Transcript Overview of Climate Science (Ch. 1) Earth as a habitable planet

Overview of Climate Science (Ch. 1)
• Earth as a habitable planet
• climate vs. weather
• temperature scales
• geologic time
• time scales of climate change
• hypotheses, theories, models
• forcing and response
• feedbacks
Earth:
The only habitable planet in
our solar system
~70% oceans
~30% land
Taverage (mean) ~ 15 oC (59 oF) now
But not always so comfortable
Climate vs. weather:
Weather is the shorter-term condition that
changes on a hourly, daily, or weekly basis
• not covered in this class
Climate is the longer-term condition (temperature,
precipitation, wind, ice cover) of a region or planet
• this is what we will be learning about
Climates on three planets
Venus
Earth
Mars
hot
mild
cold
“greenhouse
world”
“icehouse
world”
Temperature scales
oF
scale.
Not used by anybody in world except
American public.
oC
scale.
Degrees Celsius or Centigrade.
Water freezes at 0 oC and boils at 100
oC.
K scale.
Degrees Kelvin. K = oC + 273.15
0 K = absolute zero, coldest anything
can get.
T (oC) = 5/9 * [T(oF) – 32]
T (oF) = [9/5 * T (oC)] + 32
Temperature
scales
Climates on three planets
Venus
Earth
Mars
avg. temp.
460 oC
15 oC
-55 oC
avg. distance
to sun
0.7 x Earth
1.5 x Earth
atmosphere
90 x Earth
0.007 x Earth
pressure
Geologic time:
Earth’s age (= solar system age) is ~4.55 billion years
(b.y. or Ga) old
--this is much longer than the timescales we will
be considering (<100 million years &
mainly <few million years)
--hard to imagine
--even hard to represent (logarithmic scales
can be useful)
Climate change occurs on various timescales
Natural climate variations
time scale
type according to book
~few-100s years
“historical”
~10-1000 years
“historical / millenial”
~10,000 years
“orbital”
millions of years
“tectonic”
Climate change occurs on various timescales
Natural climate variations
time scale
causes
~few years
volcanic eruptions; El Nino
~10-100 years
changes in the brightness of the sun
~10,000 years
variations in Earth’s orbit &
spin state (Earth-sun distance,
inclination and wobble of spin axis)
millions of years
shifting position of Earth’s
continents (plate tectonics)
Theories, hypotheses, models:
a scientific theory is a well-accepted way of how
things work (e.g., gravity, plate tectonics, biologic
evolution)
a hypothesis is an idea that has not been widely
tested (e.g., Milankovich cycle)
a model is a representation of how things work,
which is devised to explain data that have been
collected (e.g., global circulation models, “GCMs”)
Climate forcings & responses:
forcing is a factor that changes climate
response is the climate change that occurs
these can have different timescales
Anthropogenic forcing:
“Anthropogenic” means human-caused
Anthropogenic forcings are the things that people do
that can affect the environment
e.g. burning fossil fuels
Response lags forcing
response larger
with ample time
response smaller
with less time
Feedbacks:
a positive feedback is a process that
amplifies a change
a negative feedback is a process that
suppresses a change
feedbacks are very important in climate science!
Feedback examples
“China syndrome”
More initial
response
house thermostat
Less initial
response
A possibly more obvious example of a positive
feedback…
A possibly more obvious example of a positive
feedback… two babies screaming
time
Baby 1 has eye
infection, starts crying
Baby 1 keeps crying
Baby 2 hears crying
initial forcing
Baby 1 cries more
Baby 2 starts crying
continued forcing
initial effect
reinforced