Poster's note : Worth comparing the Miller et al paper previously attached on this thread by Ken to this one below, which suggests positive feedbacks affected the magnitude and duration of the LIA. From recollection of my shared papers, at least one of the unattributed eruptions referred to below has been found in the 4 yrs since this was published.
Climate response to large, high-latitude and low-latitude volcanic eruptions in the Community Climate System Model Schneider, D. P., C. M. Ammann, B. L. Otto-Bliesner, and D. S. Kaufman (2009), J. Geophys. Res., 114, D15101, doi:10.1029/2008JD011222. http://onlinelibrary.wiley.com/doi/10.1029/2008JD011222/abstract Keywords: volcanic eruptions;climate change;climate model Abstract Explosive volcanism is known to be a leading natural cause of climate change. The second half of the 13th century was likely the most volcanically perturbed half-century of the last 2000 years, although none of the major 13th century eruptions have been clearly attributed to specific volcanoes. This period was in general a time of transition from the relatively warm Medieval period to the colder Little Ice Age, but available proxy records are insufficient on their own to clearly assess whether this transition is associated with volcanism. This context motivates our investigation of the climate system sensitivity to high- and low-latitude volcanism using the fully coupled NCAR Community Climate System Model (CCSM3). We evaluate two sets of ensemble simulations, each containing four volcanic pulses, with the first set representing them as a sequence of tropical eruptions and the second representing eruptions occurring in the mid-high latitudes of both the Northern and Southern hemispheres. The short-term, direct radiative impacts of tropical and high-latitude eruptions include significant cooling over the continents in summer and cooling over regions of increased sea-ice concentration in Northern Hemisphere (NH) winter. A main dynamical impact of moderate tropical eruptions is a winter warming pattern across northern Eurasia. Furthermore, both ensembles show significant reductions in global precipitation, especially in the summer monsoon regions. The most important long-term impact is the cooling of the high-latitude NH produced by multiple tropical eruptions, suggesting that positive feedbacks associated with ice and snow cover could lead to long-term climate cooling in the Arctic. On Tue, Jan 31, 2012 at 12:17 AM, Andrew Lockley <[email protected]>wrote: > http://www.agu.org/pubs/crossref/2012/2011GL050168.shtml > > Northern Hemisphere summer temperatures over the past 8000 years have been > paced by the slow decrease in summer insolation resulting from the > precession of the equinoxes. However, the causes of superposed > century-scale cold summer anomalies, of which the Little Ice Age (LIA) is > the most extreme, remain debated, largely because the natural forcings are > either weak or, in the case of volcanism, short lived. Here we present > precisely dated records of ice-cap growth from Arctic Canada and Iceland > showing that LIA summer cold and ice growth began abruptly between 1275 and > 1300 AD, followed by a substantial intensification 1430–1455 AD. Intervals > of sudden ice growth coincide with two of the most volcanically perturbed > half centuries of the past millennium. A transient climate model simulation > shows that explosive volcanism produces abrupt summer cooling at these > times, and that cold summers can be maintained by sea-ice/ocean feedbacks > long after volcanic aerosols are removed. Our results suggest that the > onset of the LIA can be linked to an unusual 50-year-long episode with four > large sulfur-rich explosive eruptions, each with global sulfate loading >60 > Tg. The persistence of cold summers is best explained by consequent > sea-ice/ocean feedbacks during a hemispheric summer insolation minimum; > large changes in solar irradiance are not required. > > -- > You received this message because you are subscribed to the Google Groups > "geoengineering" group. > To post to this group, send email to [email protected]. > To unsubscribe from this group, send email to > [email protected]. > For more options, visit this group at > http://groups.google.com/group/geoengineering?hl=en. > -- You received this message because you are subscribed to the Google Groups "geoengineering" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To post to this group, send email to [email protected]. Visit this group at http://groups.google.com/group/geoengineering. For more options, visit https://groups.google.com/groups/opt_out.
