scholarly journals Radiative forcing and climate response to projected 21st century aerosol decreases

2015 ◽  
Vol 15 (6) ◽  
pp. 9293-9353 ◽  
Author(s):  
D. M. Westervelt ◽  
L. W. Horowitz ◽  
V. Naik ◽  
D. L. Mauzerall
Keyword(s):  
Global Warming ◽  
Greenhouse Gas ◽  
21St Century ◽  
Radiative Forcing ◽  
Cloud Droplet ◽  
Effective Radius ◽  
Climate Impacts ◽  
Climate Response ◽  
Aerosol Emission ◽  
Global Emissions

Abstract. It is widely expected that global emissions of atmospheric aerosols and their precursors will decrease strongly throughout the remainder of the 21st century, due to emission reduction policies enacted to protect human health. For instance, global emissions of aerosols and their precursors are projected to decrease by as much as 80% by the year 2100, according to the four Representative Concentration Pathway (RCP) scenarios. The removal of aerosols will cause unintended climate consequences, including an unmasking of global warming from long-lived greenhouse gases. We use the Geophysical Fluid Dynamics Laboratory Climate Model version 3 (GFDL CM3) to simulate future climate over the 21st century with and without the aerosol emission changes projected by each of the RCPs in order to isolate the radiative forcing and climate response resulting from the aerosol reductions. We find that the projected global radiative forcing and climate response due to aerosol decreases do not vary significantly across the four RCPs by 2100, although there is some mid-century variation, especially in cloud droplet effective radius, that closely follows the RCP emissions and energy consumption projections. Up to 1 W m−2 of radiative forcing may be unmasked globally from 2005 to 2100 due to reductions in aerosol and precursor emissions, leading to average global temperature increases up to 1 K and global precipitation rate increases up to 0.09 mm d−1. Regionally and locally, climate impacts can be much larger, with a 2.1 K warming projected over China, Japan, and Korea due to the reduced aerosol emissions in RCP8.5, as well as nearly a 0.2 mm d−1 precipitation increase, a 7 g m−2 LWP decrease, and a 2 μm increase in cloud droplet effective radius. Future aerosol decreases could be responsible for 30–40% of total climate warming by 2100 in East Asia, even under the high greenhouse gas emissions scenario (RCP8.5). The expected unmasking of global warming caused by aerosol reductions will require more aggressive greenhouse gas mitigation policies than anticipated in order to meet desired climate targets.

scholarly journals Radiative forcing and climate response to projected 21st century aerosol decreases

2015 ◽  
Vol 15 (22) ◽  
pp. 12681-12703 ◽  
Author(s):  
D. M. Westervelt ◽  
L. W. Horowitz ◽  
V. Naik ◽  
J.-C. Golaz ◽  
D. L. Mauzerall
Keyword(s):  
Global Warming ◽  
Greenhouse Gas ◽  
21St Century ◽  
Radiative Forcing ◽  
Cloud Droplet ◽  
Effective Radius ◽  
Climate Impacts ◽  
Global Temperature ◽  
Climate Response ◽  
Global Emissions

Abstract. It is widely expected that global emissions of atmospheric aerosols and their precursors will decrease strongly throughout the remainder of the 21st century, due to emission reduction policies enacted to protect human health. For instance, global emissions of aerosols and their precursors are projected to decrease by as much as 80 % by the year 2100, according to the four Representative Concentration Pathway (RCP) scenarios. The removal of aerosols will cause unintended climate consequences, including an unmasking of global warming from long-lived greenhouse gases. We use the Geophysical Fluid Dynamics Laboratory Coupled Climate Model version 3 (GFDL CM3) to simulate future climate over the 21st century with and without the aerosol emission changes projected by each of the RCPs in order to isolate the radiative forcing and climate response resulting from the aerosol reductions. We find that the projected global radiative forcing and climate response due to aerosol decreases do not vary significantly across the four RCPs by 2100, although there is some mid-century variation, especially in cloud droplet effective radius, that closely follows the RCP emissions and energy consumption projections. Up to 1 W m−2 of radiative forcing may be unmasked globally from 2005 to 2100 due to reductions in aerosol and precursor emissions, leading to average global temperature increases up to 1 K and global precipitation rate increases up to 0.09 mm day−1. However, when using a version of CM3 with reduced present-day aerosol radiative forcing (−1.0 W m−2), the global temperature increase for RCP8.5 is about 0.5 K, with similar magnitude decreases in other climate response parameters as well. Regionally and locally, climate impacts can be much larger than the global mean, with a 2.1 K warming projected over China, Japan, and Korea due to the reduced aerosol emissions in RCP8.5, as well as nearly a 0.2 mm day−1 precipitation increase, a 7 g m−2 LWP decrease, and a 2 μm increase in cloud droplet effective radius. Future aerosol decreases could be responsible for 30–40 % of total climate warming (or 10–20 % with weaker aerosol forcing) by 2100 in East Asia, even under the high greenhouse gas emissions scenario (RCP8.5). The expected unmasking of global warming caused by aerosol reductions will require more aggressive greenhouse gas mitigation policies than anticipated in order to meet desired climate targets.

