scholarly journals Significant climate benefits from near-term climate forcer mitigation in spite of aerosol reductions

2021 ◽  
Author(s):  
Robert Allen ◽  
Larry Horowitz ◽  
Vaishali Naik ◽  
Naga Oshima ◽  
Fiona O'Connor ◽  
...  
Keyword(s):  
Air Quality ◽  
Climate Model ◽  
Climate Impacts ◽  
Ozone Pollution ◽  
Surface Cooling ◽  
Methane Mitigation ◽  
Surface Warming ◽  
Near Term ◽  
Climate Model Simulations ◽  
Reactive Gases

<p>Near-term climate forcers (NTCFs), including aerosols and chemically reactive gases such as tropospheric ozone and methane, offer a potential way to mitigate climate change and improve air quality--so called "win-win" mitigation policies.   Prior studies support improved air quality under NTCF mitigation, but with conflicting climate impacts that range from a significant reduction in the rate of global warming to only a modest impact.  Here, we use state-of-the-art chemistry-climate model simulations conducted as part of the Aerosol and Chemistry Model Intercomparison Project (AerChemMIP) to quantify the 21st-century impact of NTCF reductions, using a realistic future emission scenario with a consistent air quality policy.  Non-methane NTCF (NMNTCF; aerosols and ozone precursors) mitigation improves air quality, but leads to significant increases in global mean precipitation of 1.3% by mid-century and 1.4% by end-of-the-century, and corresponding surface warming of 0.23 and 0.21 K.  NTCF (all-NTCF; including methane) mitigation further improves air quality, with larger reductions of up to 45% for ozone pollution, while offsetting half of the wetting by mid-century (0.7% increase) and all the wetting by end-of-the-century (non-significant 0.1% increase) and leading to surface cooling of -0.15 K by mid-century and -0.50 K by end-of-the-century.  This suggests that methane mitigation offsets warming induced from reductions in NMNTCFs, while also leading to net improvements in air quality.</p>

scholarly journals Flexible parameter-sparse global temperature time profiles that stabilise at 1.5 and 2.0  °C

2017 ◽  
Vol 8 (3) ◽  
pp. 617-626 ◽  
Author(s):  
Chris Huntingford ◽  
Hui Yang ◽  
Anna Harper ◽  
Peter M. Cox ◽  
Nicola Gedney ◽  
...  
Keyword(s):  
Climate Model ◽  
Algebraic Curves ◽  
Climate Impacts ◽  
Global Temperature ◽  
Temperature Profiles ◽  
Average Temperature ◽  
Time Profiles ◽  
Generational Changes ◽  
Climate Model Simulations ◽  
Two Parameters

Abstract. The meeting of the United Nations Framework Convention on Climate Change (UNFCCC) in December 2015 committed parties at the convention to hold the rise in global average temperature to well below 2.0 °C above pre-industrial levels. It also committed the parties to pursue efforts to limit warming to 1.5 °C. This leads to two key questions. First, what extent of emissions reduction will achieve either target? Second, what is the benefit of the reduced climate impacts from keeping warming at or below 1.5 °C? To provide answers, climate model simulations need to follow trajectories consistent with these global temperature limits. It is useful to operate models in an inverse mode to make model-specific estimates of greenhouse gas (GHG) concentration pathways consistent with the prescribed temperature profiles. Further inversion derives related emissions pathways for these concentrations. For this to happen, and to enable climate research centres to compare GHG concentrations and emissions estimates, common temperature trajectory scenarios are required. Here we define algebraic curves that asymptote to a stabilised limit, while also matching the magnitude and gradient of recent warming levels. The curves are deliberately parameter-sparse, needing the prescription of just two parameters plus the final temperature. Yet despite this simplicity, they can allow for temperature overshoot and for generational changes, for which more effort to decelerate warming change needs to be made by future generations. The curves capture temperature profiles from the existing Representative Concentration Pathway (RCP2.6) scenario projections by a range of different Earth system models (ESMs), which have warming amounts towards the lower levels of those that society is discussing.

