Transcript Climate and Climate Change - UW

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:
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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