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 ?