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Scientists: Strong evidence that human-caused climate change intensified 2015 heat waves
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Human-caused climate change very likely increased the severity of heat waves that plagued India, Pakistan, Europe, East Africa, East Asia, and Australia in 2015 and helped make it the warmest year on record, according to new research published today in a special edition of the Bulletin of the American Meteorological Society.
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Significant anthropogenic-induced changes of climate classes since 1950
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Anthropogenic forcings have contributed to global and regional warming in the last few decades and likely affected terrestrial precipitation. Here we examine changes in major Köppen climate classes from gridded observed data and their uncertainties due to internal climate variability using control simulations from Coupled Model Intercomparison Project 5 (CMIP5). About 5.7% of the global total land area has shifted toward warmer and drier climate types from 1950–2010, and significant changes include expansion of arid and high-latitude continental climate zones, shrinkage in polar and midlatitude continental climates, poleward shifts in temperate, continental and polar climates, and increasing average elevation of tropical and polar climates. Using CMIP5 multi-model averaged historical simulations forced by observed anthropogenic and natural, or natural only, forcing components, we find that these changes of climate types since 1950 cannot be explained as natural variations but are driven by anthropogenic factors.
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Global non-linear effect of temperature on economic production
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Growing evidence demonstrates that climatic conditions can have a profound impact on the functioning of modern human societies (1,2), but effects on economic activity appear inconsistent. Fundamental productive elements of modern economies, such as workers and crops, exhibit highly non-linear responses to local temperature even in wealthy countries (3,4). In contrast, aggregate macroeconomic productivity of entire wealthy countries is reported not to respond to temperature (5), while poor countries respond only linearly (5,6). Resolving this conflict between micro and macro observations is critical to understanding the role of wealth in coupled human–natural systems (7,8) and to anticipating the global impact of climate change (9,10). Here we unify these seemingly contradictory results by accounting for non-linearity at the macro scale. We show that overall economic productivity is non- linear in temperature for all countries, with productivity peaking at an annual average temperature of 13 6C and declining strongly at higher temperatures. The relationship is globally generalizable, unchanged since 1960, and apparent for agricultural and non-agricultural activity in both rich and poor countries. These results provide the first evidence that economic activity in all regions is coupled to the global climate and establish a new empirical foundation for modelling economic loss in response to climate change (11,12), with important implications. If future adaptation mimics past adaptation, unmitigated warming is expected to reshape the global economy by reducing average global incomes roughly 23% by 2100 and widening global income inequality, relative to scenarios without climate change. In contrast to prior estimates, expected global losses are approximately linear in global mean temperature, with median losses many times larger than leading models indicate.
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Medieval warming initiated exceptionally large wildfire outbreaks in the Rocky Mountains
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Many of the largest wildfires in US history burned in recent decades, and climate change explains much of the increase in area burned. The frequency of extreme wildfire weather will increase with continued warming, but many uncertainties still exist about future fire regimes, including how the risk of large fires will persist as vegetation changes. Past fire-climate relationships provide an opportunity to constrain the related uncertainties, and reveal widespread burn- ing across large regions of western North America during past warm intervals. Whether such episodes also burned large portions of individual landscapes has been difficult to determine, however, because uncertainties with the ages of past fires and limited spatial resolution often prohibit specific estimates of past area burned. Accounting for these challenges in a subalpine landscape in Colorado, we estimated century-scale fire synchroneity across 12 lake- sediment charcoal records spanning the past 2,000 y. The percent- age of sites burned only deviated from the historic range of vari- ability during the Medieval Climate Anomaly (MCA) between 1,200 and 850 y B.P., when temperatures were similar to recent decades. Between 1,130 and 1,030 y B.P., 83% (median estimate) of our sites burned when temperatures increased ∼0.5 °C relative to the preceding centuries. Lake-based fire rotation during the MCA decreased to an estimated 120 y, representing a 260% higher rate of burning than during the period of dendroecological sampling (360 to −60 y B.P.). Increased burning, however, did not persist throughout the MCA. Burning declined abruptly before temperatures cooled, indicating possible fuel limitations to continued burning.
