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Climate and Climate Change Val Bennington Weather Versus Climate ◊ Weather is a day to day experience ◊ Climate describes the persistent, longterm characteristics of a region ◊ We can predict weather for a couple days ◊ How can one predict climate? Global Climate Controls: ◊ ◊ ◊ ◊ ◊ Earth’s orbit and tilt Sun’s strength (again, long-term) Greenhouse Gases Earth’s albedo Volcanic Eruptions (alter albedo) Orbit and Tilt ◊ Saw this in 100 ◊ Governs how much sunlight Earth receives and where ◊ Tilt naturally changes over 100s of thousands of years Sun’s Strength ◊ Sun goes through natural cycles of increasing and decreasing strength ◊ These cycles are tens of thousands of years long ◊ More sun = warmer Earth Albedo ◊ The Earth actually reflects much of the sunlight it receives ◊ The reflected light DOES NOT warm the Earth ◊ The percent of sunlight the earth reflects is called the albedo (~ 30% currently) ◊ Changing this albedo changes the amount of energy from the sun that is absorbed by the Earth! Albedo Examples: Ocean: 3-30% Forest: 14-20% Fresh Snow: ~90% Old Snow: ~50% Sand: 18-28% Entire Earth: ~30% Greenhouse Gases ◊ The atmosphere absorbs almost ZERO of the sun’s radiation (energy) ◊ The surface of the Earth absorbs part of the sun’s energy and warms ◊ The earth’s surface warms the atmosphere from below ◊ Without greenhouse gases, ALL of the energy radiated by the surface of the Earth would escape to space! ◊ More greenhouse gas == more energy kept at the Earth’s surface ◊ This is a scientific fact ! ◊ This is not a new theory ! 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 ◊ He predicted a change in average surface temperatures of 2-3 K over the next couple centuries By the way, 2-3 K is 3.6-5.4°F Early 1900s ◊ Scientists discounted and ignored the theory, saying the ocean will “suck up” all of the CO2 we emit as pollution ◊ The ocean has sucked up half of ALL human CO2 emissions since the industrial revolution, but this is a slow process Sabine et al. (2004) 1930s - a warm spell ◊ US and North Atlantic were warmer than previous 50 years ◊ G.S. Callendar proposed that this was due to rising atmospheric CO2 1950s - new technologies ◊ Callendar’s theory couldn’t really be tested without being able to measure how much CO2 is actually in the atmosphere ! ◊ Measuring concentrations began ◊ Indeed, humans were altering the amount of CO2 in the atmosphere Calculations and Models (1960s) ◊ Began using computer models to understand where all the emitted CO2 was going (into oceans, trees, atmosphere) and to predict changes in temperature ◊ Tried to include all possible changes to the Earth brought on by initial warming (feedbacks) ◊ Predicted change in temperature of 2K over a century 1970s ◊ People became interested in the environment and became concerned about human changes to it ◊ Confused by cooling in temperatures between 1940s and 1970s ◊ Worried about ice cap melt and catastrophy ◊ Wanted a better understanding (research) Research led to scientific theories ◊ Would natural cycles swamp out effects due to humans? ◊ Why cooler in 1940s? ◊ Could feedbacks correct the warming? ◊ 1940s cooling: ◊ Due to the nasty black pollutants that were being emitted with the CO2! ◊ Too bad those pollutants are deadly! Feedbacks ◊ Warm earth --> melt ice --> reduce Earth’s albedo --> warmer Earth ◊ OR… ◊ Warm earth --> more precipitation --> more snow over Antarctica --> higher albedo --> cool the Earth Next Week ◊ How can scientists determine if there has been significant warming? ◊ We will examine the record of ice on Lake Mendota to see if there has been a change Feedbacks ◊ Positive feedback increases your original change (warming the Earth increases the warming by ice melt) ◊ Negative feedback works against your original change (warming the Earth is fought by cooling due to increased albedo) Models ◊ We need models because no one person could say whether warming will have a greater effect melting Greenland ice or increasing ice in Antarctica ◊ Too many things change at once! ◊ There is no such thing as absolute certainty, but the likelihood of changes is now better understood Not all smokers die from lung cancer, but would you smoke? Current Understanding ◊ Increased concentrations of CO2 and CH4 will cause a temperature increase of 2.5-11ºF (1.4-6ºC) ◊ Scientists can model historical temperature changes ◊ However, they cannot get current temperatures correct unless they include increased CO2 concentrations ◊ How we continue to pollute, cut down trees, etc gives us a range of future temperatures ◊ Surprises are possible - what if a volcano erupts? ◊ Will trees absorb more or less in future? The oceans? Will we continue to emit more and more and more? Take Home Message ◊ Climate change has been politicized ◊ The vast, vast, vast majority of scientists believe that human emissions are currently altering the global climate (similar to the number who believe smoking is bad for you) ◊ How much we alter it is up to us More CO2 doesn’t just mean more air conditioning: ◊ Increased temperatures are great for disease-carrying insects ◊ Increased CO2 in the oceans has already lowered the ocean’s pH and is expected to kill many of the coral reefs ◊ We will adjust to a new climate, but how much will it cost? ◊ May need to relocate agricultural land, move homes away from shore ◊ Entire island countries may become refugees - who will take them in? ◊ Citizens of poor countries are at a higher risk ◊ Those same poor countries have contributed the LEAST to global CO2 emissions ◊ This becomes an economic, social justice, and sociological problem Tutorial ◊ http://profhorn.aos.wisc.edu/wxwise/Ac kermanKnox/chap2/SimpleGreen.html