Bulletin of the American Physical Society
APS March Meeting 2018
Volume 63, Number 1
Monday–Friday, March 5–9, 2018; Los Angeles, California
Session F16: Energy Flows in The Climate SystemInvited
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Sponsoring Units: GPC GSNP Chair: Michael Mann, Pennsylvania State Univ Room: LACC 305 |
Tuesday, March 6, 2018 11:15AM - 11:51AM |
F16.00001: The Spectroscopic Foundation of Radiative Forcing by Carbon Dioxide Invited Speaker: Martin Mlynczak The radiative forcing (RF) of carbon dioxide (CO2) is the leading contribution to climate change from anthropogenic activities. Calculating CO2 RF requires detailed knowledge of spectral line parameters for thousands of infrared absorption lines. A reliable spectroscopic characterization of CO2 forcing is critical to scientific and policy assessments of present climate and climate change. Our results show that CO2 RF in a variety of atmospheres is remarkably insensitive to known uncertainties in the three main CO2 spectroscopic parameters: the line shapes, line strengths, and line half widths. We specifically examine uncertainty in RF due to line mixing as this process is critical in determining line shapes in the far wings of CO2 absorption lines. RF computed with a pure Voigt line shape is also examined. Overall, the spectroscopic uncertainty in present-day CO2 RF is less than 1% (global average), indicating a robust foundation in our understanding of how rising CO2 warms the climate system. |
Tuesday, March 6, 2018 11:51AM - 12:27PM |
F16.00002: Abyssal Ocean Warming: How the climate system is transferring excess anthropogenic energy into the isolated deep ocean Invited Speaker: Sarah Purkey The ocean is by far the largest sink for anthropogenic heat introduced into Earth’s climate system, currently absorbing over 90% of the global energy imbalance. How efficiently the oceans can continue to drawdown heat in the future will be determined by its ability to export heat from the surface into the interior ocean. Here, we present observational evidence of current Deep Ocean warming rates and the likely physical mechanisms driving this warming. Deep ocean warming trends are determined using all available ship based full depth high-quality deep ocean temperature measurements taken along ocean transects repeated multiple times between 1980 and present. These measurements reveal a global scale multi-decadal abyssal warming signal, with the strongest warming in the Southern Ocean near deep-water formation sites, and extending northward following the deep flow pathways. The integrated global deep warming below 3000 m over the past three decades is equivalent to a heat flux of 0.05 (±0.04) Wm-2 over the entire surface of the earth, or roughly 5% of the global 1 Wm-2 energy imbalance. In addition, this warming produces a 0.1 (±0.08) mm year-1 increase in global average sea level from thermostatic expansion. The vertical distribution of the observed hydrography changes provides strong evidence that the warming is primarily driven by isopycnal heave, rather than an advected change. This could be driven by a decrease in the rate of abyssal ventilation. Transient tracer analysis provides additional evidence that this is indeed a contributing mechanism, suggesting a global scale slowdown of the bottom limb of the meridional overturning circulation. |
Tuesday, March 6, 2018 12:27PM - 1:03PM |
F16.00003: Climate Model-Based Assessments of Regional Responses to Solar Geoengineering Invited Speaker: Katharine Ricke The most straightforward way to avoid the potentially dangerous climate change is to reduce, and eventually eliminate, carbon dioxide emissions from the combustion of fossil fuels. However, given the slow progress on this front, a growing number of proposals have been made for deliberate intervention in the climate through “geoengineering”. Several methods have been proposed for deliberately tinkering with the Earth’s energy balance to counteract the warming effects of carbon dioxide and other greenhouse gases (GHGs): reflecting an increased fraction of sunlight back into space before it is absorbed by the Earth’s surface, increasing the transparency of the Earth’s atmosphere to outgoing longwave radiation, or even pumping water from the deep ocean to the surface ocean to cool surface air temperatures. All these proposals imperfectly compensate for the effects of GHGs, altering the intensity of the global hydrological cycle and resulting in shifting regional climate states even when global temperatures are held steady. Here I explore these tradeoffs, as simulated in earth system models. |
Tuesday, March 6, 2018 1:03PM - 1:39PM |
F16.00004: Radiative Transfer and Aerosol Scattering Invited Speaker: John Dykema One of the most fundamental energy flows in the climate system is constituted by the radiative input of energy from the sun and the outgoing energy flow from thermal infrared radiation. Aerosols in the atmosphere provide a significant modulation of these energy flows. Depending on the location of the aerosol, its composition, and its physical details (particularly its size), the aerosol may introduce a positive or negative net perturbation to the balance between these incoming and ougoing radiative flows. This radiative impact of aerosols has been observed to produce a subsantial short-term impact on climate in the case of major volcanic eruptions, which have resulted for some well-known instances in a significant global temperature anomaly persisting for more than a year. A quantitative understanding of aerosol perturbations to the climate radiative balance requires a detailed understanding of the processes that govern radiative transfer in the atmosphere. These processes rest on fundamental optical properties, such as the complex refractive index, of the condensed phase materials that constitute aerosols. While laboratory measurements to quantify complex refractive index are routine, the samples used for laboratory measurements may not be representative of atmospheric particulates in important ways. These differences can lead to substantially different quantitative assessments of the radiative perturbations caused by aerosol scattering. This is particularly the case for studies investigating the risks and efficacy of albedo modification by deliberate introduction of aerosols into the atmosphere as a form of climate intervention. This talk will survey relevant aspects of radiative transfer and aerosol scattering and examine their implications in recent research studying hypothetical scenarios of albedo modification. |
Tuesday, March 6, 2018 1:39PM - 2:15PM |
F16.00005: Climate Response to Radiative Forcing By (Dust) Aerosols: Energy and Moisture Constraints Invited Speaker: Ron Miller The radiative perturbation to climate by aerosols has large regional variations, reflecting the localized sources and short lifetime of aerosols compared to greenhouse gases like carbon dioxide. The climate adjusts to aerosol forcing far beyond regions of high concentration through atmospheric transport of energy and moisture. This combination of local sources and planetary scale adjustment makes it challenging to identify the robust climate response to aerosols that is consistent among different climate models and is expected to appear in future model simulations. Constraints from the atmospheric budgets of energy and moisture help to identify robust aspects of both the global and regional climate response. We will illustrate some of these constraints for the example of dust aerosols that are created by soil erosion and make a leading contribution to the emitted aerosol mass. |
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