Thriving on Our Changing Planet A Decadal Strategy for Earth Observation from Space (2018) / Chapter Skim
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9 Climate Variability and Change: Seasonal to Centennial
9 Climate Variability and Change: Seasonal to Centennial
Pages 421-498
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From page 421... ...
Beginning with a focus on the impacts of improved understanding of climate variability and change, the Panel on Climate Variability and Change: Seasonal to Centennial identified a number of priority science topics for which key satellite measurements, together with complementary measurements from other platforms, will make a significant scientific impact with corresponding societal benefits. Table 9.1 summarizes the panel's scientific and application priorities, as addressed in its questions and the measurement objectives.
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A number of new techniques, measurement strategies, and observational technologies are now available for the production of new, cost-effective, and beneficial measurements, thus providing an invaluable opportunity to advance the science for improved understanding of the Earth system and societal benefits. 1Not mapped here are cases where the Targeted Observables may provide a narrow or an indirect benefit to the objective, although such connections may be cited elsewhere in this report.
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C-1b. Determine the change in the global oceanic heat uptake to within ocean heat storage?
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C-8a. Improve our understanding of the drivers behind polar climate change already observed in the Arctic amplification by quantifying the relative impact of snow/ice-albedo feedback and projected for Antarctica on global trends versus changes in atmospheric and oceanic circulation, water vapor, and of sea-level rise, atmospheric circulation, lapse rate feedback.
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Priority Targeted Observables Science and Applications Objectives Aerosol Vertical Profiles C-2g, C-2h, C-5a, C-7a Aerosol Properties C-2g, C-2h, C-5a, C-7a Temperature, Water Vapor, Planetary Boundary Layer (PBL) C-2b, C-2g, C-2h, C-4a, C-7a, C-7c, C-8a Height Atmospheric Winds C-2h, C-4a, C-5a, C-7a, C-7c Radiance Intercalibration C-2a, C-2b, C-2c, C-2h, C-5c, C-7c Precipitation and Clouds C-2a, C-2g, C-2h, C-5c, C-7a, C-7c Ice Elevation C-1c, C-8a, C-8b, C-8c Mass Change C-1a, C-1b, C-1c, C-1d Greenhouse Gases C-2d, C-3a, C-4a Surface Characteristics C-2h, C-3a, C-5a, C-8c Ozone and Trace Gases C-2g Sea-Surface Height (SSH)
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concludes that "it is extremely likely that human influence has been the dominant cause of the observed warming since the mid-20th century,"2 with more than half of the observed increase in global average surface temperature caused by the anthropogenic increase of greenhouse gas concentrations (arising from burning of fossil fuels, cement production, deforestation, and agriculture) and other anthropogenic forcings together.
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Predictions beyond the decadal scale are essentially limited by uncertainties (and associated modeling deficiencies) in aerosol radiative forcing, in climate feedbacks such as those involving clouds (IPCC WG1, 2013)
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. • is possible to track land use change and ecosystem responses to climate variations, which contribute It to improving the understanding of the carbon cycle, while methods to quantify carbon stocks and fluxes are rapidly evolving (Landsat, MODIS, AVHRR, OCO-2)
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For instance, difficulties persist in trying to narrow the bounds on the estimate of Earth's climate sensitivity. Reducing the uncertainty in this parameter will require global measurements of key variables -- for example, aerosols, clouds, radiation, ocean heat
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global climate observations, contributing to assessments of the rapidity of change in essential climate variables (e.g., frequency and severity of extreme events)
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This has laid the foundation for a more quantitative understanding of critical mechanisms through comprehensive and sustained observations, which in turn can lead to increased certainty of our understanding of the central challenges -- for example, variation and trends in climate variables, climate feedbacks and sensitivity, rate of regional sealevel rise, weather-to-climate information on the mean and extremes, and so on. In this regard, further development and expanded use of Climate Observing System Simulation Experiments (COSSEs)
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. current reanalyses focus on the ocean or atmosphere components separately, although studies have pointed to new methods involving multiple components of the Earth system -- for example, ensemble coupled atmosphere-ocean data assimilation (Zhang et al., 2005)
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-- there now emerges the ability to quantify the role of the ocean in the Earth system with enhanced perspectives of ocean-atmosphere interactions -- for example, subseasonal-to-decadal prediction, energy and hydrologic cycle variations linked to climate variations and change, and heat and CO2 exchange between the atmosphere and ocean and storage of these quantities in the ocean (e.g., the Southern Ocean Carbon and Climate Observations and Modeling [SOCCOM] Project is performing measurements of carbon and other variables in the Southern Ocean;5 carbon-climate feedback is one of the World Climate Research Programme [WCRP]
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The quantified Earth science/ application objectives producing the Most Important priorities are associated with the following questions. C-1: Sea-level Rise: Ocean Heat Storage and Land-Ice Melt The rise of the global mean sea level is an integrated response to the change of a major part of the Earth system caused by the warming of the planet.