Maize Drought Hazard in the Northeast Farming Region of China: Unprecedented Events in the Current Climate

2019 ◽  
Vol 58 (10) ◽  
pp. 2247-2258 ◽  
Author(s):  
Chris Kent ◽  
Edward Pope ◽  
Nick Dunstone ◽  
Adam A. Scaife ◽  
Zhan Tian ◽  
...  
Keyword(s):  
Large Scale ◽  
Agricultural Sector ◽  
Climate Model ◽  
Height Anomaly ◽  
Climate Services ◽  
Climate Conditions ◽  
Drought Hazard ◽  
Climate Exposure ◽  
Near Term ◽  
Climate Model Simulations

AbstractThe Northeast Farming Region (NFR) of China is a critically important area of maize cultivation accounting for ~30% of national production. It is predominantly rain fed, meaning that adverse climate conditions such as drought can significantly affect productivity. Forewarning of such events, to improve contingency planning, could therefore be highly beneficial to the agricultural sector. For this, an improved estimate of drought exposure, and the associated large-scale circulation patterns, is of critical importance. We address these important questions by employing a large ensemble of initialized climate model simulations. These simulations provide 80 times as many summers as the equivalent observational dataset and highlight several limitations of the recent observational record. For example, the chance of a drought greater in area than any current observed event is approximately 5% per year, suggesting the risk of a major drought is significantly underestimated if based solely on recent events. The combination of a weakened East Asian jet stream and intensified subpolar jet are found to be associated with severe NFR drought through enhanced upper-level convergence and anomalous descent, reducing moisture and suppressing precipitation. We identify a strong 500-hPa geopotential height anomaly dipole pattern as a useful metric to identify this mechanism for relevance to seasonal predictability. This work can inform policy planning and decision-making through an improved understanding of the near-term climate exposure and form the basis of new climate services.

scholarly journals The net climate impact of coal-fired power plant emissions

2010 ◽  
Vol 10 (7) ◽  
pp. 3247-3260 ◽  
Author(s):  
D. Shindell ◽  
G. Faluvegi
Keyword(s):  
Air Quality ◽  
Power Plants ◽  
Climate Impacts ◽  
Rate Of Change ◽  
Pollutant Emissions ◽  
Climate Forcing ◽  
Plant Emissions ◽  
Near Term ◽  
Mean Climate ◽  
Global Mean

Abstract. Coal-fired power plants influence climate via both the emission of long-lived carbon dioxide (CO2) and short-lived ozone and aerosol precursors. Using a climate model, we perform the first study of the spatial and temporal pattern of radiative forcing specifically for coal plant emissions. Without substantial pollution controls, we find that near-term net global mean climate forcing is negative due to the well-known aerosol masking of the effects of CO2. Imposition of pollution controls on sulfur dioxide and nitrogen oxides leads to a rapid realization of the full positive forcing from CO2, however. Long-term global mean forcing from stable (constant) emissions is positive regardless of pollution controls. Emissions from coal-fired power plants until ~1970, including roughly 1/3 of total anthropogenic CO2 emissions, likely contributed little net global mean climate forcing during that period though they may have induce weak Northern Hemisphere mid-latitude (NHml) cooling. After that time many areas imposed pollution controls or switched to low-sulfur coal. Hence forcing due to emissions from 1970 to 2000 and CO2 emitted previously was strongly positive and contributed to rapid global and especially NHml warming. Most recently, new construction in China and India has increased rapidly with minimal application of pollution controls. Continuation of this trend would add negative near-term global mean climate forcing but severely degrade air quality. Conversely, following the Western and Japanese pattern of imposing air quality pollution controls at a later time could accelerate future warming rates, especially at NHmls. More broadly, our results indicate that due to spatial and temporal inhomogenaities in forcing, climate impacts of multi-pollutant emissions can vary strongly from region to region and can include substantial effects on maximum rate-of-change, neither of which are captured by commonly used global metrics. The method we introduce here to estimate regional temperature responses may provide additional insight.

scholarly journals Weighting climate model projections using observational constraints

2015 ◽  
Vol 373 (2054) ◽  
pp. 20140425 ◽  
Author(s):  
Nathan P. Gillett
Keyword(s):  
Climate Change ◽  
Radiative Forcing ◽  
Climate Model ◽  
Historical Period ◽  
Intergovernmental Panel ◽  
Transient Climate Response ◽  
Detection And Attribution ◽  
Future Warming ◽  
Near Term ◽  
Climate Model Simulations

Projected climate change integrates the net response to multiple climate feedbacks. Whereas existing long-term climate change projections are typically based on unweighted individual climate model simulations, as observed climate change intensifies it is increasingly becoming possible to constrain the net response to feedbacks and hence projected warming directly from observed climate change. One approach scales simulated future warming based on a fit to observations over the historical period, but this approach is only accurate for near-term projections and for scenarios of continuously increasing radiative forcing. For this reason, the recent Fifth Assessment Report of the Intergovernmental Panel on Climate Change (IPCC AR5) included such observationally constrained projections in its assessment of warming to 2035, but used raw model projections of longer term warming to 2100. Here a simple approach to weighting model projections based on an observational constraint is proposed which does not assume a linear relationship between past and future changes. This approach is used to weight model projections of warming in 2081–2100 relative to 1986–2005 under the Representative Concentration Pathway 4.5 forcing scenario, based on an observationally constrained estimate of the Transient Climate Response derived from a detection and attribution analysis. The resulting observationally constrained 5–95% warming range of 0.8–2.5 K is somewhat lower than the unweighted range of 1.1–2.6 K reported in the IPCC AR5.

