The document discusses frequently asked questions about climate change. It summarizes that there is overwhelming scientific evidence that climate change is occurring and is caused by human activities. While models have uncertainties, they consistently project warming trends that are useful for considering risks over decades or more. The best approach is to use multiple models and consider a range of possible futures, as uncertainties are inherent in long-term climate projections. Questions about the topic are encouraged, but the evidence clearly shows the climate is changing due to human emissions of greenhouse gases.

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...)

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

4. Debate?
Doran et al. 2009, Anderegg et al. 2010, Cook et al. 2013

5. 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.

6. Is it climate change or
global warming?

7. Climate change or global warming?
The average global surface temperature has risen 1.53°F over
the past 100 years
IPCC 2007, 2013

8. NCA 2014
Climate change or global warming?
Contiguous US: 1991-2012 departure from 1901-1960 average

9. Climate change or global warming?
NCA 2014
Contiguous US: 1991-2011 departure from 1901-1960 average

10. Climate change or global warming?
NCA 2014

11. 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.

12. Didn’t climate change stop
about 15 years ago?
(What about the pause?)

13. 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

14. 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

15. Courtesy of www.skepticalscience.com (calculated from IPCC AR4 5.2.2.3)
Are we done yet?

16. 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.

17. The atmosphere is
massive – how can we
actually change it?

18. Anthropogenic change?
Net sources
and sinks

19. Anthropogenic change?

20. Anthropogenic change?
▪ Global GHG emissions from human activities increased
70% between 1970-2004
▪ Emissions of CO2, the most important anthropogenic
GHG, grew about 80% between 1970 and 2004.
IPCC 2007

21. 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.

22. Hasn’t climate always
changed? Why worry now?

23. IPCC 2007
Change happens.

24. -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.

25. 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.

26. 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.

27. 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.

28. Isn’t future climate
change uncertain?
(I don’t trust climate models!)

29. Uncertainty?
IPCC 2007

30. Uncertainty?
Emissions Model sensitivity
IPCC 2007

31. NCA 2014
Uncertainty?

32. Tamino, 2010 (blog: http://tamino.wordpress.com/ )
From IPCC AR4: 22 models, 106 runs
*Omits Canadian CCCMA
Uncertainty?

33. Uncertainty in simulations of future climate:
Least
Projected
Change
Most
Projected
Change
CSIRO
Low emissions (B1)
Model with less warming sensitivity to greenhouse gases
Fewer emissions
Uncertainty?

34. Climate data courtesy of R. Neilson and MAPSS Vegetation Modeling Lab
Uncertainty?

35. Uncertainty in simulations of future climate:
Least
Projected
Change
Most
Projected
Change
MIROC
High emissions (A2)
Model with more warming sensitivity to greenhouse gases
Higher emissions
Uncertainty?

36. Uncertainty …simulations
Climate data courtesy of R. Neilson and MAPSS Vegetation Modeling Lab

37. Uncertainty …simulations
Climate data courtesy of R. Neilson and MAPSS Vegetation Modeling Lab

38. A2A1BB1
Change in Mean Monthly Temperature (°C)
2070-2099 vs 1961-1990
Future Emissions Higher
CSIRO
MIROC
HAD
Higher
ModelSensitivity
Uncertainty

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.

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.

41. Thank you!
Chris Swanston
cswanston@fs.fed.us