OTTAWA (CP) - An Environment Canada study has detected the first direct evidence of human influence in changing global patterns of rain and snowfall - including a significant increase in precipitation in Canada.
The study published in the science journal Nature finds that precipitation increased by 10 per cent in northern regions during the 20th century, a change that cannot be explained by natural variability or volcanic eruptions.
Human activity can be the only explanation for the changes, according to the study co-led by Francis Zwiers and Xuebin Zhang of Environment Canada.
"These are pretty big changes over the better part of the century and what we're able to say from our study is that a substantial part of that change is due to human influence," Zwiers said in an interview.
Zwiers and Zhang examined global rainfall data from 1925 to 1999 and compared it with 14 complex computer climate models.
The study confirms the reliability of the computer models that are widely used to study climate, showing that actual changes are in line with computer predictions. But the changes are happening faster than predicted.
"The observed changes, which are larger than estimated from model simulations, may have already had significant effects on ecosystems, agriculture and human health," says the report.
Almost all computer models predict that global warming will bring increased precipitation along the equator, with more moisture transported toward the poles, resulting in greater precipitation at higher latitudes.
And while adapting to global warming is difficult, preparing for changes in precipitation is even more challenging because it will have a greater impact on the food supply and movement of peoples.
The picture is complicated by seasonal and geographical factors, and by volcanic eruptions, making it extremely difficult to detect the trends caused by human activity.
For example, the increase in northern precipitation is a winter phenomenon, offset by a decline in summer rainfall. And despite the overall moistening in upper latitudes, the models predict a drying in the interior of North America.
"We've run climate models over the 20th century. They simulate a certain response in precipitation that corresponds on the large global scale with these changes that we've seen," said Zwiers.
"It has to do basically with a strengthening of the hydrological cycle and greater transport of moisture vapour away from the warm parts of the world toward cold parts of the world."
The current flooding in Britain is consistent with the predictions but no specific event can be definitively attributed to climate change, he said. Scientists can only say that global warming will increase the risk of extreme weather events in broad regions of the planet.
The study adds to the already large body of evidence showing the climate is changing because of rising concentrations of greenhouse gases, released mainly by the burning of fossil fuels such as coal, oil and natural gas.
"Human induced changes have not previously been detected in global studies of precipitation, partly because drying in some regions cancels moistening in others, reducing the global signal," says a summary released by Environment Canada.
"Here the scientists used the pattern of changes in different latitude bands instead of the global average."
Zwiers conceded that the quality of precipitation records varies enormously but he is nevertheless confident in the study's conclusions.
"We really tried to understand what has driven the change that has been observed and you have to do this on very large scales. We looked at large latitude bands.
"You have to do this in climate-change detection studies so that you can separate out the natural internal variability of the climate system, and there's lots of it in precipitation, and what is the response to an external influence on the climate."
http://www.cfrb.com/news/14/560214
The study published in the science journal Nature finds that precipitation increased by 10 per cent in northern regions during the 20th century, a change that cannot be explained by natural variability or volcanic eruptions.
Human activity can be the only explanation for the changes, according to the study co-led by Francis Zwiers and Xuebin Zhang of Environment Canada.
"These are pretty big changes over the better part of the century and what we're able to say from our study is that a substantial part of that change is due to human influence," Zwiers said in an interview.
Zwiers and Zhang examined global rainfall data from 1925 to 1999 and compared it with 14 complex computer climate models.
The study confirms the reliability of the computer models that are widely used to study climate, showing that actual changes are in line with computer predictions. But the changes are happening faster than predicted.
"The observed changes, which are larger than estimated from model simulations, may have already had significant effects on ecosystems, agriculture and human health," says the report.
Almost all computer models predict that global warming will bring increased precipitation along the equator, with more moisture transported toward the poles, resulting in greater precipitation at higher latitudes.
And while adapting to global warming is difficult, preparing for changes in precipitation is even more challenging because it will have a greater impact on the food supply and movement of peoples.
The picture is complicated by seasonal and geographical factors, and by volcanic eruptions, making it extremely difficult to detect the trends caused by human activity.
For example, the increase in northern precipitation is a winter phenomenon, offset by a decline in summer rainfall. And despite the overall moistening in upper latitudes, the models predict a drying in the interior of North America.
"We've run climate models over the 20th century. They simulate a certain response in precipitation that corresponds on the large global scale with these changes that we've seen," said Zwiers.
"It has to do basically with a strengthening of the hydrological cycle and greater transport of moisture vapour away from the warm parts of the world toward cold parts of the world."
The current flooding in Britain is consistent with the predictions but no specific event can be definitively attributed to climate change, he said. Scientists can only say that global warming will increase the risk of extreme weather events in broad regions of the planet.
The study adds to the already large body of evidence showing the climate is changing because of rising concentrations of greenhouse gases, released mainly by the burning of fossil fuels such as coal, oil and natural gas.
"Human induced changes have not previously been detected in global studies of precipitation, partly because drying in some regions cancels moistening in others, reducing the global signal," says a summary released by Environment Canada.
"Here the scientists used the pattern of changes in different latitude bands instead of the global average."
Zwiers conceded that the quality of precipitation records varies enormously but he is nevertheless confident in the study's conclusions.
"We really tried to understand what has driven the change that has been observed and you have to do this on very large scales. We looked at large latitude bands.
"You have to do this in climate-change detection studies so that you can separate out the natural internal variability of the climate system, and there's lots of it in precipitation, and what is the response to an external influence on the climate."
http://www.cfrb.com/news/14/560214