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THE COST OF INACTION: RECOGNISING THE VALUE AT RISK FROM CLIMATE CHANGE
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The asset management industry—and thus the wider community of investors of all sizes— is facing the prospect of significant losses from the effects of climate change. Assets can be directly damaged by floods, droughts and severe storms, but portfolios can also be harmed indirectly, through weaker growth and lower asset returns. Climate change is a long-term, probably irreversible problem beset by substantial uncertainty. Crucially, however, climate change is a problem of extreme risk: this means that the average losses to be expected are not the only source of concern; on the contrary, the outliers, the particularly extreme scenarios, may matter most of all.
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Too late for two degrees? Low carbon economy index 2012
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Even doubling our current rate of decarbonisation would still lead to emissions consistent with 6 degrees of
warming by the end of the century. To give ourselves a more than 50% chance of avoiding 2 degrees will
require a six-fold improvement in our rate of decarbonisation.
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A long-term perspective on a modern drought in the American Southeast
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The depth of the 2006–9 drought in the humid, southeastern US left several metropolitan areas
with only a 60–120 day water supply. To put the region’s recent drought variability in a long-term
perspective, a dense and diverse tree-ring network—including the first records throughout the
Apalachicola–Chattahoochee–Flint river basin—is used to reconstruct drought from 1665 to 2010
CE. The network accounts for up to 58.1% of the annual variance in warm-season drought during
the 20th century and captures wet eras during the middle to late 20th century. The reconstruction
shows that the recent droughts are not unprecedented over the last 346 years. Indeed, droughts of
extended duration occurred more frequently between 1696 and 1820. Our results indicate that the
era in which local and state water supply decisions were developed and the period of instrumental
data upon which it is based are amongst the wettest since at least 1665. Given continued growth
and subsequent industrial, agricultural and metropolitan demand throughout the southeast, insights
from paleohydroclimate records suggest that the threat of water-related conflict in the region has
potential to grow more intense in the decades to come.
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Adapting to a Changing Climate in the Southeast
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Whether it’s change to native terrestrial habitats or sea level rise and impacts to vital coastal wetlands and marshes, we are only beginning to understand what is happening across the country, what is likely to occur in the years ahead, and how our agency will act. Indeed, of the 128 national wildlife refuges in the Southeast more than half are located along the coast. The number of days per year with peak temperatures over 90F is expected to rise significantly. By the end of this century, projections indicate much of North Carolina will have 90F plus days for one-third of the year, up from less than 30 days in that temperature zone in the 1960s and 1970s. Arkansas will see 90F days for up to 150 days a year, and NorthFlorida for nearly 6 months a year.
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Climatic extremes improve predictions of spatial patterns of tree species
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Understanding niche evolution, dynamics, and the response of species to climate change requires knowledge of the determinants of the environmental niche and species range limits. Mean values of climatic variables are often used in such analyses. In contrast, the increasing frequency of climate extremes suggests the importance of understanding their additional influence on range limits. Here, we assess how measures representing climate extremes (i.e., interannual variability in climate parameters) explain and predict spatial patterns of 11 tree species in Switzerland. We find clear, although comparably small, improvement (20% in adjusted D2, 8% and 3% in cross-validated True Skill Statistic and area under the receiver operating characteristics curve values) in models that use measures of extremes in addition to means. The primary effect of including information on climate extremes is a correction of local overprediction and underprediction. Our results demonstrate that measures of climate extremes are important for understanding the climatic limits of tree species and assessing species niche characteristics. The inclusion of climate variability likely will improve models of species range limits under future conditions, where changes in mean climate and increased variability are expected.
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Dramatically increasing chance of extremely hot summers since the 2003 European heatwave
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Socio-economic stress from the unequivocal warming of the global climate system(1)could be mostly felt by societies through weather and climate extremes (2). The vulnerability of European citizens was made evident during the summer heatwave of 2003 (refs 3,4) when the heat-related death toll ran into tens of thousands (5). Human influence at least doubled the chances of the event according to the first formal event attribution study (6), which also made the ominous forecast that severe heatwaves could become commonplace by the 2040s. Here we investigate how the likelihood of having another extremely hot summer in one of the worst affected parts of Europe has changed ten years after the original study was published, given an observed summer temperature increase of 0.81 K since then. Our analysis benefits from the availability of new observations and data from several new models. Using a previously employed temperature threshold to define extremely hot summers, we find that events that would occur twice a century in the early 2000s are now expected to occur twice a decade. For the more extreme threshold observed in 2003, the return time reduces from thousands of years in the late twentieth century to about a hundred years in little over a decade.
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