Climate and Climate Change Val Bennington
Weather Versus Climate • Weather is a day to day experience • Climate describes the persistent, long-term 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
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 Calculations and Models (1960s)
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) 1970s
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! Research led to scientific theories
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/AckermanKnox/chap2/SimpleGreen.html