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20th Century Climate Change Data, Causation


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Title: 20th Century Climate Change Data, Causation

20th Century Climate Change Data, Causation
Current Climate Change Data and Causes
  • This is how Ill group the slides in this
  • A. Global Temperatures
  • B. Sea Level Changes
  • C. Arctic Ocean Ice
  • D. Glacier Retreats
  • E. Permafrost and methane

A. Global Temperatures
  • Temperature rise in the Industrial Age in the
    context of the past recent and geologic time

The Global Temperature Record for the past 150
Years Can Be Roughly Divided into 4 Regimes
1. Up to 1912
  • Human generated GHGs are still fairly small.
    Cars are a rarity, human population is a small
    fraction of todays.
  • We are still in the general regime of the past
    interglacial 6000 years, which shows little
    trend in global temperatures
  • However, an unusually large number of major
    volcanic eruptions added significant cooling
    stratospheric aerosols Krakatoa 1883
    (climatically strongest in modern record, see
    especially Gleckler et.al. 2006), Santa Maria
    (1902, one of the 5 biggest of the past 200
    years), Katmai 1912 (largest of the 20th century)
  • The Katmai eruption set the minimum of global
    temperatures for the 20th century (and very
    likely beyond)

2. Period 1912 to 1942
  • The long term solar cycles show a modulation such
    that successive solar maxima are roughly similar,
    and change slowly, over roughly century time
  • Sunspot numbers are a fairly good proxy for solar
    activity, and recall that there is a 0.1
    modulation in the solar luminosity with the solar
    cycle, and stronger solar cycles are associated
    with higher solar luminosity of similar scale
  • During this period, solar sunspot maxima were
    trending higher, and the inferred solar
    luminosity (we have no direct measurements of
    solar luminosity back in those days) was rising
  • Climate models show that in addition to rising
    anthropogenic CO2, solar activity likely
    accounted for a significant part of the
    temperature rise seen at this time, with
    deforestation and emergence from the Katmai
    eruption cooling also being significant.
  • Also contributing, was a quiet period of no
    significant volcanic eruptions to inject cooling
    aerosols, compared to the 1883-1912 period.
  • See next slide.

Climate modelling (e.g. Hansen 2005) shows
increasing solar activity and accompanying
luminosity rise likely accounts for a part of
1900-1945 global temperature rise. Forcing level
is not shown on these graphs. Timing is what is
being shown.
3. Period WWII to 1970
  • Post WWII period of rapid rebuilding and rapid
  • While CO2 levels are rising, what is rising
    faster is the smoky, choking pollution of
    aerosols associated with coal burning, rapidly
    rising vehicle-miles, and power plants.
  • Unburned hydrocarbons combine with sunlight, and
    water with sulfates to produce hydrosulfuric acid
    droplets and other particles which reflect
    incoming sunlight and cool the surface.
  • The so-called aerosol indirect effect - These
    particles are also large enough to act as cloud
    nucleation sites and increase low clouds (this
    air pollution usually hangs low to the ground due
    to temperature inversions).
  • (I grew up in L.A. in this period. You youngsters
    cannot believe how bad it was back then. You were
    lucky to be able to see 2 miles through the smog,
    and seeing the San Gabriel Mountains 20 miles
    away was a rarity.

  • At the same time, World War II destroyed a lot of
    life and industrial capability, and it took some
    time for this to be rebuilt. There was a period
    of reduced growth in greenhouse gases at the
    beginning of this period.
  • Also, the rising solar luminosity (as inferred
    from the sunspot cycle) came to a top in mid
    1950s and has been declining every since.
  • The combination of lowered rate of GHG emission
    and much higher anthropogenic reflective
    pollutants, and a halt to solar-induced
    luminosity increases was enough to halt global
    warming and keep temperatures roughly constant
    during this 25 year period.

