Dry season water availability changes attributed to human-induced climate change

2020 ◽  
Author(s):  
Ryan S. Padrón ◽  
Lukas Gudmundsson ◽  
Agnès Ducharne ◽  
David M. Lawrence ◽  
Jiafu Mao ◽  
...  
Keyword(s):  
Climate Change ◽  
Greenhouse Gas ◽  
Water Availability ◽  
Land Surface ◽  
Radiative Forcing ◽  
Climate Model ◽  
Dry Season ◽  
Eastern Africa ◽  
Northern Asia ◽  
Climate Model Simulations

<p><span>Human-induced climate change poses potential impacts on the availability of water resources. Previous assessments of warming-induced changes in dryness, however, are influenced by short observational records and show conflicting results due to uncertainties in the response of evapotranspiration. In this study we use novel observation-based water availability reconstructions from data-driven and land surface models from 1902 to 2014; a period during which the Earth has warmed approximately 1°C relative to pre-industrial conditions. These reconstructions reveal consistent changes in average water availability of the driest month of the year during the last 30 years compared to the first half of the 20<sup>th </sup>century. We conduct a simple attribution approach based on a spatial correlation analysis between the reconstructions and different climate model simulations. Results indicate that the spatial pattern of changes is <em>extremely likely</em> influenced by human-induced greenhouse gas emissions as it is consistent with climate model estimates that include historical radiative forcing, whereas the pattern is not expected from natural climate variability given by climate simulations with greenhouse gas levels set to pre-industrial conditions. Changes in water availability are characterized by drier dry seasons predominantly in extratropical latitudes and including Europe, Western North America, Northern Asia, Southern South America, Australia, and Eastern Africa. Finally, we find that the intensification of the dry season is generally a consequence of increasing evapotranspiration rather than decreasing precipitation.</span></p>

scholarly journals Historical greenhouse gas concentrations

2016 ◽  
Author(s):  
Malte Meinshausen ◽  
Elisabeth Vogel ◽  
Alexander Nauels ◽  
Katja Lorbacher ◽  
Nicolai Meinshausen ◽  
...  
Keyword(s):  
Climate Change ◽  
Greenhouse Gas ◽  
Radiative Forcing ◽  
Sulfur Hexafluoride ◽  
Climate Model ◽  
Future Climate Change ◽  
Large Set ◽  
Mixing Ratios ◽  
Surface Mixing ◽  
Cooling Effects

Abstract. Atmospheric greenhouse gas concentrations are at unprecedented, record-high levels compared to pre-industrial reconstructions over the last 800,000 years. Those elevated greenhouse gas concentrations warm the planet and together with net cooling effects by aerosols, they are the reason of observed climate change over the past 150 years. An accurate representation of those concentrations is hence important to understand and model recent and future climate change. So far, community efforts to create composite datasets with seasonal and latitudinal information have focused on marine boundary layer conditions and recent trends since 1980s. Here, we provide consolidated data sets of historical atmospheric (volume) mixing ratios of 43 greenhouse gases specifically for the purpose of climate model runs. The presented datasets are based on AGAGE and NOAA networks and a large set of literature studies. In contrast to previous intercomparisons, the new datasets are latitudinally resolved, and include seasonality over the period between year 0 to 2014. We assimilate data for CO2, methane (CH4) and nitrous oxide (N2O), 5 chlorofluorocarbons (CFCs), 3 hydrochlorofluorocarbons (HCFCs), 16 hydrofluorocarbons (HFCs), 3 halons, methyl bromide (CH3Br), 3 perfluorocarbons (PFCs), sulfur hexafluoride (SF6), nitrogen triflouride (NF3) and sulfuryl fluoride (SO2F2). We estimate 1850 annual and global mean surface mixing ratios of CO2 at 284.3 ppmv, CH4 at 808.2 ppbv and N2O at 273.0 ppbv and quantify the seasonal and hemispheric gradients of surface mixing ratios. Compared to earlier intercomparisons, the stronger implied radiative forcing in the northern hemisphere winter (due to the latitudinal gradient and seasonality) may help to improve the skill of climate models to reproduce past climate and thereby reduce uncertainty in future projections.

scholarly journals Weighting climate model projections using observational constraints

2015 ◽  
Vol 373 (2054) ◽  
pp. 20140425 ◽  
Author(s):  
Nathan P. Gillett
Keyword(s):  
Climate Change ◽  
Radiative Forcing ◽  
Climate Model ◽  
Historical Period ◽  
Intergovernmental Panel ◽  
Transient Climate Response ◽  
Detection And Attribution ◽  
Future Warming ◽  
Near Term ◽  
Climate Model Simulations

