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Friday, December 28, 2012

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Measuring the Environmental Benefits of Wind Power

Joseph Cullen
American Economic Journal: Economic Policy, forthcoming

Abstract:
Production subsidies for renewable energy, such as solar or wind power, are rationalized due to their perceived environmental benefits. Subsidizing these projects allows clean, renewable technologies to produce electricity that otherwise would have been produced by dirtier, fossil-fuel power plants. In this paper, I quantify the emissions offset by wind power for a large electricity grid in Texas using the randomness inherent in wind power availability. The results indicate that one MWh of wind power offsets negligible quantities of SO2, less than one lb of NOx, and less than half a ton of CO2. Only for high estimates of the social costs of pollution do I find that the value of emissions offset by wind power are greater than the renewable energy subsidies used to induce investment in wind farms.

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Pay for Environmental Performance: The Effect of Incentive Provision on Carbon Emissions

Robert Eccles et al.
Harvard Working Paper, November 2012

Abstract:
Corporations are increasingly under pressure to improve their environmental performance and to account for potential risks and opportunities associated with climate change. In this paper, we examine the effectiveness of monetary and nonmonetary incentives provided by companies to their employees in order to reduce carbon emissions. Specifically, we find evidence that the use of monetary incentives is associated with higher carbon emissions. This result holds both in cross-sectional and time-series analysis. Moreover, we find that the use of nonmonetary incentives is associated with lower carbon emissions. Consistent with monetary incentives crowding out motivation for pro-social behavior, we find that the effect of monetary incentives on carbon emissions is mitigated when these incentives are provided to employees with formally assigned responsibility for environmental performance. Furthermore, by employing a two-stage multinomial logistic model, we provide insights into factors affecting companies' decisions on incentive provision, as well as showing that the impact of monetary incentives on carbon emissions remains significant even when we control for potential selection bias in our sample.

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Adapting to Climate Change: The Remarkable Decline in the U.S. Temperature-Mortality Relationship Over the 20th Century

Alan Barreca et al.
MIT Working Paper, December 2012

Abstract:
Adaptation is the only strategy that is guaranteed to be part of the world's climate strategy. Using the most comprehensive set of data files ever compiled on mortality and its determinants over the course of the 20th century, this paper makes two primary discoveries. First, we find that the mortality effect of an extremely hot day declined by about 80% between 1900-1959 and 1960-2004. As a consequence, days with temperatures exceeding 90°F were responsible for about 600 premature fatalities annually in the 1960-2004 period, compared to the approximately 3,600 premature fatalities that would have occurred if the temperature-mortality relationship from before 1960 still prevailed. Second, the adoption of residential air conditioning (AC) explains essentially the entire decline in the temperature-mortality relationship. In contrast, increased access to electricity and health care seem not to affect mortality on extremely hot days. Residential AC appears to be both the most promising technology to help poor countries mitigate the temperature related mortality impacts of climate change and, because fossil fuels are the least expensive source of energy, a technology whose proliferation will speed up the rate of climate change.

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Do probabilistic expert elicitations capture scientists' uncertainty about climate change?

