School of Geography, Earth and Atmospheric Sciences - Research Publications
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ItemAustralia's Unprecedented Future Temperature Extremes Under Paris Limits to Warming(AMER GEOPHYSICAL UNION, 2017-10-16)Abstract Record‐breaking temperatures can detrimentally impact ecosystems, infrastructure, and human health. Previous studies show that climate change has influenced some observed extremes, which are expected to become more frequent under enhanced future warming. Understanding the magnitude, as a well as frequency, of such future extremes is critical for limiting detrimental impacts. We focus on temperature changes in Australian regions, including over a major coral reef‐building area, and assess the potential magnitude of future extreme temperatures under Paris Agreement global warming targets (1.5°C and 2°C). Under these limits to global mean warming, we determine a set of projected high‐magnitude unprecedented Australian temperature extremes. These include extremes unexpected based on observational temperatures, including current record‐breaking events. For example, while the difference in global‐average warming during the hottest Australian summer and the 2°C Paris target is 1.1°C, extremes of 2.4°C above the observed summer record are simulated. This example represents a more than doubling of the magnitude of extremes, compared with global mean change, and such temperatures are unexpected based on the observed record alone. Projected extremes do not necessarily scale linearly with mean global warming, and this effect demonstrates the significant potential benefits of limiting warming to 1.5°C, compared to 2°C or warmer.
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ItemTrajectories toward the 1.5 degrees C Paris target: Modulation by the Interdecadal Pacific Oscillation(Wiley, 2017-05-16)Global temperature is rapidly approaching the 1.5°C Paris target. In the absence of external cooling influences, such as volcanic eruptions, temperature projections are centered on a breaching of the 1.5°C target, relative to 1850–1900, before 2029. The phase of the Interdecadal Pacific Oscillation (IPO) will regulate the rate at which mean temperature approaches the 1.5°C level. A transition to the positive phase of the IPO would lead to a projected exceedance of the target centered around 2026. If the Pacific Ocean remains in its negative decadal phase, the target will be reached around 5 years later, in 2031. Given the temporary slowdown in global warming between 2000 and 2014, and recent initialized decadal predictions suggestive of a turnaround in the IPO, a sustained period of rapid temperature rise might be underway. In that case, the world will reach the 1.5°C level of warming several years sooner than if the negative IPO phase persists.
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ItemComparison of methods: Attributing the 2014 record European temperatures to human influences(AMER GEOPHYSICAL UNION, 2016-08-28)Abstract 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.
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ItemEmergence of heat extremes attributable to anthropogenic influences(AMER GEOPHYSICAL UNION, 2016-04-16)Abstract Climate scientists have demonstrated that a substantial fraction of the probability of numerous recent extreme events may be attributed to human‐induced climate change. However, it is likely that for temperature extremes occurring over previous decades a fraction of their probability was attributable to anthropogenic influences. We identify the first record‐breaking warm summers and years for which a discernible contribution can be attributed to human influence. We find a significant human contribution to the probability of record‐breaking global temperature events as early as the 1930s. Since then, all the last 16 record‐breaking hot years globally had an anthropogenic contribution to their probability of occurrence. Aerosol‐induced cooling delays the timing of a significant human contribution to record‐breaking events in some regions. Without human‐induced climate change recent hot summers and years would be very unlikely to have occurred.
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ItemNo Preview AvailableSouthern Hemisphere subtropical drying as a transient response to warming(NATURE PUBLISHING GROUP, 2019-03)Climate projections1–3 and observations over recent decades4,5 indicate that precipitation in subtropical latitudes declines in response to anthropogenic warming, with significant implications for food production and population sustainability. However, this conclusion is derived from emissions scenarios with rapidly increasing radiative forcing to the year 21001,2, which may represent very different conditions from both past and future ‘equilibrium’ warmer climates. Here, we examine multi-century future climate simulations and show that in the Southern Hemisphere subtropical drying ceases soon after global temperature stabilizes. Our results suggest that twenty-first century Southern Hemisphere subtropical drying is not a feature of warm climates per se, but is primarily a response to rapidly rising forcing and global temperatures, as tropical sea-surface temperatures rise more than southern subtropical sea-surface temperatures under transient warming. Subtropical drying may therefore be a temporary response to rapid warming: as greenhouse gas concentrations and global temperatures stabilize, Southern Hemisphere subtropical regions may experience positive precipitation trends.
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ItemNo Preview Available
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ItemAssessing Contributions of Major Emitters' Paris-Era Decisions to Future Temperature Extremes(AMER GEOPHYSICAL UNION, 2019-04-16)Abstract The likelihood and severity of high‐impact future temperature extremes can be reduced through climate change mitigation efforts. However, meeting the Paris Agreement warming limits requires notably stronger greenhouse gas emissions reduction efforts by major emitters than existing pledges. We examine the impact of Paris‐era decision‐making by the world's three largest greenhouse gas emitters (EU, USA, and China) on projected future extreme temperature events. Country‐level contributions to the occurrence of future temperature extremes are calculated based on current emissions policies and sequential mitigation efforts, using a new metric called the Contribution to Excess Risk Ratio. We demonstrate the Contribution concept by applying it to extreme monthly temperature projections. In many regions, future extremes depend on the current and future carbon dioxide emissions reductions adopted by major emitters. By implementing stronger Paris‐era climate pledges, major emitters can reduce the frequency of future extremes and their own calculated contributions to these temperature extremes.
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ItemToward Calibrated Language for Effectively Communicating the Results of Extreme Event Attribution Studies(AMER GEOPHYSICAL UNION, 2019-09)Abstract Extreme event attribution studies attempt to quantify the role of human influences in observed weather and climate extremes. These studies are of broad scientific and public interest, although quantitative results (e.g., that a specific event was made a specific number of times more likely because of anthropogenic forcings) can be difficult to communicate accurately to a variety of audiences and difficult for audiences to interpret. Here, we focus on how results of these studies can be effectively communicated using standardized language and propose, for the first time, a set of calibrated terms to describe event attribution results. Using these terms and an accompanying visual guide, results are presented in terms of likelihood of event changes and the associated uncertainties. This standardized language will allow clearer communication and interpretation of probabilities by the public and stakeholders.