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Authors
Shiogama H, Emori S, Hanasaki N, Abe M, Masutomi Y, Takahashi K, Nozawa T (2011)
Title
Observational constraints indicate risk of drying in the Amazon basin. Nature Communications, 2, Article number 253, doi: 10.1038/ncomms1252.
Keywords
Metrics, Impact assessment, Climate change projection, Observational constrain, Hydrological cycle
Abstract

Climate warming due to human activities will be accompanied by hydrological cycle changes. Economies, societies and ecosystems in South America are vulnerable to such water resource changes. Hence, water resource impact assessments for South America, and corresponding adaptation and mitigation policies, have attracted increased attention. However, substantial uncertainties remain in the current water resource assessments that are based on multiple coupled Atmosphere Ocean General Circulation models. This uncertainty varies from significant wetting to catastrophic drying. By applying a statistical method, we characterized the uncertainty and identified global-scale metrics for measuring the reliability of water resource assessments in South America. Here, we show that, although the ensemble mean assessment suggested wetting across most of South America, the observational constraints indicate a higher probability of drying in the Amazon basin. Thus, over-reliance on the consensus of models can lead to inappropriate decision making.

Journal
NATURE COMMUNICATIONS
Authors
Shiogama, Hideo, Seita Emori, Kiyoshi Takahashi, Tatsuya Nagashima, Tomoo Ogura, Toru Nozawa and Toshihiko Takemura (2010)
Title
Emission scenario dependency of precipitation on global warming in the MIROC3.2 model. J. Climate, 23, 2404-2417.
Keywords
Hydrological cycle, Aerosols, Climate change projection, Pattern Scaling
Abstract

The precipitation sensitivity per 1 Kof global warming in twenty-first-century climate projections is smaller in an emission scenario with larger greenhouse gas concentrations and aerosol emissions, according to the Model for Interdisciplinary Research on Climate 3.2 (MIROC3.2) coupled atmosphere-ocean general circulation model. The authors examined the reasons for the precipitation sensitivity to emission scenarios by performing separated individual forcing runs under high and low emission scenarios. It was found that the dependency on emission scenario is mainly caused by differences in black and organic carbon aerosol forcing (the sum of which is cooling forcing) between the emission scenarios and that the precipitation is more sensitive to carbon aerosols than well-mixed greenhouse gases. They also investigated the reason for the larger precipitation sensitivity (larger magnitude of precipitation decrease per 1 K cooling of temperature) in the carbon aerosol runs. Surface dimming due to the direct and indirect effects of carbon aerosols effectively decreases evaporation and precipitation, which enhances the precipitation sensitivity in the carbon aerosol runs. In terms of the atmospheric moisture cycle, although changes of vertical circulation offset the effects of changes in the atmospheric moisture in both the carbon aerosol and greenhouse gas runs, the amplitude of vertical circulation change per 1 K temperature change is less in the carbon aerosol runs. Furthermore, the second indirect effect of organic carbon aerosol counteracts the influence of the vertical circulation change. These factors lead to suppression of changes in the moisture¡Çs atmospheric residence time and increase of the precipitation sensitivity in the carbon aerosol runs.

Journal
AMS Journals Online
Authors
Shiogama, Hideo, Naota Hanasaki, Yuji Masutomi, Tatsuya Nagashima, Tomoo Ogura, Kiyoshi Takahashi, Yasuaki Hijioka, Toshihiko Takemura, Toru Nozawa and Seita Emori (2010)
Title
Emission scenario dependencies in climate change assessments of the hydrological cycle. Climatic Change, 99, 321-329, doi: 10.1007/s10584-009-9765-1.
Keywords
Hydrological cycle, Aerosols, Climate change projection, Impact assessment, Pattern Scaling
Abstract