Antony Millner et al.
Climatic Change, January 2013, Pages 427-436

Abstract:
Expert elicitation studies have become important barometers of scientific knowledge about future climate change (Morgan and Keith, Environ Sci Technol 29(10), 1995; Reilly et al., Science 293(5529):430-433, 2001; Morgan et al., Climate Change 75(1-2):195-214, 2006; Zickfeld et al., Climatic Change 82(3-4):235-265, 2007, Proc Natl Acad Sci 2010; Kriegler et al., Proc Natl Acad Sci 106(13):5041-5046, 2009). Elicitations incorporate experts' understanding of known flaws in climate models, thus potentially providing a more comprehensive picture of uncertainty than model-driven methods. The goal of standard elicitation procedures is to determine experts' subjective probabilities for the values of key climate variables. These methods assume that experts' knowledge can be captured by subjective probabilities-however, foundational work in decision theory has demonstrated this need not be the case when their information is ambiguous (Ellsberg, Q J Econ 75(4):643-669, 1961). We show that existing elicitation studies may qualitatively understate the extent of experts' uncertainty about climate change. We designed a choice experiment that allows us to empirically determine whether experts' knowledge about climate sensitivity (the equilibrium surface warming that results from a doubling of atmospheric CO2 concentration) can be captured by subjective probabilities. Our results show that, even for this much studied and well understood quantity, a non-negligible proportion of climate scientists violate the choice axioms that must be satisfied for subjective probabilities to adequately describe their beliefs. Moreover, the cause of their violation of the axioms is the ambiguity in their knowledge. We expect these results to hold to a greater extent for less understood climate variables, calling into question the veracity of previous elicitations for these quantities. Our experimental design provides an instrument for detecting ambiguity, a valuable new source of information when linking climate science and climate policy which can help policy makers select decision tools appropriate to our true state of knowledge.

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Early warning signals and the prosecutor's fallacy

Carl Boettiger & Alan Hastings
Proceedings of the Royal Society: Biological Sciences, 7 December 2012, Pages 4734-4739

Abstract:
Early warning signals have been proposed to forecast the possibility of a critical transition, such as the eutrophication of a lake, the collapse of a coral reef or the end of a glacial period. Because such transitions often unfold on temporal and spatial scales that can be difficult to approach by experimental manipulation, research has often relied on historical observations as a source of natural experiments. Here, we examine a critical difference between selecting systems for study based on the fact that we have observed a critical transition and those systems for which we wish to forecast the approach of a transition. This difference arises by conditionally selecting systems known to experience a transition of some sort and failing to account for the bias this introduces - a statistical error often known as the prosecutor's fallacy. By analysing simulated systems that have experienced transitions purely by chance, we reveal an elevated rate of false-positives in common warning signal statistics. We further demonstrate a model-based approach that is less subject to this bias than those more commonly used summary statistics. We note that experimental studies with replicates avoid this pitfall entirely.

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Projected changes of extreme weather events in the eastern United States based on a high resolution climate modeling system

Y. Gao et al.
Environmental Research Letters, October-December 2012

Abstract:
This study is the first evaluation of dynamical downscaling using the Weather Research and Forecasting (WRF) Model on a 4 km × 4 km high resolution scale in the eastern US driven by the new Community Earth System Model version 1.0 (CESM v1.0). First we examined the global and regional climate model results, and corrected an inconsistency in skin temperature during the downscaling process by modifying the land/sea mask. In comparison with observations, WRF shows statistically significant improvement over CESM in reproducing extreme weather events, with improvement for heat wave frequency estimation as high as 98%. The fossil fuel intensive scenario Representative Concentration Pathway (RCP) 8.5 was used to study a possible future mid-century climate extreme in 2057-9. Both the heat waves and the extreme precipitation in 2057-9 are more severe than the present climate in the Eastern US. The Northeastern US shows large increases in both heat wave intensity (3.05 °C higher) and annual extreme precipitation (107.3 mm more per year).

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Projected Increases in North Atlantic Tropical Cyclone Intensity from CMIP5 Models

Gabriele Villarini & Gabriel Vecchi
Journal of Climate, forthcoming

Abstract:
Tropical cyclones - particularly intense ones - are a hazard to life and property, so an assessment of the changes in North Atlantic tropical cyclone intensity has important socio-economic implications. In this study we focus on the seasonally integrated Power Dissipation Index (PDI) as a metric to project changes in tropical cyclone intensity. Based on a recently developed statistical model, we examine projections in North Atlantic PDI using output from 17 state-of-the-art global climate models and three radiative forcing scenarios. Overall, we find that North Atlantic PDI is projected to increase with respect to the 1986-2005 period across all scenarios. The difference between the PDI projections and those of the number of North Atlantic tropical cyclones, which are not projected to increase significantly, indicates an intensification of North Atlantic tropical cyclones in response to both greenhouse gas (GHG) increases and aerosol changes over the current century. At the end of the 21st century, the magnitude of these increases shows a positive dependence on projected GHG forcing. The projected intensification is significantly enhanced by non-GHG (primarily aerosol) forcing in the first half of the 21st century.