The Pennsylvania Smog Attack of 1948
London Smog 1952, killed 12,000 people
London THE Smog Capital of that Time
But L.A. Provided Strong Competition
Los Angeles Famous then as the of Smog Capitol
of the United States
New York Not Much Better
The Smog Machine!
Smog Particles from R. Healy (looks like a
couple of pollen grains at upper left as well)
4. 1970-Today
  • Greenhouse gas emissions accelerate
  • The Clean Air Act of 1970 and other air pollution
    laws in the U.S. and Europe cause a significant
    reduction in cooling aerosols, while China and
    Asia make up for these improvements with large
    post-Mao industrialization, largely coal-fired.
    Net global aerosol effect is approximately a
    wash, as can be seen in Hansen et.al. 2005.
  • Solar and other effects are negligible compared
    to greenhouse gas emissions, primarily CO2 from
    oil, gas, gasoline, and coal burning
  • Strong and accelerating greenhouse warming
    dominates climate forcings

14 sec video Worldwide Temps 1976-2012
  • https//www.youtube.com/watch?featureplayer_embed

  • Heating and Cooling Forcings to the Earths Heat
    Budget (from Hansen et.al. 2005). Forcings
    calibrated from observations. Combined with the
    GISS Climate Model, they reproduce observed
    global temperature in detail very well. See next

  • (from Hansen et.al. 2005) Before 1900, the
    observed curve is based on observations at
    meteorological stations and the model is sampled
    at the same points, whereas after 1900 the
    observations include sea surface temperatures for
    the ocean area, and the model is the true global
    mean (Hansen et. al. 2001).

Notes on Climate Forcings from Hansen et. al. 2005
  • Effective forcings are derived from five-member
    ensembles of 120-year simulations for each
    individual forcing and for all forcings acting at
    once see (9) and supporting online material.
    The sum of individual forcings differs slightly
    from all forcings acting at once because of
    nonlinearities in combined forcings and unforced
    variability in climate simulations.
  • This is the ozone forcing in our principal
    IPCC simulations it decreases from 0.24 to 0.22
    W/m2 when the stratospheric ozone change of
    Randel and Wu (S1) is used
  • Ozone and black carbon forcings are less than
    they would be for conventional forcing
    definitions (11), because their efficacy is
    only 75 (9)

IPCC AR4 (2007) Climate Forcings Human and
Natural from 1750-present
2. Sea Level Changes
  • Thermal, melt water, salinity, geoid changes and
    relation to global temperatures

On the 60 year time scale, sea level rises for
two reasons, both are climate-related
  • 1. Thermal expansion of warmer water (simple
    physics. Observe temperature profile of the
    ocean, integrate, derive the thermal expansion)
  • 2. Melting of continental permanent ice
    (glaciers, land ice caps)
  • While thermal expansion has provided most of the
    total of the past 100 years continental melt is
    rapidly increasing, and now contributing 1/3 of
    the current sea level rise rate.
  • Sea Level Rise rate 1.8mm/year avgd over past
    100 years, but is 3.3mm/year avgd over the past
    20 years.
  • Note that sea ice melting contributes nothing to
    sea level rise, since floating ice already
    displaces water (Archimedes Principle). Thus,
    melting of the Arctic Ocean ice happening now is
    not contributing to sea level rise
  • On longer time scales, there is minor
    contributions from slow rebound of the land from
    the last Ice Age (loss of heavy glaciation causes
    continental land to float a bit higher, and this
    process is very slow).
  • On time scales of a few years and shorter, there
    are many factors affecting sea level tides, El
    Ninos, tsunamis, changing atmospheric pressure
    associated with storms, floods and associated
    salinity changes
  • 34 second video of Greenland areas of ice melting
    (in red)

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Sea Level Rise vs. Time and Place
  • El Ninos tend to cause sharper rises in sea
    level where the warm surface waters are, from the
    thermal expansion of water
  • La Ninas (the cold surface water phase) does the
  • The height of the geoid (the gravitational
    potential surface of the Earth a surface
    parallel to sea level if all other factors are
    ignored) changes near Greenland and Antarctica
    especially, as glacial melt takes mass away from
    these continental masses
  • Hence, the rate of sea level rise varies from
    place to place at different times. Must take
    account of geoid changes (straight-forward
    gravity) and other data sampled widely in
    location and time to get it right.
  • The following data shows the many tidal gauges
    and satellite measurements are doing a good job
    of tracking global sealevel rise

