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