Revisiting the existence of the global warming slowdown during the early 21st century

2021 ◽  
pp. 1-40
Keyword(s):  
Global Warming ◽  
Greenhouse Gas ◽  
Selection Bias ◽  
21St Century ◽  
Linear Trend ◽  
Warming Trend ◽  
Short Term ◽  
Early 21St Century ◽  
Decadal Scale ◽  
Global Temperature Change

Abstract There are heated debates on the existence of the global warming slowdown during the early 21st century. Although efforts have been made to clarify or reconcile the controversy over the issue, it is not explicitly addressed, restricting the understanding of global temperature change particularly under the background of increasing greenhouse-gas concentrations. Here, using extensive temperature datasets, we comprehensively reexamine the existence of the slowdown under all existing definitions during all decadal-scale periods spanning 1990-2017. Results show that the short-term linear-trend dependent definitions of slowdown make its identification severely suffer from the period selection bias, which largely explains the controversy over its existence. Also, the controversy is further aggravated by the significant impacts of the differences between various datasets on the recent temperature trend and the different baselines for measuring slowdown prescribed by various definitions. However, when the focus is shifted from specific periods to the probability of slowdown events, we find the probability is significantly higher in the 2000s than in the 1990s, regardless of which definition and dataset are adopted. This supports a slowdown during the early 21st century relative to the warming surge in the late 20th century, despite higher greenhouse-gas concentrations. Furthermore, we demonstrate that this decadal-scale slowdown is not incompatible with the centennial-scale anthropogenic warming trend, which has been accelerating since 1850 and never pauses or slows. This work partly reconciles the controversy over the existence of the warming slowdown and the discrepancy between the slowdown and anthropogenic warming.

scholarly journals Aerosol indirect effects on continental low-level clouds over Sweden and Finland

2014 ◽  
Vol 14 (22) ◽  
pp. 12167-12179 ◽  
Author(s):  
M. K. Sporre ◽  
E. Swietlicki ◽  
P. Glantz ◽  
M. Kulmala
Keyword(s):  
Boundary Layer ◽  
Radiative Forcing ◽  
Remote Sensing Data ◽  
Cloud Droplet ◽  
Weather Radar ◽  
Number Concentration ◽  
Effective Radius ◽  
Distribution Data ◽  
Low Level ◽  
Radar Images

Abstract. Aerosol effects on low-level clouds over the Nordic Countries are investigated by combining in situ ground-based aerosol measurements with remote sensing data of clouds and precipitation. Ten years of number size distribution data from two aerosol measurement stations (Vavihill, Sweden and Hyytiälä, Finland) provide aerosol number concentrations in the atmospheric boundary layer. This is combined with cloud satellite data from the Moderate Resolution Imaging Spectroradiometer and weather radar data from the Baltic Sea Experiment. Also, how the meteorological conditions affect the clouds is investigated using reanalysis data from the European Centre for Medium-Range Weather Forecasts. The cloud droplet effective radius is found to decrease when the aerosol number concentration increases, while the cloud optical thickness does not vary with boundary layer aerosol number concentrations. Furthermore, the aerosol–cloud interaction parameter (ACI), a measure of how the effective radius is influenced by the number concentration of cloud active particles, is found to be somewhere between 0.10 and 0.18 and the magnitude of the ACI is greatest when the number concentration of particles with a diameter larger than 130 nm is used. Lower precipitation intensity in the weather radar images is associated with higher aerosol number concentrations. In addition, at Hyytiälä the particle number concentrations is generally higher for non-precipitating cases than for precipitating cases. The apparent absence of the first indirect effect of aerosols on low-level clouds over land raises questions regarding the magnitude of the indirect aerosol radiative forcing.

