific region or whole Earth) • One example that is the topic of concern right now is how the climate for the entire globe has become warmer. • A skeptic to the fact of global warming might say “What about the temperature record in the interior of Antarctica where there is a cooling trend?”
History of Climate Science • Most people think global warming is a new theory - it is not! • Svante Arrhenius first theorized that surface temperatures would increase with increasing CO2 concentrations in the 1890s
Early 1900’s • Scientists ignored the theory, saying the ocean will “suck up” all of the CO2 we emit • The ocean has sucked up HALF of all human CO2 emissions since the industrial revolution, but is becoming saturated
Global Warming Evidence More Observations Has Led To Better Knowledge http://www.globalwarmingart.com/wiki/Image:2000_Year_Temperature_Comparison_png Also: http://data.giss.nasa.gov/gistemp/graphs/
Observations of CO2 concentrations • Increase in greenhouse gases from 1700 to today results in 2.43 W/m2 more energy at the surface CO2 accounts for 60% of the increase → 1.46 W/m2
Recent Global Warming • CO2 has increased 25% in the last century and solar radiation incident on earth has slightly increased • Why has the rise in global temperatures been relatively small? → Reflective sulfate aerosols • Major volcanic eruptions between 1880 -1920 and 1960-1991 • Sulfur particles into the stratosphere → lower the albedo → cooling effect Cooling effect (increased albedo) + Warming effect (increased greenhouse gases) = Small net warming
Climate Modeling The last 150 years
Projected Global Warming • Modeling the last 150 years, we have a good idea of • Greenhouse gas emissions by humans • Vegetation changes • Future projections of climate change needs estimations of • Greenhouse gas emissions • Population changes • New technologies • Vegetation
Intergovernmental Panel on Climate Change • IPCC established in 1988 by the World Meteorological Organization and UN • Publishes special reports on topics relevant to climate change • “Most of the observed increase in global average temperatures since the mid-20th century is very likely (90% likelihood) due to the observed increase in anthropogenic GHG concentrations.” • “The probability that this is caused by natural climatic processes alone is less than 5%.”- IPCC 4th Assessment Report
Projected Global Warming • A2 → Slow economic/technological growth, high population growth • A1B → Rapid economic/technological growth, population peaks midcentury • B1 → Medium population/economic growth, emphasizing local solutions and sustainability
How will a potential global average warming affect climate? • Land areas are going to warm more than ocean areas • As snow-covered tundra melts, boreal forests will absorb 3 times as much solar energy • More frequent intense precipitation events and flooding • Warmer air temperatures hold more water vapor • Polar front and jet will shift northward • Subtropical regions will be warmer and drier • Shift in mid-latitude weather systems northward • A warmer planet will see a rise in sea level. • Warmer water is “thicker” • Melting ice caps
Supporters of Global Warming and its Connection to Increased Amounts of Greenhouse Gases say… • The rise in CO2 and other greenhouse gases is definitely anthropogenic • Historical temperature records show an increase of 0.4-0.8oC in the last 100 years • This has been an unusually warm period when comparing it to the last 1000 years • CO2 is a first order forcing of climate change • There will be long term ramifications if we don’t do something now!
Opponents of Global Warming and its Connection to Greenhouse Gases Say… • IPCC, and other atmospheric scientists, draw most of their conclusions from climate models. These models have major flaws with cloud physics, and don’t necessarily include every kind of climate forcing! • On that note, climate models don’t even include all climate feedbacks (ice-albedo feedback, etc.) • Just because we’ve observed the temperature to rise around the start of the Industrial Revolution doesn’t necessary mean that increased fossil fuel use has caused the temperatures to increase • The observational records are flawed • The Earth has observed many climatic shifts of its history, some of which aren’t that well understood