Climate Change

1
Climate Change

• The 4-point consensus view of global warming
• Some objections impartially considered
• Evaluating Impacts
• Stern Review

2
Audience Test

• How much has global temperature risen over the
  past 100 years?
• How much might sea level rise over the next 100
  years?

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(1) Global Warming is happening...
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GW is happening (cont...)
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(2) We're causing it
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(2) We're causing it (cont...)
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(2) ...we're causing it (...cont 2)
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(3) It will get worse
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(4) This will be a Bad Thing

• Sea level rise is bad, but slow (even with recent
  speedups?) http//www.realclimate.org/index.php/ar
  chives/2006/03/greenland-ice-and-other-glaciers/
• Temperature rise regionally varying winners and
  losers, political tradeoffs
• Ecological impacts important, but I don't know

10
Common myths, impartially considered

• Satellite temperatures - show warming too
• The urban heat island - negligible effect
• The hockey stick controversy
• The Day After Tomorrow - will not happen
• Little relation between the Ozone hole and GW
• CO2 increase is anthropogenic (more than...)
• Hurricanes (and severe weather)

11
Satellite temperature measurements

• Mears et al 0.193 C/decade
• Spencer and Christy version 5.2, 0.123 C/decade
• Fu et al, 0.2 C/decade (May 04)
• Vinnikov and Grody, with 0.22C to 0.26C per
  decade (Oct. 03)
• Surface record 0.06 C/decade over the past
  century and 0.15 C/decade since 1979.

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(No Transcript)
13
Urban Heat Island (1)

• 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 0.05C over the
  period 1900 to 1990, because
• land, sea, and borehole records are in agreement
• the trends in urban stations for 1951 to 1989
  (0.10C/decade) are not greatly more than those
  for all land stations (0.09C/decade).
• 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.

14
Urban Heat Island (2)

• 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.

15
Hockey Stick controversy... or,The temperature
over the last 1-2 kyr
Osbourn and Briffa http//www.realclimate.org/ind
ex.php/archives/2006/02/a-new-take-on-an-old-mille
nnium/
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The day after tomorrow...will not happen

• 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 1950-2000, 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

17
Ozone hole/depletion and climate change

• 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.

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CO2 emissions... reductions?
The bill will set out a statutory commitment to
cut CO2 emissions by 60 from 1990 levels by
2050, requiring annual cuts way above anything
the Labour government has achieved so far...
Guardian, 2006/11/15

• Of the "frontrunners" one is an order of
  magnitude bigger than the rest Extend UK
  participation in EU carbon trading scheme (4.2).
  Means don't actually produce less CO2, but buy
  permits to emit it.
• Of the "emerging" category, the two biggest are
  Introduce ways to store carbon pollution
  underground (0.5-2.5) (i.e., don't produce any
  less, just...) and Force energy suppliers to use
  more offshore wind turbines (Up to 1). Which
  would actually save CO2.
• In the "difficult" category the biggest is Change
  (read enforce) road speed limits (1.7) - a
  surprisingly large number.

19
Hurricanes and severe weather

• There is some evidence for hurricanes becoming
  more stronger and some suggestions for this in
  the future in the models
• But most impacts come from more people living
  near the beach
• Katrina was unlucky

http//www.realclimate.org/index.php?p181
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Stern Review

• Received to rapturous applause from UK
  politicians and press
• Apparently intended to be used to beat Bush over
  the head
• Not much science (one chapter of 27). Purports to
  take the IPCC position
• Finds higher costs of climate change, and lower
  costs of fixing this, than just about everyone
  else, but doesn't really explain why
• Objections raised in the blogosphere and beyond,
  mostly to the economics
• Nordhaus Stern is using a social discount rate
  that is essentially zero. And The Review's
  unambiguous conclusions about the need for
  extreme immediate action will not survive the
  substitution of discounting assumptions that are
  consistent with today's market place.
• The review uses a high-end emission scenario (A2)
  together with what appears to be excess weight to
  higher climate sensitivities Several new studies
  suggest up to a 20 chance that warming could be
  greater than 5C. I think sensitivities that high
  are distinctly unlikely.
• Won't work.

21
Evaluating Impacts

• 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
  polar bears (were that the choice).