Reply to comment on rethinking the lower bound on aerosol radiative forcing journal, august 2017. The individual terms of the model are interpreted in light of comprehensive modeling, constraints from observations, and physical understanding to provide further support for the less negative. Aerosol effects on cloud water amounts were successfully. The paper rethinking the lower bound on aerosol radiative forcing by bjorn stevens of the max planck institute for meteorology in hamburg, germany, published in the american meteorological society journal finds that the effects of aerosols on climate are much smaller than those in almost all the computer models used by the. Equilibrium climate sensitivity and transient climate. The new study rethinking the lower bound on aerosol forcing in the journal of climate, written by prof. Aerosolinduced modification of organised convection and. Bjorn stevens, director at the max planck institute for meteorology mpim and head of th e department the. Since then over 30 estimates of rfaci from aerosol. The direct radiative effect of anthropogenic aerosols combined with subsequent rapid adjustments of the surface energy budget, atmospheric state variables, and cloudiness to aerosol radiative effects is referred to as effective radiative forcing from aerosol radiation interactions erfari boucher et al.
Scientists explain the impacts of aerosol radiative forcing. Energy budget constraints on historical radiative forcing. The challenges that climate models face in estimating aerosol forcing and there are many more than malavelle and colleagues natural experiment. Why does knowledge of past aerosol forcing matter for. Rethinking the lower bound on aerosol radiative forcing article in journal of climate 2812. Released journal article reply to comment on rethinking the lower bound on aerosol radiative forcing kretzschmar, j. Direct indirect cloudfree allsky topofatmosphere surface total aerosol rf anthropogenic aerosol rf shortwave longwave instantaneous 24hr to annual average at least 64 aerosol radiative forcing quantities. The implications for climate sensitivity of ar5 forcing and heat uptake estimates, climate dynamics doi. Analyses of aerosol optical properties and direct radiative. The net forcing at the top of atmosphere toa is estimated as0.
Rethinking the lower bound on aerosol radiative forcing bjorn stevens max planck institute for meteorology, hamburg, germany bjorn. Sensitivity of aerosol radiative forcing to various. Changes in atmospheric constituents and in radiative forcing. Jan 14, 2015 the aerosol optical depth aod, angstrom exponent alpha, single scattering albedo ssa, and volumes of aerosol size distributions were all retrieved from measurements made by a ce318 sunphotometer at four urban and industrial sites shenyang, anshan, benxi and fushun in northeast china from 2009 to 20. Adapted from nicholas lewis, implications of lower aerosol forcing for climate sensitivity, climate etc. Stevens 2015, hereinafter s15 used three lines of reasoning to argue that presentday effective aerosol radiative forcing. Key to the s15 analysis is the amount of aerosol forcing realized by 1950 and the assumption that the same nonlinearity applies. This radiative forcing of anthropogenic aerosols was first postulated by twomey and therefore is also referred to as the twomey effect, cloud albedo effect, or the radiative forcing due to aerosol. The ar5 best estimate aerosol forcing strengthens by. Request pdf comment on rethinking the lower bound on aerosol radiative forcing in an influential and interesting study, stevens 2015 suggested that the global and also northern.
Values for direct radiative forcing drf were then estimated using these. Jul 31, 2017 due to the lifetime of co 2, the thermal inertia of the oceans 1,2, and the temporary impacts of shortlived aerosols 3,4,5 and reactive greenhouse gases 6, the earths climate is not. In such retrievals, pixels having radiances that surpass prescribed thresholds are assumed to be overcast even if they are only partially cloud covered. Radiative forcing due to dust aerosol over east asianorth. Released journal article reply to comment on rethinking the lower bound on aerosol radiative forcing booth. A paper that i recently wrote, entitled rethinking the lower bound on aerosol radiative forcing has been accepted for publication in the journal of climate. Reply to comment on rethinking the lower bound on aerosol radiative forcing kretzschmar, j. Global estimate of aerosol direct radiative forcing from. Based on research showing that in the case of a strong aerosol forcing, this forcing establishes itself early in. The inclusion of this process in a global aerosol model raises baseline 38 preindustrial aerosol concentrations, and could lead to a reduction of 27% 39 in estimates of anthropogenic aerosol radiative forcing. Radiative forcing is a measure of the change in energy balance as a result of a change in a forcing agent e.
