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CO2, 14C, the Sun and Climate Change
over the Last Millennium
1. CO2 and climate variability (Gerber et al.,2003)
2. 14C and solar activity (Muscheler et al., 2005) Fortunat JoosClimate and Environmental PhysicsUniversity of [email protected]/~joos
Motivation?
• Can we evaluate climate-carbon cycle models over the decadal-to-century time scale?
• How big is the carbon cycle‘s response to climate change?
• What is the role of solar forcing and solar forcing amplification?
The ice core CO2 record: a new quantitative constraint.
Preindustrial atmospheric CO2 variations: a joint constraint on carbon cycle - climate feedbacks
and past climate variations
Siegenthaler et al., 2004
(Etheridge al.)(Neftel al.)
Simulations with theBern Carbon Cycle Model
All simulations:
solar+volcanic +anthropogenic forcing
Bern CC: T2xCO2= [1.5 K – 4.5 K].
Varying solar forcing:
a) “Low Solar Forcing” : Bard et al., 2000, low solar forcing
( Maunder Minimum Reduction: 0.25%; Lean et al., 95)
b) “High Solar Forcing” : Bard et al, high
(Maunder Minimum Reduction: 0.65% ; ~ Reid, 97)
Low solar forcing: Simulated atmospheric CO2 versus ice core data
Model results: smoothed with DML age distribution
Large low frequency temperature variations are not compatible with the ice core CO2 record
High Solar Forcing
How big is the carbon cycle-climate feedback in current models ?
Millennium simulations with the Bern model shows that a low frequency NH temperature change of 1 K induces a CO2 change of 12 ppm
d CO2/d ppm K-1
The 20th century simulations with the ten C4MIP models yield a range of ~4 to 16 ppm K-1
(Friedlingstein et al., 2005)
How big is the carbon cycle-climate feedback in current models ?
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The ice core CO2 and NH temperature records constrain the carbon cycle-climate feedback
Preindustrial CO2 variations, CO2:
~ 6-10 ppmLow-frequency NH temperature variationsT:
~ 0.4 to 0.9 K
The carbon cycle-climate feedback:
d CO2/d ppm K-1
Conclusions: Last Millennium CO2
• The ice core CO2 record and the (low-frequency) NH temperature records constrain the carbon cycle-climate feedback to 7 - 25 ppm/K (for modest climatic variations), comparable to the C4MIP range (4 to 16 ppm/K).
• A high low-frequency variability in NH temperature and a high solar forcing or solar forcing amplification are not compatible with the CO2 record within the framework of carbon cycle - climate models. This is consistent with new evidence from solar like stars.
How Unusual is Today‘s Solar Activity?
• Solanki et al. (Nature, 2004) suggest that
today’s solar activity is unprecedented
during the Holocene
The tree-ring 14C record: a solar proxy
Radiocarbon production depends on the shielding
by the earth and solar magnetic fields.
Reconstructing solar magnetic activity from the tree ring 14C record
carbon cycle model
Deduced radiocarbon production rate
Tree ring radiocarbon record
production model for radiocarbon
+geomagnetic field intensity
Deduced solar modulation /solar magnetic activity
Normalisation to neutron monitor and
ionisation chamber data
Conclusions
• Solar magnetic activity can be reconstructed from the radiocarbon tree ring record.
• Today‘s solar magnetic activity appears not to be unusual in the context of the last millennium
• Different solar proxies yield broadly consistent results.
?? Is there a link between solar magnetic activity and irradiance ??