Scientific evidence for the human influence on current climate change, paleoclimate perspectives, and future projections.

1. Human Influence on
Global Climate
Andreas Schmittner
Associate Professor
College of Earth, Ocean, and Atmospheric Sciences
Oregon State University
Earth Week Keynotes, Snell Hall International Forum, OSU Apr. 18, 2016

2. Observations: The Atmosphere Is Warming

3. http://www.nodc.noaa.gov/OC5/3M_HEAT_CONTENT/
The Ocean Is Warming

5. https://svs.gsfc.nasa.gov/cgi-bin/details.cgi?aid=4355
Arctic Sea Ice

6. Total annual mean sea ice loss since 1979
is ~ 2 M km2 or 8 times the size of Oregon
Arctic Sea Ice Is Melting

7. 1980 1985 1990 1995 2000 2005 2010 2015
0
1
2
3
4
5
6
7
8
Arctic, September
Antarctic, February
Sea Ice Extent at Minimum Months
Extent(106
km2
)
1980 1985 1990 1995 2000 2005 2010 2015
0
2
4
6
8
10
12
14
16
18
20
Arctic, March
Antarctic, September
Sea Ice Extent at Maximum Months
Extent(106
km2
)
Antarctic Sea Ice Is Growing
(but less than Arctic sea ice is melting)
http://www.columbia.edu/~mhs119/UpdatedFigures/

8. glaciers shrinking worldwide
Muir Glacier, SE Alaska
USGS & NPS photographs
1941
1950
2004

9. http://www.arctic.noaa.gov/reportcard/greenland_ice_sheet.html
GRACE satellite
observations
Greenland Ice Sheet
Melting

10. Antarctic Ice Sheet
Mass gain in East Antarctica
Mass loss in West Antarctica

11. 1900 1920 1940 1960 1980 2000
0
50
100
150
200
Adjusted Tide Gauge Data
Satellite Radar Altimetry
Global Mean Sea Level Change
SeaLevelAnomaly(mm)
0.6 mm/yr
(1900−1930)
1.4 mm/yr
(1930−1992)
3.3 mm/yr
(1993−2015)
1900 1920 1940 1960 1980 2000
0
50
100
150
200
http://www.columbia.edu/~mhs119/SeaLevel/

12. Summary Observations
• Temperatures are increasing
• Ice is melting
• Sea levels are rising

13. How unusual are these changes?
How did climate change in the
past?

14. Today

15. 20,000 years ago

16. Paleoclimate
Reconstructions
Surface (planktonic)
Sea Floor (benthic)
Foraminifera
(Zooplankton)
Pollen from lake sediments can be used to
reconstruct past vegetation
Some like it hot (tropical species)
Some like it cold (polar species)
Isotopes give infos on temperature and sea level
OSU research on paleoclimate: Alan Mix, Peter
Clark, Ed Brook

17. Bubbles in the ice
contain ancient air
CO2, CH4 measurements and temperatures (isotopes)

18. Ice Age Cycles
Caused by changes in
Earth’s orbit around sun
CO2 is high when Earth
is warm, low when cold
Temperature changes more
at poles, less in tropics
Sea level high when warm,
low when cold
lines: proxy data based reconstructions
shading: model simulations
LGM
Last Glacial Maximum

19. The Last Glacial Maximum 20,000 years ago
Wallowa Lake

20. Surface Temperature Reconstructions from the Last Glacial
Maximum 20,000 years ago
Large Ice
Sheets over
Canada and
N. Europe
Sea Level 120 m lower
From Newport 1/2 h longer
drive to beach
°C
Globally 4°C colder

21. Vegetation (Europe)
Modern (Pre-Anthropogenic) Last Glacial Maximum

22. Perspectives from the Past
• CO2 is an important control on global climate
• Climate changes are not uniform
• smaller in tropics and over oceans
• larger at higher latitudes and over land
• Relatively small changes in global mean
temperatures can have large impacts (e.g.
vegetation, sea level)

23. Causes
• Human
• Natural (solar, volcanic)

24. We have put
lots of carbon in
the atmosphere.
And we
continue to do
so.
Some is taken
up by land and
ocean but
about half
stays in
atmosphere.
Le Quere et al. (2015) Earth System Science Data

26. http://www.pmodwrc.ch/pmod.php?topic=tsi/composite/SolarConstant
Natural causes such as volcanic eruptions and changes
in solar irradiance also contribute to climate change but
their effects are smaller and don’t exhibit a trend.
Satellite measurements of solar radiation on surface perpendicular to sun’s rays
for average on Earth’s surface divide by 4 (ratio area sphere over disc)
1980 1985 1990 1995 2000 2005 2010 2015
1362
1364
1366
1368
TSI(Wm−2
,originalVIRGOscale)
1980 1985 1990 1995 2000 2005 2010 2015
1358
1360
1362
1364
TSI(Wm−2
,newVIRGOscale)
Min21/22 Min22/23 Min23/24
HF
ACRIMI
HF
ACRIMI
HF
ACRIMII
VIRGO
Average TSI, org & new: 1366.07 & 1361.12 Wm−2
Minimum 21/22, org & new: 1365.68 & 1360.74 Wm−2
Minimum 23/24, org & new: 1365.47 & 1360.53 Wm−2

27. Models including human
effects reproduce
observed warming
Models including natural
effects only (sun,
volcanoes) do not
reproduce observed
warming

28. Summary Causes
• Natural causes cannot explain the observed
changes
• Human greenhouse gas (mainly CO2)
emissions are the main reason

29. The Future
• How may climate change?
• What will be the impacts?

30. We still have a choice between moderate
(RCP2.6) and large (RCP8.5) climate changes.
Projections with Climate Models

31. optimistic
scenario
pessimistic
scenario
More warming over land and near poles,
less over ocean and in tropics, consistent with paleo data

32. Precipitation
Wet get wetter
dry get dryer

33. Soil Moisture
Evaporation increases and soils get dryer

34. RCP2.6
RCP8.5
Sea level will continue to rise

35. Clark et al. (2016) Nature Climate Change

36. Clark et al. (2016) Nature Climate Change

37. Lessons from the Future
• Future warming can be moderate or extreme
depending on future emissions.
• Impacts (sea level rise, drought, vegetation shifts)
get more severe the larger the warming
• We still have the choice to avoid worst case
scenarios.
• But we also have to adapt to the changes that are
already in the pipeline.

38. Thank You !
Any questions ?
Comments ?