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Making sense of palaeoclimate sensitivity

PALAEOSENS Project Members
Nature, 29 November 2012, Pages 683-691

Abstract:
Many palaeoclimate studies have quantified pre-anthropogenic climate change to calculate climate sensitivity (equilibrium temperature change in response to radiative forcing change), but a lack of consistent methodologies produces a wide range of estimates and hinders comparability of results. Here we present a stricter approach, to improve intercomparison of palaeoclimate sensitivity estimates in a manner compatible with equilibrium projections for future climate change. Over the past 65 million years, this reveals a climate sensitivity (in K W-1 m2) of 0.3-1.9 or 0.6-1.3 at 95% or 68% probability, respectively. The latter implies a warming of 2.2-4.8 K per doubling of atmospheric CO2, which agrees with IPCC estimates.

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Adaptation of US maize to temperature variations

Ethan Butler & Peter Huybers
Nature Climate Change, January 2013, Pages 68-72

Abstract:
High temperatures are associated with reduced crop yields, and predictions for future warming have raised concerns regarding future productivity and food security. However, the extent to which adaptation can mitigate such heat-related losses remains unclear. Here we empirically demonstrate how maize is locally adapted to hot temperatures across US counties. Using this spatial adaptation as a surrogate for future adaptation, we find that losses to average US maize yields from a 2 °C warming would be reduced from 14% to only 6% and that loss in net production is wholly averted. This result does not account for possible changes in temperature variability or water resources, nor does it account for all possible forms of adaptation, but it does show that adaptation is of first-order importance for predicting future changes in yield. Further research should be undertaken regarding the ability to adapt to a changing climate, including analysis of other crops and regions, the application of more sophisticated models of crop development, and field trials employing artificially increased temperature.

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Comparing climate projections to observations up to 2011

Stefan Rahmstorf, Grant Foster & Anny Cazenave
Environmental Research Letters, October-December 2012

Abstract:
We analyse global temperature and sea-level data for the past few decades and compare them to projections published in the third and fourth assessment reports of the Intergovernmental Panel on Climate Change (IPCC). The results show that global temperature continues to increase in good agreement with the best estimates of the IPCC, especially if we account for the effects of short-term variability due to the El Niño/Southern Oscillation, volcanic activity and solar variability. The rate of sea-level rise of the past few decades, on the other hand, is greater than projected by the IPCC models. This suggests that IPCC sea-level projections for the future may also be biased low.

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Identifying human influences on atmospheric temperature

Benjamin Santer et al.
Proceedings of the National Academy of Sciences, forthcoming

Abstract:
We perform a multimodel detection and attribution study with climate model simulation output and satellite-based measurements of tropospheric and stratospheric temperature change. We use simulation output from 20 climate models participating in phase 5 of the Coupled Model Intercomparison Project. This multimodel archive provides estimates of the signal pattern in response to combined anthropogenic and natural external forcing (the fingerprint) and the noise of internally generated variability. Using these estimates, we calculate signal-to-noise (S/N) ratios to quantify the strength of the fingerprint in the observations relative to fingerprint strength in natural climate noise. For changes in lower stratospheric temperature between 1979 and 2011, S/N ratios vary from 26 to 36, depending on the choice of observational dataset. In the lower troposphere, the fingerprint strength in observations is smaller, but S/N ratios are still significant at the 1% level or better, and range from three to eight. We find no evidence that these ratios are spuriously inflated by model variability errors. After removing all global mean signals, model fingerprints remain identifiable in 70% of the tests involving tropospheric temperature changes. Despite such agreement in the large-scale features of model and observed geographical patterns of atmospheric temperature change, most models do not replicate the size of the observed changes. On average, the models analyzed underestimate the observed cooling of the lower stratosphere and overestimate the warming of the troposphere. Although the precise causes of such differences are unclear, model biases in lower stratospheric temperature trends are likely to be reduced by more realistic treatment of stratospheric ozone depletion and volcanic aerosol forcing.