The estimates of financial cost and co2eq emission were subjected to sensitivity analyses in several key parameters, including aircraft operational empty weight, engine specific fuel consumption, fuel price and aerosol price. Clouds and the earths radiant energy system ceres publications for 2015 adebiyi, a. Positive radiative forcing means earth receives more incoming energy. Request pdf sensitivity of aerosol radiative forcing to various aerosol parameters over the bay of bengal in the shortwave solar spectrum \0. It has been used as a measure to investigate the climate sensitivity of an earth system component in recent intergovernmental panel on climate change ipcc. Improved aerosol processes and effective radiative forcing. Ramanathanb, and damien decremera aschool of environmental science and engineering, gwangju institute of science and technology, gwangju 500712, korea. Radiative forcing or climate forcing is the difference between insolation sunlight absorbed by the earth and energy radiated back to space. The individual terms of the model are interpreted in light of comprehensive modeling, constraints from observations, and insights from the literature, to provide further support for the less negative 1. Fiedler no static citation data no static citation data cite. The seasonal averaged radiative forcing in spring, 2001 over east asianorth pacific region is simulated employing the new dust optical model.
Mar 19, 2015 the paper rethinking the lower bound on aerosol radiative forcing by bjorn stevens of the max planck institute for meteorology in hamburg, germany, published in the american meteorological society journal finds that the effects of aerosols on climate are much smaller than those in almost all the computer models used by the. Observationally constrained estimates of carbonaceous aerosol radiative forcing chul e. Anthropogenic aerosol aa forcing plays a direct role in the planetary energy budget primarily by influencing scattering and absorption of solar radiation and an indirect role through its influence on cloud formation and the hydrological cycle boucher et al. Comments on rethinking the lower bound on aerosol radiative forcing booth, bbb, harris, gr, jones, a et al. The aerosol extinction coefficient, single scattering albedo, and asymmetric factor are computed as wavelengthdependent radiative forcing in the radiative transfer scheme of the fvgcm, and as a function of the aerosol loading and ambient relative humidity. From the model results it can be observed that the aerosols induce negative radiative. Comment on rethinking the lower bound on aerosol radiative.
Dec 22, 2005 probability density functions obtained for the direct radiative forcing at the top of the atmosphere give a clearsky, global, annual average of 1. A plan for a research program on aerosol radiative forcing. Aerosol absorption and radiative forcing researchgate. This paper presents a number of arguments as to why the radiative forcing from aerosols is neither as negative, nor as uncertain, as has previously been thought. Comments on rethinking the lower bound on aerosol radiative. 150319112745003 march 2015 with 45 reads how we measure reads. This paper presents a number of arguments as to why the radiative forcing from aerosols is neither as negative, nor. Radiative forcing is a fundamental quantity for understanding anthropogenic and natural drivers of past and future climate change1, yet significant uncertainty remains in our quantification of. If one adopts an upper bound for the aerosol forcing of. Aerosol cloud forcing indirect effects are locally nonlinear, with stronger radiative responses to aerosol concentrations in cleaner conditions, but this response weakens as the as the background becomes increasingly polluted twomey and squires 1959. Dimensions of aerosol radiative forcing at least six dimensions to definition of aerosol rf. Based on research showing that in the case of a strong aerosol forcing, this forcing establishes itself early in the historical record, a simple model is constructed to explore the implications of a strongly negative aerosol forcing on the early pre 1950 part of the instrumental record.
