First, I would like to supplement my original message which was kindly communicated by James Annan:
On Mon, 15 Jan 2007 23:04:46 +0900, James Annan wrote: >> Kooiti MASUDA said... >> I agree that slow a climate change is not a catastrophe and we can and >> should adapt to it. I made a typo error here. Sorry. I meant "... a slow climate change ...". >> > Crop yields will decline, particularly in Africa >> I think that THIS is likely -- a very unfortunate thing. The phrase "particularly in Africa" is not what I would say myself, though I think that it is not far off the point. A quantitative outlook of river runoff from currently available climate projections is shown in the following scientific paper: Nohara D., Kitoh A., Hosaka M. and Oki T., (2007): Impact of climate change on river runoff using multi-model ensembles. (Acceped for publication in Journal of Hydrometeorology. Its preprint is available from the page of the research project at http://kyousei.aesto.or.jp/~k041open/ipcc_ar4/ .) The model-to-model variability of the projection is large, and we do not know how reliable the multi-model composite is. But I think that it can be used to know where to watch. It seems that there are as much land where water availability increases as where it decreases. But it seems to me that the distribution of increases and decreases is something unhelpful for agricultural productivity. According to the composite map, runoff decreases in the following areas: Europe and Central Asia to the south of 50 deg. N; Mexico, Central America and U.S. West; Argentina; Southern Africa. Also, West Africa and the southern half of Australia have negative sign. Thus, the major zones of production of wheat and corn (maize) of the world are covered, where their productivity is generally water-limited. On the other hand, the composite suggest that runoff will increase in higher latitudes (to the north of 55 deg. N and around the southern tip of South America), and in the greater Southeast Asia including southern China and eastern India. In these regions, agriculture is generally not water-limited, and the risk of flood seems to be more important than that of drought. ***** Now I comment on the outlook of John McCormick. On Sat, 20 Jan 2007 12:12:40 -0800, John McCormick wrote; > He might not be ready to saddle the South Australian drought to climate > change, just yet. Though, there is observation of a shift in the > subtropical jet stream being drawn closer to the Antarctic pole by the > tightening of the Antarctic Polar Vortex. It seems to be pulling the > Ssouth Australian coast precip patterns with it. Australia wheat crop > is down by 60 percent this year According to composites of currently available projections, the change of average precipitation in Australia in the 21st century is not so great. The analysis of the following paper shows that while strengthened subsidence in the subtropical zone acts to decrease precipitation, increased amount of moisture compensates it. Emori S. and Brown S.J., 2005: Dynamic and thermodynamic changes in mean and extreme precipitation under changed climate. Geophysical Research Letters, 32, L17706, doi:10.1029/2005GL023272. (Abstract is at http://www.agu.org/pubs/crossref/2005/2005GL023272.shtml . Some figures are reproduced in the Japanese press release at http://www.jamstec.go.jp/jamstec-j/PR/0508/0829/index.html ). On the other hand, evaporation will increase in warmer climate. Thus the amount of available water will decrease somewhat. > and China is feeling the hurt of lower > yields, expanding desertification and drought. First, please recognize that China has vast heterogeneity of climate. The northern and western parts are arid, while the southern part is humid. It is true that many parts of the arid region of northern China experience desertification. But, I guess that the problem is more of conservation of soil and water rather than of climate change. (I do not mean that climate does not change there, but it is not so systematically related to greenhouse effect.) Maybe situation in Australia is similar. > Throw in the melting > Himalayan glaciers that are headwaters for five major rivers in South > Asia, home to nearly 600 million people reliant upon those rivers for > irrigation. It is true that people in many small regions around the central Asian highlands rely on glacier meltwater, and their agriculture will not be sustainable when the glaciers disappear. But, for the most part of major South Asian river basins, glacier meltwater comprises only a tiny part of water flow in the rivers. (Those rivers have more sources besides the headwaters at high locations.) Also precipitation is not expected to decrease there, though its variability is likely to increase. Seasonal snowcover is expected to decrease, so that the seasonal march of river discharge will change (more discharge in winter and less in spring). Thus there is a problem about water resources there, but it is more of its distribution rather than of the average amount. > Should I also mention the Ogallala Aquifer and the Rocky > Mountain snow pack diminishing water availability in the Western North > American grain basket. I guess that agriculture in the U.S. West is not sustainable at the current level and that the main reason is its dependence on fossil water. It needs to be restructured within the margin of natural replenishment. Climate change is something which will make this requirement tighter -- Probably evaporation will increase there but precipitation will not. Whether the precipitation come as snow or rain does not affect average water availability downstream so much, though it does affect its seasonality. Ko-1 M. (Kooiti Masuda) --~--~---------~--~----~------------~-------~--~----~ You received this message because you are subscribed to the Google Groups Global Change ("globalchange") newsgroup. Global Change is a public, moderated venue for discussion of science, technology, economics and policy dimensions of global environmental change. Posts will be admitted to the list if and only if any moderator finds the submission to be constructive and/or interesting, on topic, and not gratuitously rude. 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/globalchange -~----------~----~----~----~------~----~------~--~---