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are to radiative forcing of the climate system. Radiative forcings can occur due to natural factors, such as solar irradiance and emissions from volcanic eruptions, or arise due to human influences -- for example, greenhouse gas and aerosol emissions and land use changes.
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C-3: Carbon Cycle, Including Carbon Dioxide and Methane Changes in radiative forcing arising from greenhouse gas emissions, principally CO2 and CH4 (see Figure 9.4) , have been and will likely continue to be the most important driver of climate change in the twenty-first century.
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An additional critical factor is the influence of the radiative forcings on regional precipitation, with indications that the effect of anthropogenic aerosols could be comparable to that of the greenhouse gases (e.g., Asian monsoon, Bollasina et al., 2011; northern hemisphere precipitation, Polson et al., 2014)
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. In addition, land-ice changes can affect global-to-regional sea-level rise, glacier changes will affect river hydrology and freshwater supply for large populations, while thaw of the large permafrost carbon pool will affect the global carbon cycle.
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Climate feedbacks and sensitivity Other subjects that yielded Very Important and Important objectives are listed here: • C-3. Carbon cycle, including carbon dioxide and methane • C-4.
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Such analysis has shown that we are able to determine the change of the rate of global sea-level rise FIGURE 9.5 Global mean sea-level record from a series of satellite altimetry missions. This figure was based on precision altimetry missions covering 66 degrees N to 66 degrees S
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On global average the difference between the altimetric measurement of sea-level change and the part caused by melting land ice provides an estimate of the steric sea-level associated with thermal expansion, from which ocean heat storage can be estimated. Taking into account the vertical variation of thermal expansion, Wunsch and Heimbach (2014)
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have contributed about 14 mm to global mean sea-level change, and the ice sheets have contributed nearly equally, because the mass loss from the ice sheets has been increasing faster than that from GIC (Shepherd et al., 2012) (Figure 9.6)
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. The mechanisms of ice melting by the ocean and ice fracturing are most important to understand since they can increase the rates of glacier flow by one order of magnitude over the coming century, with concomitant effects on the rate of sea-level rise from ice sheets.
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How much will sea level rise, globally and regionally, over the next decade and beyond, and what will be the role of ice sheets and ocean heat storage? ios supporting the US National Climate Assessment November 2012 | 3 In order to make substantial improvement in the ability to predict sea-level rise, several objectives have been identified by the panel: • -1a.
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This is essential for determining the part of sea-level change caused by O the change of ocean mass, from which the difference with the total sea-surface height, the steric sea level caused by ocean heat storage change, can be derived. The steric sea level is used to determine the change of ocean heat storage.
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describes the Earth system response to radiative forcing on longer time scales (centuries) and is composed of a wide range of feedback processes involving clouds, water vapor, temperature lapse rate, surface albedo, and the carbon cycle.
