Fine-scale rainfall over New Caledonia under climate change

Abstract Global climate models projections indicate no clear future rainfall changes over the Southwestern Pacific islands in response to anthropogenic forcing. Yet, these models have low (~ 100–200 km) spatial resolution and suffer from large systematic biases, such as the trademark “double ITCZ”. Here, 4 km-resolution simulations were used with a nested regional atmospheric model, which resolves the New Caledonian mountainous topography. The resulting present-day rainfall amount, spatial structure, seasonal cycle, and extremes compare much better with observations than at 20 km resolution. We applied projected changes from global climate models under the RCP8.5 scenario at the boundaries, following an approach that corrects both their present-day and projected sea surface temperature biases. Unlike climate models, our refined projections reveal an 18% decrease in annual mean rainfall over New Caledonia by 2080–2100, especially on the leeward side of the island (up to 30%) and during the hot season (that accounts for ~ 80% of the rainfall decrease). This drying is robust without bias correction, and much stronger than at ~ 20 km resolution. It is mainly driven by circulation changes. A weather regime classification further demonstrates that ~ 80% of the hot season drying relates to a strong anti-cyclonic and air subsidence anomalies centred on the north of NC, which reduces moisture convergence over the archipelago. The frequency and intensity of extreme precipitation events is also reduced by ~ 20% by 2080–2100. This drastic projected drying would have dramatic impacts on water resources and terrestrial ecosystems, pleading for carefully-planned adaptation policies for New Caledonia.

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Future Australian Severe Thunderstorm Environments. Part II: The Influence of a Strongly Warming Climate on Convective Environments

Journal of Climate ◽

10.1175/jcli-d-13-00426.1 ◽

2014 ◽

Vol 27 (10) ◽

pp. 3848-3868 ◽

Cited By ~ 30

Author(s):

John T. Allen ◽

David J. Karoly ◽

Kevin J. Walsh

Keyword(s):

Climate Models ◽

Global Climate ◽

Convective Available Potential Energy ◽

Vertical Wind Shear ◽

Atmospheric Model ◽

Global Climate Models ◽

Historical Period ◽

Severe Thunderstorm ◽

Warming Climate ◽

Eastern Australia

Abstract The influence of a warming climate on the occurrence of severe thunderstorm environments in Australia was explored using two global climate models: Commonwealth Scientific and Industrial Research Organisation Mark, version 3.6 (CSIRO Mk3.6), and the Cubic-Conformal Atmospheric Model (CCAM). These models have previously been evaluated and found to be capable of reproducing a useful climatology for the twentieth-century period (1980–2000). Analyzing the changes between the historical period and high warming climate scenarios for the period 2079–99 has allowed estimation of the potential convective future for the continent. Based on these simulations, significant increases to the frequency of severe thunderstorm environments will likely occur for northern and eastern Australia in a warmed climate. This change is a response to increasing convective available potential energy from higher continental moisture, particularly in proximity to warm sea surface temperatures. Despite decreases to the frequency of environments with high vertical wind shear, it appears unlikely that this will offset increases to thermodynamic energy. The change is most pronounced during the peak of the convective season, increasing its length and the frequency of severe thunderstorm environments therein, particularly over the eastern parts of the continent. The implications of this potential increase are significant, with the overall frequency of potential severe thunderstorm days per year likely to rise over the major population centers of the east coast by 14% for Brisbane, 22% for Melbourne, and 30% for Sydney. The limitations of this approach are then discussed in the context of ways to increase the confidence of predictions of future severe convection.

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Estimates of global terrestrial isoprene emissions using MEGAN (Model of Emissions of Gases and Aerosols from Nature)

Atmospheric Chemistry and Physics Discussions ◽

10.5194/acpd-6-107-2006 ◽

2006 ◽

Vol 6 (1) ◽

pp. 107-173 ◽

Cited By ~ 96

Author(s):

A. Guenther ◽

T. Karl ◽

P. Harley ◽

C. Wiedinmyer ◽

P. I. Palmer ◽

...

