Our understanding of the
climate and how it can change
SUM4015 – spring 2012 – first lecture:
1. The Earth and its climate – how does it all work?
2. How do we know we’re changing the climate?
Bjørn H. Samset - Forsker, CICERO
b.h.samset@cicero.uio.no | kollokvium.no
Syllabus:
Climate Change: A Multidisciplinary Approach (on ARK.no)
Chapters:
1: Introduction
2: Radiation and the Earth’s energy balance
3: The elements of climate
6: The natural causes of climate change
7: Human activities
8: Evidence of climate change
Bjørn H. Samset | b.h.samset@cicero.uio.no | kollokvium.no
Motivation:
It’s getting hotter…
http://svs.gsfc.nasa.gov/vis/a000000/a003600/a003674/index.html
Motivation:
It’s getting hotter…
According to the 2007
Fourth Assessment Report
by the
Intergovernmental Panel on
Climate Change (IPCC),
global surface temperature
increased
0.74 ± 0.18 °C (1.33 ± 0.32 °F)
during the 20th century.
Source: NASA GISS
Part 1: The Earth and its
climate
Key questions:
• What is ‘weather’ and what is ‘climate’?
• What keeps the climate stable from
year to year?
• What factors can, over time, alter the
climate?
Bjørn H. Samset | b.h.samset@cicero.uio.no | kollokvium.no
Weather vs climate
Whether or not it’s «cold» when
you wait for the bus or «a very
warm spring this year» doesn’t
tell you anything about climate
change – only about the current
weather.
Bjørn H. Samset | b.h.samset@cicero.uio.no | kollokvium.no
Climate variability and
«climate change»
• The temperature varies all the time – with position, season, time of day, …
• It’s very hard to measure a «global» temperature, so we measure temp. differences
• «Climate change» is a change in average properties of the weather – e.g. a change
in global, annual mean sea surface temperature, rainfall, cloudiness, number or
strength of hurricanes, etc.
• Science says: We need to average over at least 15 years to get anything meaningful
Bjørn H. Samset | b.h.samset@cicero.uio.no | kollokvium.no
What is energy and where
does it come from?
To understand climate change, we can view the earth as an energy problem.
Energy is always conserved – it cannot be created or destroyed.
Heat – which we need more of if there is to be «global warming» – is just one
special kind of energy.
Global warming – that the sea surface temperature is increasing - means that
• either energy is flowing from somewhere in the earth system and into
the atmosphere
• or energy is flowing from outside the earth system and into the atmosphere
If we understand the energy flow into and around the Earth, then we understand
climate change. (But not the weather – that’s way more complicated.)
Bjørn H. Samset | b.h.samset@cicero.uio.no | kollokvium.no
Bjørn H. Samset | b.h.samset@cicero.uio.no | kollokvium.no
The Earth/Sun system
Bjørn H. Samset | b.h.samset@cicero.uio.no | kollokvium.no
Radiation balance
Bjørn H. Samset | b.h.samset@cicero.uio.no | kollokvium.no
The land (and sea) albedo
Albedo = the fraction of sunlight reflected back to space
100% (red) means everything is reflected back
Bjørn H. Samset | b.h.samset@cicero.uio.no | kollokvium.no
The atmosphere
Bjørn H. Samset | b.h.samset@cicero.uio.no | kollokvium.no
The oceans
Bjørn H. Samset | b.h.samset@cicero.uio.no | kollokvium.no
Radiation balance
Bjørn H. Samset | b.h.samset@cicero.uio.no | kollokvium.no
The «greenhouse effect»?
CO2:
Certain molecules can store
energy as vibrations in the
«rubber bands» (atomic
bindings) that hold the
atoms together.
+ water vapor!
The hydrological cycle
Bjørn H. Samset | b.h.samset@cicero.uio.no | kollokvium.no
The carbon cycle
Bjørn H. Samset | b.h.samset@cicero.uio.no | kollokvium.no
Radiation balance
Bjørn H. Samset | b.h.samset@cicero.uio.no | kollokvium.no
Natural climate change
and variability
Burroughs mentions e.g.
• Solar variability
• Orbital variations
• Volcanoes
• Changes in the atmosphere and ocean
• Tidal forces
• Continental drift
• Changes in atmospheric composition (natural)
• Sudden releases of methane from deep oceans or permafrost
• Asteroid impacts
Bjørn H. Samset | b.h.samset@cicero.uio.no | kollokvium.no
Solar variability
Lockwood and Fröhlich 2007.
