Transcript geog510_intro_climatechange - Cal State LA

Climate Change
1.
2.
(1)
Climate State: is described in terms of an average value, a
measure of variation about the mean, the extreme values,
and the shape of frequency distribution (30 yrs).
Change in climate can occur in several different ways
Shift in the mean; (2) graduate trend in the mean; (3)
variability (periodic; quasi-periodic; non-periodic) (handout
figure 11.1)
3.
4.
Observed changes can be real or artifact of changes in
instrumentation, observational practices, station location, or the
surroundings of the instrumental site, or due to errors in the
transcribed data.
Causes of changes: difficult to ascribe because of the complexity
of the climate system. Natural variability operates over a wide
range of time scales and superimposed on effects of human
activities.
Climate system (handout question 1.1)
A complex, interactive system
consisting of the
atmosphere, land
surface, snow and ice,
oceans and other bodies
of water, and living
things.
Climate changes in respond to
changes in external
factors and internal
dynamics.
Three fundamental ways to change
climate:
(1)
Incoming solar radiation
(2)
reflectivity of the earth
(albedo)
(3)
longwave radiation from the
earth towards the space
Energy balance of the earth
system (Figure 1)
(1) About 30% solar radiation
is reflected back to space
(2) about 49% solar radiation is
absorbed by the earth’s
surface
(3) greenhouse gases absorb
most of the longwave
radiation from the earth and
keep the earth warm.
Greenhouse effect
Greenhouse gases: CO2, H2O,CH4
,N2O,O3,CFCs
Atmospheric effect = blanket effect:
greenhouse gases absorb
longwave radiation from the earth
and re-radiate back to the earth,
keep the earth warm (Fig 1.3)
Anthropogenic related climate
warming: human activities
increases greenhouse gases and
increases earth’s surface air
temperature
Radiative forcing: is a measure of
how the energy balance of earthatmosphere system is influenced
when factors that affect climate
are altered. Positive forcing lead
to increase energy and warming,
negative is decreasing energy
and cooling.
Climate Forcings
External forcings (outside of the earth’s system)
1.
2.
Solar variability: 11-year solar cycle (sunspots), 22-year magnetic field cycle (solar
flare).
Tectonic processes: changes in continental positions, sizes, and in the
configuration of ocean basins, location and size of mountain ranges and plateaus
modify the atmospheric and ocean circulation at geological time scales.
3. Astronomical
periodicities:
(1) eccentricity of the
orbit changes at a
period of 95,000410,000 years;
(2) the tilt of the earth’s
axis has a period of
41,000 years;
(3) a wobble in earth’s
axis of rotation
causes changes in
the timing of
perihelion at time
scale of about
21,000 years
(handout figure
11.3)
4. Volcanic eruption: major explosive
eruptions inject dusts and sulfur dioxide
aerosols into the stratosphere, cause a
hemispheric/global cooling of 0.5-1.0C in
the year following the events
5. Atmospheric composition: changes in
CO2 and CH4 and global temperature
are coincident during both glacial and
interglacial transitions.
Internal forcing
Involves in changes in atmospheric composition, cloud cover,
aerosols and surface albedo that affects climate through a set
of feedback mechanisms of positive (self-enhancing) or
negative (self-regulating or damping) processes.
Increases in water vapor
Example:
Increasing temperature  Increases in plant respiration
Decreases in CO2 dissolved in the oceans
Increases CH4 emissions from wetlands


Increases in greenhouse gases
Global-average radiative forcing estimates
and ranges (handout Question 2.1, Fig2)
Gradual cooling about 40-50 million years ago is theorized
due to the formation of the Himalayan Mountain system
during the Paleocene and Eocene epochs caused an increase
in chemical reactions between newly exposed tock of the
mountain system and the atmosphere that reduced CO2 level
(Uplift Weathering Hypothesis)
We currently live in the latest interglacial, known as the
Holocene Epoch, began about 10,000 years ago.
Climate records
1.
2.
Paleo-records (10,000-23,000 years): proxy data from
pollens preserved in lake sediments and peat bogs for
vegetation info; former lake shorelines for moisture
info; annual snow/ice layer in ice cores for seasonal
change information; micro-particles and chemical
compounds in the ice for volcanic events; tree ring for
moisture and summer temperature(1500); historical
documents record of crop harvests or extreme weather
events; isotopes in sediments and ice cores; etc.
