Climate Change Science
description
Transcript of Climate Change Science
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Climate Change Science David Stevenson Institute of Atmospheric and
Environmental Science Room 314 Crew Building [email protected] Short questions – please interrupt Long questions – save until end
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Plan 5 x ½ hour ‘lectures’:
0900-0930 Observations of climate change0930-1000 Greenhouse effect and human
influence on climate1000-1030 Natural climate variability1030-1100 Break1100-1130 Modelling the climate system1130-1200 Future climate1200-1215 Questions and discussion
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What is Climate Change? Climate is the average weather at a given point
and time of year, over a long period (typically 30 years).
We expect the weather to change a lot from day to day, but we expect the climate to remain relatively constant.
If the climate doesn’t remain constant, we call it climate change.
The key question is what is a significant change – and this depends upon the underlying level of climate variability
Crucial to understand difference between climate change and climate variability…
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Global meansurfacetemperature
Time/years0 300
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Temperature
Time
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Key Sources of Information The Intergovernmental Panel on Climate
Change (IPCC) (www.ipcc.ch) Authoritative reports supported by >95% of
climate scientists Fourth assessment report (AR4) published
2007
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Recommended Books JT Houghton (2009)
Global Warming: The Complete Briefing, 4th Ed. Cambridge University Press ISBN 0-521-52874-7 (£24.99)
WJ Burroughs (2001) Climate Change: A Multidisciplinary Approach. Cambridge University Press ISBN 0-521-56771-8 (£24.99)
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1. Observationsof
climate change
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Global mean temperatures are rising faster with time
100 0.0740.018 50 0.1280.026
Warmest 12 years:1998,2005,2003,2002,2004,200
6, 2001,1997,1995,1999,1990,200
0
Period Rate
Years /decade
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Global surface temperature 1855-2010
How is this curve calculated?
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CET
Warming in Central Englandre
lativ
e to
177
2-19
00
T
empe
ratu
re r
ise
deg
C
Hadley Centre
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Aberdeen Temperatures 1871-2002
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Edinburgh Temperatures 1764-1960
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Edinburgh Airport Temperatures 1951-1999
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Possible Problems with station data Instrument/human errors Changes of instrument/observer or observing technique Changes in station surroundings, e.g. urbanisation – this
is a common criticism from climate change sceptics Some solutions: compare adjacent stations, compare with
stations known to be unchanged All data in the ‘global’ picture have been carefully checked
for these possible artifacts, and where necessary corrected or discarded
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Observed surface temperature trend
Trends significant at the 5% level indicated with a ‘+’. Grey: insufficient data
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Other evidence of Climate Change
Glacier retreat
1875 2004
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Glaciers and frozen ground are receding
Area of seasonally frozen ground in NH has decreasedby 7% from 1901 to 2002
Increased Glacier retreat since the early 1990s
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Snow cover and Arctic sea ice are decreasing
Spring snow covershows 5% stepwise drop during 1980s
Arctic sea ice area decreased by 2.7% per decade(Summer: -7.4%/decade)
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Other evidence of Climate Change Ocean heat content has increased Temperatures in the Atlantic:
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Change in heat content over last 50 years
[units: 1022 Joules]
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Rise in global ocean heat content 1955-2005
Some ups and downs, but clear overall increaseLevitus et al., 2005, GRL
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25
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Sea-level from satellites: 4 cm rise in last 10 years
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Evidence from Phenology (timings of natural events)
www.phenology.org.uk
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Some aspects of climate have not been observed to change:
• Tornadoes
• Dust-storms
• Hail
• Lightning
• Antarctic sea ice
Direct Observations of Recent Climate Change
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Records further back in time (paleo-data or proxy data)
E.g. tree rings
Bristlecone Pine(USA) – up to 10000 years old
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Northern Hemisphere Temperature AD 700-2000 – several different reconstructions from proxy data
Warming in last 100 years appears exceptional.But is the uncertainty range (the spread of different reconstructions) large enough?
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Ice cores – store past samples of the atmosphere
Bubbles of airtrapped whenice formed Analyse oxygen isotopes => Temperature
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Rate ofchangeofcombinedforcing
Grey bars:natural variabilitylast 650,000 yrs
IPCC(2007)
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Summary 1 (Observations) Global surface temperatures have risen by about 0.6°C since 1900 It is likely that this warming is larger than for any century since 200AD,
and that the 1990s were the warmest decade in the last millennium. The warming differs in different parts of the world, but over the last 25
years, almost everywhere has warmed, and very few places have cooled.
Other changes have occurred, e.g.: Sea level has risen by about 20 cm, Ocean heat content has increased, Almost all mountain glaciers have retreated
Coincident with this global warming, levels of CO2 (and other ‘greenhouse’ gases) have dramatically increased, to levels higher than those experienced for maybe millions of years.
Next: are temperatures and atmospheric composition linked?