Proc. R. Soc
“There is considerable evidence for solar
influence on the Earth’s pre-industrial climate
and the Sun may well have been a factor in postindustrial climate change in the first half of the
last century. Here we show that over the past
20 years, all the trends in the Sun that could
have had an influence on the Earth’s climate
have been in the opposite direction to that
required to explain the observed rise in global
mean temperatures.”
Bjørn H. Samset | b.h.samset@cicero.uio.no | kollokvium.no
NB: We live in extremely
stable times!
Climate change isn’t an issue for the world as such – it will manage fine.
We, however, have created a fragile society under extremely stable conditions.
If those change, so will the foundations of our civilization.
Bjørn H. Samset | b.h.samset@cicero.uio.no | kollokvium.no
Atmosphere/ocean:
El Nino Southern Oscillaion
(ENSO)
Hansen, J., R. Ruedy, Mki. Sato, and K. Lo, 2010: Global surface temperature change. Rev. Geophys., 48, RG4004
Bjørn H. Samset | b.h.samset@cicero.uio.no | kollokvium.no
Atmosphere/ocean:
North Atlantic Oscillaions
(AMO and NAO)
FromTracking the Atlantic Multidecadal Oscillation through the last 8,000 years
Mads Faurschou Knudsen et Al,
Nature Communications 2, Article number: 178 doi:10.1038/ncomms1186
Bjørn H. Samset | b.h.samset@cicero.uio.no | kollokvium.no
Volcanoes
Hansen,
J., R. Ruedy, Mki. Sato, and K. Lo, 2010: Global surface temperature change. Rev. Geophys., 48, RG4004
Bjørn H. Samset | b.h.samset@cicero.uio.no
| kollokvium.no
Conclusions for part 1:
The climate is complex, but
not too complex to understand
• To understand the climate, Key questions:
• What is ‘weather’ and what is ‘climate’?
first remove all the
• What keeps the climate stable from
variability caused by
year to year?
weather, solar cycle, ocean • What factors can, over time, alter the
climate?
currents, etc.
• What remains is mostly an energy problem. Where does energy
get lost or gained, where and how is it transported?
• Any long-term change in energy flow will result in climate change
Bjørn H. Samset | b.h.samset@cicero.uio.no | kollokvium.no
Part 2: How we affect the
atmosphere – and hence the
climate
Key questions:
• How do human activities influence
the atmosphere?
• How do we know how the climate
has changed in the past?
• How can we link our activities to
the current observed changes?
Bjørn H. Samset | b.h.samset@cicero.uio.no | kollokvium.no
CO2-emissions are rising
year by year
G. Peters et al., Nature Climate Change (2011)
Does this matter for the climate?
Why? How? How much?
Bjørn H. Samset | b.h.samset@cicero.uio.no | kollokvium.no
We’re changing the
composition of the atmosphere
http://www.esrl.noaa.gov/gmd/ccgg/trends/
We’re changing the
composition of the atmosphere
IPCC AR4
See e.g. here:
http://www.realclimate.org/index.php/archives/2004/12/
how-do-we-know-that-recent-cosub2sub-increases-aredue-to-human-activities-updated/
Emissions of greenhouse
gases
Bjørn H. Samset | b.h.samset@cicero.uio.no | kollokvium.no
Radiation balance
Bjørn H. Samset | b.h.samset@cicero.uio.no | kollokvium.no
Paleoclimate:
Studying the climate experiments that nature has
already performed. Do we understand them?
Solar variability
Lockwood and Fröhlich 2007.
Proc. R. Soc
“There is considerable evidence for solar
influence on the Earth’s pre-industrial climate
and the Sun may well have been a factor in
post-industrial climate change in the first half of
the last century. Here we show that over the
past 20 years, all the trends in the Sun that could
have had an influence on the Earth’s climate
have been in the opposite direction to that
required to explain the observed rise in global
mean temperatures.”
Bjørn H. Samset | b.h.samset@cicero.uio.no | kollokvium.no
Two main factors:
The greenhouse effect from (primarily) CO2
The change in reflectance (albedo) from changes in snow and ice cover
We (mostly) understand all this! Both qualitatively and quantitavely.
…so…
390 ppm
Energy imbalance per 2007
IPCC – det internasjonale
klimapanelet:
• Etablert i 1988, består av
flere tusen forskere
• Mandatet er å vurdere og
rapportere
• Den største og mest
enige gruppen av forskere
i verdens historie!!!
