Heidi Cullen

Attribution of the record high Central England temperature of 2014 to anthropogenic influences

In 2014, Central England experienced its warmest year in a record extending back to 1659. Using both state-of-the-art climate models and empirical techniques, our analysis shows a substantial and significant increase in the likelihood of record-breaking warm years, such as 2014, due to human influences on climate. With 90% confidence we find that anthropogenic forcings on the climate have increased the chances of record warm years in Central England by at least 13-fold. This study points to a large influence of human activities on extreme warm years despite the small region of study and the variable climate of Central England. Our analysis shows that climate change is clearly visible on the local-scale in this case.

Perspectives on the causes of exceptionally low 2015 snowpack in the western United States

Augmenting previous papers about the exceptional 2011-15 California drought, we offer new perspectives on the ‘snow drought’ that extended into Oregon in 2014 and Washington in 2015. Over 80% of measurement sites west of 115°W experienced record low snowpack in 2015, and we estimate a return period of 400-1000 years for Californias snowpack under the questionable assumption of stationarity. Hydrologic modeling supports the conclusion that 2015 was the most severe on record by a wide margin. Using a crowd-sourced superensemble of regional climate model simulations, we show that both human influence and sea surface temperature anomalies contributed strongly to the risk of snow drought in Oregon and Washington: the contribution of SST anomalies was about twice that of human influence. By contrast, SSTs and humans appear to have played a smaller role in creating Californias snow drought. In all three states, the anthropogenic effect on temperature exacerbated the snow drought.

Climate Change Education Through TV Weathercasts: Results of a Field Experiment

TV weathercasters are well positioned to educate Americans about the relationships among weather, climate, and climate change. Through a collaboration involving TV meteorologists, climatologists, and social scientists, we produced a series of educational segments to assess the impact of such an education. The educational segments were branded “Climate Matters” and aired over one year during the nightly weather segment on WLTX TV (Columbia, South Carolina). Prior to airing, we conducted a telephone survey of adult TV news viewers in the Columbia media market using random digit dialing (n = 1,068) to establish baseline measures; respondent screening was used to sample approximately equal numbers of WLTX viewers and viewers of competing stations. Approximately one year later, we resurveyed all available members of the baseline cohort (n = 502) and an independent sample of randomly selected residents (n = 910). The longitudinal data showed that—after controlling for baseline measures, demographics, and politi...

Factors Other Than Climate Change, Main Drivers of 2014/15 Water Shortage in Southeast Brazil

Introduction. The southeast region of Brazil (SEB, defined as the area between 15°–25°S and 40°–48°W; Fig. 9.1a) experienced remarkably dry conditions from January 2014 to February 2015, comprising the 14-month period that includes two rainy seasons investigated here. This region includes Sao Paulo, Brazil ś most populated city, which suffered impacts due to water shortages, and the watersheds and reservoirs feeding the city’s water supply system. The wet season occurs during austral summer and the dry season during austral winter. The South Atlantic convergence zone (SACZ) is the main mechanism responsible for the region’s austral summer rainfall. During summer 2014, there was a complete absence of SACZ episodes (Coelho et al. 2015). Previous major droughts occurred in the region in 1953/54, 1962/63, 1970/71, and 2001. While droughts have very complex criteria, these were all characterized by large rainfall deficits while the effect of the SACZ needs further investigation. The 1953/54 rainfall deficit prompted construction of the largest water supply system (Cantareira) used for Sao Paulo (Porto et al. 2014). The 2014/15 drought had major impacts in Sao Paulo due partly to a four-fold population increase since 1960 (Fig. 9.1b). Although new water supply systems were constructed after Cantareira, it is still by far the largest in terms of capacity and number of people supplied (until early 2015) and hence is used as an indicator of the impacts of the SEB drought on water supply. In January 2015, Cantareira, which used to supply 8.8 million people in Sao Paulo, sank to a water volume of just 5% of capacity (Fig. 9.1c), and currently supplies just 5.3 million people. Other systems (Guarapiranga and Alto Tiete) started to supply the excess population, those previously supplied by Cantareira, after the water crisis was established. In this analysis, we investigate potential changes in the hydrometeorological hazard, defined by accumulated precipitation and the difference between precipitation and evaporation (P − E) in the SEB region. The true impact, however, is due to a combination of a physical event with vulnerability and exposure, in this case on millions of people in the affected area (Field et al. 2012). The current drought reflects increasing trends in exposure. Sao Paulo’s population grew by 20% in the past 20 years. Water use has increased at an even faster rate over the same period (Fig. 9.1b). Vulnerability of water supply systems remains high. Recognizing that water governance is key to reducing vulnerability, Southeast Brazil experienced profound water shortages in 2014/15. Anthropogenic climate change is not found to be a major influence on the hazard, whereas increasing population and water consumption increased vulnerability.