Anthropogenic global warming will lead to changes in the global hydrological cycle. The uncertainty in precipitation sensitivity per 1 K of global warming across coupled atmosphere-ocean general circulation models (AOGCMs) has been actively examined. On the other hand, the uncertainty in precipitation sensitivity in different emission scenarios of greenhouse gases (GHGs) and aerosols has received little attention. Here we show a robust emission-scenario dependency (ESD); smaller global precipitation sensitivities occur in higher GHG and aerosol emission scenarios. Although previous studies have applied this ESD to the multi-AOGCM mean, our surprising finding is that current AOGCMs all have the common ESD in the same direction. Different aerosol emissions lead to this ESD. The implications of the ESD of precipitation sensitivity extend far beyond climate analyses. As we show, the ESD potentially propagates into considerable biases in impact assessments of the hydrological cycle via a widely used technique, so-called pattern scaling. Since pattern scaling is essential to conducting parallel analyses across climate, impact, adaptation and mitigation scenarios in the next report from the Intergovernmental Panel on Climate Change, more attention should be paid to the ESD of precipitation sensitivity.

Journal
SplingerLink
Authors
Sugiyama, Masahiro, Hideo Shiogama and Seita Emori (2010)
Title
Precipitation extreme changes exceeding moisture content increases in MIROC and IPCC climate models. Proceedings of the National Academy of Sciences, vol. 107 no. 2, pp571-575, doi: 10.1073/pnas.0903186107.
Keywords
Extreme Precipitation, Climate change projection
Abstract

Precipitation extreme changes are often assumed to scale with, orare constrained by, the change in atmospheric moisture content.Studies have generally confirmed the scaling based on moisturecontent for the midlatitudes but identified deviations for the tropics.In fact half of the twelve selected Intergovernmental Panel onClimate Change (IPCC) models exhibit increases faster than theclimatological-mean precipitable water change for high percentilesof tropical daily precipitation, albeit with significant intermodelscatter. Decomposition of the precipitation extreme changes revealsthat the variations among models can be attributed primarilyto the differences in the upward velocity. Both the amplitude andvertical profile of vertical motion are found to affect precipitation extremes. A recently proposed scaling that incorporates these dynamical effects can capture the basic features of precipitation changes in both the tropics and midlatitudes. In particular, the increases in tropical precipitation extremes significantly exceed the precipitable water change in Model for Interdisciplinary Research on Climate (MIROC), a coupled general circulation model with the highest resolution among IPCC climate models whose precipitation characteristics have been shown to reasonably match those of observations. The expected intensification of tropical disturbances points to the possibility of precipitation extreme increases beyond the moisture content increase as is found in MIROC and some of IPCC models.

Journal
PNAS
Authors
Watanabe, S. and Y. Kawatani (2012)
Title
Sensitivity of the QBO to mean tropical upwelling under a changing climate simulated with an Earth system model, J. Metorol. Soc. Jpn., 90A, 351-360, DOI:10.2151/jmsj.2012-A20.
Keywords
QBO, tropical upwelling, Brewer-Dobson circulation, MIROC-ESM
Abstract

The sensitivity of the equatorial quasi-biennial oscillation (QBO) to increasing greenhouse gas (GHG) concentrations over time is evaluated using a high-top (85 km) earth system model, which generates the QBO using a non-orographic gravity wave drag parameterization. Based on a pre-industrial control run (1850), a 1/2 CO2 run and a 4xCO2 run are performed as sensitivity experiments. In addition, long-term transient behaviors of the QBO in a historical climate run (1850-2005) and a future projection run (2006-2100) are investigated. The period of the simulated QBO lengthens in a GHG-rich warmer climate, changing from a quasi-regular 24 months in 1850-1980 to a variable 24-31 months in 1980-2050, although never exceeding 31 months even in the extremely warm 4xCO2 run. Such elongation of the QBO period is mostly caused by strengthening of the mean tropical upwelling of the Brewer-Dobson circulation, which counteracts the wave forcing that drives the QBO. Simultaneous reductions in the easterly wind maximum of the QBO are also caused by this mechanism.

