More extreme weather coming due to climate change: international scientists

Nations can anticipate more climate extremes, says a new international report

OTTAWA — Record-breaking temperatures, stronger winds and heavy precipitation in the form of rain and snow are becoming more frequent events in the 21st century due to climate change that evidence indicates is being caused by human activity, says a new assessment released Friday by governments from around the world.

Canadian scientists who contributed to the review, a special report on managing the risks of extreme weather events and disasters to advance climate change adaptation, also say Canada is facing more violent weather that could cause greater economic damage at home than in developing countries.

The assessment, agreed to by Canada and all other countries participating in the Intergovernmental Panel on Climate Change, has reiterated scientific evidence confirming a warming trend that is increasing the number of warmer days and nights and decreasing the number of colder days and nights.

Many extreme events that can be caused by natural variability every 20 years — such as droughts in some seasons and regions — are also more likely to return more frequently, the assessment concluded.

The report highlighted strong statistical evidence linking an increase in extreme weather events such as heavy precipitation to human consumption of fossil fuels such as gasoline. Greenhouse gas emissions such as carbon dioxide can trap heat in the atmosphere and allow it to retain more water vapour.

“There is evidence that some extremes have changed as a result of anthropogenic influences, including increases in atmospheric concentrations of greenhouse gases,” said the 29-page summary for policy-makers that was approved by governments at a negotiating session in Uganda. “It is likely that anthropogenic (human-caused) influences have led to warming of extreme daily minimum and maximum temperatures on the global scale. There is medium confidence that anthropogenic influences have contributed to intensification of extreme precipitation on the global scale.”

The report also said it was likely that human activity is linked to higher water levels in coastal areas, but recognized uncertainties regarding tropical storm activity and the absence of scientific research to project the “magnitude” of potential events in the future and their links to climate change.

During a media conference call, Canadian scientists noted that a country like Canada could face higher economic losses than a developing country due to the anticipated rise in extreme weather events since it has more infrastructure. But the report also said that fatality rates and the proportional losses in developing countries, based on the size of their economies, could be relatively greater.

The Canadian scientists listed numerous examples of climate-related events in recent years that have cost the country’s economy billions of dollars in losses, such as the 1998 ice storm in Eastern Canada, the spread of the mountain pine beetle in British Columbia’s forests and a 2005 extreme rain event that caused $500 million in damage in the Toronto region.

The report said that “it is virtually certain that increases in the frequency and magnitude of warm daily temperature extremes and decreases in cold extremes will occur in the 21st century on the global scale.”

It also said it was likely — meaning a probability greater than 66 per cent — that heavy precipitation events would also increase over many parts of the planet, particularly in high latitudes and tropical regions, as well as in winter for northern mid-latitudes.

“Based on a range of emissions scenarios . . . a 1-in-20 year annual maximum daily precipitation amount is likely to become a one-in-five to one-in-15 event by the end of the 21st century in many regions, and in most regions the higher emissions scenarios lead to a stronger projected decrease in return period.”

Francis Zwiers, a former Environment Canada scientist who now directs a climate change impacts consortium at the University of Victoria, said the negotiations between countries in Uganda over the final summary document lasted four days, including a line-by-line review of every statement to allow the governments to agree on the best way to communicate about the existing scientific literature.

“I didn’t get very much sleep last night,” Zwiers said. “It’s . . . a negotiation that turns into a very positive result by engaging governments in the process of determining how to communicate this kind of information. The process allows them to take ownership of the report and have confidence in it, therefore it also allows them to produce policy on the basis of the report.”

The IPCC process has been challenged by climate skeptics ever since its first major assessment report in 1990, but Environment Canada scientists say that its range of projections have been consistent with actual observed climate and weather impacts. A recent 2009 controversy over stolen emails from climate scientists also galvanized skeptics with renewed accusations of an international conspiracy involving the evidence, but a series of independent inquiries have all rejected the accusations and cleared the researchers, whose emails were hacked, of any wrongdoing.

At a separate news conference, Green Party leader Elizabeth May criticized the federal government for reducing the number of scientists working at Environment Canada on plans to help the country to adapt to climate change, saying the government’s overall plan is inadequate and puts the economy at risk.

The international community will meet later this month in South Africa for the next round of negotiations on climate change.