Can Climate Science Predict Extreme Weather?: Scientific American
Wednesday, November 2, 2011 | 5
Halloween Weekend Snow Paints a Ghostly Picture in the U.S. Northeast Image: NASA Goddard Photo and Video
DENVER, Colo. - 2011 may well be remembered as the year of extreme weather in the United States, with drought in Texas, floods along the Mississippi River, a freak October snowstorm on the East Coast. Tornadoes alone would make the year memorable, with some 1,270 twisters causing 544 deaths and $25 billion in damages.
The outbreak is reshaping climate science, as researchers hone their abilities to predict severe weather and link the record-shattering destruction to humanity's increasing emissions.
The goal: To provide better information to policymakers and local officials who must plan for and adapt to changes. "It's a rapidly developing field," said Peter Stott, head of climate monitoring and attribution at the, Britain's national weather service.
Stott led one of the first studies attributing a single extreme weather event to climate change: The 2003 European heat wave, which killed 40,000 and was the hottest summer on record since 1540. The study concluded that human influence more than doubled the event's likelihood.
Last week, a study published in the journal Proceedings of the National Academy of Sciences concluded there was an 80 percent chance that the killer Russian heat wave of 2010 would not have happened without the added push of global warming.
Now, Stott and other researchers are melding weather forecasting skills with pioneering computer models to attribute - or link - individual weather events to climate change. Understanding how climate change influences the weather is increasingly seen as key to predicting natural disasters, Stott said, and the new studies should help policymakers anticipate the conditions and trends associated with weather extremes. "There's this very strong connection between attribution and prediction," noted Stott, who spoke on these issues before colleagues last week at the World Climate Research Programme conference here in Denver.
The efforts are steering the next steps of the Intergovernmental Panel on Climate Change, the international body of scientists that reviews and assesses the vast pool of climate research for policymakers worldwide. The next IPCC assessment is due in 2013 - the fifth from the panel since 1990. For the first time it will include "predictions" - near-term and long-term climate forecasts based on actual conditions - instead of "projections" that simulate hypothetical scenarios and carbon emission rates.
The distinction is an advance for climate science and the IPCC, said, who runs the Climate Analysis Section at the National Center for Atmospheric Research in Boulder, Colo.
Previous IPCC assessments have cited projections that are not grounded in current or historical conditions. Instead, policymakers are given "what-if" scenarios, such as how the future climate might react to different greenhouse-gas emissions over the coming decades. The results show changes between two assumed moments in time, Trenberth said, but they lack a starting point tied to observed data and, ultimately, are informed guesses of future carbon dioxide levels and their consequences.
Climate model predictions, on the other hand, are like weather forecasts. They start from a current or historical moment to analyze climate changes. By grabbing more measurements and using new techniques, advanced climate models reveal more clearly how the atmosphere responds to increased water moisture, warmer sea temperatures and melting sea ice, all impacts of increased carbon. Compared to projections, predictions allow scientists to offer near-term climate forecasts, which should help policymakers prepare for potential adaptations in the next few decades.
The change from projections to predictions is made possible in part by a new generation of more powerful computer models. The last IPCC assessment report, published in 2007, made minor mention of feedbacks - environmental processes and interactions that can intensify extreme climate events, said Sonia Seneviratne, a professor at the Swiss Federal Institute of Technology in Zurich, who specializes on the topic. New data have since opened up scientists' understanding of their importance.
Seneviratne is the lead author of an IPCC special report to be released later this month that focuses on climate change and extreme events. Research in this area has been "substantial and justifies a separate assessment," she said, adding that it's particularly a topic of interest for officials concerned with disaster preparedness and risk reduction.
The special report concludes that scientists are "virtually certain" the world will see more extremes in heat and that some places in the world will become "increasingly marginal as places to live," according to the Associated Press, which obtained a draft. The draft also concludes there is at least a two-in-three chance that man-made global warming has already worsened weather extremes, according to the AP. The document is subject to change and needs approval from diplomats meeting in Uganda mid-month.
There are some caveats to these new climate predictions, however.
Writing in a scientific journal last year, Trenberth warned colleagues that the promise of more accurate representations of climate change will introduce new scientific uncertainties inherent to modeling more complex and realistic situations. Just as weather forecasting evokes its share of skepticism and doubt, climate predictions will likely represent a new communications challenge - and fodder for controversy and criticism - for climate scientists, said Trenberth.
"It's about communication," agreed Stott, who is the lead author of the 2013 IPCC report's section on attribution and detection of climate change. "An understanding of where extreme weather fits into the longer-term picture of a changing climate helps people put this into context, and [whether] this is something that is going to become more common in the future and therefore we need to give more attention and be more prepared for these things."
Stott and other scientists at a handful of modeling centers worldwide are focusing on the relation between climate change and extreme weather through a new initiative, Attribution of Climate-related Events. Stott says the project will move scientists further along toward forecasting extreme events and mapping the interactions with climate change.
"The goal is to be able to develop the tools and the skills, so we know when we can be confident and provide trustworthy assessments, and to do this in a timely fashion - in the immediate aftermath of a particular situation," Stott said. "At the moment, we're not really geared up for that. It's very much research mode.> We've hardly scratched the surface."
This article originally appeared at The Daily Climate, the climate change news source published by Environmental Health Sciences, a nonprofit media company.