The Biggest Control Knob The more we learn of the large natural changes of the past, the more confident we are that humans are driving today - PowerPoint PPT Presentation

Loading...

PPT – The Biggest Control Knob The more we learn of the large natural changes of the past, the more confident we are that humans are driving today PowerPoint presentation | free to download - id: 6fd5be-NDZlN



Loading


The Adobe Flash plugin is needed to view this content

Get the plugin now

View by Category
About This Presentation
Title:

The Biggest Control Knob The more we learn of the large natural changes of the past, the more confident we are that humans are driving today

Description:

The Biggest Control Knob The more we learn of the large natural changes of the past, the more confident we are that humans are driving today Richard B. Alley, Penn State – PowerPoint PPT presentation

Number of Views:17
Avg rating:3.0/5.0
Slides: 41
Provided by: Richard1633
Learn more at: http://www.meteo.psu.edu
Category:

less

Write a Comment
User Comments (0)
Transcript and Presenter's Notes

Title: The Biggest Control Knob The more we learn of the large natural changes of the past, the more confident we are that humans are driving today


1
The Biggest Control KnobThe more we learn of
the large natural changes of the past, the more
confident we are that humans are driving today
Richard B. Alley, Penn State
Please note I work for Penn State University,
And help UN IPCC, NRC, etc.,
But I am not representing them, Just me.
Meteorology, 2011
G. Comer Foundation
2
Paleoclimatology
  • What happened? Reconstruct past climate
  • When did it happen? Date past events
  • Why did it happen? Reconstruct possible causes
    of climate change, such as drifting continents,
    changes in the suns output, shifts in Earths
    orbit, eruptions of sun-blocking dust or fall of
    meteorite dust, changes in greenhouse gases, etc.

3
CO2 Paleobarometers
  • Gold standard is ice-core record
  • So far only 800,000 years, duplicated to
    450,000 yrs, and multiply duplicated younger
  • How do we know it works?
  • Youngest samples agree with instrumental record
  • Antarctic sites with different temperature,
    snowfall and impurities give same record
  • Sensible failures e.g., in rare
    refrozen-meltwater layers expect and find excess
    CO2 localized, so diffusion isnt smearing
    record. In warm tropical-glacier ice with dead
    bugs, find anomalously high CO2 as expected.

4
CO2 Paleobarometers
  • Many others, based on influence of CO2 abundance
    on something else that is preserved in
    sedimentary record, plus data-driven
    biogeochemical modeling
  • Nothing as simple and easy as ice-core data
  • Systematic errors of the different techniques are
    largely independent, so look for agreement among
    multiple techniques

5
CO2 Paleobarometers
  • d13C of alkenones, soil carbonates, or
    liverworts faster diffusion of lighter species
    allows preferential use in plants if CO2
    abundant, but heavier used if CO2 scarce
  • d11B or BCa of foraminiferal shells B(OH) 3
    enriched in 11B vs. the B(OH)4- incorporated in
    shells, and B residence time long, so d11B or
    BCa paleo-pH meters linked to CO2
  • Plant leaves grow more stomata when CO2 lower
  • Offspring-of-BLAG modelingtrack inputs and
    outputs of CO2 from independent data (e.g., more
    volcanoes release more CO2, and more fossil-fuel
    formation removes CO2 from air)

6
History of Climate
  • No instruments way back, so use proxies
  • Find sediment-climate relations
  • Past sand dunes, glaciers, or lakes easy to
    identify, tell different things about climate
  • Some are mainly physics (Greenlands ice is
    colder a mile down than ice above or below
    because still warming from ice age, tells how
    cold ice age was)
  • Some based on assuming little change in modern
    correlations (e.g., relation between temperature
    and who lives where)for such, we look for
    agreement among multiple independent indicators

7
History of Climate
  • Find ages of sediments in many ways
  • Oldest tree 5000 years, but overlapping pattern
    of thick and thin rings in living and nearby dead
    wood to gt12,000 years we counted gt100,000 years
    in Greenland ice (match historical volcanic
    fallout, etc. as far back as written history
    goes)
  • Older, a host of damage-accumulation and
    radiometric-dating techniques
  • Again, look for agreement among multiple ways

