Download Topic 12A: Climate Change, Part III Online Lecture: The Earth`s

12A_3 – Slide 1
Topic 12A:
Climate Change, Part III
Online Lecture:
The Earth’s Climate
○ Factors that Affect Climate
○ Rapid Climate Change
○ Climate Change & Humans
Astronomy & the Earth’s Climate
Earth's orbit
changes
shape
orbit closer
to the Sun
at some times
Earth
Sun
Earth
orbit farther
from the Sun
at other times
12A_3 – Slide 2
Earth's
"tilt"
wobbles
N. Pole
Equ
more
sunlight
at the Poles
S. Pole
a to r
less sunlight
at the Poles
○ Where Sunlight Falls (and Amount of Sunlight)
– variations in the Earth’s orbit and tilt
(Milankovitch cycles)
– too small to explain large changes
Amplified?
in the Earth’s climate (e.g., Ice Ages)
Plate Tectonics & the Earth’s Climate
12A_3 – Slide 3
volcanoes adding dust
& greenhouse gases
mountains grow &
continents move, affecting
winds & rainfall patterns
oceans grow & shrink,
connect & separate,
changing ocean currents
The Ocean & the Earth’s Climate
12A_3 – Slide 4
○ The surface currents carry
warm water to the
Poles and cold
water to the Equator
○ Thermohaline Circulation
– helps the ocean absorb
more greenhouse gases from the atmosphere
○ High Heat Capacity of Ocean Water:
– water covers 70% of the Earth
– It is hard to change the temperature of water:
keeps Earth from getting too hot or too cold quickly
The Atmosphere & the Earth’s Climate I
○ Clouds (water from the ocean):
12A_3 – Slide 5
Greenhouse Gases like…
– reflect sunlight back into space
● cooling the Earth
– absorb infrared “light” from the Earth,
and send some of the energy back
● warming
the Earth
Visible Light
Cloud
never warms
the Earth
( cooling )
clouds are
warmed,
emit some
heat back
to the Earth
Cloud
Infrared "Light"
The Atmosphere & the Earth’s Climate II
○ Dust particles (“aerosols”):
– reflect sunlight or absorb sunlight
(keeping heat from reaching the surface)
– encourage cloud formation
Human activities
have significantly
increased the
amount of dust in
the atmosphere –
this is the second
major way which
we affect the
Earth’s climate.
12A_3 – Slide 6
The ocean a
natural source
of aerosols:
crashing waves
add bits of salt to
the air that act as
“dust” too!
How will Global Warming Affect
the Amount of Life in the Ocean?
12A_3 – Slide 7
This has been
observed when
temperatures
rise…
Goddess
of the
Earth
in Greek
Mythology
The Gaia
Hypothesis
If global warming reduces the amount of life in the ocean,
will that help warm or cool the Earth? Why?
How Does Extra CO2 in Ocean Water
Affect Ocean Life?
○ In what ways might this
benefit life in the ocean?
○ In what ways will this
harm life in the ocean?
12A_3 – Slide 8
The ocean absorbs more &
more of our CO2 pollution
from the atmosphere.
There is already plenty of CO2
available in ocean water, but
not much in air…
Makes ocean water more acidic, which will dissolve
calcium carbonate shells (harder to grow).
Silica Shells?
Overall, benefit or harm?
Good News: This neutralizes
the acid in ocean water.
“Take One for the Team”
Past Changes in Climate I: Ice Ages
12A_3 – Slide 9
large changes
(almost 20oF!) over
10,000 of years
Past Changes in Climate II: “Recent” Climate 12A_3 – Slide 10
Today
Earth’s Climate
has been
unusually stable
for the last
10,000 years.
Variations have
been small (1-2oC,
2-4oF), but had
significant effects.
The “Little”
Ice Age
Medieval
Warm
Period
Rapid Climate Change I: 16,000 Years Ago 12A_3 – Slide 11
There have also been
larger, rapid
(within a decade)
changes in the past.
○ Cold water sinks
in the North Atlantic;
warm water moves
north to replace it.
(Thermohaline Circulation)
Sinking
Ice Sheets
16,000 years ago
Mississippi River
○ The warm water helped melt the ice.
○ Melting water mainly flowed down
the Mississippi River.
Equator
North
Pole
Rapid Climate Change II: 12,500 Years Ago 12A_3 – Slide 12
○ Melting water started
Global
warming
flowing
down
the
conditions
St.caused
Lawrence
River.
to get colder!
○ North Atlantic water
becomes too fresh
(too low density):
no longer sinks
Ice Sheets
12,500 years ago
Sinking
St Lawrence River
No sinking, so
no warm water
comes north
○ The thermohaline circulation shuts down:
warm water stops coming north to replace the sinking
water, so the North Atlantic gets colder.
○ The ice stops melting; instead, the glaciers start growing.
Climate flips back & forth for a few thousand years…
Based on evidence like fossils in ocean sediments…
Is Global Warming Bad?
Why or Why not?
There will be
○ People who live
Winners and
Losers.
near the Poles
○ People who live near the Equator
○ People who live near the Coast
○ Shipping & Mining
Resources in the Arctic
12A_3 – Slide 13
We do not want to
disturb our nice climate
and go back to the days
of wild climate swings.
“What is the use of a house
if you haven't got a tolerable
planet to put it on?”
- Henry David Thoreau
Will It Really Be “Global Warming?”
○ If the Earth’s climate
continues to warm,
the ice sheets on
Greenland will melt,
and the thermohaline
circulation could shut down.
12A_3 – Slide 14
Greenland
Ice Sheet
Why?
○ Will this cause Europe
to get warmer or colder? Why?
Global warming will cause shifts in
winds and ocean currents which will
make some places warmer and other
places cooler, give some places
more rain and other places less rain.
“The Day
After
Tomorrow”
Sinking