A National Strategy for Advancing Climate Modeling (2012) / Chapter Skim
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4 Scientific Frontiers
4 Scientific Frontiers
Pages 81-108
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From page 81... ...
It takes time to add and properly validate new processes and components to a model. Extensive testing and sensitivity experiments are required, involving hierarchical regional climate models and global climate models with a variety of scale-sensitive parameterizations.
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From page 82... ...
No other global scientific endeavor enjoys this level of international cooperation, or is subject to the same degree of scientific and public scrutiny; although this presents some challenges, this has helped to drive climate modeling forward. Several considerations underlie the reliability of climate models for many aspects of climate change.
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From page 83... ...
The next section examines some of these weaknesses and outlines several high-priority scientific frontiers that can be better addressed through advances in climate models. GRAND CHALLENGES FOR CLIMATE MODELS Climate change is expected to affect society in many ways, including impacts on health, infrastructure, food and water security, ecological integrity, and geopolitical stability.
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From page 84... ...
The severity of future warming affects most aspects of climate change, and mitigation and adaptation strategies hinge on this question, so better constraints on this question are one of the highest priorities in the climate modeling enterprise. If climate models cannot capture the mean state and main features of atmosphere and ocean circulation, they cannot provide meaningful insight regarding regional details.
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From page 85... ...
While this may not be commonplace for multicentury global climate simulations, it is already feasible for global simulations of a few weeks or for longer simulations with regional models and will likely become attractive within the next decade for some types of global climate modeling. Such simulations give much 85
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From page 86... ...
Although these are short-term processes, they have a potentially large spatial and cumulative effect on modeled tropical circulation; systematic biases can influence overall climate sensitivity in decadal to centennial predictions in climate models. Carbon-Cycle Feedbacks The cumulative extent of greenhouse gas emissions, primarily the amount of carbon dioxide (CO2)
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From page 87... ...
generation of climate models do not agree on whether soil moisture near the end of the 21st century will increase or decrease with global warming (see IPCC, 2007c, Chapter 10)
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From page 88... ...
Most climate models now include an interactive simulation of aerosols to describe aerosol-climate interactions, but the underlying chemistry and microphysics are only crudely parameterized. This limitation introduces uncertainty in model quantification of aerosol radiative forcing and its dependence on the hydrologic cycle, both through hygroscopic growth and precipitation scavenging.
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From page 89... ...
Like the land-cover impacts and feedbacks that are involved in the carbon cycle, understanding of these effects requires coupling of sophisticated, dynamic ecosystem and land-surface models. The advance of coupled land-surface, vegetation, boundary-layer, and aerosol chemistry models promises to be an exciting frontier that may transform aspects of climate modeling, and climate model utility in, for example, air quality and land-use simulations.
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From page 90... ...
Model differences in regional precipitation trends have multifaceted causes, including grid resolution but also treatments of cumulus convection, air-sea interaction, land-surface processes, upper ocean dynamics, aerosols, cloud microphysics, and the simulated global climate sensitivity. These factors interact.
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From page 91... ...
In addition to precipitation, many other processes involving land surface-atmosphere moisture, energy, and chemical exchange at regional scales are expected to be better represented as coupling schemes and resolution improve, for example, influences of land-use changes on the climate, aerosol sources, crop- and biome-specific evapotranspiration rates, and the influence of built structures (e.g., cities, wind farms)
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From page 92... ...
Improved model fidelity at regional scales is essential to assessment of water resource and agricultural stress and to drought and flood hazards, which are also an element of climate extremes. Another challenge for global and regional climate models is their representation of patterns or modes of variability, such as ENSO, the Southern Annual Mode, the Arctic and North Atlantic Oscillations, and Pacific decadal variability.
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From page 93... ...
Tropical cyclones are only roughly represented in many climate models, primarily because of low spatial resolution of the tight circulation and sharp gradients found in tropical cyclones. Simulations done with very high (25 km or less)
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From page 94... ...