Keyword(s):

Climate Models ◽

Global Climate ◽

Model Development ◽

Terrestrial Ecosystems ◽

Global Climate Models ◽

Earth System ◽

Area Index ◽

Isoprene Emission ◽

Global Emission ◽

High Emission

Abstract. Reactive gases and aerosols are produced by terrestrial ecosystems, processed within plant canopies, and can then be emitted into the above-canopy atmosphere. Estimates of the above-canopy fluxes are needed for quantitative earth system studies and assessments of past, present and future air quality and climate. The Model of Emissions of Gases and Aerosols from Nature (MEGAN) is described and used to quantify net terrestrial biosphere emission of isoprene into the atmosphere. MEGAN is designed for both global and regional emission modeling and has global coverage with ~1 km2 spatial resolution. Field and laboratory investigations of the processes controlling isoprene emission are described and data available for model development and evaluation are summarized. The factors controlling isoprene emissions include biological, physical and chemical driving variables. MEGAN driving variables are derived from models and satellite and ground observations. Broadleaf trees, mostly in the tropics, contribute about half of the estimated global annual isoprene emission due to their relatively high emission factors and because they are often exposed to conditions that are conducive for isoprene emission. The remaining flux is primarily from shrubs which are widespread and dominate at higher latitudes. MEGAN estimates global annual isoprene emissions of ~600 Tg isoprene but the results are very sensitive to the driving variables, including temperature, solar radiation, Leaf Area Index, and plant functional type. The annual global emission estimated with MEGAN ranges from about 500 to 750 Tg isoprene depending on the driving variables that are used. Differences in estimated emissions are more than a factor of 3 for specific times and locations. It is difficult to evaluate isoprene emission estimates using the concentration distributions simulated using chemistry and transport models due to the substantial uncertainties in other model components. However, comparison with isoprene emissions estimated from satellite formaldehyde observations indicates reasonable agreement. The sensitivity of isoprene emissions to earth system changes (e.g., climate and landcover) suggests potentially large changes in future emissions. Using temperature distributions simulated by global climate models for year 2100, MEGAN estimates that isoprene emissions increase by more than a factor of two. This is considerably greater than previous estimates and additional observations are needed to evaluate and improve the methods used to predict future isoprene emissions.

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Comparison of warming trends over the last century around Antarctica from three coupled models

Annals of Glaciology ◽

10.3189/1998aog27-1-565-570 ◽

1998 ◽

Vol 27 ◽

pp. 565-570 ◽

Cited By ~ 6

Author(s):

William M. Connolley ◽

Siobhan P. O'Farrell

Keyword(s):

Climate Models ◽

Climate Model ◽

Global Climate ◽

Atmospheric Model ◽

Global Climate Models ◽

Large Temperature ◽

Coupled Models ◽

Temperature Changes ◽

Model Variability ◽

The Antarctic

We compare observed temperature variations in Antarctica with climate-model runs over the last century. The models used are three coupled global climate models (GCMs) — the UKMO, the CSIRO and the MPI forced by the CO2 increases observed over the last century, and an atmospheric model experiment forced with observed sea-surface temperatures and sea-ice extents over the last century. Despite some regions of agreement, in general the GCM runs appear to be incompatible with each other and with the observations, although the short observational record and high natural variability make verification difficult. One of the best places for a more detailed study is the Antarctic Peninsula where the density of stations is higher and station records are longer than elsewhere in Antarctica. Observations show that this area has seen larger temperature rises than anywhere else in Antarctica. None of the three GCMs simulate such large temperature changes in the Peninsula region, in either climate-change runs radiatively forced by CO2 increases or control runs which assess the level of model variability.

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Cold season emissions dominate the Arctic tundra methane budget

Proceedings of the National Academy of Sciences ◽

10.1073/pnas.1516017113 ◽

2015 ◽

Vol 113 (1) ◽

pp. 40-45 ◽

Cited By ~ 149

Author(s):

Donatella Zona ◽

Beniamino Gioli ◽

Róisín Commane ◽

Jakob Lindaas ◽

Steven C. Wofsy ◽

...

Keyword(s):

