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Lecture 01
Climate variability and climate change
 Greenhouse effect and global warming
 Arguments concerning climate change
 Kyoto Protocol basics
 IPCC conclusions
 Natural vs. anthropogenic climate variability
S.-P. Weng Dept of Geography
What is climate?
 Narrow sense: Average weather
 Wider sense: State of the climate system
State: Statistical description in terms of the mean and
variability (at least) of relevant quantities over a period of
time (months, several, thousands, or millions of years)
over a certain area. The classical period is 30 years, as
defined by the WMO (1961-1990), IPCC (1971-2000).
Climate system: complex system consisting of five major
subsystems: atmosphere, hydrosphere, cryosphere, land
surface and the biosphere, and the interactions/feedbacks
of the atmosphere and the change of land-use.
S.-P. Weng
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天氣預報 氣候預報
Role of
forcing ?
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Role of
forcing ?
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Many believe that O2 concentration underwent a dramatic increase between 2.2 and 2.4
billion years ago and was produced initially by cyanobacteria (藍綠藻 ), the only
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(初核質 ) organisms [Bacteria and Archaea (古菌 )] capable of oxygenic10
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Deforestation: Rondonia, Brazil
Body text
•1975 -Healthy
natural vegetation
•1986 -“Fishbone”
pattern on the
landscape indicate
agriculture fields
•2000 -Agriculture
continues to replace
forest cover.
S.-P. Weng
(Alvarez hypothesis)
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What is Climate Variability?
Variations in the mean state and other higher order
statistics (such as standard deviations, variances,
and occurrences of extremes, etc.) of the climate on
all temporal and spatial scales beyond that of
individual weather events.
Variability may be due to either natural internal
processes within the climate system (i.e. internal
variability) or to variations in natural or
anthropogenic external forcing (external variability).
S.-P. Weng
What is Climate Change?
Statistically significant variation in either the mean
state of the climate or in its variability, persisting
for an extended period (typically decades or
Climate change may be due to natural internal
processes or external forcings, OR to persistent
anthropogenic changes in the composition of the
atmosphere OR in the land use.
S.-P. Weng
UNFCCC makes a distinction between
“climate change” attributable to human
activities altering the atmospheric
“climate variability” attributable to natural
causes (both internal and external).
United Nations Framework Convention on Climate Change
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The National Research Council recommends that more
research should be focused on understanding the
mechanisms that lead to abrupt climate changes, and
special attention paid to providing realistic estimates of
the likelihood of such extreme events.
S.-P. Weng
Development of EVT in statistical community
Movie scenario. Temperatures in New York City change
from sweltering to freezing in hours.
Actual climate change. Temperatures in parts of the world
could drop, but not nearly as rapidly or dramatically as
portrayed in the movie. In a warmer world, additional rain
at middle and high latitudes, plus melt from glaciers, will
add more fresh water to the oceans. This could affect
currents, such as the Gulf Stream, that transport heat north
from the tropics and might result in parts of North America
and Europe becoming relatively cooler. Even if this were to
occur, it would take many years or decades because
oceans move heat and cold much more slowly than the
atmosphere. (Some ocean changes, however, such as the
periodic warming of Pacific Ocean waters known as El
Niño, may affect regional weather patterns within weeks.)
Movie scenario. A massive snowstorm batters New
Delhi as an ice age advances south.
Actual climate change. Although human-related
emissions of carbon dioxide and other greenhouse
gases might cool some parts of Earth by affecting ocean
currents, they cannot trigger a widespread ice age.
That is because increased levels of greenhouse gases
will increase temperatures across much of the planet.
In addition, Earth's orbit is in a different phase than
during the peak of the last major ice age 20,000 years
ago, and the Northern Hemisphere is receiving more
solar energy in the summer than would be associated
with another ice age.
Movie scenario. Tornadoes strike Los Angeles and
grapefruit-sized hail falls on Tokyo.