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Energy and climate change in China

Carlo Carraro & Emanuele Massetti
Environment and Development Economics, December 2012, Pages 689-713

Abstract:
This paper examines future energy and emissions scenarios in China generated by the Integrated Assessment Model WITCH. A Business-as-Usual scenario is compared with five scenarios in which greenhouse gases emissions are taxed, at different levels. The elasticity of China's emissions is estimated by pooling observations from all scenarios and comparing them with the elasticity of emissions in OECD countries. China has a higher elasticity than the OECD for a carbon tax lower than US$50 per ton of CO2-eq. For higher taxes, emissions in OECD economies are more elastic than in China. Our best guess indicates that China would need to introduce a tax equal to about US$750 per ton of CO2-eq in 2050 to achieve the Major Economies Forum goal set for mid-century. In our preferred estimates, the discounted cost of following the 2°C trajectory is equal to 5.4 per cent and to 2.7 per cent of GDP in China and the OECD, respectively.

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A detection of Milankovitch frequencies in global volcanic activity

Steffen Kutterolf et al.
Geology, forthcoming

Abstract:
A rigorous detection of Milankovitch periodicities in volcanic output across the Pleistocene-Holocene ice age has remained elusive. We report on a spectral analysis of a large number of well-preserved ash plume deposits recorded in marine sediments along the Pacific Ring of Fire. Our analysis yields a statistically significant detection of a spectral peak at the obliquity period. We propose that this variability in volcanic activity results from crustal stress changes associated with ice age mass redistribution. In particular, increased volcanism lags behind the highest rate of increasing eustatic sea level (decreasing global ice volume) by 4.0 ± 3.6 k.y. and correlates with numerical predictions of stress changes at volcanically active sites. These results support the presence of a causal link between variations in ice age climate, continental stress field, and volcanism.

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The mystery of recent stratospheric temperature trends

David Thompson et al.
Nature, 29 November 2012, Pages 692-697

Abstract:
A new data set of middle- and upper-stratospheric temperatures based on reprocessing of satellite radiances provides a view of stratospheric climate change during the period 1979-2005 that is strikingly different from that provided by earlier data sets. The new data call into question our understanding of observed stratospheric temperature trends and our ability to test simulations of the stratospheric response to emissions of greenhouse gases and ozone-depleting substances. Here we highlight the important issues raised by the new data and suggest how the climate science community can resolve them.

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How much can air conditioning increase air temperatures for a city like Paris, France?

Cécile de Munck et al.
International Journal of Climatology, January 2013, Pages 210-227

Abstract:
A consequence of urban heat islands in summer is an increase in the use of air conditioning in urbanized areas, which while cooling the insides of buildings, releases waste heat to the atmosphere. A coupled model consisting of a meso-scale meteorological model (MESO-NH) and an urban energy balance model (TEB) has been used to simulate and quantify the potential impacts on street temperature of four air conditioning scenarios at the scale of Paris. The first case consists of simulating the current types of systems in the city and was based on inventories of dry and evaporative cooling towers and free cooling systems with the river Seine. The other three scenarios were chosen to test the impacts of likely trends in air conditioning equipment in the city: one for which all evaporative and free cooling systems were replaced by dry systems, and the other two designed on a future doubling of the overall air conditioning power but with different technologies. The comparison between the scenarios with heat releases in the street and the baseline case without air conditioning showed a systematic increase in the street air temperature, and this increase was greater at nighttime than day time. It is counter-intuitive because the heat releases are higher during the day. This is due to the shallower atmospheric boundary layer during the night. The increase in temperature was 0.5 °C in the situation with current heat releases, 1 °C with current releases converted to only sensible heat, and 2 °C for the future doubling of air conditioning waste heat released to air. These results demonstrated to what extent the use of air conditioning could enhance street air temperatures at the scale of a city like Paris, and the importance of a spatialized approach for a reasoned planning for future deployment of air conditioning in the city.

