I was somewhat flippant, but my comment holds ... Tom indicates that for the ranges expected this century, climate effects are largely in a linear domain, and this seems reasonable to me.
As Mike points out, we know that the climate responds differently to different patterns and types of radiative forcing even if they have the same global mean radiative forcing. Whether these effects are additive depends mostly on whether you are in a range where linear approximation is "good enough" for some specific purpose. However, if you think the world is full of "tipping points" (where that is an irreversibility or perhaps a discontinuity) but neither A nor B would be sufficient to push you past the "tipping point" but A + B collectively would be enough, then we would expect the linear approximation to fail. ___________________________________________________ Ken Caldeira Carnegie Institution Dept of Global Ecology 260 Panama Street, Stanford, CA 94305 USA [email protected]; [email protected] http://dge.stanford.edu/DGE/CIWDGE/labs/caldeiralab +1 650 704 7212; fax: +1 650 462 5968 On Wed, Dec 31, 2008 at 11:55 AM, Mike MacCracken <[email protected]>wrote: > Dear Stuart: > > The issue is a bit more complicated than Ken indicates: > > > 1. Radiative forcing is measured (well, actually calculated) for the > tropopause. It does make a difference in the response the degree to which > the resulting forcing results in a change in the surface relative to the > tropospheric energy balance, especially for the hydrological cycle > influence. > 2. The geographic pattern also matters, though perhaps not for the > short term. But if one has all the forcing in the Northern Hemisphere > versus > Southern, one will get a different response due to the land/ocean > difference, etc. (this was the case for example during mid-20th century > when > sulfate forcing in NH led to a slowing of warming or even a cooling, but > did > not do so in the SH). Also, the orbital changes that drive the ice age > cycling actually create (independent of changes at the surface) virtually > no > annual global forcing—all they do is redistribute energy by season and > latitude, so for that case, a zero forcing is causing ice age cycling > (through a lot of feedbacks, etc.). > 3. There is also the issue of how long the forcing persists—short time > ones like volcanic eruptions have a large forcing, but due to short time > they are aloft, the response does not reach equilibrium and eventually goes > away. A small, persistent change can, however, have a longer term effect as > it activates some of the longer term feedback processes. > > > And I am sure there are further nuances. > > Mike MacCracken > > > > On 12/31/08 2:29 PM, "Ken Caldeira" <[email protected]> wrote: > > You can of course add radiative forcing "linearly". (What other kind of > addition is there?) > > An important question is whether climate response to the sum of radiative > forcings is the same as the sum of the climate responses to individual > radiative forcings. > > The answer to this question depends on the size of the perturbation and > your tolerance for approximation. > > Recall the maxim: "*To first order, everything is linear !!" > * > ( More strictly speaking, "*To first order, differentiable functions are > linear.*" ) > > > > On Wed, Dec 31, 2008 at 11:13 AM, Stuart Strand <[email protected]> > wrote: > > > Is radiative forcing additive linearly? > > = Stuart = > > Stuart E. Strand > 167 Wilcox Hall, Box 352700, Univ. Washington, Seattle, WA 98195 > voice 206-543-5350, fax 206-685-3836 > http://faculty.washington.edu/sstrand/ > > Using only muscle power, who is the fastest person in the world? > Flying start, 200 m: 82.3 mph! > http://en.wikipedia.org/wiki/Sam_Whittingham > Hour http://en.wikipedia.org/wiki/Hour_record > 55 miles, upside down, backwards, and head first! > > > > > > > > > --~--~---------~--~----~------------~-------~--~----~ 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 -~----------~----~----~----~------~----~------~--~---
