Nature - Rainfall Patterns Changing Thanks To Warming - Pattern Outside Of Natural Variability - AFP

[hatrack]

A study has yielded the first confirmation that global warming is already affecting world's rainfall patterns, bringing more precipitation to northern Europe, Canada and northern Russia but less to swathes of sub-Saharan Africa, southern India and Southeast Asia. The changes "may have already had significant effects on ecosystems, agriculture and human regions that are sensitive to changes in precipitation, such as the Sahel," warns the paper, released on Monday by Nature, the British science journal.

Scientists have long said that global warming is bound to interfere with snow and rainfall patterns, because air and sea temperatures and sea-level atmospheric pressure -- the underlying forces behind these patterns -- are already changing.

But, until now, evidence for declaring that the interference is already happening existed anecdotally or in computer models, rather than from observation.

One problem for researchers has been a lack of accurate, long-term rainfall data from around the world that would enable them to distinguish between regional or cyclical shifts in rainfall. Francis Zwiers, a scientists with Environment Canada, Toronto, found a way around these problems by using two data-sets of global rainfall pattern beginning, conservatively, in 1925 and ending in 1999.

EDIT

http://www.terradaily.com/2007/070723125401.iuag29r0.html

[OKIsItJustMe]

1. Study - Requires Subscription

http://www.nature.com/nature/journal/vaop/ncurrent/full/nature06025.html

Detection of human influence on twentieth-century precipitation trends

Xuebin Zhang1, Francis W. Zwiers1, Gabriele C. Hegerl2, F. Hugo Lambert3, Nathan P. Gillett4, Susan Solomon5, Peter A. Stott6 & Toru Nozawa7

Human influence on climate has been detected in surface air temperature1–5, sea level pressure6, free atmospheric temperature7, tropopause height8 and ocean heat content9. Human-induced changes have not, however, previously been detected in precipitation at the global scale10–12, partly because changes in precipitation in different regions cancel each other out and thereby reduce the strength of the global average signal13–19. Models suggest that anthropogenic forcing should have caused a small increase in global mean precipitation and a latitudinal redistribution of precipitation, increasing precipitation at high latitudes, decreasing precipitation at sub-tropical latitudes15,18,19, and possibly changing the distribution of precipitation within the tropics by shifting the position of the Intertropical Convergence Zone20. Here we compare observed changes in land precipitation during the twentieth century averaged over latitudinal bands with changes simulated by fourteen climate models. We show that anthropogenic forcing has had a detectable influence on observed changes in average precipitation within latitudinal bands, and that these changes cannot be explained by internal climate variability or natural forcing. We estimate that anthropogenic forcing contributed significantly to observed increases in precipitation in the Northern Hemisphere mid-latitudes, drying in the Northern Hemisphere subtropics and tropics, and moistening in the Southern Hemisphere subtropics and deep tropics. The observed changes, which are larger than estimated from model simulations, may have already had significant effects on ecosystems, agriculture and human health in regions that are sensitive to changes in precipitation, such as the Sahel.

...

[IndyOp]

2. Again we see that the observed changes are larger than estimated by the models...

:(

Climate Change Model Projections Likely Conservative
Posted by Stephen Nodvin on May 14th, 2007

Contrary to what most climate change naysayers claim, scientists are mostly a conservative lot. The peer review process can sometimes be brutal. It is often only after significant resistance and repeated attempts and additional substantiation that new research ideas and findings traverse the gauntlet of reviewers and are published in the top scientific journals.

<snip>

Recently, at least three reports have been published that document that recent scientific projections of global warming have likely been conservative. The reports indicate that climate change models, used by the world’s scientists to make the projections, likely are providing underestimates of both future warming and the global impacts of a warming earth.

First, new analyses reported in the journal Science, indicate that climate projections published in 2001 by the IPCC were conservative compared to actual warmings observed. The 2001 projections were part of the IPCC Third Assessment Report and modeled changes in key global climate parameters since 1973, compared with a series of differing emissions scenarios. Although published in 2001, the model projections were essentially independent from the observed climate data since 1990.

<snip>

Second, a NASA report suggests that existing climate models may be significantly underestimating future warmings in eastern North America due to limitations in their ability to accurately project future precipitation regimes.To focus on more local scales, the NASA scientists scaled the simulations from a global climate model developed by NASA’s Goddard Institute for Space Studies and coupled the simulations with those of a widely-used weather prediction model.Coupling the weather prediction model with the global climate model allowed the scientists to assesses details about future climate at a finer geographic scale than global models alone. The coupling provided reliable simulations not only on the amounts of summer precipitation, but also on its frequency and timing. Accurately predicting the timing and frequency of precipitation events is important because daily temperatures are usually higher on rainless days and when precipitation falls less frequently than normal.Once more accurate information on the timing and frequency of summer rainfall events were incorporated, the simulations projected much higher summer temperatures that had been projected with the global model alone.The new projections indicate that eastern U.S. summer daily high temperatures that currently average in the low-to-mid-80s (degrees Fahrenheit) will most likely soar into the low-to-mid-90s during typical summers by the 2080s. In extreme seasons — when precipitation falls infrequently — July and August daily high temperatures could average between 100 and 110 degrees Fahrenheit in cities such as Chicago, Washington, and Atlanta.

<snip>

Third, another new study released by the National Snow and Ice Data Center (NSIDC) and the National Center for Atmospheric Research (NCAR) found that arctic sea ice is melting at a significantly faster rate than projected by the most advanced computer models.Satellite and other observations showed the Arctic ice cover is retreating more rapidly than estimated by any of the eighteen computer models used by the IPCC in preparing its 2007 assessments.Similar to the reports above, the authors of this study concluded that current model projections are providing conservative estimates of future global warming impacts such as the melting of the Arctic ice cap. The findings show that the shrinking of summertime ice is about thirty years ahead of the climate model projections.The 2007 IPCC report projected that the Arctic would become seasonally ice free sometime between 2050 to well beyond 2100. The new results suggest the Arctic could become ice free in summers even earlier than the year 2050.

<snip>

http://www.earthportal.org/forum/?p=210

The Eleventh Hour

"If success or failure of the planet and of human beings depended on how I am and what I do ... How would I be? What would I do?" - Buckminster Fuller

[lostnfound]

3. We have been having the most bizarre daily rains for 3 weeks now

At least 3 weeks, in Houston. At my son's small school, 3 healthy old oak trees have fallen in 3 weeks, from saturated soil. People joke about Noah's ark. This is so unusual. Anecdotally, I'll check in for my city and say "yes, this is bizarre."

[Javaman]

5. Yeah, I agree. Austin here. we have had so much rain my

garden failed due to mold and to much water. :(

Yesterday it was like a monsoon.

[The Backlash Cometh]

4. In the Central Florida area we have had more direct thunderstorm strikes

than I ever remember. There have been at least three homes that were hit with lightning and burned down. One guy actually got hit by lightning while he was in his garage.

Weird, weird weather.