Expert Commentary

Rising temperatures, extreme weather and climate change knowledge: Research roundup

Roundup of recent studies on global warming, rising average temperatures, and public and private opinions on climate change.

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Reporting on the issue of climate change has sometimes been characterized by “false balance” — the tendency to cover scientific findings as if there were always two “sides” that each legitimately differed over facts. But over the past decade, the scientific consensus has grown even clearer: Global warming is happening and humans are the cause.

One area of scientific debate that remains open is the speed, character and magnitude of climate change over Earth’s diverse regions. Quantifying the role of human-induced global warmiong in catalyzing extreme events such as powerful storms, droughts, heat waves or flooding is an evolving field of inquiry. New scientific papers are published nearly every month on the topic. And research reports are focusing on how scientific predictions and models are lining up with real-world patterns.

Many observers say that ignoring the scientific literature increasingly comes with greater perils for policy-makers, citizens and the media. For example, in the wake of Hurricane Sandy, it is worth noting that a 2012 study published in Nature Climate Change, titled “Physically Based Assessment of Hurricane Surge Threat Under Climate Change,” found that the “change of storm climatology will probably increase the surge risk” for New York City and “may cause the present NYC 100-year surge flooding to occur every 3–20 years.” (See below for more on this study.)

The following includes examples of scientific research at the edge of understanding; it also features useful background studies and reports that can anchor coverage and communication in baseline knowledge and combat misinformation:


“Physically Based Assessment of Hurricane Surge Threat under Climate Change”
Lin, Ning; Emanuel, Kerry; Oppenheimer, Michael; Vanmarcke, Erik. Nature Climate Change 2, 462–467 (2012) doi:10.1038/nclimate1389

Abstract: “Storm surges are responsible for much of the damage and loss of life associated with landfalling hurricanes. Understanding how global warming will affect hurricane surges thus holds great interest. As general circulation models (GCMs) cannot simulate hurricane surges directly, we couple a GCM-driven hurricane model with hydrodynamic models to simulate large numbers of synthetic surge events under projected climates and assess surge threat, as an example, for New York City (NYC). Struck by many intense hurricanes in recorded history and prehistory, NYC is highly vulnerable to storm surges. We show that the change of storm climatology will probably increase the surge risk for NYC; results based on two GCMs show the distribution of surge levels shifting to higher values by a magnitude comparable to the projected sea-level rise (SLR). The combined effects of storm climatology change and a 1 m SLR may cause the present NYC 100-yr surge flooding to occur every 3–20 yr and the present 500-yr flooding to occur every 25–240 yr by the end of the century.”

“Perception of Climate Change”
Hansen, James; Sato, Makiko; Ruedy, Reto. Proceedings of the National Academy of Sciences, March 2012.

Abstract: “‘Climate dice,’ describing the chance of unusually warm or cool seasons, have become more and more ‘loaded’ in the past 30 [years], coincident with rapid global warming. The distribution of seasonal mean temperature anomalies has shifted toward higher temperatures and the range of anomalies has increased. An important change is the emergence of a category of summertime extremely hot outliers, more than three standard deviations warmer than the climatology of the 1951-1980 base period. This hot extreme, which covered much less than 1% of Earth’s surface during the base period, now typically covers about 10% of the land area. It follows that we can state, with a high degree of confidence, that extreme anomalies such as those in Texas and Oklahoma in 2011 and Moscow in 2010 were a consequence of global warming because their likelihood in the absence of global warming was exceedingly small.”

“Explaining Extreme Events of 2011 from a Climate Perspective”
Peterson, Thomas C.; Stottand, Peter A.; Herring, Stephanie, et al. Bulletin of the American Meteorological Society, July 2012, 1041-1067. doi:10.1175/BAMS-D-11-00021.1

Findings: “Extreme heat events were roughly 20 times more likely in 2008 than in other La Niña years in the 1960s and indications of an increase in frequency of low seasonal precipitation totals. With 2008 serving as our proxy for 2011, this suggests that conditions leading to droughts such as the one that occurred in Texas in 2011 are, at least in the case of temperature, distinctly more probable than they were 40-50 years ago…. Quantifying the absolute probability of such extreme conditions is much more difficult, since the models we use are subject to bias, particularly affecting tails of distri­butions, and data records are too short to quantify absolute probabilities empirically. Hence, while we can provide evidence that the risk of hot and dry conditions has increased, we cannot say that the 2011 Texas drought and heat wave was ‘extremely unlikely’ (in any absolute sense) to have occurred before this recent warming.”

“Managing the Risks of Extreme Events and Disasters to Advance Climate Change Adaptation”
Field, C.B., et al. Special Report of Working Groups I and II of the United Nations’ Intergovernmental Panel on Climate Change, Cambridge University Press, 2012.

Findings: Global nighttime and daytime temperature extremes are “very likely” to increase, with an “overall decrease in the number of cold days and nights, and an overall increase in the number of warm days and nights.” This is “likely” to be the result of human activity, the report states. Climate change models predict a “substantial” increase in temperature extremes by the end of the 21st century. “It is very likely that the length, frequency and/or intensity of warm spells, or heat waves, will increase over most land areas…. A 1-in-20 year hottest day is likely to become a 1-in-2 year event by the end of the 21st century in most regions.” The frequency of heavy precipitation events is “likely” to increase over many areas of the globe, in particular high latitudes and tropical regions. In addition, “heavy rainfalls associated with tropical cyclones are likely to increase with continued warming.”

