The fence appears to, anyhow. The New York Times reported this week that a 2,000-mile-long fence built in 1907 to keep rabbits out of farmland in Western Australia has had an unusual effect on the climate. (Note: You can also read the story in the International Herald Tribune here.)
On one side of the fence is dark, native vegetation — scrubland; on the other side is farmland, lighter in color. Clouds form over the dark scrubland, but the skies over the farms are clear. Rainfall on the farm side of the fence has dropped 20 percent since the 1970s. (See the Times’ story for a good photo of the fence line.)
Scientists have three theories for why one side of the fence gets more rain than the other:
1. The dark, native vegetation absorbs and releases more heat than the light-colored crops. This heat combines with water vapor to form more clouds.
2. The warmer air on the dark, native vegetation side of the fence rises and cool air comes over from the farmland side, forming clouds over the dark scrubland.
3. According to the story, “A third idea is that a high concentration of aerosols — particles suspended in the atmosphere — on the agricultural side results in small water droplets and a decrease in the probability of rainfall. On the native landscape, the concentration of aerosols is lower, translating into larger droplets and more rainfall. ”
All of these, or a combination of two or more of them, sound plausible to me. I guess the length of the border between the two types of land cover is a big factor in the climate differences. The paradox here is that as we clear more land for food production, we could be creating conditions that result in less rain — and potentially less food production.
One of the researchers studying this phenomenon hopes that his work will help scientists “understand the relationships between the land surface and atmosphere and to provide ideas for sustainable agricultural practices.”
Wow. That’s remarkable. It seems hard to argue now that humans don’t have an effect on the atmosphere. I’m surprised it’s so localized, though.
Well, if something as simple as that can have such a large effect and the mechanism isn’t fully understood. Shouldn’t we support more research in to climate change and not be so quick to say the science is settled. The work of Roger A. Pielke Sr. and Anthony Watts should be taken more seriously.
See the Jules Charney 1975 paper on desertification where he postulates a “bio-geophysical feedback” where human caused changes in the surface albedo change the energy dynamic of the atmosphere with a direct relationship to moisture and rainfall amounts.
Would it make sense, then, to plant crops in a checkerboard, with alternate squares for farm crops and the others for native scrub? Perhaps the squares could even be rotated after an interval to let the farmland rest and rejuvinate?
RE: M. Clemen’s checkerboard idea - It does not make sense in this case, as each square of farmland would need to be surrounded by a rabbit-proof fence, increasing the thousands of miles of fence to millions of miles. Also farmland that is let go wild will more likely sprout invasive weeds than native vegetation.
It’s 2007. Why should we be referring to research from 1975?
The New York Times link isn’t working. Anyway, instead of the checkerboard thing, which does waste fencing, you could just alternate what side of the fence you grow vegetation on.
Just another example of what happens when humans mess with nature. And what does that say about fences?
What happened around 1970 (that had not happened from 1907) that would be involved in the change?
As scientists (writers, investigators, reporters) and readers, we should try some critical thinking about interesting findings such as these.
George Curtis
We wouldn’t need more fencing as the rabbit proof fence didn’t work. And the weeds would probably dimish as they wouldn’t be able to compete with trees. Many organisations (eg the AWC) have successfully rehabilitated farmlands back to ‘original’ woodland.
The changes would have started post the first world war - returning soldiers given farmland, again post second world war for the same reason. This accelerated through the 60s as it was a govt requirement to clear a certain amount of land each year or lose the lease. This was stopped once they realised it was a bad idea due to the start of salinisation. I may have some dates wrong but that is why it started around 1970.
I would think (as with most things) it’s a combination of a number of effects; clearing, warming, ‘natural’ variations in rainfall, African monsoon cycles etc.
Glad to see people were interested in this story! Here are a few more related links:
- The Bunny Fence Experiment, from the University of Alabama-Huntsville site, http://www.nsstc.uah.edu/~nair/BUFEX05/
- The N.Y. Times’ story republished in the International Herald Tribune, http://www.iht.com/articles/2007/08/16/news/australia.php