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How does this rise rate compare with Ice Age
transitions? Red line is 1.8mm/yr 20th century
average. Recent rate is higher 1993-2003
satellite observed rate is 3.3mm/yr
GRACE Satellite uses gravity to measure total ice
mass loss from Greenland. Ice loss is
Estimates of total Antarctic land ice changes and
approximate sea level contributions using many
different measurement techniques. Adapted from
The Copenhagen Diagnosis. (CH Chen et al. 2006,
WH Wingham et al. 2006, R Rignot et al. 2008b,
CZ Cazenave et al. 2009 and VVelicogna 2009)
(Source here)
  • Ice mass changes for the Antarctic ice sheet
    from April 2002 to February 2009. Unfiltered data
    are blue crosses. Data filtered for the seasonal
    dependence are red crosses. The best-fitting
    quadratic trend is shown as the green line
    (Velicogna 2009).

  • Monthly changes in Antarctic ice mass, in
    gigatons, as measured by NASAs GRACE satellites
    from 2003 to 2011. Results from five different
    IMBIE team members using different methods. The
    data have been adjusted to reflect new models of
    post-glacial rebound.(Shepherd et.al. 2012).

What about glaciers globally? Maybe its just
Greenland and Antarctic glaciers that are melting?
  • No.

Global Melt of Glaciers, in equivalent water
thickness (black boxes, m/yr), and cumulative
total thickness loss (red boxes, right scale,
meters). Glacier melt is clearly accelerating
Annual change in global glacier melting to sea
level rise (left axis, mm of water equivalent,
mm/yr) and cumulative value (right axis, mm),
based on surface area-weighted mass balance
observations. (source)
The speed of melting (meters of glacier depth per
year) of 23 different Antarctic glaciers vs. the
temperature of the seawater into which they
contact, where 0 is the freezing point of (salt)
water. Clearly the rate of melting rises rapidly
with even small temperature differences above the
freezing point. Data from satellites and ground
surveys (Rignot Jones 2002)
Arctic Ocean Ice Cover Dropping More Rapidly
than the 2007 IPCC AR4 models
Arctic ice coverage is dropping in all seasons,
not just summer
Not just ice coverage area, but ice volume is
dropping even more dramatically, as the permanent
ice rapidly disappears, leaving only thin
seasonal ice
Summer Sea Ice Area past 1,450 years. In 2012, a
new record low of 3.5x106 km2. That is less
than half the value of the bottom point of this
curve. See the Latest data
Lets Put Recent Global Warming in Context of the
Last 1000 Years
  • From Mann et.al. 1999. The Hockey Stick made
    famous in An Inconvenient Truth

Temperature Proxies for Century, Millenium Time
  • (See Mann et.al. 2008 and here, for more
    details), but briefly
  • Foraminifora growth sensitive to temperature
    different for different species. Preserved in
  • Tree rings show good correlation to other
    proxies, until the 20th century (likely because
    CO2 levels also affect tree rings and CO2 levels
    now far above typical values of past 1000 years
  • Stalagmites annual growth ring thickness (water
    from above) sensitive to temperature and climate
    in general
  • Ice cores trapped air bubbles preserve
    atmosphere, and isotope ratios are sensitive to
    temperature. Also trap pollen, species sensitive
    to temperature
  • Pollen species composition in sediments from
    lakes, layering showing annual runoff, charcoal
    shows major fires which can be cross correlated
    with other data
  • Borehole temperatures surface temperatures
    conduct downward through the ground, and deep
    measurements contain information on ancient
    temperatures. See NOAAs site on borehole science