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The current uncertainty in ECS is a factor of 4 at 73 percent confidence level with a range of 1.5°C to 6°C for the radiative forcing caused by a doubling of CO2 in the atmosphere. Figure 9.8 summarizes the range of ECS estimates from climate models and climate observations (IPCC, 2013, Box 12.12)
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Science Question and Application Goals Question C-2. How can we reduce the uncertainty in the amount of future warming of Earth as a function of fossil fuel emissions, improve our ability to predict local and regional climate response to natural and anthropogenic forcings, and reduce the uncertainty in global climate sensitivity that drives uncertainty in future economic impacts and mitigation/adaptation strategies?
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The second largest uncertainty is the determination of the combined water vapor feedback and temperature lapse rate feedback. These two feedbacks have a strong negative correlation and are therefore normally considered as a combined feedback uncertainty even though uncertainty in each component can be much larger than the two in combination (IPCC, 2013)
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Similarly, aerosol forcing is considered separately in the following sections in terms of the processes governing their direct effect and their interactions with clouds, but here we note briefly two considerations of relevance for ECS. First, one of the key methods to estimate climate sensitivity from observations is to compare the time series of radiative forcing with that of temperature increase.
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carbon cycle feedback, and (4) aerosol radiative forcing.
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microwave radio occultation High vertical resolution boundary layer profiles of temperature, Surface scatterometer winds, wind lidar, DIAL lidar, water vapor water vapor, wind speed/direction radio occultation, temperature lidar using molecular oxygen density High time resolution (e.g., 15-minute sampling) Smallsat constellations, geostationary satellites High-accuracy precipitation and drop size distribution Multiwavelength doppler radar, multifield of view lidar Multilayer cloud vertical profiles Radar, lidar Thin cirrus vertical distribution, optical properties High spectral resolution lidar Surface pressure Molecular oxygen lidar, Molecular oxygen A-band, numerical weather prediction (NWP)
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We also note that the World Climate Research Programme (WCRP) Grand Challenge on climate sensitivity is focused on several cloud and general circulation modeling studies, along with studies of past observations to move toward improved cloud process models.8 Ultimately, development and testing of improved cloud and aerosol process models will require advanced short time scale process observations (say, from weather to seasonal time scales)
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. While cloud feedback is by far the largest uncertainty in ECS, the combination of water vapor feedback and temperature lapse rate feedback (Objective C-2c)
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This observation does not require intercalibration of VIIRS to the high accuracy of the CLARREO reference spectrometer mentioned for cloud feedback or temperature and water vapor feedback to achieve.
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In the same sense climate feedbacks also link closely to the Water and Energy Integrating Theme, the Water Cycle Integrating Theme, and the Carbon Cycle Integrating Theme, as well as the Natural Hazards and Extreme Events Integrating Theme. In some cases the linkage is obvious, as for the carbon cycle climate feedback objective, which overlaps with the Ecosystems Panel as well as the Carbon Cycle Integrating Theme.
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These estimates of global warming potential (GWP) of CH4 rise to 86 and 34 for the two time horizons, respectively, when allowance is made for carbon cycle feedback (IPCC, 2013)
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Variations of CO2 in 2100 ranged from 795 to 1145 ppm for the same fossil fuel emission scenario, with differences mainly attributable to the response of the land carbon cycle. Booth et al.
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to understand the processes controlling the natural components of the carbon cycle, which in turn will lead to models with better predictive abilities under changing climate conditions. Satellite observations of CO2, such as those provided by the Orbiting Carbon Observatory-2 (OCO-2)
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Future satellite sensors may employ a variety of combined approaches, including active/passive, geostationary versus low-Earth orbit, high spatiotemporal resolution over targeted areas versus broad-area mapping, and combined near-IR/mid-IR spectroscopy. For flux estimation, systematic biases in retrievals are more problematic than random errors and can be reliably detected and quantified only if sufficiently informative ground truth data are available.
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Consequently, the best flux estimates will come from a combination of remote-sensing and in situ measurements from a variety of platforms. Connections to Other Panels and Integrating Themes Ecosystems Panel Carbon cycle-climate feedbacks are also addressed by the Ecosystems Panel, and discussion of measurements such as vegetation indices, biomass, and solar-induced fluorescence are described in Chapter 8.
