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Climate Change to Cause More Extreme Weather

Map indicating the extent of the Artic sea ice in the summer that reached a record low in September 2012
The extent of the Arctic sea ice in the summer reached a record low in September 2012; it rebounded somewhat last year, but still reflects a dramatic decrease since satellite records began to be generated in the 1970s. National Snow and Ice Data Center

The earth’s changing climate will impact the frequency and strength of extreme weather events in the coming years, according to a new state-of-the-field report.

April 1, 2014—“Climate change is one of the defining issues of our time.” So begins the state-of-the-field report Climate Change: Evidence and Causes, produced as the result of a joint effort by the United Kingdom’s Royal Society and the U.S. National Academy of Sciences. Climate change impacts much more than just sea level rise, the report reveals; for example, the frequency of floods and the strength of hurricanes are expected to continue to grow as a result of these changes.

“The evidence now shows clearly that climate change is real, and that much of what has happened and will happen is due to carbon dioxide emitted as a result of human activities,” said Eric Wolff, Ph.D., a research professor who studies paleoclimatology at the University of Cambridge and the Royal Society’s lead author for the report. Wolff wrote in response to written questions posed by Civil Engineering online. “We should now be having a serious discussion, based on this information, about what, if anything, individuals, governments, and the world as a whole should do,” he said.

“Two of the world's leading independent (nongovernmental) scientific bodies are lending their voices to the public discussion about climate change at this critical time,” said Inez Fung, Ph.D., a professor of atmospheric science at the University of California Berkeley and the lead author for the National Academy of Sciences, who wrote in response to written questions posed by Civil Engineering online. “[The report] reiterates the evidence for climate change, defines current scientific understanding, identifies areas of wide consensus, and makes clear where understanding is developing.”

Observations have established that human activity—in particular, the burning of fossil fuels since the Industrial Revolution began in the 19th century—has increased atmospheric carbon dioxide concentrations by about 40 percent, according to the report. Half of that increase has occurred since 1970. As a result, the global average surface temperature has increased about 0.8 °C (1.4 °F). Combined, these two changes have resulted in a warming of the ocean as heat is transferred from the atmosphere to the water, as well as a strong decline in the amount of summer sea ice in the Arctic and a concurrent rise in sea level. These greenhouse gas-induced developments are now occurring 10 times faster than the global warming that occurred at the end of the last ice age, 18,000 years ago , according to the report.

As the earth’s lower atmosphere becomes warmer and moister as a result of greenhouse gas emissions, the report explains, the potential increases that such severe weather events as heat waves and heavy precipitation will be fueled by more energy. This increases the chance of both flooding and drought in certain areas. At the same time, “attributing extreme weather events to climate change is challenging because these events are by definition rare and hard to evaluate reliably, and are affected by patterns of natural climate variability,” the report notes.

Ongoing research shows “considerable uncertainty” about how hurricanes are affected by climate change, according to the report. However, “basic physical understanding and model results suggest that the strongest hurricanes (when they occur) are likely to become more intense and possibly larger in a warmer, moister atmosphere over the oceans.”

Tornado formation is an area in which even more additional research is needed. While some conditions that favor the formation of tornado-spawning thunderstorms are expected to increase, a greater understanding of the factors that affect tornado formation, such as vertical and horizontal variations of winds, is required, according to the report.

“The science about climate change is robust, and is built of a long history of research that has been tested and validated,” Fung said. “Of course there will always be uncertainties in our projections, as the climate system is changing as we are observing it and learning about it.” Additionally, predicting the future emissions of carbon dioxide and other greenhouse gases is difficult to do, says Fung. “However, the uncertainties do not change the bottom-line: that climate is warming, and will continue to warm, as a result of human activities,” she said.

Faced with this information, policy makers and individuals must decide how they will respond to the information. “People can choose from a range of options: doing nothing, reducing carbon emissions, adapting to expected changes in climate and sea level, or geoengineering to reverse the changes,” Wolff said.

“This requires a debate about what options will be effective and affordable—a debate that involves politicians, economists, and certainly civil engineers,” he said. “However, pretending that there isn’t a problem is no longer an option.”

There is no immediate fix possible for the emission of greenhouse gases, the report warns. Even if all emissions stopped immediately, warming would continue for some time. “Once the carbon dioxide is in the atmosphere, it takes a very long time for natural systems to remove it, and even longer for the heat to disappear from the system,” Wolff said. “Thus without intervention, the emissions of the next 50 years will alter the climate experienced by generations in the year 3000 and beyond.”

While the trends of climate change on a global scale have been firmly established and are understood, according to the report, there is still much to be learned. Wolff and Fung said that a multipronged approach to future research related to climate change will be necessary. “We are not yet very good at providing guidance about what will happen at a regional scale, which is what people need to know if they are to adapt to the changes,” Wolff noted.

Fung agreed, noting that additional study into such natural mechanisms of climate variability as El Niño and La Niña events are needed, as these may change as the global climate warms.

Research into forecasting extreme events—heat waves, floods, and hurricanes—also needs to be further developed, according to Wolff. “Because these are, by their very nature, quite rare, our ability to forecast how their occurrence will change is still at an early stage,” he said.

Fung calls for the study of cloud behavior and aerosols in particular, as well as the study of the ocean as a heat sink. “The oceans are grossly underobserved and understudied,” she said. “The oceans absorb 90 percent of the extra heat resulting from additional greenhouse gases—a small change [or] wiggle in the ocean’s heat uptake would give us a very warm or not-so-warm atmosphere.” Ultimately, she said, the speed with which the oceans can remove the heat will determine how fast the atmosphere warms.

While knowing how and why climate change is occurring is crucial, so is planning responses to protect the future and existing built environment. “This goes outside the realm of climate scientists like myself and into that of civil engineers, among others,” Wolff said. “We need a lot more research to find effective ways to reduce emissions, and to protect people from the climate changes that will occur.”

The research that went into creating the report was funded by the Raymond and Beverly Sackler U.S.-U.K. Scientific Forum.



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