Projected climate change integrates the net response to multiple climate feedbacks. Whereas existing long-term climate change projections are typically based on unweighted individual climate model simulations, as observed climate change intensifies it is increasingly becoming possible to constrain the net response to feedbacks and hence projected warming directly from observed climate change. One approach scales simulated future warming based on a fit to observations over the historical period, but this approach is only accurate for near-term projections and for scenarios of continuously increasing radiative forcing. For this reason, the recent Fifth Assessment Report of the Intergovernmental Panel on Climate Change (IPCC AR5) included such observationally constrained projections in its assessment of warming to 2035, but used raw model projections of longer term warming to 2100. Here a simple approach to weighting model projections based on an observational constraint is proposed which does not assume a linear relationship between past and future changes. This approach is used to weight model projections of warming in 2081–2100 relative to 1986–2005 under the Representative Concentration Pathway 4.5 forcing scenario, based on an observationally constrained estimate of the Transient Climate Response derived from a detection and attribution analysis. The resulting observationally constrained 5–95% warming range of 0.8–2.5 K is somewhat lower than the unweighted range of 1.1–2.6 K reported in the IPCC AR5.

Time-evolving sea-surface warming patterns modulate the climate change response of precipitation in Mediterranean-like regions

2021 ◽  
Author(s):  
Giuseppe Zappa ◽  
Paulo Ceppi ◽  
Theodore Shepherd
Keyword(s):  
Climate Change ◽  
Time Evolution ◽  
Water Availability ◽  
Radiative Forcing ◽  
Climate Models ◽  
Climate Model ◽  
Sea Surface ◽  
Surface Warming ◽  
The Mediterranean ◽  
Change Response

<p>Regions with a Mediterranean-like climate, apart for California, are projected to receive less rainfall due to climate change, thus posing serious implications for future water availability for societal and agricultural needs. At a first order, it is often assumed that water availability is proportional to global mean warming. Yet, the mechanisms controlling the precipitation response in Mediterranean climates remain only partly understood, as shown by the substantial uncertainty that still characterises the climate model projections. Here, by analysing projections from the CMIP5 climate models, we show that the linear scaling with warming does not apply in three key Mediterranean-like regions, namely Chile, California and the Mediterranean proper. In particular, despite long-term warming, the models show that the projected precipitation reduction in Chile and the Mediterranean halts as soon as anthropogenic forcing is stabilised, while the precipitation increase in California accelerates. By examining the response to an abrupt quadrupling of CO2, we demonstrate that such non-linearity in the time-evolution of precipitation cannot be solely explained by the well-known rapid adjustment to radiative forcing, but it is instead due to distinct fast and slow patterns of atmospheric circulation change, that are themselves forced by the time-evolution in the spatial patterns of sea-surface temperature warming. In particular, while the fast warming is favourable to force a poleward shift of the mid-latitudes jets, hence drying the Mediterranean and Chile, the slow warming, including an el nino-like pattern in the tropical Pacific, inhibits such shifts and precipitation changes, while favouring the wetting of California. The results show that stabilising GHG concentrations will have an immediate benefit to the hydro-climate of these Mediterranean-like regions, while pointing to constraining uncertainty in the patterns of surface warming as an important step to increase confidence in the future projections.<span> </span></p>

Greenhouse-gas feedbacks estimated from Dansgaard-Oeschger events

2021 ◽  
Author(s):  
Mengmeng Liu ◽  
Laurie Menviel ◽  
Iain Colin Prentice ◽  
Sandy P. Harrison
Keyword(s):  
Greenhouse Gas ◽  
Radiative Forcing ◽  
Climate Model ◽  
Ice Core ◽  
Temperature Changes ◽  
Model Based ◽  
Global Mean Temperature ◽  
Feedback Strength ◽  
Climate Model Simulations ◽  
Global Mean

<p>There are large uncertainties in the estimation of greenhouse-gas feedbacks: model-based estimates vary considerably; recent observations are too short provide strong constraints. Rapid climate changes during the last glacial period (Dansgaard-Oeschger, D-O, events) are potentially valuable because they are comparable in rate and magnitude to projected future climate warming, and are registered near-globally. Here we use D-O events to quantify the centennial-scale feedback strength of feedbacks involving CO<sub>2</sub>, CH<sub>4</sub> and N<sub>2</sub>O. We use climate model simulations of the D-O events to estimate the relationship between global mean and Greenland temperature. We then relate global mean temperature changes to changes in greenhouse-gas concentrations derived from ice-core records, and then estimate the associated radiative forcing. We found the magnitude of the feedbacks (expressed in gain, with 95 % confidence interval) to be 0.07 ± 0.02 for CO<sub>2,</sub> 0.04 ± 0.01 for CH<sub>4</sub>, 0.04 ± 0.01 for N<sub>2</sub>O. These estimates are more constrained than previous model-based estimates but comparable to estimates based on recent observations.</p>

