Canadians prove humans are causing climate change
TENILLE BONOGUORE AND CAROLINE ALPHONSO
Globe and Mail Update
July 23, 2007 at 3:16 PM EDT
TORONTO — Humans are directly affecting global rainfall patterns and have been doing so for most of a century, according to a new study that gives the first solid proof that people are causing critical climate change.
Researchers from Environment Canada say their analysis of global data shows rainfall has effectively shifted away from the region immediately north of the equator — including sub-Saharan Africa, southern India and south east Asia — and moved north to Canada and Europe, and south to the tropics below the equator.
And the main cause behind the global change is human activity, say lead authors Xuebin Zhang and Francis Zwiers, from Environment Canada.
“It's the first time that we've detected in precipitation data a clear imprint of human influence on the climate system,” Mr. Zwiers told The Globe and Mail.
“Temperature changes we can cope with. But water changes are much more difficult to cope with. That will have economic impacts, and impacts on food production, and could ultimately displace populations.”
The scientists gathered global rainfall data from 1925 to 1999, and then compared it to 14 complex computer climate models.
The rainfall data confirmed what the scientists had speculated could occur thanks to human activity, and in some cases the weather changes went beyond what scientists had predicted.
“These shifts may have already had significant effects on ecosystems, agriculture and human health, especially in regions that are sensitive to changes in precipitation, such as the Sahel region in northern Africa,” the report states.
In essence, human activity is creating a stronger water cycle, moving more water vapour away from the warmest parts of the planet and pushing it towards the poles. That is making wet areas wetter, and dry areas drier, Mr. Zwiers explained.
The effect is not symmetrical, though. Higher use of fossil fuels in the Northern Hemisphere appear to be nudging the central rain band off the equator, driving it into the southern tropics.
Gordon McBean, former head of the Meteorological Service of Canada and a professor at the University of Western Ontario said the report reinforces that climate change is about much more than rising temperatures.
“The reality is that the climate is changing. It's not just warming. It's getting wetter in certain places and unfortunately also dryer in other places,” he said.
Science, he said, is providing solid information that individuals and governments need to understand so they can plan development and regulations. “We need strategies both within Canada and ... working globally on making informed choice,” he said.
The average of the 14 computer models underestimated how much the weather would change, and also underestimated how much the warming of tropical oceans due to El Nino events would affect tropical rainfall.
Natural factors like volcanic activity do play a part in changing rain patterns, but the scientists say the impact of those events pales in comparison to the effect of human activity.
“Robust” human influence is behind the changes to rainfall on Earth, the researchers say, due mainly to steady increases in greenhouse gases and sulphate aerosol concentrations produced by burning fossil fuels.
Overall, human activity had “a detectable and attributable influence” on regional rain patterns over the time period analyzed, the report states.
Human-caused climate change has been shown responsible for higher air temperatures and hotter seas and is widely expected to lead to more droughts, wildfires and floods, but the authors say this is the first study to specifically link it to changes in rainfall.
The study looked at annual average rainfall on land, not at sea, and did not look at extreme weather events like drought and flooding, the frequency of which is expected to increase due to global warming.
The paper is to be published by Nature on Thursday.
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