scholarly journals Flexible parameter-sparse global temperature time-profiles that stabilise at 1.5 °C and 2.0 °C

2017 ◽  
Author(s):  
Chris Huntingford ◽  
Hui Yang ◽  
Anna Harper ◽  
Peter M. Cox ◽  
Nic Gedney ◽  
...  
Keyword(s):  
Climate Model ◽  
Algebraic Curves ◽  
Climate Impacts ◽  
Global Temperature ◽  
Temperature Profiles ◽  
Average Temperature ◽  
Generational Changes ◽  
Scenario Model ◽  
Climate Model Simulations ◽  
Two Parameters

Abstract. The UNFCCC Paris climate meeting of December 2015 committed to holding the rise in global average temperature to below 2.0 °C above pre-industrial levels. It also committed to pursue efforts to limit warming to 1.5 °C. This leads to two key questions. First, what extent of reductions in emissions will achieve either target? Second, given emissions cuts to achieve the lower target may be especially difficult to achieve, then what is the benefit from reduced climate impacts by keeping warming at or below 1.5 °C? To provide answers climate model simulations need to follow trajectories consistent with these global temperature limits. This implies operating models in an invertible form, to make model-specific estimates of greenhouse gas (GHG) concentration pathways consistent with prescribed temperature profiles. Further inversion derives related emissions pathways for these concentrations. For this to happen, and to enable climate research centres to compare GHG concentrations and emissions estimates, common temperature trajectory scenarios are required. Here we define algebraic curves which asymptote to a stabilised limit, while also matching the magnitude and gradient of recent warming levels. The curves are deliberately parameter-sparse, needing prescription of just two parameters plus the final temperature. Yet despite this simplicity they can allow for temperature overshoot and for generational changes where more effort occurs to decelerate warming change by future generations. The curves capture temperature profiles from the existing rcp2.6 scenario model projections, which have warming amounts towards the lower levels of those that society is discussing.

scholarly journals Climate and air quality impacts due to mitigation of non-methane near-term climate forcers

2020 ◽  
Author(s):  
Robert J. Allen ◽  
Steven Turnock ◽  
Pierre Nabat ◽  
David Neubauer ◽  
Ulrike Lohmann ◽  
...  
Keyword(s):  
Climate Change ◽  
Air Quality ◽  
Carbon Dioxide Emissions ◽  
Surface Ozone ◽  
Control Measures ◽  
The Arctic ◽  
Model Simulations ◽  
Surface Warming ◽  
North Asia ◽  
Near Term

Abstract. Over the next few decades, policies that optimally address both climate change and air quality are essential. Although targeting near-term climate forcers (NTCFs), defined here as aerosols, tropospheric ozone and precursor gases (but not methane), should improve air quality, NTCF reductions will also impact climate. How future policies affect the abundance of NTCFs and their impact on climate and air quality remains uncertain. Here, we quantify the 2015–2055 climate and air quality effects of non-methane NTCFs using state-of-the-art chemistry-climate model simulations conducted for the Aerosol and Chemistry Model Intercomparison Project (AerChemMIP). Simulations are driven by two future scenarios featuring similar increases in greenhouse gases (GHGs) but with weak versus strong levels of air quality control measures. Unsurprisingly, we find significant improvements in air quality under NTCF mitigation (strong versus weak air quality controls). Surface ozone (O3) and fine particulate matter (PM2.5) decrease by −15 % and −25 %, respectively, over global land surfaces, with larger reductions in some regions including south and southeast Asia. Non-methane NTCF mitigation, however, leads to additional climate change due to the removal of aerosol which causes a net warming effect, including global mean surface temperature and precipitation increases of 0.24 K and 1.1 %, respectively, with similar increases in extreme weather indices. Regionally, the largest warming and wetting trends occur over Asia, including central and north Asia (0.56 K and 2.1 %), south Asia (0.48 K and 4.6 %) and east Asia (0.44 K and 4.7 %). Relatively large warming and wetting of the Arctic also occurs at 0.41 K and 2.1 %, respectively. Similar surface warming occurs in model simulations with aerosol-only mitigation, implying weak cooling due to ozone reductions. Our findings suggest that future policies that aggressively target non-methane NTCF reductions will improve air quality, but will lead to additional surface warming, particularly in Asia and the Arctic. Policies that address other NTCFs including methane, as well as carbon dioxide emissions, must also be adopted to meet mitigation goals.

scholarly journals Climate and air quality impacts due to mitigation of non-methane near-term climate forcers