Instrumental records (since 1861)
Climate data derived from
geologic indicators and other
sources rather than
instrumental records.
(Fossilized plankton, coral
from sediments on seafloors,
chemical telltales from ice
sheet, glaciers)
Ice drilling:
Ice core: air trapped in the
glacial can derive CO2 level to
approx temperature
Ocean floor drilling:
Fossil Plankton (from phylum
Foraminifera)provide chemical
clues to the climate when they
were formed
Global mean temperatures are rising faster with time
Warmest 12 years:
1998,2005,2003,2002,2004,2006,
2001,1997,1995,1999,1990,2000
Period
Rate
50 0.1280.026
100 0.0740.018
Years /decade
Arctic vs Global annual temperature anomalies (°C)
Warming in the Arctic is
double that for the
globe from 19th to 21st
century and from late
1960s to present.
Warmth 1925 to 1950 in
Arctic was not as
widespread as recent
global warmth.
Note different scales
Human and Natural Drivers
of Climate Change
CO2, CH4 and N2O Concentrations
- far exceed pre-industrial values
- increased markedly since 1750
due to human activities
Relatively little variation before
the industrial era
Projections of Future Changes in Climate
Best estimate for
low scenario (B1)
is 1.8°C (likely
range is 1.1°C to
2.9°C), and for
high scenario
(A1FI) is 4.0°C
(likely range is
2.4°C to 6.4°C).
Broadly
consistent with
span quoted for
SRES in TAR, but
not directly
comparable
Attribution
Asks whether observed
changes are consistent
with
expected responses to
forcings (red)
inconsistent with
alternative explanations
TS-23
All forcings-black
Natural forcings only-blue
Data analysis
• Load data in excel sheet (or cut and paste) and reformat
• Correlation analysis
• Trend identification (simple linear regression with Time
as independent variable and the variable examining as
dependent variable, Temp=a+b*Time). To simplify the
project for this class, we only need to calculation
correlation between the variable and the Time.
Correlation analysis
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•
To determine the strength of relationship between 2 variables (based on
how they change with time or space).
-1.0 to 1.0
Use Pearson’s correlation analysis
Significant test: the significant value used most common is 95% (or 0.05)
confidence level. The value of correlation coefficient associated with this
significance level is depend on the sample size.
Correlation coefficient
Critical Values of the Correlation Coefficient
If your degree of freedom is not on this table, use the value for next lower degree of freedom:
Level of Significance (p) for a Two-Tailed Test
df (n-2):
0.10
0.05
0.02
0.01
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0.988
0.900
0.805
0.729
0.669
0.622
0.582
0.549
0.521
0.497
0.476
0.458
0.441
0.426
0.412
0.400
0.389
0.378
0.369
0.360
0.352
0.344
0.337
0.330
0.323
0.317
0.311
0.306
0.301
0.296
0.275
0.257
0.243
0.231
0.211
0.195
0.183
0.173
0.164
0.997
0.950
0.878
0.811
0.754
0.707
0.666
0.632
0.602
0.576
0.553
0.532
0.514
0.497
0.482
0.468
0.456
0.444
0.433
0.423
0.413
0.404
0.396
0.388
0.381
0.374
0.367
0.361
0.355
0.349
0.325
0.304
0.288
0.273
0.250
0.232
0.217
0.205
0.195
0.9995
0.980
0.934
0.882
0.833
0.789
0.750
0.716
0.685
0.658
0.634
0.612
0.592
0.574
0.558
0.542
0.528
0.516
0.503
0.492
0.482
0.472
0.462
0.453
0.445
0.437
0.430
0.423
0.416
0.409
0.381
0.358
0.338
0.322
0.295
0.274
0.256
0.242
0.230
0.9999
0.990
0.959
0.917
0.874
0.834
0.798
0.765
0.735
0.708
0.684
0.661
0.641
0.623
0.606
0.590
0.575
0.561
0.549
0.537
0.526
0.515
0.505
0.496
0.487
0.479
0.471
0.463
0.456
0.449
0.418
0.393
0.372
0.354
0.325
0.303
0.283
0.267
0.254