scholarly journals The sensitivity of global climate to the episodicity of fire aerosol emissions

2013 ◽  
Vol 13 (9) ◽  
pp. 23691-23717
Author(s):  
S. K. Clark ◽  
D. S. Ward ◽  
N. M. Mahowald
Keyword(s):  
Direct Effect ◽  
Radiative Forcing ◽  
Global Climate ◽  
Sensitivity Study ◽  
Climate Impacts ◽  
Mixed Effect ◽  
Fire Emissions ◽  
Aerosol Emission ◽  
The Tropics ◽  
Aerosol Emissions

Abstract. One of the major ways in which forest and grass fires have an impact on global climate is through the release of aerosols. Most studies focusing on calculating the radiative forcing and other climate impacts of fire aerosols use monthly mean emissions derived from the Global Fire Emissions Database that captures only the seasonal cycle of fire aerosol emissions. Here we present the results of a sensitivity study that investigates the climate response to the episodicity of the fires, based on the standard approach which releases emissions every day, and contrasts that to the response when fires are represented as intense pulses of emissions that occur only over 1–2 days on a monthly, yearly, or five-yearly basis. Overall we find that in the modified cases with increased levels of episodicity, the all sky direct effect radiative forcing increases, the clear sky direct effect radiative forcing remains relatively constant, and the magnitude of the indirect effect radiative forcing decreases by about 1 W m−2 (from −1.6 to −0.6 W m−2). In the long term, we find that an increase in aerosol emission episodicity leads to an asymmetric change in indirect radiative forcing in the Northern Hemisphere compared to the Southern Hemisphere contributes to a slight shift in the annual average position of the intertropical convergence zone (ITCZ). This shift is found to have a mixed effect on the overall performance of the model at predicting precipitation rates in the tropics. Given these results we conclude that future studies that look to assess the present day global climate impacts of fire aerosols should consider the need to accurately represent fire episodicity.

scholarly journals Technical note: On comparing greenhouse gas emission metrics

2021 ◽  
Vol 21 (6) ◽  
pp. 4699-4708
Author(s):  
Ian Enting ◽  
Nathan Clisby
Keyword(s):  
Global Warming ◽  
Greenhouse Gas ◽  
Global Warming Potential ◽  
Radiative Forcing ◽  
Greenhouse Gas Emission ◽  
Technical Note ◽  
Short Term ◽  
Rates Of Change

Abstract. Many metrics for comparing greenhouse gas emissions can be expressed as an instantaneous global warming potential multiplied by the ratio of airborne fractions calculated in various ways. The forcing equivalent index (FEI) provides a specification for equal radiative forcing at all times at the expense of generally precluding point-by-point equivalence over time. The FEI can be expressed in terms of asymptotic airborne fractions for exponentially growing emissions. This provides a reference against which other metrics can be compared. Four other equivalence metrics are evaluated in terms of how closely they match the timescale dependence of FEI, with methane referenced to carbon dioxide used as an example. The 100-year global warming potential overestimates the long-term role of methane, while metrics based on rates of change overestimate the short-term contribution. A recently proposed metric based on differences between methane emissions 20 years apart provides a good compromise. Analysis of the timescale dependence of metrics expressed as Laplace transforms leads to an alternative metric that gives closer agreement with FEI at the expense of considering methane over longer time periods. The short-term behaviour, which is important when metrics are used for emissions trading, is illustrated with simple examples for the four metrics.

scholarly journals A quantitative approach to evaluating the GWP timescale through implicit discount rates

2018 ◽  
Author(s):  
Marcus C. Sarofim ◽  
Michael R. Giordano
Keyword(s):  
Sensitivity Analysis ◽  
Global Warming ◽  
Radiative Forcing ◽  
Time Horizon ◽  
Climate Impact ◽  
Climate Impacts ◽  
Quantitative Approach ◽  
Discount Rates ◽  
Political Implications ◽  
Complicating Factors