• Ny rapport i 2013/2014
• http://kollokvium.no/2011/
10/13/ipcc-femte-rapport/
Dust and aerosols
• Sulphate, nitrate,
dust, …: Cooling,
due to sunblockeffect
• Soot: Warming and
cooling, with the
warming effect
dominating, since
soot is black and
hence absorbs
sunlight
Bjørn H. Samset | b.h.samset@cicero.uio.no | kollokvium.no
Dust and aerosols
• Sulphate, nitrate,
dust, …: Cooling,
due to sunblockeffect
• Soot: Warming and
cooling, with the
warming effect
dominating, since
soot is black and
hence absorbs
sunlight
Bjørn H. Samset | b.h.samset@cicero.uio.no | kollokvium.no
Dust and aerosols
• Sulphate, nitrate,
dust, …: Cooling,
due to sunblockeffect
• Soot: Warming and
cooling, with the
warming effect
dominating, since
soot is black and
hence absorbs
sunlight
Bjørn H. Samset | b.h.samset@cicero.uio.no | kollokvium.no
Changes in cloud cover
Bjørn H. Samset | b.h.samset@cicero.uio.no | kollokvium.no
Energy imbalance per 2007
What does this mean
in terms of temperature
change over time?
Climate feedbacks
The climate impact from a change in e.g. CO2 is not simply the associated change
in greenhouse effect. It’s how the whole earth system responds to this change.
Bjørn H. Samset | b.h.samset@cicero.uio.no | kollokvium.no
Climate sensitivity
Linking a certain amount of CO2 to a certain temperature increase
DTs = l x RF
If we double the concentration of CO2 in the
atmosphere, how much will the temperature change?
Alt gir samme konklusjon:
[The climate sensitivity]
likely to be in the range 2 to 4.5°C
with a best estimate of about 3°C,
and is very unlikely to be less than
1.5°C. (IPCC AR4)
Vet vi hvordan noe påvirker strålingsbalansen, kan vi beregne temperaturendring
Teaser for next lecture:
Models provide
independent link
Havtemperatur
Lufttemperatur
Teaser for next lecture:
Models provide
independent link
Temperature Trends in the Lower Atmosphere: Steps for Understanding and Reconciling Differences.
Thomas R. Karl, Susan J. Hassol, Christopher D. Miller, and William L. Murray, editors, 2006.
A Report by the Climate Change Science Program and the Subcommittee on Global Change
Research, Washington, DC.
Human-induced climate
change in 5 steps
1. We are changing the composition of the atmosphere, by emissions of long-lived
greenhouse gases such as CO2 and methane, and aerosols and other short-lived
components
Key item: The Keeling curve of CO2 concentration
2. We know from basic science how such gases and particles affect the surface
temperature – in particular the warming effect of CO2
Key item: The research of Joseph Fourier (1768-1830), John Tyndall (1820-1893) ,
Svante Arrhenius (1859-1927) and many others
3. The global surface temperature of the Earth is indeed increasing
Key item: Global temperature analyses by NASA, the UK Met Office and others
4. Sophisticated mathematical models allow us to study causal mechanisms in
the Earths climate, using past changes as tests
Key item: NASAs James Hansen used a model to predict the temperature effects
of the 1991 Mount Pinatubo eruption
5. Only when known human emissions are included do the models reproduce the
observed temperature and climate changes
Key item: The four IPCC reports – and the one coming in 2013
Inspiration: «The Hockey Stick and the Climate Wars», Michael E. Mann, Columbia University Press, 2012
Bjørn H. Samset | b.h.samset@cicero.uio.no | kollokvium.no
Conclusions for part 2
• Through various emissions Key questions:
we’re changing the energy • How do human activities influence
the atmosphere?
balance of the Earth
• How do we know how the climate
• Past changes and basic
has changed in the past?
science both tell us how
• How can we link our activities to
the current observed changes?
much our emissions will
matter in the long run
• Climate models pull it all together
Bjørn H. Samset | b.h.samset@cicero.uio.no | kollokvium.no
From the article “Communicating the Science of Climate Change,”
by Richard C. J. Somerville and Susan Joy Hassol,
October 2011 issue of Physics Today
NB: Be aware of
«climate science language»
Bjørn H. Samset | b.h.samset@cicero.uio.no | kollokvium.no