CLIMATE CHANGEFAQsChris Swanston, cswanston@fs.fed.usDirector, Northern Institute of Applied Climate ScienceDirector, USDA Northern Forests Climate Hub

Isn’t there still a scientific debate about climate change?(So you believe…; Who am I supposed to believe...)

2

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

3

Debate?

Doran et al. 2009, Anderegg et al. 2010, Cook et al. 2013

4

Doran et al. 2009, Anderegg et al. 2010, Cook et al. 2013

Debate? 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

Figures courtesy of NOAA.

Has El Niño increased global warming?

Nope. Heat was transferred from ocean to surface air.

BONUS: EL NIÑO! 17

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.

18

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

19

Anthropogenic change?Net sources and sinks

20

Anthropogenic change? 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

graph data from the NOAA NCDC and Mauna Loa Observatory

Milankovitch Cycles

Eccentricity – more or less oval orbit, every ~100,000 yearsTilt – earth shifts its tilt every ~41,000 yearsPrecession – earth wobbles on its axis, every ~23,000 years

Change happens. 24

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. 25

IPCC 2007

Change happens. 26

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

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 CO2greatest in situations with less water vapor (dry, cold)• Less heat escaping overall.

BONUS: GREENHOUSE EFFECT! 28

-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. 29

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.

30

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

31

Uncertainty?

IPCC 2007

32

Uncertainty?Emissions Model sensitivity

IPCC 2007

33

Tamino, 2010 (blog: http://tamino.wordpress.com/ )

From IPCC AR4: 22 models, 106 runs

*Omits Canadian CCCMA

Uncertainty? 34

NCA 2014

Uncertainty? 35

A2A1BB1

Change in Mean Monthly Temperature (°C)2070-2099 vs 1961-1990

Future Emissions Higher

CSIRO

MIROC

HAD

Higher

Model

Sensiti

vityUncertainty? 36

Simple representation of uncertainty:

Least Projected ChangeMost Projected Change

Insensitive modelLow emissions (B1)

Uncertainty?

Sensitive modelHigh emissions (A2)

37

Simple representation of uncertainty:

Least Projected ChangeMost Projected Change

Uncertainty?38

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.

39

SummaryClimate• 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 futuresQuestions• Questions are good. Keep asking.

Chris Swanstoncswanston@fs.fed.us

40