More rain in Canada, the United States, Europe, Russia, Indonesia and Brazil. Drought-like conditions in Mexico and Africa's Sahara and Sahel regions. Ever rising levels of greenhouse gases. Mere coincidence? Not according to an international team of scientists from the Canadian Center for Climate Modeling and Analysis that has provided the first empirical evidence that humans have indeed been affecting rainfall patterns around various regions of the planet for the past century.
After analyzing rainfall pattern data going back over 8 decades side-by-side with an array of climate change simulations taking into account two types of anthropogenic emissions — sulfate aerosols and greenhouse gases — they found that human activity caused up to two-thirds of the extra rain observed in northern temperate regions (Canada, Europe, U.S., etc), all of the extra rain in the southern tropics and subtropics and removed close to a third of the rain once seen in the northern tropics and subtropics. In the case of the northern temperate regions like North America and Europe, human activity may have accounted for an additional 62 millimeters of rainfall per year between 1925 and 1999 while, in the case of the southern tropics and subtropics, it may have accounted for an additional 82 millimeters per year over the past century. The scientists estimate that 50 - 85% of this increase can directly be attributed to humans.
The next step for the scientists will be to differentiate the individual contributions of greenhouse gases and aerosols to determine which are exerting the strongest influence on rainfall patterns. This study could help scientists and policymakers forecast future precipitation within specific regions more accurately and allow them to better prepare for fluctuations in the weather regimes. Though some scientists will take exception to the study's findings, claiming that, rainfall being so erratic in some areas, it's often too "difficult to separate the signal from the noise," it's clear that anthropogenic effects are having a measurable effect on changing climate patterns. The extent to which they are doing so remains the only question.
Via ::ScienceNOW: The Power to Influence Showers (news website), ::The Blue Marble Blog: Rainfall Changes Linked To Human Activity (blog)