Comparison of methods: Attributing the 2014 record European temperatures to human influences

The year 2014 broke the record for the warmest yearly average temperature in Europe. Attributing how much this was due to anthropogenic climate change and how much it was due to natural variability is a challenging question but one that is important to address. In this study, we compare four event attribution methods. We look at the risk ratio (RR) associated with anthropogenic climate change for this event, over the whole European region, as well as its spatial distribution. Each method shows a very strong anthropogenic influence on the event over Europe. However, the magnitude of the RR strongly depends on the definition of the event and the method used. Across Europe, attribution over larger regions tended to give greater RR values. This highlights a major source of sensitivity in attribution statements and the need to define the event to analyze on a case-by-case basis.

Real-time extreme weather event attribution with forecast seasonal SSTs

Within the last decade, extreme weather event attribution has emerged as a new field of science and garnered increasing attention from the wider scientific community and the public. Numerous methods have been put forward to determine the contribution of anthropogenic climate change to individual extreme weather events. So far nearly all such analyses were done months after an event has happened. Here we present a new method which can assess the fraction of attributable risk of a severe weather event due to an external driver in real-time. The method builds on a large ensemble of atmosphere-only general circulation model simulations forced by seasonal forecast sea surface temperatures (SSTs). Taking the England 2013/14 winter floods as an example, we demonstrate that the change in risk for heavy rainfall during the England floods due to anthropogenic climate change, is of similar magnitude using either observed or seasonal forecast SSTs. Testing the dynamic response of the model to the anomalous ocean state for January 2014, we find that observed SSTs are required to establish a discernible link between a particular SST pattern and an atmospheric response such as a shift in the jetstream in the model. For extreme events occurring under strongly anomalous SST patterns associated with known low-frequency climate modes, however, forecast SSTs can provide sufficient guidance to determine the dynamic contribution to the event.

If They Like You, They Learn from You: How a Brief Weathercaster-Delivered Climate Education Segment Is Moderated by Viewer Evaluations of the Weathercaster

AbstractLocal television (TV) weathercasters are a potentially promising source of climate education, in that weather is the primary reason viewers watch local TV news, large segments of the public trust TV weathercasters as a source of information about global warming, and extreme weather events are increasingly common (Leiserowitz et al.; U.S. Global Change Research Program). In an online experiment conducted in two South Carolina cities (Greenville, n = 394; Columbia, n = 352) during and immediately after a summer heat wave, the effects on global warming risk perceptions were examined following exposure to a TV weathercast in which a weathercaster explained the heat wave as a local manifestation of global warming versus exposure to a 72-h forecast of extreme heat. No main effect of the global warming video on learning was found. However, a significant interaction effect was found: subjects who evaluated the TV weathercaster more positively were positively influenced by the global warming video, and vie...

Climate change increases the probability of heavy rains in Northern England/Southern Scotland like those of storm Desmond—a real-time event attribution revisited

On 4–6 December 2015, storm Desmond caused very heavy rainfall in Northern England and Southern Scotland which led to widespread flooding. A week after the event we provided an initial assessment of the influence of anthropogenic climate change on the likelihood of one-day precipitation events averaged over an area encompassing Northern England and Southern Scotland using data and methods available immediately after the event occurred. The analysis was based on three independent methods of extreme event attribution: historical observed trends, coupled climate model simulations and a large ensemble of regional model simulations. All three methods agreed that the effect of climate change was positive, making precipitation events like this about 40% more likely, with a provisional 2.5%–97.5% confidence interval of 5%–80%. Here we revisit the assessment using more station data, an additional monthly event definition, a second global climate model and regional model simulations of winter 2015/16. The overall result of the analysis is similar to the real-time analysis with a best estimate of a 59% increase in event frequency, but a larger confidence interval that does include no change. It is important to highlight that the observational data in the additional monthly analysis does not only represent the rainfall associated with storm Desmond but also that of storms Eve and Frank occurring towards the end of the month.

Climate Matters: A Comprehensive Educational Resource Program for Broadcast Meteorologists

AbstractLocal TV meteorologists are optimally positioned to educate the public about the local implications of global climate change: They have high public trust as a source of climate science information, local TV is the #1 source of weather information in America, and most weathercasters have relevant scientific training and excellent communication skills. Surveys show that most TV meteorologists would like to report on climate change, but lack of time, lack of broadcast-quality graphics, and lack of access to appropriate experts are barriers that inhibit such coverage.With funding from the National Science Foundation and philanthropic foundations, we developed Climate Matters as an educational resources program to help interested local TV meteorologists educate their viewers about the local impacts of global climate change. Currently, the program provides more than 160 participating weathercasters nationwide with weekly localized broadcast-ready graphics and script ideas, short videos, and opportunitie...

Most Americans Want to Learn More about Climate Change

AbstractAs American Meteorological Society (AMS) members who study Americans’ understanding of climate change and who are engaged in programs to educate Americans about climate change, we want our AMS colleagues to realize their key role in public education. In this article we make the case that 1) AMS members are well positioned to play important leadership roles in educational outreach on climate change, 2) the public wants to learn more about climate change, 3) there is a need for more effective public engagement efforts, and 4) we have successful outreach and educational models that we can start using today.