Actual climate change. Research has shown that
climate change might lead to more intense hurricanes
and certain other types of storms. In a hotter world,
evaporation will happen more quickly, providing the
atmosphere with more fuel for storms. In fact, scientists
have found this is already happening with rain and
snowfall in the United States. But even when scientists
run scenarios on the world's most powerful
supercomputers, they cannot pinpoint how climate will
change in specific places or predict whether Los
Angeles or other cities will face violent weather.
What is an abrupt climate change?
When scientists talk about climate change, they are
usually referring to “gradual climate change.” In
other words, if the planet warms steadily, the climate
changes steadily. But there's evidence that some parts
of the climate system work more like a switch than a
dial: if a certain temperature level is reached, there
may be an abrupt and large change in the climate.
That’s why some scientists worry about a catastrophic
event — like the breakup of the West Antarctic ice
sheet or the collapse of the Atlantic thermohaline
Could an abrupt climate change really happen?
Scientists have just begun to study the possibility
of an abrupt climate change. But when scientists
talk about abrupt climate change, they mean
climate change that occurs over decades, rather
than centuries. It’s too soon to know for certain
whether abrupt climate change could occur, but if
it does, it’s not expected to happen within the next
several decades.
Do scientists agree about global warming?
Although scientists still argue about how fast and
how much the atmosphere will warm, the
mainstream scientific community agrees on 3 key
1. the earth is warming;
2. the warming can only be explained by the build-up
of greenhouse gases in the atmosphere; and that
3. the warming will continue if we don’t reduce
How can global warming cause cold weather?
Without the thermohaline circulation, not as much
heat would be transported from the tropics to the
North Atlantic region. Eastern North America and
Western Europe would cool, while the rest of the
world continues to warm. We don’t know how much
of this cooling would be balanced by the simultaneous
warming in the atmosphere.
(a) Increase the mean
(b) Increase variance
(c) Increase both
mean and variance
S.-P. Weng
Water-holding capacity in atmosphere
is governed by C-C relationship
The Clausius–Clapeyron equation: des /es = LdT/RT2,
(es : the saturation vapor pressure at temp.=T, L: latent
heat of vaporization, R: gas constant.)
Changes in saturation-specific humidity [also involve the
ratio of the gas constant of dry air to that of water vapor (0.622)] range
from 6.0% K−1 at 300 °K to 7.4% K−1 at 270 °K.
Global mean temperatures at 850 and 700 hPa are
about 280° and 273°K, so that 7% K−1 is a reasonable
approximation. (Trenberth et al. 2003, BAMS)
S.-P. Weng
“Secular change of diurnal rainfall activity in Taipei”
S.-P. Weng
Climate Change detection and attribution
Detection of climate change is the process of
demonstrating that climate has changed in some
defined statistical sense, without providing a
reason for that change.
Attribution of causes of climate change is the
process of establishing the most likely causes for
the detected change with some defined level of
S.-P. Weng
Ten facts about global warming
The earth today is warming at a rate faster than in
any time in the last 1,000 years
It has been particularly enhanced over the past 20
Electricity generation in the US accounts for 33% of
the total global warming emissions, transportation
activities for 27%, and industrial activities for 19%
Temperatures are predicted to rise another 2.5 to
10.4 degrees Fahrenheit by the end of the century
The sea level across the globe has climbed between
4-10 inches in the past century
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Ten facts about global warming
The Arctic sea ice has shrunk almost 40% in
recent decades, attributable in part due to global
If the West Antarctic ice sheet were to melt, sea
level could rise by another 16 to 30 feet
Droughts and floods could become more frequent
El Nino events could become more frequent and
Tropical diseases could expand their range into
areas further north
S.-P. Weng
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Kyoto Protocol Basics
1. What is the Kyoto Protocol?
It's a pact agreed by government delegates at a 1997 U.N. conference in Kyoto, Japan,
to reduce the amount of greenhouse gases emitted by developed countries by 5.2
percent of 1990 levels during 2008-2012. A total of 141 nations have ratified the pact,
according to U.N. data.
