Those ice sheets again (Photo credit: swan-scot)
Reader “Markx” writes in Tips and Notes on a paper I hadn’t noticed before (because it was published before WUWT was born). Of course it only works if CO2 has a long residence time and/or our elevated emission levels continue. We need at least 3x more CO2 to pull off the delay.
A movable trigger: Fossil fuel CO2 and the onset of the next glaciation. David Archer and Andrey Ganopolski
Published in G3 Geochemistry Geophysics Geosystems Research Letter Volume 6, Number5 5 May 2005
Abstract:
The initiation of northern hemisphere ice sheets in the last 800 kyr appears to be closely controlled by minima in summer insolation forcing at 65N. Beginning from an initial typical interglacial pCO2 of 280 ppm, the CLIMBER-2 model initiates an ice sheet in the Northern Hemisphere when insolation drops 0.7 s (standard deviation) or 15 W/m2 below the mean. This same value is required to explain the history of climate using an orbitally driven conceptual model based on insolation and ice volume thresholds (Paillard, 1998). When the initial baseline pCO2 is raised in CLIMBER-2, a deeper minimum in summertime insolation is required to nucleate an ice sheet. Carbon cycle models indicate that 25% of CO2 from fossil fuel combustion will remain in the atmosphere for thousands of years, and 7% will remain beyond one hundred thousand years (Archer, 2005). We predict that a carbon release from fossil fuels or methane hydrate deposits of 5000 Gton C could prevent glaciation for the next 500,000 years, until after not one but two 400 kyr cycle eccentricity minima. The duration and intensity of the projected interglacial period are longer than have been seen in the last 2.6 million years.
Some excerpts:
“Models require some amplifying feedback, from sea ice … or the terrestrial biosphere ….to nucleate on the basis of insolation forcing, but insolation is always the primary driver.”
and
An anthropogenic release of 300 Gton C (as we have already done) has a relatively small impact on future climate evolution, postponing the next glacial termination 140 kyr from now by one precession cycle.
Release of 1000 Gton C … is enough to decisively prevent glaciation in the next few thousand years, and given the long atmospheric lifetime of CO2, to prevent glaciation until 130 kyr from now.
If the anthropogenic carbon release is 5000 Gton or more….[…]… The model predicts the end of the glacial cycles, with stability of the interglacial for at least the next half million years…
Figure 3. Effect of fossil fuel CO2 on the future evolution of climate. Green represents natural evolution, blue represents the results of anthropogenic release of 300 Gton C, orange is 1000 Gton C, and red is 5000 Gton C. (a) Past and future pCO2 of the atmosphere. Past history is from the Vostok ice core [Petit et al., 1999], and future anthropogenic perturbations are from a carbon cycle model [Archer, 2005]. (b) June insolation at 65N latitude, normalized and expressed in s units. 1 s equals about 20 W m2. Green, blue, orange, and red lines are values of the critical insolation i0 that triggers glacial inception. The i0 values are capped at 3 s to avoid extrapolating beyond model results in Figure 3; in practice, this affects only the 5000 Gton C scenario for about 15 kyr. (c) Interglacial periods of the model. (d) Global mean temperature estimates.
Not having mile thick ice sheets crush northern hemisphere cities is a good thing, don’t you think?
Full PDF here: http://geosci.uchicago.edu/~archer/reprints/archer.2005.trigger.pdf