NIACS Director Dr. Chris Swanston's climate science overview at the Adaptive Silviculture for Climate Change (ASCC) Workshop for the Northern Rockies.

1. CLIMATE CHANGE
FAQs
Chris Swanston, cswanston@fs.fed.us
Director, Northern Institute of Applied Climate Science
Director, USDA Northern Forests Climate Hub

2. Isn’t there still a scientific
debate about climate change?
(So you believe…; Who am I supposed to believe...)
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3. Debate?
Intergovernmental Panel on Climate Change (2007, 2010, 2013)
 Evidence for climate change is “unequivocal”
 It is “extremely likely” that humans are main cause since 1950
• “Human influence on the climate system is clear.”
 Future changes depend partly on human actions
18 National Academies have endorsed the consensus position of
the IPCC on climate change
 National Academy of Sciences (USA)
 Royal Society of Canada
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4. Debate?
Doran et al. 2009, Anderegg et al. 2010, Cook et al. 2013
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5. Doran et al. 2009, Anderegg et al. 2010, Cook et al. 2013
Debate? 5

6. Is there still a debate?
 No scientific debate on “if”.
 Current scientific debate revolves around how
much, how fast, and feedback mechanisms.
 Virtually all climate scientists agree humans are a
driver.
A practical risk assessment may be a better strategy
than belief.
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7. Is it climate change or
global warming?
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8. Climate change or global warming?
The average global surface temperature has risen 1.53°F over
the past 100 years
IPCC 2007, 2013
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9. NCA 2014
Climate change or global warming?
Contiguous US: 1991-2012 departure from 1901-1960 average
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10. Climate change or global warming?
NCA 2014
Contiguous US: 1991-2011 departure from 1901-1960 average
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11. Climate change or global warming?
NCA 2014
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12. Is it climate change or global warming?
• About 1.5F warming globally.
• US warming similar, with regional variation.
• General increases in US annual precipitation,
except in the southwest.
• More big rain events, more of annual precip within
those events.
Both. The earth has warmed and the climate is
changing as a result, with regional variations.
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13. Didn’t climate change stop
about 15 years ago?
(What about the pause?)
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14. Are we done yet?
Recent years - La Niña, lower solar activity, volcanic cooling,
and sulfate aerosols have reduced the rate of warming in
surface air…
NASA Goddard Institute for Space Studies: http://data.giss.nasa.gov/gistemp/graphs_v3/; see also , Schmidt et al. 2014; Saffioti et al. 2015;
Lewandowsky et al. 2015
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15. Are we done yet?
…but not in oceans – which account for ~93% of earth system
warming since 1955.
Levitus et al. 2012, Balmeseda et al. 2013; see also Guemas et al. 2013
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16. Courtesy of www.skepticalscience.com (calculated from IPCC AR4 5.2.2.3)
Are we done yet?
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17. Figures courtesy of NOAA.
Has El Niño increased global warming?
Nope. Heat was transferred from ocean to surface air.
BONUS: EL NIÑO! 17

18. Didn’t climate change stop?
• The rate of surface air warming slowed recently.
• Oceans continued to absorb heat rapidly.
• The oceans have absorbed >90% of warming since
1955.
No – the earth is still warming.
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19. The atmosphere is
massive – how can we
actually change it?
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20. Anthropogenic change?
Net sources
and sinks
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21. Anthropogenic change?
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22. The atmosphere is massive, how can we
change it?
• We move massive amounts of carbon into the
atmosphere.
• Fossil carbon is an addition – it has been isolated
from the carbon cycle for millions of years.
• GHGs have different atmospheric lifetimes – CO2
may last decades to centuries.
• Land cover change transfers carbon to the
atmosphere.
The measurement record clearly shows our
additions to the atmosphere.
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23. Hasn’t climate always
changed? Why worry now?
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24. graph data from the NOAA NCDC and Mauna Loa Observatory
Milankovitch Cycles
Eccentricity – more or less oval orbit, every ~100,000 years
Tilt – earth shifts its tilt every ~41,000 years
Precession – earth wobbles on its axis, every ~23,000 years
Change happens.
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25. Courtesy of K. Marcinkowski, NIACS;
see also: Hansen et al. 1990, Petit et al. 1999, Shackleton 2000, Ruddiman 2006, Shakun et al. 2012
Change happens.
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26. IPCC 2007
Change happens.
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27. http://www.globalwarmingart.com
• The sun and earth emit energy in different wavelengths.
• Shorter wavelengths (sun) move through the atmosphere more
easily.
BONUS: GREENHOUSE EFFECT! 27

28. http://www.globalwarmingart.comHarries et al. 2001
• More absorption
and scattering for
outgoing energy
• Water vapor is
important
• CO2 absorbs only
outgoing energy
• Impact of CO2
greatest in situations
with less water
vapor (dry, cold)
• Less heat escaping
overall.
BONUS: GREENHOUSE EFFECT! 28

29. -0.4 °F
Average
Surface
Temperature
Temperature
without
greenhouse
effect
+57 °F
Others ~15%
CO2 9-26%
H2O 36-66%
Kiehl and Trenberth 1997,
realclimate.org (G. Schmidt, NASA)
Change happens.
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30. Hasn’t the climate always changed? Why
worry now?
• Milankovitch cycles have previously driven climate
changes.
• Humans are driving the current change.
• The change is very rapid.
The rapidity and potential severity of climate change
will affect forestry, agriculture, infrastructure,
demographics, economies, …virtually everything.
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31. Isn’t future climate
change uncertain?
(I don’t trust climate models!)
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32. Uncertainty?
IPCC 2007
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33. Uncertainty?
Emissions Model sensitivity
IPCC 2007
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34. Tamino, 2010 (blog: http://tamino.wordpress.com/ )
From IPCC AR4: 22 models, 106 runs
*Omits Canadian CCCMA
Uncertainty?
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35. NCA 2014
Uncertainty?
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36. A2A1BB1
Change in Mean Monthly Temperature (°C)
2070-2099 vs 1961-1990
Future Emissions Higher
CSIRO
MIROC
HAD
Higher
ModelSensitivity
Uncertainty?
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37. Simple representation of uncertainty:
Least
Projected
Change
Most
Projected
Change
Insensitive model
Low emissions (B1)
Uncertainty?
Sensitive model
High emissions (A2)
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38. Simple representation of uncertainty:
Least
Projected
Change
Most
Projected
Change
Uncertainty?
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39. Isn’t future climate change uncertain?
• Models have acknowledged shortcomings.
• They do well globally with air temps, much less well
with precip, and will likely never be “good enough”
at a management scale.
• Great at multi-decadal trends, poor at multi-year.
• Emissions uncertainties are inherent.
All models are wrong, some are useful – best to use
multiple models, think long term, and consider a range
of futures.
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40. Summary
Climate
• overwhelming evidence for change, from thousands
of sources
Uncertainty
• it’s inherent in climate projections, and this will not
change
• we’ll always have a range of plausible futures
Questions
• Questions are good. Keep asking.
Chris Swanston
cswanston@fs.fed.us
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