Journal
-
Authors
Watanabe, S. and T. Yokohata (2012)
Title
Future Increase in the All-sky UV-B Radiation over Asia Projected by an Earth System Model, J. Metorol. Soc. Jpn., 90A, 295-305, DOI:10.2151/jmsj.2012-A15.
Keywords
UV-B validation and projection over Asia, MIROC-ESM-CHEM
Abstract

Direct simulations of the surface all-sky UV-B radiation in an Earth system model (MIROC-ESM-CHEM) are validated against the operational ground-based measurements of spectral UV radiation at Sapporo, Tateno, Kagoshima, Naha, and Chengkung. The model reasonably reproduces the mean seasonal evolution of the surface UV-B radiation at Sapporo and Naha, but substantially overestimates it at Tateno and Kagoshima during the summer. Underestimation of the cloud effect at these two sites contributes to the overestimation. A projection of the seasonal evolution of the monthly mean UV-B radiation into the future shows a general increase in the 2090s compared to the 2000s. While a slight reduction of the column ozone contributes to the UV-B increase, the effects of the reduction in cloud forcing and, especially, of the reduction in aerosols contribute more significantly. The month for which the largest increase in the UV-B radiation is projected varies site-by-site, reflecting local changes in forcing due to aerosols and clouds.

Journal
-
Authors
Watanabe, S., K. Sudo, T. Nagashima, T. Takemura, H. Kawase and T. Nozawa (2011)
Title
Future projections of surface UV¡¾B in a changing climate, J. Geophys. Res., 116, D16118, doi:10.1029/2011JD015749.
Keywords
long-term UV-B projection, ozone, aerosols, MIROC-ESM-CHEM
Abstract

Results of comprehensive long¡¾term simulations of surface all¡¾sky and clear¡¾skyultraviolet (UV) radiation through 1960-2100 are presented. A new earth system model,MIROC¡¾ESM¡¾CHEM, is used for the simulation, which considers key processes thatchange the surface UV radiation: atmospheric dynamics and chemistry affecting ozonein the stratosphere and troposphere, aerosols and clouds in the troposphere, and changesin surface albedo with sea ice and snow cover. In contrast to previous assessmentsconsidering only the effect of long¡¾term change in stratospheric ozone, the simulatedlong¡¾term behavior of UV radiation in this study is strongly affected by other processes.In one of two simulations, all¡¾sky UV radiation in the northern midlatitudes is projectedto increase in the 21st century despite the expected recovery of the stratospheric ozonelayer. Reductions in aerosols and clouds are expected to overcompensate for the effectof ozone recovery. The results are sensitive to the future socioeconomic scenario,describing GHG concentrations and emissions of aerosol and ozone precursors in thetroposphere. The interannual variability of UV radiation associated with the 11 year solarcycle and local processes is also discussed.

Journal
JGR
Authors
Tachiiri, K., Ito, A., Hajima, T., Hargreaves, J. C., Annan, J. D. and Kawamiya, M (2012)
Title
Nonlinearity of land carbon sensitivities in climate change simulations, J. Metorol. Soc. Jpn., to be published in January 2012.
Keywords
climate-carbon cycle system, climate-carbon feedback, concentration-carbon feedback, RCP4.5 scenario, EMIC, terrestrial ecosystem model
Abstract

