Wednesday, October 9, 2013

Science team identifies tipping point in climate change: 2047

If you’ve been wondering when global warming will show up on your doorstep, Camilo Mora has an answer for you.

Dr. Mora, an associate professor at the University of Hawaii at Manoa, leads a team that has tackled the challenging question of when the climate will shift entirely beyond what could be considered natural.

Their result: The turning point arrives in 2047 as a worldwide average if fossil fuel consumption continues unabated; as late as 2069 if carbon emissions are curbed. Broken down by city the numbers are a bit more revealing. In Montreal, for example, the new normal will arrive a year sooner. For Toronto it’s 2049 and for Vancouver not until 2056. But the real spotlight of Dr. Mora’s study is what happens in the tropics, where profound changes could be entrenched within little more than a decade.

“By looking at timing we’ve come up with an entirely new set of implications on climate change,” Dr. Mora said.

Dr. Mora is not a climate scientist but an expert in dealing with huge amounts of data to pull out hidden information – a skill he honed over six years at Dalhousie University in Halifax, working with the likes of the late Ransom Myers. It was Dr. Myers’ number crunching skills that turned the plight of the world’s fish stock into headline news in 2003.

Ten years later, Dr. Mora is following in his mentor’s footsteps with a study that seems certain to grab attention.

“I want to let the numbers do the talking,” he said.

Climate scientists have long expressed high confidence that the planet is warming as a result of the heat trapping action of greenhouse gasses. The latest assessment from the UN’s Intergovernmental Panel on Climate Change puts that confidence at 95 per cent. Where scientists have been less confident is on the timing of the change. Different models show the global temperatures rising at different rates and the hundreds of scientists behind the IPCC assessment can’t say which model will turn out to be the best predictor of what actually happens over the course of this century.

Starting with an idea that came out of a course he was teaching last spring, Dr. Mora decided to address the gap with some nuts and bolts analysis.

His team combined data from all 39 currently available global climate models and went back nearly 150 years to see what the range of normal climate variability was over that time period.

“We looked at the minimum and maximum values that occurred in that 150-year window and that’s how we set our bounds of recent historical variability,” said Ryan Longman, a doctoral student who worked on the analysis, published Wednesday in the journal Nature.

Then the team tracked the combined predictions of the models forward at different points on the globe to watch how soon the predictions drifted completely out of their normal range. Once the coldest year at any given location was consistently warmer than the hottest year prior to 2005 the team considered the climate to have changed completely. The dates when this happens are different for different locations and they depend on the emissions scenario.

“I think this analysis is valuable and sheds new light on impacts,” said Jane Lubchenco, the former administrator of the U.S. National Oceanic and Atmospheric Administration in an e-mail.

Dr. Lubchenco, who was not involved in the study, stepped down earlier this year to return to academic research at Oregon State University. She said “no one has gone to the immense effort they did to really look critically at the data from so many places and over the entire period of time for which records are reliable.”

The key result of the finding, Dr. Mora said, is that tropical locations will leave the range of normal climate variability much sooner because they typically experience a narrow range of temperature and precipitation levels. That’s a worry Dr. Mora said, because species there are not well adapted to living outside those ranges. Similarly, cities and nations found along Earth’s equator are among the poorest and least equipped to deal with the health and environmental burden of climate change.

“Today when people talk about climate change the images that come to mind are melting ice and polar bears,” Dr. Mora said. “People might infer from this that the tropics will be less affected.”

Instead, he said, the new analysis showed that species and ecosystems in the tropics would soon be experiencing “unprecedented climate stress.” The trend also goes for marine ecosystems where the study shows that ocean acidification has already departed from the normal range with a disastrous outlook for coral reefs.

Ken Caldeira, an expert in global ecology at the Carnegie Institution in Stanford added that while the timing and global breakdown from Dr. Mora’s analysis represent solid science, what matters more is the response.

“Whether an ecosystem goes a decade or two earlier or later doesn’t really matter that much,” Dr. Caldeira said. “We must stop using the atmosphere as a waste dump for our greenhouse-gas pollution. Everything else is nuance.” More