Elevation-dependent drying signals under future climate change – a case study for Austria

2021 ◽  
Author(s):  
Klaus Haslinger ◽  
Gregor Laaha ◽  
Wolfgang Schöner ◽  
Andre Konrad ◽  
Marc Olefs ◽  
...  
Keyword(s):  
Climate Change ◽  
Surface Water ◽  
Water Balance ◽  
Water Availability ◽  
Climate Model ◽  
Potential Evapotranspiration ◽  
Regional Climate ◽  
Future Climate Change ◽  
Return Periods ◽  
Climate Model Simulations

<p>In this contribution future changes of surface water availability over the Austrian domain is investigated. We use an ensemble of downscaled and bias-corrected regional climate model simulations of the EURO-CORDEX initiative under moderate mitigation (RCP4.5) and Paris agreement (RCP2.6) emission scenarios. The climatic water balance and its components (rainfall, snow melt, glacier melt and potential evapotranspiration) are used as indicators for surface water availability and we focus on different altitudinal classes (lowland, mountainous and high alpine) to depict a variety of processes in complex terrain. Apart from analysing the mean changes of these quantities we also pursue a hazard risk approach by estimating changes in return periods of drought events of a given magnitude as observed in the reference period. The results show in general wetter conditions over the course of the 21<sup>st</sup> century over Austria. Considering seasonal differences, winter and spring will be getting wetter due to an increase in precipitation along with a higher rainfall/snowfall fraction as a consequence of rising temperatures. In summer only little changes in the ensemble median of the climatic water balance are visible, hence uncertainties are large due to a considerable ensemble spread. However, by analysing changes in return periods of drought events, a robust signal of increasing risk of moderate and extreme drought events during summer is apparent. It emerges from an increase in interannual variability of the climatic water balance, which likely stems from intensified land-atmosphere coupling under climate change sustaining and intensifying spring preconditions towards even wetter or dryer summers.</p>

scholarly journals Incorrect Asian aerosols affecting the attribution and projection of regional climate change in CMIP6 models

2021 ◽  
Vol 4 (1) ◽  
Author(s):  
Zhili Wang ◽  
Lei Lin ◽  
Yangyang Xu ◽  
Huizheng Che ◽  
Xiaoye Zhang ◽  
...  
Keyword(s):  
Climate Change ◽  
Radiative Forcing ◽  
Impact Analysis ◽  
Climate Model ◽  
Regional Climate ◽  
Eastern China ◽  
Coupled Model ◽  
Regional Climate Change ◽  
Anthropogenic Aerosol ◽  
Wide Range

AbstractAnthropogenic aerosol (AA) forcing has been shown as a critical driver of climate change over Asia since the mid-20th century. Here we show that almost all Coupled Model Intercomparison Project Phase 6 (CMIP6) models fail to capture the observed dipole pattern of aerosol optical depth (AOD) trends over Asia during 2006–2014, last decade of CMIP6 historical simulation, due to an opposite trend over eastern China compared with observations. The incorrect AOD trend over China is attributed to problematic AA emissions adopted by CMIP6. There are obvious differences in simulated regional aerosol radiative forcing and temperature responses over Asia when using two different emissions inventories (one adopted by CMIP6; the other from Peking university, a more trustworthy inventory) to driving a global aerosol-climate model separately. We further show that some widely adopted CMIP6 pathways (after 2015) also significantly underestimate the more recent decline in AA emissions over China. These flaws may bring about errors to the CMIP6-based regional climate attribution over Asia for the last two decades and projection for the next few decades, previously anticipated to inform a wide range of impact analysis.

scholarly journals Anthropogenic forcing and response yield observed positive trend in Earth’s energy imbalance

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Shiv Priyam Raghuraman ◽  
David Paynter ◽  
V. Ramaswamy
Keyword(s):  
Radiative Forcing ◽  
Climate Model ◽  
Solar Spectrum ◽  
Internal Variability ◽  
Satellite Observations ◽  
Positive Trend ◽  
Energy Imbalance ◽  
Model Simulations ◽  
Heat Uptake ◽  
Climate Model Simulations

AbstractThe observed trend in Earth’s energy imbalance (TEEI), a measure of the acceleration of heat uptake by the planet, is a fundamental indicator of perturbations to climate. Satellite observations (2001–2020) reveal a significant positive globally-averaged TEEI of 0.38 ± 0.24 Wm−2decade−1, but the contributing drivers have yet to be understood. Using climate model simulations, we show that it is exceptionally unlikely (<1% probability) that this trend can be explained by internal variability. Instead, TEEI is achieved only upon accounting for the increase in anthropogenic radiative forcing and the associated climate response. TEEI is driven by a large decrease in reflected solar radiation and a small increase in emitted infrared radiation. This is because recent changes in forcing and feedbacks are additive in the solar spectrum, while being nearly offset by each other in the infrared. We conclude that the satellite record provides clear evidence of a human-influenced climate system.