Climate Models ◽

Global Climate ◽

Regional Scale ◽

Terrestrial Ecosystems ◽

Arctic Tundra ◽

Cold Season ◽

Global Climate Models ◽

The Arctic ◽

Late Season ◽

Aircraft Data

Arctic terrestrial ecosystems are major global sources of methane (CH4); hence, it is important to understand the seasonal and climatic controls on CH4 emissions from these systems. Here, we report year-round CH4 emissions from Alaskan Arctic tundra eddy flux sites and regional fluxes derived from aircraft data. We find that emissions during the cold season (September to May) account for ≥50% of the annual CH4 flux, with the highest emissions from noninundated upland tundra. A major fraction of cold season emissions occur during the “zero curtain” period, when subsurface soil temperatures are poised near 0 °C. The zero curtain may persist longer than the growing season, and CH4 emissions are enhanced when the duration is extended by a deep thawed layer as can occur with thick snow cover. Regional scale fluxes of CH4 derived from aircraft data demonstrate the large spatial extent of late season CH4 emissions. Scaled to the circumpolar Arctic, cold season fluxes from tundra total 12 ± 5 (95% confidence interval) Tg CH4 y−1, ∼25% of global emissions from extratropical wetlands, or ∼6% of total global wetland methane emissions. The dominance of late-season emissions, sensitivity to soil environmental conditions, and importance of dry tundra are not currently simulated in most global climate models. Because Arctic warming disproportionally impacts the cold season, our results suggest that higher cold-season CH4 emissions will result from observed and predicted increases in snow thickness, active layer depth, and soil temperature, representing important positive feedbacks on climate warming.

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Sensitivity of Limiting Hurricane Intensity to SST in the Atlantic from Observations and GCMs

Journal of Climate ◽

10.1175/jcli-d-12-00433.1 ◽

2013 ◽

Vol 26 (16) ◽

pp. 5949-5957 ◽

Cited By ~ 14

Author(s):

James B. Elsner ◽

Sarah E. Strazzo ◽

Thomas H. Jagger ◽

Timothy LaRow ◽

Ming Zhao

Keyword(s):

Climate Models ◽

North Atlantic Ocean ◽

Global Climate ◽

Atmospheric Model ◽

Global Climate Models ◽

Lower Sensitivity ◽

Hurricane Intensity ◽

University Center ◽

The North ◽

Low Sensitivity

Abstract A statistical model for the intensity of the strongest hurricanes has been developed and a new methodology introduced for estimating the sensitivity of the strongest hurricanes to changes in sea surface temperature. Here, the authors use this methodology on observed hurricanes and hurricanes generated from two global climate models (GCMs). Hurricanes over the North Atlantic Ocean during the period 1981–2010 show a sensitivity of 7.9 ± 1.19 m s−1 K−1 (standard error; SE) when over seas warmer than 25°C. In contrast, hurricanes over the same region and period generated from the GFDL High Resolution Atmospheric Model (HiRAM) show a significantly lower sensitivity with the highest at 1.8 ± 0.42 m s−1 K−1 (SE). Similar weaker sensitivity is found using hurricanes generated from the Florida State University Center for Ocean–Atmospheric Prediction Studies (FSU-COAPS) model with the highest at 2.9 ± 2.64 m s−1 K−1 (SE). A statistical refinement of HiRAM-generated hurricane intensities heightens the sensitivity to a maximum of 6.9 ± 3.33 m s−1 K−1 (SE), but the increase is offset by additional uncertainty associated with the refinement. Results suggest that the caution that should be exercised when interpreting GCM scenarios of future hurricane intensity stems from the low sensitivity of limiting GCM-generated hurricane intensity to ocean temperature.

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Some Counterintuitive Dependencies of Tropical Cyclone Frequency on Parameters in a GCM

Journal of the Atmospheric Sciences ◽

10.1175/jas-d-11-0238.1 ◽

2012 ◽

Vol 69 (7) ◽

pp. 2272-2283 ◽

Cited By ~ 70

Author(s):

Ming Zhao ◽

Isaac M. Held ◽

Shian-Jiann Lin

Keyword(s):

High Resolution ◽

Climate Models ◽

Global Climate ◽

Atmospheric Model ◽

Global Climate Models ◽

Geophysical Fluid Dynamics Laboratory ◽

Mixing Rate ◽

Continuous Increase ◽

Mean Intensity ◽

Two Parameters

Abstract High-resolution global climate models (GCMs) have been increasingly utilized for simulations of the global number and distribution of tropical cyclones (TCs), and how they might change with changing climate. In contrast, there is a lack of published studies on the sensitivity of TC genesis to parameterized processes in these GCMs. The uncertainties in these formulations might be an important source of uncertainty in the future projections of TC statistics. This study investigates the sensitivity of the global number of TCs in present-day simulations using the Geophysical Fluid Dynamics Laboratory High Resolution Atmospheric Model (GFDL HIRAM) to alterations in physical parameterizations. Two parameters are identified to be important in TC genesis frequency in this model: the horizontal cumulus mixing rate, which controls the entrainment into convective cores within the convection parameterization, and the strength of the damping of the divergent component of the horizontal flow. The simulated global number of TCs exhibits nonintuitive response to incremental changes of both parameters. As the cumulus mixing rate increases, the model produces nonmonotonic response in global TC frequency with an initial sharp increase and then a decrease. However, storm mean intensity rises monotonically with the mixing rate. As the strength of the divergence damping increases, the model produces a continuous increase of global number of TCs and hurricanes with little change in storm mean intensity. Mechanisms for explaining these nonintuitive responses are discussed.

