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Summary climate & society
SPM
IPCC = Panel with governmental deputies from all UN countries subscribed to Rio protocol.
Tasks: To assess scientific knowledge on climate change
IPCC process = scoping → approval of Outline → nomination of authors → government and
expert review – 2nd order draft → Expert review 1st order draft → selection of authors →
final draft report and SPM → government review of final draft SPM → approval and
acceptance of report → publication
Evaluate evidence and agreement
Confidence = qualitative judgment about the validity of a finding
Likelihood = quantified measure of the certainty in a finding, expressed as a probability,
based on statistical or modelling analysis, expert judgement, or other approaches.
Assessment = evaluation of scientific literature
IPCC:
- Organizes writing
- Determines which reports when
- Table of content
- Set rules how to make the reports
- Approves the reports
Key messages WG1
*20th century
Global Warming 1 K
Sea level rise 15-20 cm
Human activity dominate since 1950
*CO2 higher than preceding millions of years
*High emission scenario (RCP8.5)
Temperature increase 2.5-4.8 K
Sea level projection 45 – 82 cm
*Ambitious climate policy (RCP2.6)
Temperature increase 0.3-1.7 K
Sea Level projection 26-55 cm
Socio-economic scenarios rule the uncertainty for projection at the end of the century
Sea Level Change
Subjective risk = likelihood x impact
Major uncertainties:
- Climate sensitivity (not sure about the relation between CO2 and temperature
change)
- Feedbacks
- Natural variability
, - Socio economic scenarios (we don’t know for sure yet what scenario we are going to
follow)
Only the collapse of the marine-based sectors of the Antarctic ice sheet, if initiated, could
cause global mean sea level (GMSL) to rise substantially above the likely range during the
21st century.
Five components contributing to global average sea level (rise):
- Thermal expansion
- Glaciers and ice caps
- Greenland ice sheet surface mass balance
- Antarctic ice sheet surface mass balance
- Scaled-up ice sheet dynamical imbalance
SROCC:
- AR4 excluding the effect of ice dynamics
- AR5 of ice dynamics important than max 20 cm
- SROCC ice dynamics 10cm → estimate of high end
El Nino is causing noise in the average DSLC / Time rate. A lot of water stored on the
continent so sea level drop. Water partly goes back into the ocean via groundwater instead
of rivers so takes a few years to restore sea level. Hydrological cycle.
Projections of key climate variables:
- Temperature increase depends strongly on scenario (political action)
- More hot and less cold events (virtually certain
- More heatwaves (very likely)
- Sea ice will decrease (very likely). No summer sea-ice in Arctic likely by mid-century in
RCP8.5
- Very likely that ocean circulations will weaken in 21st century (no collapse)
- Biosphere and ocean uptake of CO2 will decrease (high confidence)
Less landmass in southern hemisphere than in the northern so less CO2 uptake in
atmosphere in the southern part.
Decrease in ocean pH important (acidification) because concentrations in atmosphere
increase much faster because ocean takes up less → more warming → feedback system
Possible mechanisms:
Mass balance → Accumulation = ablation + calving
Accumulation = calving + ablation + bottom melt
,Buttressing effect = Ice-shelf buttressing can be defined as the mechanical effect of an ice
shelf on the state of stress at the grounding line. Along the grounding line, the grounded and
the floating parts of the ice are in direct contact.
Warmer water will result in more icebergs.
Lubrication effect = smoothening
SMB = surface mass balance = sum of ablation and accumulation
SLR = sea level rise
Ice mass changes → climate & dynamics
1 mm/yr = 360 Gt/yr
Ice sheets → Floating ice does not contribute directly to SLR (Archimedes’ law), but it does
contribute indirectly through reduced buttressing. Iceshelfs keep the ice into place. When
they disappear, the ice gets the change to flow into the ocean.
Ice sheets can change mass because of climate changes and dynamical changes (interaction
with ocean etc.) taking place in the icesheet.
Dynamical imbalance: q – Dq (downwards) & q + Dq sideways/horizontally
When in balance → amount of mass which is falling on to the Antarctic icesheet being equal
to what is released via the production of ice bergs ( q + q in balance)
When imbalance → the amount of accumulation decreases so the icesheet will get smaller.
And when it gets smaller it will get into deeper water. And when it’s in deeper water than
there is a tendency that there is a higher production of icebergs. So that means that the
difference between what goes in and goes out is increasing. So icesheet will propagate to
, decrease. This can particularly take place if you have an icesheet which is resting on a slope
which goes downwards in the interior direction. Water can flow in under the ice sheet
because of that so the process won’t stop. (is the case for Antartica)
Uncertainty Antarctic dynamics:
MISI: retrograde slope; Retreating grounding line (in ice sheet direction)
→ Flux at the grounding line (in ocean direction)
MICI: pro/retrograde slopes; Hydro-fracturing (in ocean) & cliff failure (on land)
Key processes:
- Enhanced ablation (warmer more melt)
- Increased precipitation (warmer more snow)
- Ice-ocean interaction
For Greenland 1>2
Ablation > Accumulation for T +2-3 K for Greenland
For Antarctica 2>1 but 3 most important
Impact is local, not global
Sea level rise
Relative sea level rise= absolute sea level rise + local land movement
Why spatial pattern in sea level?
- Sea-level change is not the same everywhere
- Causes of regional variability:
Steric (temperature & salinity)
Land ice melt (gravitational effects)
Glacial Isostatic Adjustment (GIA)
Ocean dynamics (circulation)
- Model regional patterns
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