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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:. - PowerPoint PPT Presentation
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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
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/AckermanKnox/chap2/SimpleGreen.html