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Estimates of global terrestrial isoprene emissions using MEGAN (Model of Emissions of Gases and Aerosols from Nature)

Atmospheric Chemistry and Physics ◽

10.5194/acp-6-3181-2006 ◽

2006 ◽

Vol 6 (11) ◽

pp. 3181-3210 ◽

Cited By ~ 2666

Author(s):

A. Guenther ◽

T. Karl ◽

P. Harley ◽

C. Wiedinmyer ◽

P. I. Palmer ◽

...

Keyword(s):

Climate Models ◽

Global Climate ◽

Model Development ◽

Terrestrial Ecosystems ◽

Global Climate Models ◽

Earth System ◽

Area Index ◽

Isoprene Emission ◽

High Emission ◽

Reactive Gases

Abstract. Reactive gases and aerosols are produced by terrestrial ecosystems, processed within plant canopies, and can then be emitted into the above-canopy atmosphere. Estimates of the above-canopy fluxes are needed for quantitative earth system studies and assessments of past, present and future air quality and climate. The Model of Emissions of Gases and Aerosols from Nature (MEGAN) is described and used to quantify net terrestrial biosphere emission of isoprene into the atmosphere. MEGAN is designed for both global and regional emission modeling and has global coverage with ~1 km2 spatial resolution. Field and laboratory investigations of the processes controlling isoprene emission are described and data available for model development and evaluation are summarized. The factors controlling isoprene emissions include biological, physical and chemical driving variables. MEGAN driving variables are derived from models and satellite and ground observations. Tropical broadleaf trees contribute almost half of the estimated global annual isoprene emission due to their relatively high emission factors and because they are often exposed to conditions that are conducive for isoprene emission. The remaining flux is primarily from shrubs which have a widespread distribution. The annual global isoprene emission estimated with MEGAN ranges from about 500 to 750 Tg isoprene (440 to 660 Tg carbon) depending on the driving variables which include temperature, solar radiation, Leaf Area Index, and plant functional type. The global annual isoprene emission estimated using the standard driving variables is ~600 Tg isoprene. Differences in driving variables result in emission estimates that differ by more than a factor of three for specific times and locations. It is difficult to evaluate isoprene emission estimates using the concentration distributions simulated using chemistry and transport models, due to the substantial uncertainties in other model components, but at least some global models produce reasonable results when using isoprene emission distributions similar to MEGAN estimates. In addition, comparison with isoprene emissions estimated from satellite formaldehyde observations indicates reasonable agreement. The sensitivity of isoprene emissions to earth system changes (e.g., climate and land-use) demonstrates the potential for large future changes in emissions. Using temperature distributions simulated by global climate models for year 2100, MEGAN estimates that isoprene emissions increase by more than a factor of two. This is considerably greater than previous estimates and additional observations are needed to evaluate and improve the methods used to predict future isoprene emissions.

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Simulations of the 1979–88 polar climates by global climate models

Annals of Glaciology ◽

10.3189/s0260305500015640 ◽

1995 ◽

Vol 21 ◽

pp. 83-90 ◽

Cited By ~ 3

Author(s):

Biao Chen ◽

David H. Bromwich ◽

Keith M. Hines ◽

Xuguang Pan

Keyword(s):

Climate Models ◽

Comprehensive Evaluation ◽

Global Climate ◽

Precipitable Water ◽

Atmospheric Model ◽

Horizontal Resolution ◽

Global Climate Models ◽

Atmospheric Models ◽

Sea Level Pressure ◽

Polar Climate

The simulation of the northern and southern polar climates for 1979–88 by 14 global climate models (GCMs), using the observed monthly averaged sea-surface temperatures and sea-ice extents as boundary conditions, is part of an international effort to determine the systematic errors of atmospheric models under realistic conditions, the so-called Atmospheric Model Intercomparison Project (AMIP), In this study, intercomparison of the models’ simulation of polar climate is discussed in terms of selected surface and vertically integrated monthly averaged quantities, such as sea-level pressure, cloudiness, precipitable water, precipitation and evaporation/sublimation. The results suggest that the accuracy of model-simulated climate features in high latitudes primarily depends on the horizontal resolution and the treatment of physical processes in the GCMs. AMIP offers an unprecedented opportunity for the comprehensive evaluation and validation of current atmospheric models and provides valuable information for model improvement.

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