In the climate-carbon cycle system, the terrestrial ecosystem feedback is significant. In studies on feedback analysis, the ecosystem feedback is divided into the sensitivity of carbon storage to atmospheric CO2 concentration (¦ÂL), and temperature change (¦ÃL). Although ecosystems include many nonlinear processes, the scenario- and time-dependency of ¦ÂL and ¦ÃL have not been explicitly discussed. To check the validity of this simplification and its robustness, we carried out two, 1% per year (p.a.) and RCP4.5 scenario, experiments using 300 ensemble members perturbing twelve important and a priori unconstrained parameters. In the 1% p.a. experiment, ¦ÂL peaked around 500 ppm and then gradually decreased with increasing CO2 level, while ¦ÃL decreased with some variability as temperature increases. The time-dependency of ¦ÂL was small (at least for CO2 level > 550 ppm), but that of ¦ÃL was significant, and the effect of this was larger than that of the non-linear term (i.e., combined effect of CO2 and temperature change). The scenario-dependency is also significant, but the effect in the estimated carbon uptake was smaller than that by the time-dependency. By investigating the background of this effect, we found that in the 1% p.a. CO2 increase scenario, the maximum photosynthesis rate and specific leaf area (SLA, leaf area per unit dry mass) had the most significant contribution to both of ¦ÂL and ¦ÃL, and the contributions are dependent on the climate state (i.e., temperature and atmospheric CO2 level). For carbon uptake in both experiments, SLA and coefficient of plant respiration were most significant. We also attempted to constrain the ensemble members, and found that for net primary production, soil carbon and soil respiration, the default parameter set was already well-tuned, while observations of leaf area index (LAI) strongly constrains ¦ÂL, ¦ÃL, airborne fraction and ecosystem carbon balance as the default model overestimated the LAI.

Journal
-
Authors
Yokohata, T., M. J. Webb, M. Collins, K. D. Williams, M. Yoshimori, J. C. Hargreaves, and J. D. Annan, 2010
Title
Structural similarities and differences in climate responses to CO2 increase between two perturbed physics ensembles, J. Climate 23, 1392-1410, doi:10.1175/2009JCLI2971.1.
Keywords
Climate Sensitivity, Perturbed Parameter Ensembles, Cloud Feedback
Abstract

The equilibrium climate sensitivity (ECS) of the two perturbed physics ensembles(PPE) generated using structurally different GCMs, MIROC3.2 andHadSM3, is investigated. We develop a method to quantify the SW cloud feedbackby clouds with different cloud top pressure. We find that the difference inthe ensemble means of the ECS between the two ensembles is mainly caused bydifferences in the SW low level cloud feedback. The ensemble mean SW cloudfeedback and ECS of the MIROC3.2 ensemble is larger than the HadSM3 ensembleand this is likely related to the 1XCO2 low level cloud albedo of the formerbeing larger than that of the latter. We also find that the largest contribution tothe within-ensemble variation of ECS comes from the SWlow level cloud feedbackin both ensembles. The mechanism which causes the within-ensemble variationis different between the two ensembles. In the HadSM3 ensemble, members withlarge 1XCO2 low level cloud albedo have large SWcloud feedback and large ECS;ensemble members with large 1XCO2 cloud cover have large negative SW cloudfeedback and relatively low ECS. In the MIROC3.2 ensemble, the 1xCO2 lowlevel cloud albedo is much more tightly constrained, and no relationship is foundbetween it and the cloud feedback. These results indicate that both the parametricuncertainties sampled in PPEs and the structural uncertainties of GCMsare important and worth further investigation.

Journal
AMS Journals Online
Authors
Kawatani, Y., K. Hamilton, S. Watanabe, 2011
Title
The Quasi-Biennial Oscillation in a Double CO2 Climate, J. Atmos. Sci., 68, 265-283.
Keywords
Future change of the Quasi-biennial oscillation in a high-resolution MIROC-AGCM
Abstract

The effects of anticipated twenty-first-century global climate change on the stratospheric quasi-biennial oscillation (QBO) have been studied using a high-resolution version of the Model for Interdisciplinary Research on Climate (MIROC) atmospheric GCM. This version of the model is notable for being able to simulate a fairly realistic QBO for present-day conditions including only explicitly resolved nonstationary waves. A long control integration of the model was run with observed climatological sea surface temperatures (SSTs) appropriate for the late twentieth century, followed by another integration with increased atmospheric CO2 concentration and SSTs incremented by the projected twenty-first-century warming in a multimodel ensemble of coupled ocean-atmosphere runs that were forced by the Special Report on Emissions Scenarios (SRES) A1B scenario of future atmospheric composition. In the experiment for late twenty-first-century conditions the QBO period becomes longer and QBO amplitude weaker than in the late twentieth-century simulation. The downward penetration of the QBO into the lowermost stratosphere is also curtailed in the late twenty-first-century run. These changes are driven by a significant (30%-40%) increase of the mean upwelling in the equatorial stratosphere, and the effect of this enhanced mean circulation overwhelms counteracting influences from strengthened wave fluxes in the warmer climate. The momentum fluxes associated with waves propagating upward into the equatorial stratosphere do strengthen overall by (10%-15%) in the warm simulation, but the increases are almost entirely in zonal phase speed ranges that have little effect on the stratospheric QBO but that would be expected to have important influences in the mesosphere and lower thermosphere.