High-Resolution Climate Change Impact Analysis on Expected Future Water Availability in the Upper Jordan Catchment and the Middle East

2014 ◽  
Vol 15 (4) ◽  
pp. 1517-1531 ◽  
Author(s):  
Gerhard Smiatek ◽  
Harald Kunstmann ◽  
Andreas Heckl
Keyword(s):  
Climate Change ◽  
High Resolution ◽  
Water Availability ◽  
Impact Analysis ◽  
River Flow ◽  
Climate Model ◽  
Mesoscale Model ◽  
Global Climate Model ◽  
Full Range ◽  
The Impact

Abstract The impact of climate change on the future water availability of the upper Jordan River (UJR) and its tributaries Dan, Snir, and Hermon located in the eastern Mediterranean is evaluated by a highly resolved distributed approach with the fifth-generation Pennsylvania State University–NCAR Mesoscale Model (MM5) run at 18.6- and 6.2-km resolution offline coupled with the Water Flow and Balance Simulation Model (WaSiM). The MM5 was driven with NCEP reanalysis for 1971–2000 and with Hadley Centre Coupled Model, version 3 (HadCM3), GCM forcings for 1971–2099. Because only one regional–global climate model combination was applied, the results may not give the full range of possible future projections. To describe the Dan spring behavior, the hydrological model was extended by a bypass approach to allow the fast discharge components of the Snir to enter the Dan catchment. Simulation results for the period 1976–2000 reveal that the coupled system was able to reproduce the observed discharge rates in the partially karstic complex terrain to a reasonable extent with the high-resolution 6.2-km meteorological input only. The performed future climate simulations show steadily rising temperatures with 2.2 K above the 1976–2000 mean for the period 2031–60 and 3.5 K for the period 2070–99. Precipitation trends are insignificant until the middle of the century, although a decrease of approximately 12% is simulated. For the end of the century, a reduction in rainfall ranging between 10% and 35% can be expected. Discharge in the UJR is simulated to decrease by 12% until 2060 and by 26% until 2099, both related to the 1976–2000 mean. The discharge decrease is associated with a lower number of high river flow years.

scholarly journals Temperature-dependence of aerosol optical depth over the southeastern US

2016 ◽  
Author(s):  
Tero Mielonen ◽  
Anca Hienola ◽  
Thomas Kühn ◽  
Joonas Merikanto ◽  
Antti Lipponen ◽  
...  
Keyword(s):  
Temperature Dependence ◽  
Land Surface ◽  
Radiative Forcing ◽  
Climate Model ◽  
Biogenic Emissions ◽  
Anthropogenic Emissions ◽  
Model Estimate ◽  
Model Simulations ◽  
Southeastern Us ◽  
Biogenic Aerosols

Abstract. Previous studies have indicated that summer-time aerosol optical depths (AOD) over the southeastern US are dependent on temperature but the reason for this dependence and its radiative effects have so far been unclear. To quantify these effects we utilized AOD and land surface temperature (LST) products from the Advanced Along-Track Scanning Radiometer (AATSR) with observations of tropospheric nitrogen dioxide (NO2) column densities from the Ozone Monitoring Instrument (OMI). Furthermore, simulations of the global aerosol-climate model ECHAM-HAMMOZ have been used to identify the possible processes affecting aerosol loads and their dependence on temperature over the studied region. Our results showed that the level of AOD in the southeastern US is mainly governed by anthropogenic emissions but the observed temperature dependent behaviour is most likely originating from non-anthropogenic emissions. Model simulations indicated that biogenic emissions of volatile organic compounds (BVOC) can explain the observed temperature dependence of AOD. According to the remote sensing data sets, the non-anthropogenic contribution increases AOD by approximately 0.009 ± 0.018 K−1 while the modelled BVOC emissions increase AOD by 0.022 ± 0.002 K−1. Consequently, the regional direct radiative effect (DRE) of the non-anthropogenic AOD is −0.43 ± 0.88 W/m2/K and −0.17 ± 0.35 W/m2/K for clear- and all-sky conditions, respectively. The model estimate of the regional clear-sky DRE for biogenic aerosols is also in the same range: −0.86 ± 0.06 W/m2/K. These DRE values indicate significantly larger cooling than the values reported for other forested regions. Furthermore, the model simulations showed that biogenic emissions increased the number of biogenic aerosols with radius larger than 100 nm (N100, proxy for cloud condensation nuclei) by 28 % per one degree temperature increase. For the total N100, the corresponding increase was 4 % which implies that biogenic emissions could also have a small effect on indirect radiative forcing in this region.

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