The challenge of forecasting local and regional sea-level rise and associated hazards is therefore multifaceted. This is a true Earth system problem involving many aspects of climate dynamics and geophysics, including Earth and ice-sheet models that have not traditionally been included in climate modeling efforts.
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From page 95... ...
They are nonetheless pressing questions that require advances in climate modeling.
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From page 96... ...
Model representation of sea-ice thickness presents additional challenges because it involves not only thermodynamic interaction with the ocean below but also the dynamic and thermodynamic effects from the atmosphere above. The inability of climate models to adequately reproduce the recent states and trends of Arctic sea ice diminishes confidence in their accuracy for making future climate predictions.
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From page 97... ...
based around a core climate model configuration comprising an ocean circulation model, atmospheric model, sea-ice model, and terrestrial model. Such a model has been recently developed (Maslowski et al., 2012)
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From page 98... ...
Examples include cryosphereclimate interactions (permafrost thaw, sea-ice retreat) and the combined impacts of changes in the hydrologic cycle, ocean temperature and salinity, sea-ice formation and melt, and freshwater runoff from rivers, glaciers, and ice sheets on ocean stratification and deepwater formation.
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From page 99... ...
The anticipated progression to eddy-resolving and multigrid ocean modeling will improve model simulations of mixing, mesoscale eddies, and coastal ocean dynamics, permitting coupling of models of ocean dynamics, ocean biogeochemistry, and marine ecology. Terrestrial ecosystems are important in the Earth system because they influence the climate through physical, chemical, and biological processes that affect the hydrologic cycle and atmospheric composition.
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From page 100... ...
The future timing of other climatic influences, such as volcanic events, is also unknown. Thus, the extent to which annual to decadal predictive skill can be reasonably expected in climate models is limited, and at present it seems unlikely that, even in a decade, climate models will have high skill in predicting soci 100
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From page 101... ...
. Improvements may be possible through data assimilation methods of climate modeling, and through expanded observational data on ocean conditions for model initialization.
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From page 102... ...
The climate modeling community is already pressing on the first two points, advancing Earth system models and refining model physical parameterizations and resolution, and continued progress is needed on both of these fronts, perhaps more strategically focused on high-priority questions. In the committee's opinion, the third point, coordination of global and regional modeling efforts, as well as "research-oriented" versus operational models, is a weak spot in the U.S.
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From page 103... ...
More subtle climate events in the recent past, such as the Medieval Warm Period and the Little Ice Age, also provide examples of natural variability that can aid in understanding climate dynamics. These events are not fully understood, and they offer exceptional targets for climate modeling studies; lessons from the past can inform process representation in climate models that are used for future projections.
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From page 104... ...
Such examples are found in many other aspects of climate modeling as well (e.g., sea-ice dynamics)
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From page 105... ...
While a revolution in computational approaches or capabilities is not impossible, in simulating clouds and in the broader challenges of climate modeling, incremental improvements are more likely. Improvements are possible by tapping into model capabilities that already exist in some cases, through strategic cooperation of the sometimes disparate global and regional modeling streams, as well as increased cooperation of global, regional, research-based, and operational modeling efforts.
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From page 106... ...
climate modeling community pursue high-resolution model runs in the coming decades. Specifically, at least one national modeling effort in the next decade should aim to simulate historical and future climate change (i.e., the period 19002100)
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From page 107... ...
Recommendation 4.3: More effort should be put toward coordinated global and regional climate modeling activities to allow good representation of landsurface hydrology and terrestrial vegetation dynamics and to enable improved modeling of the hydrologic cycle and regional water resources, agriculture, and drought forecasts. This will require better integration of the various national climate modeling activities, including groups that focus on models of surface hydrology and vegetation dynamics.
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From page 108... ...
Parallel efforts need to aim for century-scale global atmospheric simulations at 1-2 km, to enable cloud-resolving physics. These national efforts would be facilitated by advances in climate model software infrastructure and computing capability discussed in Chapter 10.
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