8
Volcano erupts
Acid falls on Greenland
Cooling from volcanoes
Big volcanoes cool (1-2oC for 2-3 years). But,
big volcanoes dont get really organized (a
little Huybers Langmuir, 2009), so explosive
volcanoes dont control climate. (Note that
flood-basalt eruption does seem to warm.) (Stack
of GISP2, Greenland ?18O records from 7 VEI 6-7
eruptions Stuiver et al. 1995.)
9
Figure 6.14. Simulated temperatures during the
last 1 kyr with and without anthropogenic
forcing, and also with weak or strong solar
irradiance variations. Global mean radiative
forcing (W m2) used to drive climate model
simulations due to (a) volcanic activity, (b)
strong (blue) and weak (brown) solar irradiance
variations, and (c) all other forcings, including
greenhouse gases and tropospheric sulphate
aerosols (the thin flat line after 1765 indicates
the fixed anthropogenic forcing used in the Nat
simulations). (d) Annual mean NH temperature (C)
simulated by three climate models under the
forcings shown in (a) to (c), compared with the
concentration of overlapping NH temperature
reconstructions (shown by grey shading, modified
from Figure 6.10c to account for the 1500 to 1899
reference period used here). All (thick lines)
used anthropogenic and natural forcings Nat
(thin lines) used only natural forcings. All
forcings and temperatures are expressed as
anomalies from their 1500 to 1899 means the
temperatures were then smoothed with a
Gaussian-weighted filter to remove fluctuations
on time scales less than 30 years. Note the
different vertical scale used for the volcanic
forcing compared with the other forcings. The
individual series are identified in Table 6.3.
10
Today
Climate didnt change
Warmer
Climate didnt change
When more cosmic rays reached Earth
Cosmic rays, magnetic field dont matter much to
climate.
From Muschler et al., 2005, QSR. ?18O (proxy for
temperature) from GRIP core (top), the
concentration of 10Be (middle), and the flux of
10Be (bottom). The Laschamp event of near-zero
magnetic field (red arrow) allowed increased
cosmic-ray flux producing more 10Be, but with no
apparent effect on climate.
11
Changes in space dust have been small, and
havent affected climate much. Helium-3 is mostly
from space dust. If space dust changed a lot,
that might affect climate some. But there has
been little change in space dust over last 30,000
years (ice-core data shown here) and beyond
(other data not shown). (Very rarely, a big
meteorite does matter, such as the one that
killed the dinosaurs 65 million years ago.)
Winckler Fischer, 2006, Science
12
Vostok, Petit et al.
13
(No Transcript)
14
Vostok, Petit et al.
15
Vostok, Petit et al.
16
CO2 and temperature changed essentially together
over ice-age cycles, as shown by Antarctic
ice-core data.
17
But, the science shows that a bit of the warming
happened over a few centuries before the CO2
rose. The temperature never went far without
the CO2, but the CO2 appears to have lagged
temperature. What does that mean for CO2 causing
warming?
18
First, a modern analogy
19
Overspending
20
Overspending
Going into debt
21
Overspending
Going into debt
Interest payments
22
Overspending
Going into debt
Interest payments
More debt
23
Overspending
Interest lags debt. How do we know interest adds
to debt?
Going into debt
Interest payments
More debt
24
Overspending
Interest lags debt. How do we know interest adds
to debt?
Going into debt
We cant explain size of debt without interest
(and, economics says so)
Interest payments
More debt
25
Overspending
Interest lags debt. How do we know interest adds
to debt?
Going into debt
We cant explain size of debt without interest
(and, economics says so)
Interest payments
More debt
Climate of the past
26
Overspending
Interest lags debt. How do we know interest adds
to debt?
Going into debt
We cant explain size of debt without interest
(and, economics says so)
Interest payments
More debt
Orbits
27
Overspending
Interest lags debt. How do we know interest adds
to debt?
Going into debt
We cant explain size of debt without interest
(and, economics says so)
Interest payments
More debt
Orbits
Warming
28
Overspending
Interest lags debt. How do we know interest adds
to debt?
Going into debt
We cant explain size of debt without interest
(and, economics says so)
Interest payments
More debt
Orbits
Warming
CO2 rise
29
Overspending
Interest lags debt. How do we know interest adds
to debt?
Going into debt
We cant explain size of debt without interest
(and, economics says so)
Interest payments
More debt
Orbits
Warming
CO2 rise
More warming
30
Overspending
Interest lags debt. How do we know interest adds
to debt?
Going into debt
We cant explain size of debt without interest
(and, economics says so)
Interest payments
More debt
Orbits
CO2 lags warming. How do we know CO2 adds to
warming?
Warming
CO2 rise
More warming
31
Overspending
Interest lags debt. How do we know interest adds
to debt?
Going into debt
We cant explain size of debt without interest
(and, economics says so)
Interest payments
More debt
Orbits
CO2 lags warming. How do we know CO2 adds to
warming?
Warming
We can explain changes if and only if we include
physics of CO2 (places getting more sun cooled
when CO2 fell, and places getting less sun warmed
as CO2 rose)
CO2 rise
More warming
e.g., Jansen et al., 2007
32
CO2 as part of ice-age cycling
  • Ice ages paced by orbit
  • Climate everywhere changed the same way, but
    orbits just moved sunshine around on the planet
  • 5-6oC globally averaged surface temperature
    change despite almost zero change in total sun
  • Less summer sun in Canada?more ice?higher albedo
    (also more dust, changing vegetation, etc.)
  • Set these to ice-age values in a climate model
    and get about half the cooling (but this is
    cheating, because need help from CO2 to get
    these)
  • Add greenhouse-gas changes and get the rest
  • (e.g., Jansen et al 2007 IPCC Hansen et al 2008
    Alley 2003 Cuffey Brook 2000)