Given the importance, the work was re-done with a
wider range of temperature proxy assumptions and
additional care to avoid statistical
over-fitting. Still a Hockey stick. Note the
Medieval Warm period is actually a Northern
Hemisphere phenomenon, not global.
Glacier length change from temperature proxies
Old photos, and written accounts. Still a hockey
Global surface temperature change over the last
five centuries from boreholes (thick red line).
Shading represents uncertainty. Blue line is a
five year running average of HadCRUT global
surface air temperature (Huang 2000). Borehole
data confirms the other temperature proxies.
Jones and Mann (2004) temperature reconstructions
using proxies, now going back almost 2000 years,
with global temperatures at the bottom pane.
Actual instrumental temperatures shown in red.
Proxies and instruments both agree - still a
Hockey Stick
Other Climate Change Effects
  • Global phytoplankton has declined by an alarming
    40 since 1950, as warmer, more stratified ocean
    surface waters inhibit nutrient mixing from below
    and thus limit growth
  • The stratosphere is cooling, as rising
    stratospheric CO2 gets less IR from below but
    radiates more IR because of collisional
    excitation followed by radiative de-excitation.
    We showed this earlier in the course.

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Night Temperatures Rising Faster than Day
  • causes a decrease in the daily temperature
    range, which has been observed (Braganza 2004).
  • This too is a unique prediction of Greenhouse
    Effect warming (Alexander 2006). Why? Because
    temperatures reflect the integrated heating that
    has already happened during the day, so that peak
    temperatures occur in the late afternoon, not at
    noon as you'd naively expect if there were no
    lag. The hot ground can't efficiently radiate
    away this heat because it is trapped by CO2, and
    this keeps night-time temperatures warmer.
  • Daytime temperatures are warmer too, but not as
    much at night time temps because it is not
    increased incoming sunlight that is causing
    Global Warming, it is human-caused greenhouse
    gases inhibiting re-radiated cooling, which
    happens mostly late evening, AFTER the incoming
    solar heating.
  • A particularly dramatic demonstration of this can
    be seen in the mid/late 20th century data, when
    cooling by human-generated aerosol pollution
    caused daytime temperatures to stay roughly
    constant in spite of increasing CO2, while
    nighttime temperature actually increased (Wild,
    Ohmura, and Makowski 2007).

Night-time minimum temps are rising faster than
are daytime maximum temps, although both are
rising. This is a unique signature of GHG-caused
Why is This Happening to Us!?
  • Why?... Us! We human beings - were doing it!
    Weve raised CO2 levels from 280ppm to 400ppm in
    just the last 130 years, and its accelerating
  • How? By sheer number and dominance. As recently
    as 1900, wild mammals made up 50 of the land
    biomass. Now, only 3. Humans and their livestock
    make up 97 of the vertebrate biomass on land
    (Bodley 2008), and 72 of ALL vertebrate biomass
    on land or sea. (90 of the large fish have
    already been fished out, so that makes our
    domination that much easier).
  • 36 of the primary productivity of the entire
    planet has been diverted to humans (Haberl,
    et.al. 2012)

This 2008 graph is already out of date.
Population passed 7 Billion in 2012. Human
population is rising now at an amazing and
unsustainable rate of 1 billion additional people
every 13 years.
  • Were forcing CO2 into the atmosphere at a rapid
    rate, taking the cumulative carbon sequestration
    of hundreds of millions of years (the
    Carboniferous Era) and burning it all at once
    in a geologic instant.

CO2 Levels from ice cores, for the past 1
million years
Progressively expanded time scale needed to show
how incredibly rapid is the CO2 rise of today vs.
geologic past
CO2 Levels - past 60 years
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But maybe the CO2 is not from us, but instead
from volcanoes or something else?
  • No. The CO2 is ours.
  • Volcanoes put out only 1 of the CO2 that humans
    inject annually into the atmosphere
  • How do we know that CO2 is ours? There are many
    independent confirmations its ours, which Ill
    number as follows.