2. Is it the first agreement of its kind?
Governments originally agreed to tackle climate change at the 1992 Earth Summit in Rio
de Janeiro. At that meeting, leaders created the UNFCCC, which set a non-binding goal
of stabilizing emissions at 1990 levels by 2000, a goal not met overall. The Kyoto
protocol is the follow-up to that and is the first legally binding global agreement to cut
greenhouse gases.
3. Is it legally binding?
had legal force for its participants since Feb. 16 (2005) after meeting twin conditions -backing from at least 55 countries and support from nations representing at least 55
percent of developed countries’ carbon dioxide emissions. It passed the second hurdle
in November 2004 when Russia ratified and now has backing from nations representing
61.6 percent of emissions. The United States, the world’s biggest emitter, has pulled out,
S.-P. Weng
saying Kyoto is too expensive and wrongly omits developing nations.
4. How will it be enforced?
Under a 2001 deal made by environment ministers, if countries emit more gases than
allowed under their targets at the end of 2012, they will be required to make the cuts,
and 30 percent more, in the second commitment period, which is due to start in 2013.
They rejected the idea of a financial penalty.
5. Must all cut emissions by 5.2 percent?
No, only 39 countries -- relatively developed ones -- have target levels for the 2008-12
period, adhering to a principle that richer countries should take the lead. Each country
negotiated different targets, with Russia aiming for stabilization at 1990 levels and the
European Union taking an 8.0 percent cut.
6. How are supporters doing so far?
Many countries are lagging behind Kyoto targets. Emissions by Spain and Portugal were
40.5 percent above 1990 levels in 2002. U.S. emissions were up 13.1 percent.
Emissions by ex-communist bloc states fell most sharply due to the collapse of Sovietera industries -- Russian emissions were down 38.5 percent.
S.-P. Weng
7. How will countries comply?
The European Union set up a new market in January 2005 under which about
12,000 factories and power stations are given carbon dioxide quotas. If they
overshoot they can buy extra allowances in the market or pay a financial penalty;
if they undershoot they can sell them. Prices in the EU market are now about 7.2
euros per metric ton.
8. What if a country misses its target?
The protocol provides for "flexible mechanisms" -- ways for countries to reach
their targets without actually reducing emissions at home. These include
emissions trading -- where one country buys the right to emit from a country that
has already reduced its emissions sufficiently and has "spare" emissions
reductions. Another is the "clean development mechanism" where developed
countries can earn credits to offset against their targets by funding clean
technologies, such as solar power, in poorer countries.
Countries can also claim credits for planting trees in the Third World that soak up
CO2 -- carbon "sinks."
S.-P. Weng
Dilemma for Policy Makers
How do we weight the possible harm of our
actions against the advantage of economic
 Policy makers want scientists to make
precise predictions of the timing and
magnitude of the future global warming.
S.-P. Weng
Gliding Down A River
Toward A Waterfall
We are having fun now!
(1) How far away are we from the
 A scientific question.
(2) When should we get out of the boat?
 A political decision.
30 minutes
30±10 minutes
S.-P. Weng
A catastrophe waiting ahead!
An Example of Chaos (uncertainty)
Dropping a wallet on the top
of a snow hill…..
top of the hill
bottom of the hill
(from Philander’s “Is The Temperature Rising?”)
S.-P. Weng
It is important to accept that fact that
“..although accurate predictions are,
in principle, possible on the basis of
the laws of physics, such forecasts
may be impossible in practice..”
because the complexity of our
climate system.
S.-P. Weng
How Should Policy Makers Cope with the
Uncertainties in Science?
Rather than implement comprehensive
programs that decree a rigid course of
action to reach grand and final solution,
We should promote adaptive programs
whose evolution is determined by the
results of these programs and by the new
scientific results that become available.
