The science pointing to industrial greenhouse gases building up in Earth’s atmosphere and warming the planet is sound and convincing, says a University of Calgary climate expert.
Albertans are already experiencing the effects of human-caused global warming – including more severe drought and drier and warmer winters, said Lawrence Nkemdirim, a climatologist and hydrologist in the U of C’s geography department.
“Global warming is real,” Nkemdirim said in a talk last week at the university. “The fingerprints of warming are strong in Western Canada.”
Another climate expert, however, insists the facts don’t support human activity being a major cause of global warming.
Chris de Freitas, a climate scientist at the University of Auckland in New Zealand, said measurements by satellites of Earth’s atmosphere show no increase in global temperature since 1979.
Instruments on the planet’s surface do show that temperatures have increased slightly since 1979. But most of these surface measurements were made in or near cities which – being slightly warmer than less populated areas – skew the temperature records, de Freitas says in an article in the Canadian Society of Petroleum Geologists’ Bulletin of Canadian Petroleum Geology.
Nkemdirim, however, said the arguments of a small minority of scientists that dispute human-induced global warming have been found wanting by the vast majority of the scientific community.
“There are very few real climatologists that are questioning the science,” he said.
Compelling evidence comes from the climate change record kept by nature itself – called the “proxy” record, Nkemdirim said. This record indicates what conditions on Earth were like in ancient climates thousands of years ago.
Using evidence found in Antarctic ice cores, ocean corals, deep sediments and tree rings, scientists can accurately reconstruct past global temperatures and atmospheric carbon dioxide levels.
Based on this record, “we have now far exceeded anything we would say is (due to) natural cause,” Nkemdirim said.
Some dissenters say natural causes, such as volcanic activity, fluctuating solar radiation and the role of water vapour and oceans, play a much bigger role than human activities.
But Nkemdirim said that when all these factors are accounted for in computer models, industrial emissions are still the biggest driver of climate change now occurring.
As further evidence, he noted that there is excellent correlation between increasing carbon dioxide levels and rising temperatures as found in nature’s proxy record, and as measured by instruments since 1880.
There is also a good overlap between the instrument-measured climate changes and the changes predicted by computer models, Nkemdirim said.
De Freitas argues that there have been dramatic natural warming and cooling cycles in climate during the last 900 years, prior to the Industrial Age. These include the Medieval Warm Period (800-1200 AD) and the Little Ice Age (1200-1850 AD).
But Nkemdirim said such natural shifts in climate have occurred largely within hemispheres, unlike the warming on a global scale that is now apparent.
De Freitas also maintains that studies of past climates and glacial ice measurements in Antarctica show that carbon dioxide levels increase following warming periods, rather than the rising CO2 boosting temperatures.
But Nkemdirim said that when the entire proxy record in nature is considered, the only “logical and defensible” conclusion is that an increase in CO2 drives the rise in global temperatures – not the other way around.
Climate records from Western Canada show winters have warmed by about five degrees Celsius between 1950 and 1977, while the annual average temperature has climbed about 2.8 degrees.
Records also show a higher frequency of winter drought, with a corresponding drop in groundwater tables, stream flows and spring runoff available for such uses as irrigation.
Statistics Canada reported last week that Western Canadian farmers have just gone through two of the worst crop-production seasons in a quarter century.
For some farmers in Alberta and Saskatchewan, StatsCan said, the situation has been worse than during the 1930s Great Depression.