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Carbon Taxes, Path Dependency and Directed Technical Change: Evidence from the Auto Industry

Philippe Aghion et al.
NBER Working Paper, December 2012

Abstract:
Can directed technical change be used to combat climate change? We construct new firm-level panel data on auto industry innovation distinguishing between "dirty" (internal combustion engine) and "clean" (e.g. electric and hybrid) patents across 80 countries over several decades. We show that firms tend to innovate relatively more in clean technologies when they face higher tax-inclusive fuel prices. Furthermore, there is path dependence in the type of innovation both from aggregate spillovers and from the firm's own innovation history. Using our model we simulate the increases in carbon taxes needed to allow clean to overtake dirty technologies.

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A method for estimating the cost to sequester carbon dioxide by delivering iron to the ocean

Daniel Harrison
International Journal of Global Warming, forthcoming

Abstract:
If society wishes to limit the contribution of anthropogenic carbon dioxide to global warming then the need to find economical methods of CO2 sequestration is now urgent. Ocean iron fertilisation has been suggested as a low cost mitigation option to capture and store carbon. However previous methods of estimating the cost fail to account for many of the losses and offsets occurring over the storage period. A method for calculating the net carbon stored from iron fertilisation of high nutrient low chlorophyll (HNLC) regions is provided here. The method involves first calculating the direct cost to create phytoplankton biomass in the surface ocean. The net amount of carbon stored is then calculated by considering the fraction of this carbon exported as deep as the permanent thermocline and subtracting losses due to: ventilation, nutrient stealing, greenhouse gas production, and CO2 emitted by the sequestration operation for a given storage period. Commonly available iron fertiliser delivered by ship to the Southern Ocean is considered as a case study using parameters derived from previous fertilisation experiments and modelling studies. On average, a single fertilisation is found to result in a net sequestration of 0.01 t C km-2 sequestered for 100 years or more at a cost of US$457 per tonne CO2. Iron fertilisation experiments show high variability in the amount of biomass created and the fraction exported to depth, the range of uncertainty provides a risk of more carbon released to the atmosphere than sequestered for 100 years, or alternatively, reduced cost if optimistic parameters are assumed. Previous estimates of cost fail to recognise the economic challenge of distributing low concentrations of iron over large areas of the ocean surface and the subsequent loss processes that result in only a small net storage of carbon per km2 fertilised. The cost could be lowered by the use of more energy efficient means to distribute the small amounts of iron required over large regions of remote ocean surface, by improving the performance of the iron fertiliser, or potentially by conducting fertilisation activities only under ideal oceanographic conditions.

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The impact of climate change on agro-ecological zones: Evidence from Africa

Namrata Kala, Pradeep Kurukulasuriya & Robert Mendelsohn
Environment and Development Economics, December 2012, Pages 663-687

Abstract:
This study predicts the impact of climate change on African agriculture. We use a generalized linear model (GLM) framework to estimate the relationship between the proportion of various Agro-Ecological Zones (AEZs) in a district and climate. Using three climate scenarios, we project how climate change will cause AEZs to shift, causing changes in acreage and net revenue per hectare of cropland. Our results predict that Africa will suffer heavy annual welfare losses by 2070-2100, ranging between US$14 billion and US$70 billion, depending on the climate scenario and cropland measure considered.

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Summer-time climate impacts of projected megapolitan expansion in Arizona

M. Georgescu et al.
Nature Climate Change, January 2013, Pages 37-41

Abstract:
Efforts characterizing the changing climate of southwestern North America by focusing exclusively on the impacts of increasing levels of long-lived greenhouse gases omit fundamental elements with similar order-of-magnitude impacts as those owing to large-scale climate change. Using a suite of ensemble-based, multiyear simulations, here we show the intensification of observationally based urban-induced phenomena and demonstrate that the direct summer-time climate effects of the most rapidly expanding megapolitan region in the USA - Arizona's Sun Corridor - are considerable. Although urban-induced warming approaches 4 °C locally for the maximum expansion scenario, impacts depend on the particular trajectory of development. Cool-roof implementation reduces simulated warming by about 50%, yet decreases in summer-time evapotranspiration remain at least as large as those from urban expansion without this mode of adaptation. The contribution of urban-induced warming relative to mid- and end-of-century climate change illustrates strong dependence on built environment expansion scenarios and emissions pathways. Our results highlight the direct climate impacts that result from newly emerging megapolitan regions and their significance for overcoming present challenges concerning sustainable development.

