Human Influence on Global Climate
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Transcript of Human Influence on Global Climate
Human Influence on Global Climate
Andreas SchmittnerAssociate Professor
College of Earth, Ocean, and Atmospheric SciencesOregon State University
Earth Week Keynotes, Snell Hall International Forum, OSU Apr. 18, 2016
Observations: The Atmosphere Is Warming
http://www.nodc.noaa.gov/OC5/3M_HEAT_CONTENT/
The Ocean Is Warming
https://svs.gsfc.nasa.gov/cgi-bin/details.cgi?aid=4355
Arctic Sea Ice
Total annual mean sea ice loss since 1979 is ~ 2 M km2 or 8 times the size of Oregon
Arctic Sea Ice Is Melting
1980 1985 1990 1995 2000 2005 2010 20150
1
2
3
4
5
6
7
8
Arctic, SeptemberAntarctic, February
Sea Ice Extent at Minimum Months
Exte
nt (1
06 km
2 )
1980 1985 1990 1995 2000 2005 2010 2015 0
2
4
6
8
10
12
14
16
18
20
Arctic, MarchAntarctic, September
Sea Ice Extent at Maximum Months
Exte
nt (1
06 km
2 )
Antarctic Sea Ice Is Growing(but less than Arctic sea ice is melting)
http://www.columbia.edu/~mhs119/UpdatedFigures/
glaciers shrinking worldwide
Muir Glacier, SE Alaska
USGS & NPS photographs
1941
19502004
http://www.arctic.noaa.gov/reportcard/greenland_ice_sheet.html
GRACE satellite observations
Greenland Ice Sheet Melting
Antarctic Ice Sheet
Mass gain in East AntarcticaMass loss in West Antarctica
1900 1920 1940 1960 1980 2000
0
50
100
150
200
Adjusted Tide Gauge DataSatellite Radar Altimetry
Global Mean Sea Level Change
Sea
Leve
l Ano
mal
y (m
m)
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/
Summary Observations
• Temperatures are increasing
• Ice is melting
• Sea levels are rising
How unusual are these changes?
How did climate change in the past?
Today
20,000 years ago
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 levelOSU research on paleoclimate: Alan Mix, Peter
Clark, Ed Brook
Bubbles in the ice contain ancient air
CO2, CH4 measurements and temperatures (isotopes)
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
The Last Glacial Maximum 20,000 years ago
Wallowa Lake
Surface Temperature Reconstructions from the Last Glacial Maximum 20,000 years ago
Large Ice Sheets overCanada and N. Europe
Sea Level 120 m lowerFrom Newport 1/2 h longer
drive to beach
°C
Globally 4°C colder
Vegetation (Europe)
Modern (Pre-Anthropogenic) Last Glacial Maximum
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)
Causes
• Human
• Natural (solar, volcanic)
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
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 raysfor 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, o
rigin
al V
IRG
O s
cale
)
1980 1985 1990 1995 2000 2005 2010 2015
1358
1360
1362
1364
TSI (Wm
−2, new VIR
GO
scale)
Min21/22 Min22/23 Min23/24
HF
ACR
IM I
HF
ACR
IM I
HF
ACR
IM II
VIR
GO
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
Models including human effects reproduce observed warming
Models including natural effects only (sun, volcanoes) do not
reproduce observed warming
Summary Causes
• Natural causes cannot explain the observed changes
• Human greenhouse gas (mainly CO2) emissions are the main reason
The Future
• How may climate change?
• What will be the impacts?
We still have a choice between moderate (RCP2.6) and large (RCP8.5) climate changes.
Projections with Climate Models
optimistic scenario
pessimistic scenario
More warming over land and near poles, less over ocean and in tropics, consistent with paleo data
Precipitation
Wet get wetter dry get dryer
Soil Moisture
Evaporation increases and soils get dryer
RCP2.6
RCP8.5
Sea level will continue to rise
Clark et al. (2016) Nature Climate Change
Clark et al. (2016) Nature Climate Change
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.
Thank You !
Any questions ?
Comments ?