S.-P. Weng
A Successful Case of the
Adaptive Approach
In 1987, the world agreed in the Montreal
Protocol that each country would limit its
production of the chlorofluorocarbons (CFCs)
that contribute to the depletion of the ozone
This decision was made before clear
evidence that CFCs are harmful to the
ozone layer.
The regulations were agreed in subject to
periodic reviews to accommodate new
scientific results.
S.-P. Weng
Explosive Growth Events
A gardener finds that his pond has one lily
pad on a certain day, two the next day, four
the subsequent day and so on. After 100
days the pond is completely filled with lily
pads. On what day was the pond half full?
ANSWER: Day 99
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Global Change – An Explosive
Growth Event ?
Exponential Growth
Global Warming
(from Philander’s “Is The Temperature Rising?”)
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Consequence of Late
Suppose the gardener, once he realizes
what is happening, quickly enlarge the
pond to twice its size. On what day will
the new pond be completely filled?
ANSWER: Day 101
S.-P. Weng
Sooner Is Better Than Later
Is our global warming problem close to Day 1 or
Day 100? (This is a scientific problem)
Instead of waiting for a precise answer to end
this debate, it is more important to recognize the
explosive-growth nature of the global warming
S.-P. Weng
It is wiser to act sooner than later.
Lessons Learned
1. Uncertainties in science are inevitable.
2. familiarize ourselves with the processes that
determine Earth’s climate and the sensitivity of these
processes to perturbations.
3. Over tens of thousands of years, we are unlikely to
do great harm to our planet as a whole.
4. We can, however, cause “inconvenience” to
ourselves in the next several decades by continually
perturbing the global climate.
S.-P. Weng
Should we worry about global warming?
Global temperatures have increased by 1 degree
Fahrenheit over the past 100 years. Although this may
seem like a small change, it is enough to harm
important ecosystems, change rainfall patterns and
raise the sea level. Climate models project additional
warming of about 2-10 F over the next 100 years. The
overwhelming consensus of scientists who study the
atmosphere is that this warming is caused primarily
by the build-up of greenhouse gases in the atmosphere,
mostly from the burning of fossil fuels like coal and
What is the Atlantic thermohaline circulation?
The Atlantic thermohaline circulation, which includes
the Gulf Stream, acts like an oceanic conveyer belt that
carries heat from the tropics to the North Atlantic
region. Warm surface water from the tropics travels
northward by the Gulf Stream. As the warm water
cools in the North Atlantic, it sinks to the ocean floor,
and then slowly moves southward until it returns once
again to the tropics. This ocean circulation pattern is
caused by differences in water temperature and salinity
in the ocean.
Could climate change shut down the
thermohaline circulation?
Global warming is expected to increase ocean
temperatures and to increase the flow of
freshwater into the ocean through precipitation,
run-off, and melting of glaciers. Many climate
models have projected that increased surface
ocean temperatures and reduced salinity could
slow or completely “shut down” the thermohaline
What are the chances of the thermohaline circulation
shutting down?
We don’t yet know the probability of the thermohaline
circulation shutting down. It depends on how much
and how quickly the atmosphere warms. In general, it
is considered possible but not very likely. If it were to
occur, it would probably not happen within the next
100 years, and circulation would eventually recover,
after decades or centuries.
If “The Day After Tomorrow” is fiction, what is the
truth about global warming?
The truth is that global warming is happening and
that it is already too late to avoid some of the effects.
Even under the most optimistic circumstances,
atmospheric scientists expect global climate change
to result in increased flooding and droughts, more
severe storms, and a loss of plant and animal species.
These events will occur, even if climate change is
What can be done about global climate change?
There is no single cause of global climate change and
there is no single solution. Most experts believe that
technology will provide solutions. Technologies that
reduce emissions (energy efficiency, hydrogen fuels,
carbon storage, nuclear energy and renewable energy)
and technologies that remove carbon from the
atmosphere may all play a role. Government policies
that encourage businesses to develop and use these
and other technologies are also very important. Many
states and businesses have already found that they
can reduce emissions while saving money.