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Dazzled by diesel? The impact on carbon dioxide emissions of the shift to diesels in Europe through 2009

Lee Schipper & Lew Fulton
Energy Policy, forthcoming

Abstract:
This paper identifies trends in new gasoline and diesel passenger car characteristics in the European Union between 1995 and 2009. By 2009 diesels had captured over 55% of the new vehicle market. While the diesel version of a given car model may have as much as 35% lower fuel use/km and 25% lower CO2 emissions than its gasoline equivalent, diesel buyers have chosen increasingly large and more powerful cars than the gasoline market. As a result, new diesels bought in 2009 had only 2% lower average CO2 emissions than new gasoline cars, a smaller advantage than in 1995. A Laspeyres decomposition investigates which factors were important contributors to the observed emission reductions and which factors offset savings in other areas. More than 95% of the reduction in CO2 emissions per km from new vehicles arose because both diesel and gasoline new vehicle emissions/km fell, and only 5% arose because of the shift from gasoline to diesel technology. Increases in vehicle mass and power for both gasoline and diesel absorbed much of the technological efficiency improvements offered by both technologies. We also observe changes in the gasoline and diesel fleets in eight EU countries and find changes in fuel and emissions intensities consistent with the changes in new vehicles reported. While diesel cars continue to be driven far farther than gasoline cars, we attribute only some of this difference to a "rebound effect". We conclude that while diesel technology has permitted significant fuel savings, the switch from gasoline to diesel in the new vehicle market contributed little itself to the observed reductions in CO2 emissions from new vehicles.

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Influences of the Bermuda High and atmospheric moistening on changes in summer rainfall in the Atlanta, Georgia region, USA

Jeremy Diem
International Journal of Climatology, January 2013, Pages 160-172

Abstract:
This paper assesses the variability and trends in summer-season rainfall from 1948 to 2009 for the Atlanta, Georgia region. The rainfall variables are total rainfall, frequency of rainfall days, and frequency of heavy-rainfall days. The main methods involve classifying daily 500-hPa geopotential height fields into synoptic types, determining the rainfall characteristics of the synoptic types, testing for significant temporal trends in rainfall, middle-troposphere circulation, lower-troposphere circulation, and atmospheric humidity, and using multiple linear regression to determine the impact of circulation and humidity variables on inter-annual variations in the rainfall variables. There were a total of eight synoptic types: the wet types involved troughing across or to the immediate west of the Atlanta region, while the dry types involved either an anticyclone across or to the immediate west of the region. The rainfall variables and two lower-troposphere circulation indices, the Bermuda High Index (BHI) and the Western Bermuda High Index (WBHI), had significant positive trends in variance over time. Among the three rainfall variables, only the frequency of rainfall days had a significant trend: the periods 1976-2009 and 1977-2009 had significant positive trends in rainfall days. The BHI had a significant positive trend from the 1970s to 2009, and the western ridge of the Bermuda High moved significantly southeastward from approximately the mid-1970s to 2009. Atmospheric humidity (i.e. 850-hPa specific humidity, 500-hPa specific humidity, and precipitable water) over the region had significant positive trends during most periods, with all humidity variables having significant increases from the 1970s to 2009. Increased interannual variability in the WBHI appears to be the cause of the increased variance in rainfall variables. An increase in atmospheric humidity, which is actually a global phenomenon, appears to be the principal cause of the increase in rainfall days during the past three decades.