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, provides feedbacks through the boundary layers of the atmosphere and oceans to modulate ocean and atmospheric circulations, the ocean heat content, the global water and energy cycles, the concentration of CO2 in the atmosphere by sequestration in the ocean and subsequent evasion, and the modulation and production of low-level clouds through oceanic aerosol production of cloud condensation nuclei. These interactions occur across a wide range of time and space scales, from the relatively fast weather exchanges at storm scales to centennial global variability.
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Used with permission. The exchange of momentum in addition to heat and moisture through the ocean surface drives the ocean circulation, upper ocean mixing, and surface wave fields, and provides a drag on the atmosphere.
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In order to make progress in our understanding of this question, four key objectives have been identified: • -4a. Improve the estimates of global air-sea fluxes of heat, momentum, water vapor (i.e., mois C ture)
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In addition, increased in situ observations in key regimes will be needed in order to evaluate the uncertainty of these new measurements. As with surface winds, a signifi cant time series exists that is used for calculation of global data sets of evaporation and turbulent momentum and heat fluxes from the passive microwave Special Sensor Microwave Imager (SSMI)
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Fluxes of carbon and methane are also of high importance to the Ecosystem Panel. Variability in the air-sea heat and moisture fluxes are key to the Hydrologic Cycle Panel goals of improved understanding and representation of the global energy and water cycles, as the largest source of uncertainty in closing these budgets is the air-sea flux of latent heat (water vapor; e.g., L'Ecuyer et al., 2015)
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. Because aerosol lifetimes are much shorter than those of greenhouse gases, atmospheric loadings of anthropogenic aerosol will diminish much more rapidly when emissions are controlled, compared to greenhouse gases, and Earth's temperature will effectively be determined by the climate sensitivity to CO2 (Levy et al., 2013)
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IPCC WG1 Figure 8.16 and surrounding text indicate total forcing uncertainty is dominated by aerosol forcing uncertainty. Hence, at least a factor of 2 reduction in the uncertainty of radiative forcing of climate due to aerosols would be required to achieve a factor of 2 reduction in total forcing uncertainty, assuming contributing errors add in quadrature.
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What Are the Largest Uncertainties in Aerosol Indirect Radiative Forcing? Understanding aerosol-cloud-precipitation interactions from space is a complex problem, as it is fundamentally challenging or impossible to observe both the aerosol and the clouds in the same column.
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• erosol indirect effect. Since atmospheric aerosols serve as the nuclei for cloud particles and hence A exert a strong influence on cloud formation, microphysics, and precipitation -- that is, the hydrologic cycle -- aerosol indirect effects are manifest in a continuous arc that begins with how, when, and where aerosol are ingested into clouds, and ends with their removal to the surface in precipitation or resuspension in the atmosphere after processing, along with the changes to the atmospheric state induced that then feed back into subsequent cloud cycles.
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Dedicated field campaigns that augment space-based observations would strengthen the quantification of the aerosol indirect forcing and thus the net anthropogenic forcing. In addition, the combination of models (high-resolution global climate models [GCMs]
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. Figure 9.14 illustrates hindcast simulations using a coupled climate model and a data assimilation system to demonstrate the significance of both observed initial conditions and radiative forc FIGURE 9.14 Decadal hindcast simulations (NOAA/GFDL CM2.1 global climate model with the Ensemble Coupled Data Assimilation system, used in WCRP/CMIP3 project)
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. While the global SST is driven by the radiative forcings, the decadal-scale North Atlantic SST and heat transport in the midlatitudes are driven primarily by the initial conditions.
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Ocean heat content, particularly in the subsurface, has substantial memory and underlies our hopes for reliable decadal scale prediction and for most facets of seasonal-to-interannual prediction. The phases of the El Niño Southern Oscillation cycle (ENSO; a coupled mode of the atmosphere-ocean system)
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; • Stratospheric quantities (polar vortex winds, ozone, temperature, water vapor) ; • Ocean quantities (sea-surface height, sea-surface salinity, sea-ice thickness, sea-ice fraction, sea-sur face temperature, surface vector winds, subsurface temperatures and salinity, surface currents, ocean mass, ice-shelf slope)
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from a very wide range of measurements collected in response to missions designed for other science objectives (e.g., the measurement of sea-surface height for the study of sea-level rise or the measurement of cloud information needed for determining climate sensitivity)
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. Field campaigns may be needed to characterize relevant processes related to well-mixed and short-lived greenhouse gases, aerosols, clouds, and wind fields.
