Transcript www.wmconnolley.org.uk

Climate Change
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The 4-point consensus view of global warming
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Some objections impartially considered
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Evaluating Impacts
Nb: this is my personal view, and I am speaking in a personal capacity.
This talk is available from... http://www.wmconnolley.org.uk/sci/gw/
(1) Global Warming is happening...
http://en.wikipedia.org/wiki/Image:GIS_Global_1880_2005.gif
(2) We're causing it...
(2) ...we're causing it, continued
http://www.grida.no/climate/ipcc_tar/wg1/figspm-3.htm
(3) It will get “worse”
http://www.grida.no/climate/ipcc_tar/wg1/figspm-5.htm
(4) This will be a Bad Thing
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Sea level rise is bad, but slow
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Temperature rise regionally varying – winners and losers, political tradeoffs
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Ecological impacts – important, but I don't know
Common myths, impartially considered
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The “urban heat island” - negligible effect
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Satellite temperatures - show warming too
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The “hockey stick” controversy
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“The Day After Tomorrow” - will not happen
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Little relation between the Ozone hole and GW
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CO2 increase is anthropogenic (more than...)
Satellite temperature measurements
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Mears et al: 0.131 °C/decade
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Spencer and Christy version 5.1, 0.084 °C/decade
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Fu et al, 0.2 °C/decade (May 04)
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Vinnikov and Grody, with 0.22°C to 0.26°C per decade (Oct. 03)
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Surface record: 0.06 °C/decade over the past century and 0.15 °C/decade since 1979.
http://www.ssmi.com/msu/msu_data_description.html
Satellites (2)
http://www.met-office.gov.uk/research/hadleycentre/CR_data/Monthly/upper_air_temps.gif
Urban Heat Island (1)
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Cities tend to be hotter than the surrounding countryside. But (for the purposes of the
temperature record) we care about trends – ie are cities getting even warmer?
Hansen et al. (JGR, 2001) adjusted trends in urban stations around the world to match rural
stations in their regions, in an effort to homogenise the temperature record. Of these
adjustments, 42% warmed the urban trends: which is to say that in 42% of cases, the cities
were getting cooler relative to their surroundings rather than warmer. One reason is that
urban areas are heterogeneous, and weather stations are often sited in "cool islands" - parks,
for example - within urban areas.
IPCC: UHI does not exceed about 0.05°C over the period 1900 to 1990, because:
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land, sea, and borehole records are in agreement
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the trends in urban stations for 1951 to 1989 (0.10°C/decade) are not greatly more than
those for all land stations (0.09°C/decade).
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the differences in trend between rural and all stations are also virtually unaffected by
elimination of areas of largest temperature change, like Siberia, because such areas are
well represented in both sets of stations.
Urban Heat Island (2)
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Peterson, J Clim, 2003: "Assessment of urban versus rural in situ surface temperatures in the
contiguous United States: No difference found" indicates that the effects of the UHI may
have been overstated, finding that Contrary to generally accepted wisdom, no statistically
significant impact of urbanization could be found in annual temperatures. This was done by
using satellite-based night-light detection of urban areas, and more thorough
homogenisation of the time series (with corrections, for example, for the tendency of
surrounding rural stations to be slightly higher, and thus cooler, than urban areas).
Parker, Nature 2004: attempts to test the urban heat island theory, by comparing tempature
readings taken on calm nights with those taken on windy nights. If the urban heat island
theory is correct then instruments should have recorded a bigger temperature rise for calm
nights than for windy ones, because wind blows excess heat away from cities and away
from the measuring instruments. There was no difference between the calm and windy
nights, and the author says: we show that, globally, temperatures over land have risen as
much on windy nights as on calm nights, indicating that the observed overall warming is not
a consequence of urban development.
Publication bias: Peterson notes that essentially all large-scale studies showed some urban
centres cooling. But no individual city studies did. People were reporting what they expected
to see.
http://www.ncdc.noaa.gov/oa/rural.urban.ppt
http://en.wikipedia.org/wiki/Urban_heat_island
“Hockey Stick” controversy...
or,
The temperature over the last 1-2 kyr
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http://en.wikipedia.org/wiki/Image:1000_Year_Temperature_Comparison.png
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(dark blue): P.D. Jones, K.R. Briffa, T.P. Barnett, and
S.F.B. Tett, 1998, The Holocene 8, 1998, 455-471.
(blue): Michael E. Mann, Raymond S. Bradley, and
Malcolm K. Hughes, 1999, Geophysical Research Letters
Vol. 26 , No. 6 , p. 759, March 15, 1999.
(light blue): Crowley and Lowery 2000 (Ambio 29, 51),
Science v289 p.270, 14 July 2000.
(lightest blue, somewhat green): Briffa et al. (2001) J
Geophys Res 106, 2929-2941.
(light green): Esper, J., E.R. Cook, and F.H.
Schweingruber, 2002, Science
(yellow): Mann, M.E. and P.D. Jones, 2003 Geophysical
Research Letters, August 2003.
(orange): Jones, P.D. and M.E. Mann. 2004. Reviews of
Geophysics 42, RG2002, 6 May 2004.
(red-orange): Huang, S.. 2004. Geophys. Res, Lett. 31,
L13205, doi:10.1029/2004GL019781.
(red): Moberg, Anders et al., 2005, Nature
The “day after tomorrow”...
will not happen
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Simulations using the HadCM3
climate model of the Atlantic
thermohaline circulation from
1860-2000 (using historical
variations of greenhouse gases,
sulphate aerosol, solar radiation
and volcanic dust). The
simulations show a freshening of
the Labrador Sea from 19502000, as has been seen in
observations, but this is
associated with a slight
strengthening of the
thermohaline circulation over the
same period, rather than a
weakening as has sometimes
been suggested. When the
simulations are extended forward
from 2000-2080 (using a
projection of future greenhouse
gases and aerosols), both trends
are reversed, with a salting in the
Labrador Sea and a weakening
thermohaline circulation
http://www.metoffice.com/corporate/scitech0304/climate_surprises.html
Ozone hole/depletion and climate change
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Although they are often interlinked in the popular
press, the connection between global warming and
ozone depletion is not strong.
Global warming from CO2 radiative forcing is
expected (perhaps somewhat surprisingly) to cool
the stratosphere. This, in turn, would lead to a
relative increase in ozone depletion and the
frequency of ozone holes.
Conversely, ozone depletion represents a radiative
forcing of the climate system. O3 losses over the
past two decades have tended to cool the surface.
One of the strongest predictions of the GW theory
is that the stratosphere should cool. However,
although this is observed, it is difficult to use it for
attribution (for example, warming induced by
increased solar radiation would not have this upper
cooling effect) because similar cooling is caused
by ozone depletion.
Other stuff...
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CO2 rise is anthropogenic
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Global dimming
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Temperature rise non-uniform: largest over NH
land in winter
Evaluating Impacts
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Not really my thing: just some ideas
Of the Consensus View, the weakest point is
“...and it will be a bad thing”. Which is not to say
its wrong, just harder to evaluate. Risk: change
from what we (and ecologies) are adapted to.
Sea Level Rise is fairly obviously bad, but
probably slow (surprises?)
Ecological impacts I don't know: but difficult
political choices: how many flights to go skiing
are people prepared to forgo, in order to save