The Mechanisms of Summer Dryness Induced by Greenhouse Warming

Abstract The multidecadal modulation of the El Niño–Southern Oscillation (ENSO) due to greenhouse warming has been analyzed herein by means of diagnostics of Intergovernmental Panel on Climate Change (IPCC) Fourth Assessment Report (AR4) coupled general circulation models (CGCMs) and the eigenanalysis of a simplified version of an intermediate ENSO model. The response of the global-mean troposphere temperature to increasing greenhouse gases is more likely linear, while the amplitude and period of ENSO fluctuates in a multidecadal time scale. The climate system model outputs suggest that the multidecadal modulation of ENSO is related to the delayed response of the subsurface temperature in the tropical Pacific compared to the response time of the sea surface temperature (SST), which would lead a modulation of the vertical temperature gradient. Furthermore, an eigenanalysis considering only two parameters, the changes in the zonal contrast of the mean background SST and the changes in the vertical contrast between the mean surface and subsurface temperatures in the tropical Pacific, exhibits a good agreement with the CGCM outputs in terms of the multidecadal modulations of the ENSO amplitude and period. In particular, the change in the vertical contrast, that is, change in difference between the subsurface temperature and SST, turns out to be more influential on the ENSO modulation than changes in the mean SST itself.

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Changes in Independency between Two Types of El Niño Events under a Greenhouse Warming Scenario in CMIP5 Models

Journal of Climate ◽

10.1175/jcli-d-14-00721.1 ◽

2015 ◽

Vol 28 (19) ◽

pp. 7561-7575 ◽

Cited By ~ 2

Author(s):

Yoo-Geun Ham ◽

Yerim Jeong ◽

Jong-Seong Kug

Keyword(s):

Global Warming ◽

El Niño ◽

El Nino ◽

Western Pacific ◽

Cmip5 Models ◽

Greenhouse Warming ◽

Central Pacific ◽

El Niño Events ◽

The Western Pacific ◽

El Nino Events

Abstract This study uses archives from phase 5 of the Coupled Model Intercomparison Project (CMIP5) to investigate changes in independency between two types of El Niño events caused by greenhouse warming. In the observations, the independency between cold tongue (CT) and warm pool (WP) El Niño events is distinctively increased in recent decades. The simulated changes in independency between the two types of El Niño events according to the CMIP5 models are quite diverse, although the observed features are simulated to some extent in several climate models. It is found that the climatological change after global warming is an essential factor in determining the changes in independency between the two types of El Niño events. For example, the independency between these events is increased after global warming when the climatological precipitation is increased mainly over the equatorial central Pacific. This climatological precipitation increase extends convective response to the east, particularly for CT El Niño events, which leads to greater differences in the spatial pattern between the two types of El Niño events to increase the El Niño independency. On the contrary, in models with decreased independency between the two types of El Niño events after global warming, climatological precipitation is increased mostly over the western Pacific. This confines the atmospheric response to the western Pacific in both El Niño events; therefore, the similarity between them is increased after global warming. In addition to the changes in the climatological state after global warming, a possible connection of the changes in the El Niño independency with the historical mean state is discussed in this paper.

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Two-year consecutive concurrences of positive Indian Ocean Dipole and Central Pacific El Niño preconditioned the 2019/2020 Australian “black summer” bushfires

Geoscience Letters ◽

10.1186/s40562-020-00168-2 ◽

2020 ◽

Vol 7 (1) ◽

Author(s):

Guojian Wang ◽

Wenju Cai

Keyword(s):

Indian Ocean ◽

El Niño ◽

Indian Ocean Dipole ◽

El Nino ◽

Greenhouse Warming ◽

Central Pacific ◽

Central Pacific El Niño ◽

Positive Indian Ocean Dipole ◽

The Future ◽

Rainfall Anomalies

Abstract The 2019/20 Australian black summer bushfires were particularly severe in many respects, including its early commencement, large spatial coverage, and large number of burning days, preceded by record dry and hot anomalies. Determining whether greenhouse warming has played a role is an important issue. Here, we examine known modes of tropical climate variability that contribute to droughts in Australia to provide a gauge. We find that a two-year consecutive concurrence of the 2018 and 2019 positive Indian Ocean Dipole and the 2018 and 2019 Central Pacific El Niño, with the former affecting Southeast Australia, and the latter influencing eastern and northeastern Australia, may explain many characteristics of the fires. Such consecutive events occurred only once in the observations since 1911. Using two generations of state-of-the-art climate models under historical and a business-as-usual emission scenario, we show that the frequency of such consecutive concurrences increases slightly, but rainfall anomalies during such events are stronger in the future climate, and there are drying trends across Australia. The impact of the stronger rainfall anomalies during such events under drying trends is likely to be exacerbated by greenhouse warming-induced rise in temperatures, making such events in the future even more extreme.