Scientists explain the impacts of aerosol radiative forcing by chinese academy of sciences a hazy day dec. Rethinking the lower bound on aerosol radiative forcing. Quantitative understanding of climate change during the industrial era suffers from a highly uncertain effective radiative forcing radiative forcing plus adjustments due to anthropogenic aerosols, boucher et al. The individual terms of the model are interpreted in light of comprehensive modeling, constraints from observations, and physical understanding to provide further support for the less negative 21. Stevens 2015, hereinafter s15 proposed that the temporal and spatial characteristics of the observed warming since preindustrial times provide a powerful constraint on the. It is known that part of the temperature rise is balanced by aerosol particles in the atmosphere partly also emitted by human activity. Comments on rethinking the lower bound on aerosol radiative forcing ben b. Atmospheric aerosols are ubiquitous and often observable by eye as dust, smoke, and haze. The implications for climate sensitivity of bjorn stevens. Introduction a perturbation to the composition of earths atmosphere can be quanti. A plan for a research program on aerosol radiative forcing and climate. Substantial progress made over the past 40 years in observing, understanding, and modeling these processes helped quantify the imbalance in the earths radiation budget caused by anthropogenic aerosols, called aerosol radiative forcing, but uncertainties remain large. Both the direct and indirect roles of aa forcing are uncertain, and their simulated impacts are sensitive to. Since the rise of industrialization more and more greenhouse gases are being emitted into the atmosphere and as a result the earths climate is warming.
Committed warming inferred from observations nature climate. Download a pdf of a plan for a research program on aerosol radiative forcing and climate change by the national research council for free. Improved aerosol processes and effective radiative forcing in. It has been used as a measure to investigate the climate sensitivity of an earth system component in recent. Observationally constrained estimates of carbonaceous aerosol. Based on research showing that in the case of a strong aerosol forcing, this forcing establishes itself early in the historical record, a simple model is constructed to explore the implications of a strongly negative aerosol forcing on the early pre. Reply to comment on rethinking the lower bound on aerosol. Bounding global aerosol radiative forcing of climate.
These findings suggest that aerosol radiative forcing is less negative and more certain than is commonly believed. Empirical estimates of the aerosol indirect radiative forcing often rely on threshold cloud retrievals applied to multispectral satellite imagery data. Che et al column aerosol optical properties and aerosol radiative forcing positive arf at the top of the atmosphere at the huimin suburban site was found to be different from others as a result of the high surface albedo due to snow cover. Determination of a lower bound on earths climate sensitivity. The global mean aerosol effective radiative forcing values are shown in the title of each subpanel.
Column aerosol optical properties and aerosol radiative. Aerosol types and radiative forcing estimates over east asia. The current global mean topoftheatmosphere toa radiative forcing concept with adjusted stratospheric temperatures has both strengths and limitations. Aerosol particles masking effect of greenhouse gases lt. The individual terms of the model are interpreted in light of comprehensive modeling, constraints from observations, and physical understanding, to provide further support for the less negative. Atmospheric teleconnection over eurasia induced by aerosol. Aerosol radiative forcing and climate sensitivity deduced. Rethinking the lower bound on aerosol radiative forcing core. Reply to comments on rethinking the lower bound on. On the characteristics of aerosol indirect effect based on. Comments on rethinking the lower bound on aerosol radiative forcing booth, ben b. Title page abstract introduction conclusions references tables figures j i j i back close full screen esc printerfriendly version interactive discussion egu fore, it can be expected that the longwave aerosol radiative e.
Regional and seasonal radiative forcing by perturbations to. Changes to earths radiative equilibrium, that cause temperatures to rise or fall over decadal periods, are called climate forcings. Bjorn stevens, director at the max planck institute for meteorology mpim and head of the department the atmosphere in the earth system, presents a number of arguments as to why the cooling effect of aerosols is neither as strong nor as uncertain as has previously been thought. No impact of anthropogenic aerosols on early 21st century. Net radiative forcing due to young contrails amounts globally to 4. This model, which contains terms representing both aerosol radiation and aerosol cloud interactions, well represents the known time history of aerosol radiative forcing as well as the effect of. Particles comprising the atmospheric aerosol range in sizes from nanometers nm to tens of micrometers m, that is, from large clusters of molecules to visible flecks o. For the sake of argument, assume that both aerosol cloud and aerosol radiation interactions contribute to forcings that scale linearly with, as advocated by kretzschmar et al. An aerosol is defined as a suspension of solid or liquid particles in a gas. Aerosol induced changes in cloud structure have clear implications for cloud radiative effects and precipitation 1,2,3,4,5 via aerosol cloud interactions.
588 609 1293 189 1321 1001 230 1311 21 268 1589 1047 128 1138 580 426 1136 1012 84 941 1342 630 770 954 743 1353 933 1180 893 1185 1614 342 127 69 1278 101 903 89 1348