CHAPTER 22.docx

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Department
Environmental Science
Course
Environmental Science 1021F/G
Professor
Geoff Stewart
Semester
Fall

Description
CHAPTER 22: CLIMATE CHANGE -CLIMATE CHANGE: alteration in the long-term patterns and statistical average of meteorological events -indicators of climate change include: later winters, earlier springs, some tree species dying off, some tree species popping up in random places CLIMATE IS NOT THE SAME THING AS WEATHER -WEATHER: the meteorological condition in a given place on a given day -CLIMATE: long-term patterns or trends of meteorological conditions -TREE RANGE MIGRATION: after the North American ice cap retreated 10,000 years ago – the climate warmed so dramatically that tree species’ ranges shifted northward at a rate of 50 km a century – pines, oaks, and other deciduous species replaced the spruce trees that has covered most of the region – as summers became warmer, water levels fells, prairie plants took root, and birches and pine moved north – then, about 6,000 years ago, the climate cooled a bit and trees began migrating west and south again EVIDENCE OF GLOBAL CLIMATE CHANGE ABOUNDS -the Arctic is particularly vulnerable to climate change because warming that occurs there causes ice to melt, which triggers additional warming -climate change is altering the northern hemisphere’s polar jet stream, slowing it down and making it “wavier”, meaning the peaks and troughs of the jet stream are extending farther north and south as the jet stream moves from west to east – this brings colder air farther south and can slow down the movement of weather systems -based on the current rate of melting, the entire Arctic could be completely ice free in the summer come 2035 -as ice on land melts, sea levels rise – half of this rise is due to land-based ice melt and the other half to thermal expansion – the expansion of water molecules as they heat up -some evidence of climate change is: warmer temperatures should lead to melting ice and sea level rise and also weather extremes such as precipitation changes and hurricane intensity A VARIETY OF FACTORS AFFECT CLIMATE -GREENHOUSE GASES: molecules in the atmosphere that absorb heat and reradiate back to Earth; these gases in the atmosphere are on the rise – carbon dioxide, methane, and nitrous oxide are some examples of greenhouse gases -GREENHOUSE EFFECT: the warming of the planet that results when heat is trapped by Earth’s atmosphere -the greenhouse effect is a good thing if it is within normal range – without it, the average temperature on Earth would be -15 degrees Celsius – 30 degrees colder than the current average -the enhanced greenhouse effect is what scientists believe is from the release of greenhouse gases from burning fossil fuels and other industrial and agricultural practices -RADIATIVE FORCER: anything that alters the balance of incoming solar radiation relative to the amount of head that escapes into space -ALBEDO: the ability of a surface to reflect away solar radiation -light colored surface likes glaciers and meadows have a high albedo – thus, they reflect light and thus heat away from Earth’s surface -darker surfaces like water and dark asphalt have a low albedo – thus the absorb sunlight and heat along with it – and then reradiate the heat back to the atmosphere -POSITIVE FEEDBACK LOOP: changes caused by an initial even that then accentuate that original 1 event (for example: a warming trend gets even warmer) – as surfaces with high albedo are replaced by those with low albedo -glaciers are a good example of positive feed back – as temperatures rise, glaciers melt and ice (high albedo) gives way to water (low albedo) – because this new water surface absorbs more heat than the old icy surface, than the region will warm faster replacing even more ice with water -Canada may lose 1/5 of its ice sheet by 2100 – Canada’s ice sheet is the 3 largest in the world after Greenland and Antarctica -another positive feedback loop is in the Arctic where the upper levels of permafrost (land that normally remains frozen year-round) are melting during the summer months – when these areas thaw, they release stored carbon, adding more greenhouse gases to the atmosphere - these gases warm the area further – causing even more permafrost to melt -natural forcers are clouds – some have high albedo and thus work to cool the planet, and other trap reradiated head from the planet’s surface and thus have a warming effect – if warming temperatures cause the formation of more high-albedo clouds – this could trigger cooling through a negative feedback loop -NEGATIVE FEEDBACK LOOP: changes caused by an initial even that trigger events that then reverse the response (for example, warming leads to events that eventually result to cooling) -greenhouse gases global emissions: 56.6% are from CO2 from fossil fuel burning, 20.1% is from CO2 from deforestation and other sources, 14.3% is methane, 7.9% is nitrous oxide, and 1.1% are halocarbons -CO2 released in melting permafrost leads to increased growth of tundra vegetation – but in the longer term, the thawing leads to increased atmospheric loading of CO2 as more is releasd th can be taken up by the vegetation -positive forcers have a net effect of warming – negative forcers cool the climate -greenhouse gases trap the heat in the atmosphere and warm it -aerosols like sulphate emissions cool it -the effect of warming forcers outweighs the effect of cooling forcers such that the overall net effect for all these forcers is to warm the planet -volcanic eruptions and changes in solar irradiance are also considers as natural forcers -MILANKOVITCH CYCLES: predictable variations in Earth’s position in space relative to the Sun that affect climate -CLIMATE MODELS: computer programs that allow scientists to make future climate projections by plugging in current values – these models are used to see how altering one value can change future condi
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