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While polar amplification is largely driven by changes in sea ice and snow cover, changes in atmospheric and ocean circulation, including changes in prevailing winds driven by ozone depletion, have also contributed. Understanding these processes and their impacts on the global climate is critical to understanding climate sensitivity.
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Much of the understanding and documentation of these changes come from decades of satellite observations. Continuation of these long-term satellite observations are essential for understanding the role of natural climate variability versus anthropogenic forcing on the long-term decline of sea ice, its impact on midlatitude weather, the impact of melting land ice on global sea level, and quantifications of hydrological and biogeochemical fluxes.
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In order to make progress on this science question, the panel has identified the following objectives: • -8a. Improve our understanding of the drivers behind polar amplification by quantifying the relative C impact of snow/ice-albedo feedback versus changes in atmospheric and oceanic circulation, water vapor, and lapse rate feedback (Very Important)
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These sensors are important for other cli mate variables, including rainfall, snow cover, ice-sheet melt, sea-surface temperatures, wind speed, and soil moisture, which are critical measurements for Very Important priority climate variables such as air-sea fluxes, sea-level rise, and seasonal to decadal predictability. There is also a strong need to improve upon the resolution of these instruments (25 km for SSMI and 10 km for AMSR2)
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Sea ice, permafrost and active layer state, as well as snow extent and thickness are relevant for managing northern transportation infrastructure and ecosystems. Permafrost thaw and mobilization of previously frozen carbon is directly contributing to carbon cycle changes and observation strategies for monitoring greenhouse gas release on global scales thus also apply for permafrost regions.
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.thehas been suggested that the future recovery ofcolumn ozone in 2100 shown surface concentrations for It RCPs in 2100. The white contour lines show mean total the ozone layer will enhance surface the values of globally inozonefirst halfand ODPN2O (0.015; bottom al., 2011)
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. The goal here is to improve prediction of the ozone layer, as well as atmospheric and surface radiative forcing and its associated consequences for climate.
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Observations of temperature and key radiatively active gases in the UT/LS must have sufficient precision, vertical resolution, and geographic coverage to quantify radiative forcing; the SATM requirements are specified to meet this requirement. In addition, diagnostics of the processes that control the temperature and distributions of O3 and other radiatively active constituents must be measured with a precision, vertical resolution, and geographic coverage appropriate for the scales on which the processes occur.
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As a result, many societal decisions -- for financial investments, infrastructure design, natural resource management, and planning and policy making -- are based in part on information, or assumptions, about expected climatic conditions. By improving our understanding of the current and future states of our climate, including climate sensitivity (see "C-2: Climate Feedbacks and Sensitivity")
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From page 487... ...
on polar processes, aerosols, clouds and ozone, climate feedbacks and sensitivity, carbon cycle, atmosphere-ocean flux, sea-level rise, and ocean heat storage and glacier-ice. Improved understanding and prediction of climate changes from seasonal to centennial scales can be used to support decisions in nearly all sectors of society, with consequences on a wide spectrum of space and time scales.
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2013. A review of global ocean tem perature observations: Implications for ocean heat content estimates and climate change.
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: Mission overview. Geophysical Research Letters 32(15)
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Geophysical Research Letters 29(19)
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2010. What can be learned about carbon cycle climate feedbacks from the CO2 airborne fraction?
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Geophysical Research Letters 32(14)
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Geophysical Research Letters 27(17)
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Geophysical Research Letters 41. Polvani, L.M., D.W.
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Geophysical Research Letters 41(10)
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Geophysical Research Letters 34(9)
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Geophysical Research Letters 34(16)
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2012. Computing and partitioning cloud feedbacks using cloud property histograms.
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