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Enhanced poleward moisture transport and amplified northern high-latitude wetting trend

Xiangdong Zhang et al.
Nature Climate Change, January 2013, Pages 47-51

Abstract:
Observations and climate change projections forced by greenhouse gas emissions have indicated a wetting trend in northern high latitudes, evidenced by increasing Eurasian Arctic river discharges. The increase in river discharge has accelerated in the latest decade and an unprecedented, record high discharge occurred in 2007 along with an extreme loss of Arctic summer sea-ice cover. Studies have ascribed this increasing discharge to various factors attributable to local global warming effects, including intensifying precipitation minus evaporation, thawing permafrost, increasing greenness and reduced plant transpiration. However, no agreement has been reached and causal physical processes remain unclear. Here we show that enhancement of poleward atmospheric moisture transport (AMT) decisively contributes to increased Eurasian Arctic river discharges. Net AMT into the Eurasian Arctic river basins captures 98% of the gauged climatological river discharges. The trend of 2.6% net AMT increase per decade accounts well for the 1.8% per decade increase in gauged discharges and also suggests an increase in underlying soil moisture. A radical shift of the atmospheric circulation pattern induced an unusually large AMT and warm surface in 2006-2007 over Eurasia, resulting in the record high discharge.

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Projections and downscaling of 21st century temperatures, precipitation, radiative fluxes and winds for the Southwestern US, with focus on Lake Tahoe

Michael Dettinger
Climatic Change, January 2013, Pages 17-33

Abstract:
Recent projections of global climate changes in response to increasing greenhouse-gas concentrations in the atmosphere include warming in the Southwestern US and, especially, in the vicinity of Lake Tahoe of from about +3°C to +6°C by end of century and changes in precipitation on the order of 5-10 % increases or (more commonly) decreases, depending on the climate model considered. Along with these basic changes, other climate variables like solar insolation, downwelling (longwave) radiant heat, and winds may change. Together these climate changes may result in changes in the hydrology of the Tahoe basin and potential changes in lake overturning and ecological regimes. Current climate projections, however, are generally spatially too coarse (with grid cells separated by 1 to 2° latitude and longitude) for direct use in assessments of the vulnerabilities of the much smaller Tahoe basin. Thus, daily temperatures, precipitation, winds, and downward radiation fluxes from selected global projections have been downscaled by a statistical method called the constructed-analogues method onto 10 to 12 km grids over the Southwest and especially over Lake Tahoe. Precipitation, solar insolation and winds over the Tahoe basin change only moderately (and with indeterminate signs) in the downscaled projections, whereas temperatures and downward longwave fluxes increase along with imposed increases in global greenhouse-gas concentrations.

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Temporal and spatial trends in air temperature on the Island of Oahu, Hawaii

Mohammad Safeeq, Alan Mair & Ali Fares
International Journal of Climatology, forthcoming

Abstract:
We examined trends in minimum and maximum temperatures in the Oahu during the period of past 39 (1969-2007) and 25 (1983-2007) years. We found a strong spatial and temporal variability in the temperature trends on Oahu. During the past 39 years, island-wide minimum temperature has increased by 0.17 °C/decade and shows a considerable variability in trends at individual location. There was no detectable trend found in maximum temperature over the same time period. The year 1983 was identified as the change point in the island-wide minimum temperature. During the recent 25 years annual and summer maximum temperature showed a decline while minimum temperature continued to increase. Trend in diurnal temperature range (DTR) shows a decline during the past 39 years with a stronger decreasing trend during the recent 25 years. The trend in DTR for Oahu is much higher compared to the global DTR trend indicating a rapid warming in minimum temperature. Extreme temperature indices show a general warming during the past 39 years. There has been significant increase in tropical and warm nights at the two urban stations. Maximum temperature generally followed the Pacific Decadal Oscillation (PDO) except the period when there is an increase in Hawaii Rainfall Index (HRI). In contrast, minimum temperature showed better agreement with HRI compared to the PDO, at least up until 1999 after which it showed an increase. Despite the relative cooling in PDO during the recent decade an increase in minimum temperature can be attributed to a decline in HRI.

By KEVIN LEWIS | 09:00:00 AM