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Observational Constraints on Past Attributable Warming and Predictions of Future Global Warming

Journal of Climate ◽

10.1175/jcli3802.1 ◽

2006 ◽

Vol 19 (13) ◽

pp. 3055-3069 ◽

Cited By ~ 129

Author(s):

Peter A. Stott ◽

John F. B. Mitchell ◽

Myles R. Allen ◽

Thomas L. Delworth ◽

Jonathan M. Gregory ◽

...

Keyword(s):

Twentieth Century ◽

Greenhouse Gas Emissions ◽

Greenhouse Gas ◽

Temperature Change ◽

Greenhouse Warming ◽

Gas Emissions ◽

Aerosol Forcing ◽

Future Global Warming ◽

Cooling Effects ◽

The Impact

Abstract This paper investigates the impact of aerosol forcing uncertainty on the robustness of estimates of the twentieth-century warming attributable to anthropogenic greenhouse gas emissions. Attribution analyses on three coupled climate models with very different sensitivities and aerosol forcing are carried out. The Third Hadley Centre Coupled Ocean–Atmosphere GCM (HadCM3), Parallel Climate Model (PCM), and GFDL R30 models all provide good simulations of twentieth-century global mean temperature changes when they include both anthropogenic and natural forcings. Such good agreement could result from a fortuitous cancellation of errors, for example, by balancing too much (or too little) greenhouse warming by too much (or too little) aerosol cooling. Despite a very large uncertainty for estimates of the possible range of sulfate aerosol forcing obtained from measurement campaigns, results show that the spatial and temporal nature of observed twentieth-century temperature change constrains the component of past warming attributable to anthropogenic greenhouse gases to be significantly greater (at the 5% level) than the observed warming over the twentieth century. The cooling effects of aerosols are detected in all three models. Both spatial and temporal aspects of observed temperature change are responsible for constraining the relative roles of greenhouse warming and sulfate cooling over the twentieth century. This is because there are distinctive temporal structures in differential warming rates between the hemispheres, between land and ocean, and between mid- and low latitudes. As a result, consistent estimates of warming attributable to greenhouse gas emissions are obtained from all three models, and predictions are relatively robust to the use of more or less sensitive models. The transient climate response following a 1% yr−1 increase in CO2 is estimated to lie between 2.2 and 4 K century−1 (5–95 percentiles).

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Methane, oxygen, photosynthesis, rubisco and the regulation of the air through time

Philosophical Transactions of the Royal Society B Biological Sciences ◽

10.1098/rstb.2008.0057 ◽

2008 ◽

Vol 363 (1504) ◽

pp. 2745-2754 ◽

Cited By ~ 22

Author(s):

Euan G Nisbet ◽

R. Ellen R Nisbet

Keyword(s):

Greenhouse Gas ◽

Greenhouse Warming ◽

Biological Productivity ◽

Stable States ◽

Mixing Ratios ◽

The Past ◽

Glacial Epoch ◽

Air Control ◽

Carbon Gases

Rubisco I's specificity, which today may be almost perfectly tuned to the task of cultivating the global garden, controlled the balance of carbon gases and O 2 in the Precambrian ocean and hence, by equilibration, in the air. Control of CO 2 and O 2 by rubisco I, coupled with CH 4 from methanogens, has for the past 2.9 Ga directed the global greenhouse warming, which maintains liquid oceans and sustains microbial ecology. Both rubisco compensation controls and the danger of greenhouse runaway (e.g. glaciation) put limits on biological productivity. Rubisco may sustain the air in either of two permissible stable states: either an anoxic system with greenhouse warming supported by both high methane mixing ratios as well as carbon dioxide, or an oxygen-rich system in which CO 2 largely fulfils the role of managing greenhouse gas, and in which methane is necessarily only a trace greenhouse gas, as is N 2 O. Transition from the anoxic to the oxic state risks glaciation. CO 2 build-up during a global snowball may be an essential precursor to a CO 2 -dominated greenhouse with high levels of atmospheric O 2 . Photosynthetic and greenhouse-controlling competitions between marine algae, cyanobacteria, and terrestrial C3 and C4 plants may collectively set the CO 2 : O 2 ratio of the modern atmosphere (last few million years ago in a mainly glacial epoch), maximizing the productivity close to rubisco compensation and glacial limits.