“Drought in the United States: Causes and Issues for Congress”
Folger, Peter; Cody, Betsy A.; Carter, Nicole. Congressional Research Service, June 2012.

Findings: “Since 2000, extreme drought or drier conditions have affected approximately 6% of the nation on average. During August 2002, extreme drought extended over 19% of the country. Since 2000, exceptional drought conditions have affected approximately 1% of the nation on average.” The severity of drought conditions vary widely: “Since 2000, the total U.S. land area affected by drought of at least moderate intensity has varied from as little as 7% (August 3, 2010) to as much as 46% (September 10, 2002).” Both short-term and long-term droughts directly impact agricultural production and water levels in groundwater, streams, rivers and reservoirs…. “Some studies suggest that the American West may be transitioning to a more arid climate, possibly resulting from the buildup of greenhouse gases in the atmosphere, raising concerns that the region may become more prone to extreme drought than it was in the 20th century.”

United Nations IPCC Fourth Assessment Report on Climate Change
From “Climate Change 2007: A Synthesis Report,” U.N. Intergovernmental Panel on Climate Change.

Findings: The report begins by stating that “warming of the climate system is unequivocal,” and it presents the following data relating to temperature rise: “Eleven of the last twelve years (1995-2006) rank among the twelve warmest years in the instrumental record of global surface temperature (since 1850). The 100-year linear trend (1906-2005) of 0.74 [0.56 to 0.92]°C is larger than the corresponding trend of 0.6 [0.4 to 0.8]°C (1901-2000) given in the [IPCC’S Third Assessment Report of 2001]. The linear warming trend over the 50 years from 1956 to 2005 (0.13 [0.10 to 0.16]°C per decade) is nearly twice that for the 100 years from 1906 to 2005″…. “Annual emissions [of CO2] have grown between 1970 and 2004 by about 80%, from 21 to 38 gigatonnes, and represented 77% of total anthropogenic GHG emissions in 2004.” Additionally, “most of the observed increase in global average temperatures since the mid-20th century is very likely due to the observed increase in anthropogenic GHG [greenhouse gas] concentrations.”

“Extreme Weather, Climate and Preparedness in the American Mind”
Leiserowitz, A., et al. Maibach, E., Roser-Renouf, C., & Hmielowski, J. D.  Yale University and George Mason University, Yale Project on Climate Change Communication, 2012.

Findings: In 2011, “Americans experienced a record-breaking 14 weather and climate disasters that each caused $1 billion or more in damages, in total costing approximately $53 billion…. In the period of January through March 2012, Americans also experienced record warm temperatures, with temperatures across the contiguous United States 6.0 degrees F above the long-term average. In March alone, 15,292 warm temperature records were broken across the United States”…. Slightly more than half of Americans (52%) say that unusual weather events have happened locally; some 62% say this is true nationally. “Overall, 82% of Americans report that they personally experienced one or more types of extreme weather or natural disaster in the past year. These include extreme high winds (60%), extreme rainstorms (49%), extreme heat waves (42%), drought (34%), extreme cold temperatures (29%), extreme snowstorms (26%), tornadoes (21%), floods (19%), hurricanes (16%) or wildfires (15%)”…. “About half of all Americans say that heat waves (53%), droughts (46%) and very heavy rain storms (43%) have become more common in their local area over the past few decades”…. “A large majority of Americans believe that global warming made several high-profile extreme weather events worse, including the unusually warm winter of December 2011 and January 2012 (72%), record high summer temperatures in the U.S. in 2011 (70%), the drought in Texas and Oklahoma in 2011 (69%)….”

“The Structure of Scientific Opinion on Climate Change”
Farnsworth, Stephen J.; Lichter, S. Robert. International Journal of Public Opinion Research, October 2011. doi: 10.1093/ijpor/edr033

Findings:  Of the 489 scientists surveyed, 97% agreed that global temperatures have risen over the past century. Moreover, 84% agreed that “human-induced greenhouse warming” is now occurring.” Only 5% disagreed with the idea that human activity is a significant cause of global warming. “There was greater debate over the likelihood of substantial warming in the near future, with 56% seeing at least a 50-50 chance that temperatures will rise” 2 degrees Celsius over the next 50 to 100 years. “When [survey participants were] asked to rate the effects on a ten-point scale from trivial (1) to catastrophic (10), the mean response was 6.6, with 41% seeing great danger (ratings of 8-10), 44% moderate danger (4-7), and 13% little danger.”

“Expert Credibility in Climate Change”
Anderegg, William R.L.; Schneider, Stephen H., et al. Proceedings of the National Academy of Sciences, April 2010, Vol. 107, No. 27, 12107-12109. doi: 10.1073/pnas.1003187107

Findings: About 97% of the group with the most expertise — the 908 climate scientists with 20 or more papers published — are convinced by the evidence of human-induced climate change. Those who are unconvinced by the evidence make up “only 2% of the top 50 climate researchers as ranked by expertise (number of climate publications), 3% of researchers of the top 100, and 2.5% of the top 200.” Researchers with fewer than 20 climate publications comprise 80% the group that is unconvinced, as opposed to less than 10% of the group that is convinced by the evidence: “This indicates that the bulk of [unconvinced] researchers on the most prominent multi-signatory statements about climate change have not published extensively in the peer-reviewed climate literature.”

Tags: global warming, greenhouse gases, research roundup

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