2020 ◽  
Vol 20 (16) ◽  
pp. 9641-9663 ◽  
Author(s):  
Robert J. Allen ◽  
Steven Turnock ◽  
Pierre Nabat ◽  
David Neubauer ◽  
Ulrike Lohmann ◽  
...  
Keyword(s):  
Climate Change ◽  
Air Quality ◽  
Carbon Dioxide Emissions ◽  
The Arctic ◽  
Climate Mitigation ◽  
Model Simulations ◽  
Surface Warming ◽  
North Asia ◽  
Near Term ◽  
The Impact

Abstract. It is important to understand how future environmental policies will impact both climate change and air pollution. Although targeting near-term climate forcers (NTCFs), defined here as aerosols, tropospheric ozone, and precursor gases, should improve air quality, NTCF reductions will also impact climate. Prior assessments of the impact of NTCF mitigation on air quality and climate have been limited. This is related to the idealized nature of some prior studies, simplified treatment of aerosols and chemically reactive gases, as well as a lack of a sufficiently large number of models to quantify model diversity and robust responses. Here, we quantify the 2015–2055 climate and air quality effects of non-methane NTCFs using nine state-of-the-art chemistry–climate model simulations conducted for the Aerosol and Chemistry Model Intercomparison Project (AerChemMIP). Simulations are driven by two future scenarios featuring similar increases in greenhouse gases (GHGs) but with “weak” (SSP3-7.0) versus “strong” (SSP3-7.0-lowNTCF) levels of air quality control measures. As SSP3-7.0 lacks climate policy and has the highest levels of NTCFs, our results (e.g., surface warming) represent an upper bound. Unsurprisingly, we find significant improvements in air quality under NTCF mitigation (strong versus weak air quality controls). Surface fine particulate matter (PM2.5) and ozone (O3) decrease by -2.2±0.32 µg m−3 and -4.6±0.88 ppb, respectively (changes quoted here are for the entire 2015–2055 time period; uncertainty represents the 95 % confidence interval), over global land surfaces, with larger reductions in some regions including south and southeast Asia. Non-methane NTCF mitigation, however, leads to additional climate change due to the removal of aerosol which causes a net warming effect, including global mean surface temperature and precipitation increases of 0.25±0.12 K and 0.03±0.012 mm d−1, respectively. Similarly, increases in extreme weather indices, including the hottest and wettest days, also occur. Regionally, the largest warming and wetting occurs over Asia, including central and north Asia (0.66±0.20 K and 0.03±0.02 mm d−1), south Asia (0.47±0.16 K and 0.17±0.09 mm d−1), and east Asia (0.46±0.20 K and 0.15±0.06 mm d−1). Relatively large warming and wetting of the Arctic also occur at 0.59±0.36 K and 0.04±0.02 mm d−1, respectively. Similar surface warming occurs in model simulations with aerosol-only mitigation, implying weak cooling due to ozone reductions. Our findings suggest that future policies that aggressively target non-methane NTCF reductions will improve air quality but will lead to additional surface warming, particularly in Asia and the Arctic. Policies that address other NTCFs including methane, as well as carbon dioxide emissions, must also be adopted to meet climate mitigation goals.

scholarly journals Amplification of South Asian haze by water vapour–aerosol interactions

2020 ◽  
Vol 20 (22) ◽  
pp. 14457-14471
Author(s):  
Vijayakumar Sivadasan Nair ◽  
Filippo Giorgi ◽  
Usha Keshav Hasyagar
Keyword(s):  
Boundary Layer ◽  
Air Quality ◽  
South Asia ◽  
Water Vapour ◽  
Aerosol Optical Depth ◽  
Optical Depth ◽  
Climate Model ◽  
Mitigation Strategies ◽  
Surface Cooling ◽  
Gangetic Plain

Abstract. Air pollution and wintertime fog over South Asia is a major concern due to its significant implications for air quality, visibility and health. Using a regional climate model coupled with chemistry, we assess the contribution of the hygroscopic growth of aerosols (ambient–dry) to the total aerosol optical depth and demonstrate that the increased surface cooling due to the hygroscopic effects of aerosols further increases the humidity in the boundary layer and thus enhances the confinement of pollutants through aerosol–boundary layer interactions. This positive feedback mechanism plays an important role in the prevalence of wintertime fog and poor air quality conditions over South Asia, where water vapour contributes more than half of the aerosol optical depth. The aerosol–boundary layer interactions lead to moistening of the boundary layer and drying of the free troposphere, which amplifies the long-term trend in relative humidity over the Indo-Gangetic Plain during winter. Hence, the aerosol–water vapour interaction plays a decisive role in the formation and maintenance of the wintertime fog conditions over South Asia, which needs to be considered for planning mitigation strategies.

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