Abstract. The 100-year Global Warming Potential (GWP) is the primary metric used to compare the climate impacts of different greenhouse gases (GHGs). The GWP relies on radiative forcing rather than damages, assumes constant future concentrations, and integrates over a timescale of 100 years without discounting: these choices lead to a metric which is transparent and simple to calculate, but have also been criticized. In this paper, we take a quantitative approach to evaluating the choice of time-horizon, accounting for many of these complicating factors. By calculating an equivalent GWP timescale based on discounted damages resulting from CH4 and CO2 pulses, we show that a 100-year timescale is consistent with a discount rate of 3.3 % (interquartile range of 2.7 % to 4.1 % in a sensitivity analysis). This range of discount rates is consistent with, or larger than, those usually considered for climate impact analyses. With increasing discount rates equivalent timescales decrease. We recognize the limitations of evaluating metrics by relying only on climate impact equivalencies without consideration of the economic and political implications of metric implementation.

scholarly journals Global Warming Mitigating Role of Wood Products from Washington State’s Private Forests

Forests ◽  
2020 ◽  
Vol 11 (2) ◽  
pp. 194 ◽  
Author(s):  
Indroneil Ganguly ◽  
Francesca Pierobon ◽  
Edie Sonne Hall
Keyword(s):  
Global Warming ◽  
Greenhouse Gas Emissions ◽  
Greenhouse Gas ◽  
Carbon Storage ◽  
Radiative Forcing ◽  
Timber Harvest ◽  
Gas Production ◽  
Wood Products ◽  
Private Forests ◽  
Gas Emissions

Similar to standing trees in the forests, wood products play an important role in enhancing the global sequestered carbon pool, by retaining the atmospheric carbon in a sequestered form for the duration of the functional life of the wood products. This study uses a temporal radiative forcing analysis along with the functional half-life of different wood products to evaluate the impacts of wood products on global warming, including carbon storage and life cycle greenhouse gas production/extraction emissions. The methodology is applied to Washington State’s aboveground biomass and timber harvest data, and to the State’s comprehensive wood products mix. A moderate harvest rate simulation within Washington Biomass Calculator is used to estimate state harvest level, and statewide wood products manufacturing data is used for developing wood product mix estimates. Using this method, we estimate that the temporal carbon storage leads to a global warming mitigation benefit equivalent to 4.3 million tCO2eq. Even after factoring in the greenhouse gas emissions associated with the harvest operations and wood products manufacturing processes, within the temporal model, the results show a net beneficial impact of approximately 1.7 million tCO2eq, on an annual basis. It can further be noted that Washington State’s annual biomass growth in its private forests exceeds its annual harvest, by a significant margin. This net yearly accumulation of biomass in the State’s private forests leads to additional global warming mitigation benefits equivalent to 7.4 million tCO2eq. Based on these results, we conclude that Washington’s private forestry industry is a net global warming mitigator for the State, equivalent to 12% of the State’s greenhouse gas emissions in 2015.

scholarly journals Climate Response to Negative Greenhouse Gas Radiative Forcing in Polar Winter

2018 ◽  
Vol 45 (4) ◽  
pp. 1997-2004 ◽  
Author(s):  
M. G. Flanner ◽  
X. Huang ◽  
X. Chen ◽  
G. Krinner
Keyword(s):  
Greenhouse Gas ◽  
Radiative Forcing ◽  
Climate Response

scholarly journals Technical note: On comparing greenhouse gas emission metrics

2020 ◽  
Author(s):  
Ian Enting ◽  
Nathan Clisby
Keyword(s):  
Global Warming ◽  
Greenhouse Gas Emissions ◽  
Greenhouse Gas ◽  
Global Warming Potential ◽  
Radiative Forcing ◽  
Greenhouse Gas Emission ◽  
Technical Note ◽  
Gas Emission ◽  
Gas Emissions ◽  
Over Time

Abstract. Many metrics for comparing greenhouse gas emissions can be expressed as an instantaneous Global Warming Potential multiplied by the ratio of airborne fractions calculated in various ways. The Forcing Equivalent Index (FEI) provides a specification for equal radiative forcing at all times at the expense of generally precluding point by point equivalence over time. The FEI can be expressed in terms of asymptotic airborne fractions for exponentially growing emissions. This provides a reference against which other metrics can be compared.

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