Journal
AMS Journals Online
Authors
Kawatani, Y., K. Hamilton, A. Noda, 2012
Title
The effects of changes in sea surface temperature and CO2 concentration on the quasi-biennial oscillation, J. Atmos. Sci., doi:JAS-D-11-0265.1
Keywords
Future change of the Quasi-biennial oscillation in a high-resolution MIROC-AGCM
Abstract

The effects of sea surface temperature (SST) and CO2 on future changes in the quasi-biennial oscillation (QBO) are investigated using a climate model that simulates the QBO without parameterized nonstationary gravity wave forcing. Idealized model experiments using the future SST with the present CO2 (FS run) and the present SST with the future CO2 (FC run) are conducted, as are experiments using the present SST with the present CO2 (present run) and the future SST with the future CO2 (future run). When compared with the present run, precipitation increases around the equatorial region in the FS run and decreases in the FC run, resulting in increased and decreased wave momentum fluxes, respectively. In the mid-latitude lower stratosphere, westward (eastward) wave forcing anomalies form in the FS (FC) run. In the middle stratosphere off the equator, westward wave forcing anomalies form in both the FS and FC runs. Corresponding to these wave forcing anomalies, the residual vertical velocity significantly increases in the lower stratosphere in the FS run but decreases to below 70 hPa in the FC run, whereas residual upward circulation anomalies form in both the FS and FC runs in the middle equatorial stratosphere. Consequently, the amplitude of the QBO becomes smaller in the lower stratosphere, and the period of the QBO becomes longer by about 1-3 months in the FS run. On the other hand, in the FC run, the QBO extends farther downward into the lowermost stratosphere, and the period becomes longer by 1 month.

Journal
AMS Journals Online
Authors
Shiogama, H, DA Stone, T Nagashima, T Nozawa, S Emori (2012)
Title
On the linear additivity of climate forcing-response relationships at global and continental scales. International Journal of Climatology, submitted.
Keywords
climate change, climate model, additivity, detection and attribution, future projection
Abstract

Within the context of the prediction, detection and attribution of climate change, a number of studies have explicitly or implicitly assumed that individual climate responses to individual forcing agents can be linearly added to obtain the total climate response to the sum of the forcing agents. This assumption of the ¡Èlinear additivity of forcing-response relationships¡É has been tested by previous studies, but it remains controversial whether linear additivity holds with all combinations of forcing agents, such as ¡Ègreenhouse gases plus indirect effects of anthropogenic aerosols¡É or ¡Ègreenhouse gases plus solar irradiance.¡É This study explored whether linear additivity holds in 5-yr mean temperature/precipitation responses to various combinations of forcing agents in the 20th century and in a future-emissions scenario at global and continental scales. We used Model for Interdisciplinary Research on Climate version 3 (MIROC3), which includes the 1st and 2nd indirect effects of aerosols. The forcing factors considered were well-mixed greenhouse gases, the direct and indirect effects of sulphate and carbon aerosols, ozone, land-use changes, solar irradiance and volcanic aerosols (the latter three factors were specified only in the 20th-century runs). By performing and analysing an enormous matrix of forcing runs, we concluded that linear additivity holds in temperature responses for all of the combinations of forcing agents at the global and continental scales, but it breaks down for precipitation responses in certain cases of future projections.

Journal
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