33
Figure 4.24 Atmospheric CO2 and continental
glaciation 400 Ma to present. Vertical blue bars,
timing and palaeolatitudinal extent of ice sheets
(after Crowley, 1998). Plotted CO2 records
represent five-point running averages from each
of four major proxies (see Royer, 2006 for
details of compilation). Also plotted are the
plausible ranges of CO2 derived from the
geochemical carbon cycle model GEOCARB III
(Berner and Kothavala, 2001). All data adjusted
to the Gradstein et al. (2004) time scale.
Continental ice sheets grow extensively when CO2
is low. (after Jansen, 2007, that reports Figure
6.1)
34
CO2 and climate over longer times
  • Strong correlation of past CO2 and temperature
  • Known physics of CO2 explain most of this
  • Other things did contribute at some times
    (drifting continents, volcanic eruptions, etc.)
  • But others physically inadequate to explain most
    large changes and not strongly correlated
  • Warming increases CO2 over short times but
    decreases CO2 over long times (gt500,000 years).

35
CO2 (gas)
Rock-Weathering ThermostatToo cold, and CO2
builds up to warm.
Rock WeatheringCaSiO33H2O2CO2?
Ca2H4SiO42HCO3- Faster when warmer
CaSiO3 (solid)
Volcanoeruption rate independent of climate
Shell Growth Ca2H4SiO42HCO3- ?
CaCO3SiO23H2OCO2
Shell subduction CaCO3SiO2
Walker, J.C.G., P.B. Hays and J.F. Kasting, 1981
36
Many events show CO2-climate connection
  • Faint young sun of 4 billion years ago
  • Snowball Earths of a billion or so years ago
  • Ordovician glaciation
  • End-Permian extinction
  • Saurian Sauna of the Cretacteous
  • Ocean Anoxic Events and black-shale formation
  • Paleocene-Eocene Thermal Maximum
  • Cooling since the Eocene
  • Mid-Pliocene warmth
  • I wont subject you to all of them here, but we
    go over them in class

37
Climate sensitivity to CO2 from paleo-history
  • Overall, tests of climate models against
    paleo-record show that models are pretty good
  • Various suggested values range from lt1oC to
    12oC history excludes low and high values with
    fairly high confidence
  • 3oC warming for doubled CO2 over decades, and
    somewhat larger over centuries to millennia, may
    not be too bad (see Hansen et al., 2008)
  • No evidence that warming lowers sensitivity
    (ice-albedo isnt that big for modern and
    warmer)
  • Suggestion that there is something missing in
    models in warm climates in polar winters.

38
So, where does that leave us?
  • If higher CO2 warms, climate history sensible, as
    CO2 caused or amplified the main changes
  • There is now no plausible alternative to this
  • If higher CO2 does not warm, we must explain how
    radiation physicists are so wrong, and how a lot
    of really inexplicable climate events happened
  • CO2 may be forcing or feedbackno matter how a
    CO2 molecule got into air, it affects radiation
  • Paleoclimatic data show climate sensitivity
    similar to values in modern models (3oC for
    doubled CO2), perhaps with somewhat higher values
    over long times especially in polar regions.

39
So, where does that leave us?
  • Lots of knobs control the Earths climate system
  • The Sun knob isnt twiddled very much over
    short times, and hasnt done very much over long
    times because of CO2
  • If cosmic-ray, space-dust, magnetic-field, other
    space knobs matter, available evidence
    indicates that they do no more than fine-tune,
    and even that is not demonstrated
  • Lots of things on Earth matter regionallymoving
    a continent from equator to pole cools itbut
    evidence weak for major control of global
    climate, except through CO2

40
(No Transcript)
About PowerShow.com