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Why does the climate response to greenhouse warming and greenhouse cooling differ?

10.5194/egusphere-egu21-6534 ◽

2021 ◽

Author(s):

Jennifer Kay ◽

Jason Chalmers

Keyword(s):

Carbon Dioxide ◽

Radiative Forcing ◽

Climate Model ◽

Temperature Response ◽

Greenhouse Warming ◽

Climate Response ◽

Cloud Feedbacks ◽

Surface Climate ◽

Carbon Dioxide Concentrations ◽

Radiative Feedbacks

<p>While the long-standing quest to constrain equilibrium climate sensitivity has resulted in intense scrutiny of the processes controlling idealized greenhouse warming, the processes controlling idealized greenhouse cooling have received less attention. Here, differences in the climate response to increased and decreased carbon dioxide concentrations are assessed in state-of-the-art fully coupled climate model experiments. One hundred and fifty years after an imposed instantaneous forcing change, surface global warming from a carbon dioxide doubling (abrupt-2xCO2, 2.43 K) is larger than the surface global cooling from a carbon dioxide halving (abrupt-0p5xCO2, 1.97 K). Both forcing and feedback differences explain these climate response differences. Multiple approaches show the radiative forcing for a carbon dioxide doubling is ~10% larger than for a carbon dioxide halving. In addition, radiative feedbacks are less negative in the doubling experiments than in the halving experiments. Specifically, less negative tropical shortwave cloud feedbacks and more positive subtropical cloud feedbacks lead to more greenhouse 2xCO2 warming than 0.5xCO2 greenhouse cooling. Motivated to directly isolate the influence of cloud feedbacks on these experiments, additional abrupt-2xCO2 and abrupt-0p5xCO2 experiments with disabled cloud-climate feedbacks were run. Comparison of these &#8220;cloud-locked&#8221; simulations with the original &#8220;cloud active&#8221; simulations shows cloud feedbacks help explain the nonlinear global surface temperature response to greenhouse warming and greenhouse cooling. Overall, these results demonstrate that both radiative forcing and radiative feedbacks are needed to explain differences in the surface climate response to increased and decreased carbon dioxide concentrations.</p>

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Changes in the strength and width of the Hadley Circulation since 1871

Climate of the Past ◽

10.5194/cp-8-1169-2012 ◽

2012 ◽

Vol 8 (4) ◽

pp. 1169-1175 ◽

Cited By ~ 28

Author(s):

J. Liu ◽

M. Song ◽

Y. Hu ◽

X. Ren

Keyword(s):

20Th Century ◽

Global Climate ◽

Hadley Circulation ◽

Recent Change ◽

Early 20Th Century ◽

Greenhouse Warming ◽

Long Period ◽

The Past ◽

Period Oscillation

Abstract. Recent studies demonstrate that the Hadley Circulation has intensified and expanded for the past three decades, which has important implications for subtropical societies and may lead to profound changes in global climate. However, the robustness of this intensification and expansion that should be considered when interpreting long-term changes of the Hadley Circulation is still a matter of debate. It also remains largely unknown how the Hadley Circulation has evolved over longer periods. Here, we present long-term variability of the Hadley Circulation using the 20th Century Reanalysis. It shows a slight strengthening and widening of the Hadley Circulation since the late 1970s, which is not inconsistent with recent assessments. However, over centennial timescales (1871–2008), the Hadley Circulation shows a tendency towards a more intense and narrower state. More importantly, the width of the Hadley Circulation might have not yet completed a life-cycle since 1871. The strength and width of the Hadley Circulation during the late 19th to early 20th century show strong natural variability, exceeding variability that coincides with global warming in recent decades. These findings raise the question of whether the recent change in the Hadley Circulation is primarily attributed to greenhouse warming or to a long-period oscillation of the Hadley Circulation – substantially longer than that observed in previous studies.

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