1. Were injecting far more than enough CO2 into
the atmosphere to account for the observed rise
(some goes into the ocean, some into plants and
Global Temperatures vs Atmospheric CO2 vs CO2
Emissions by Humans Last 1000 Years.
2. Note how the growth rate of CO2 drops during
economic recessions. 10 year averages are the
unmarked bars. Ive added economic recessions
(Fed data) labeled with years. The oil shock
recessions of 74 (Arab oil embargo) and the 91
(Gulf War) are particularly obvious

Methane Coming from domesticated cattle, and
from melting permafrost and peat, is 25x more
powerful as a greenhouse gas than CO2, per kg
(avged over 100 yrs)
  • Melting Permafrost Accelerating Global Warming
    methane trapped in melting Arctic Lakes is being
  • K. Anthony (U. Fairbanks) on Arctic lake methane
  • Note, CH4 oxidizes to H2O CO2. The residence
    time of a CH4 molecule in the atmosphere is about
    10 years. Both H2O and CO2 are less powerful
    greenhouse gases than methane.

Fraction of total emission of carbon which (top
frame) remains in the atmosphere, (middle) taken
up by land biosphere, and (bottom) taken up by
ocean. Time period is 1960 2007. Note as the
ocean absorbs more CO2 and also warms, it is
becoming less effective at soaking up additional
CO2. The opposite is true on land (sorry for the
terrible repro of this tiny graph)
Deforestation Human Fingerprint Since Dawn of
  • Tropical deforestation, as countries scramble to
    sell off their timber and clear cut so they can
    grow cattle (and soybeans, sugar), accounts for
    nearly 20 of carbon emissions (Canadell et.al.
  • In Indonesias main island of Sumatra, home of
    the last Sumatran Rhinos, deforestation destroys
    5 football fields worth of rainforest per minute.
  • Forests remove 2.4 billion tons of carbon from
    atmosphere per year (Canadell et.al. 2011)
  • Regrowth from cessation of tropical forest
    clearing shows rapid carbon uptake into trees,
    and also into root systems underground
  • But Slash / burn adds significant carbon to
    atmosphere, as has been done for thousands of
    years, and still goes on in the Amazon and other

Deforestation Produces about 1/3 as much CO2 per
year as fossil fuel burning
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Causes of Amazon deforestation Cattle Ranches,
Mostly. Demand from rapid proliferation of fast
food outlets world wide
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Deforested Land Shown in Red NASA image
Effects of Deforested Land on Climate
  • 1. Carbon burned or otherwise put back into the
    atmosphere as CO2
  • 2. Loss of photosynthesis loss of ability to
    pull CO2 out of atmosphere
  • 3. Desertification of land this may actually
    cause some cooling (although I cant find data),
    via higher reflectivity of land vs. forest
  • 4. Healthy forest returns ¾ of rainfall back to
    the atmosphere where it can rain out elsewhere.
    Deforested land returns only ¼ of rain water back
    to the atmosphere for further downwind
    rainmaking, instead causing severe runoff,
    erosion, loss of topsoil, and loss to the ocean

Key Points Current Climate Change and Global
Warming (GW)
  • Solar luminosity, cosmic ray modulation, show no
    secular change since 1950s cannot be causing
  • 20-21st Century climate 3 regimes and their
  • Volcanic and human pollution aerosols net
    coolant to climate by reflecting sunlight.
    Volcanic CO2 production only 1 of
    human-generated CO2.
  • Climate models (w/ high, low clouds, aerosols,
    volcanics, GHGs, deforestation, solar) agree
    closely with observed global temps.
  • Atmospheric CO2 is human-caused, as shown by
    C13/C12 ratio changes.
  • Fossil fuel burning dominates climate forcing
  • Sea level rises due to thermal expansion of
    warmer seawater, and (rapidly increasingly)
    melting land ice
  • Deforestation removes carbon sequestering trees,
    altering carbon cycle equation.
  • Methane as greenhouse gas forces climate at 1/4
    that of CO2. Methane levels have tripled from
    human activities, since the pre-industrial times.
  • Night-time low temps are rising faster than are
    day-time maximum temperatures.
  • Tropical deforestation goes mostly to cattle
    ranches to satisfy fast-food restaurant demand
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