RESULTADOS Y DISCUSIÓN
2. Estado emocional como modo adaptativo de autoimagen
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Improvements in our understanding of volcanic forcing help to better understand past climate
3731
and make a better climate prediction. It also enables the radiative forcing and accompanying
3732
transient response due to volcanic aerosols to be placed in perspective, relative to the forcing
3733
and responses due to the increases in the anthropogenic well-mixed greenhouse gas emissions.
3734
Since 1850 volcanic forcing has offset the ocean heat content increase due to the global-mean
3735
warming by about 30% (Delworth et al. 2005). Comparison of simulated and observed climate
3736
responses to the major volcanic eruptions helps to evaluate volcanic forcing itself. The
3737
relatively large transient forcing by volcanic aerosols offers a platform to test climate model
3738
simulations of stratospheric and surface temperature perturbations against observations.
3739
The net radiative effects of volcanic aerosols on the thermal and hydrologic balance (e.g.,
3740
surface temperature and moisture) have been highlighted in (Kirchner et al., 1999; Free and
3741
Angell, 2002; Jones et al., 2004; Trenberth and Dai, 2007). Atmospheric temperature after
3742
volcanic eruptions relaxes for 7-10 years, while the deep ocean retains a thermal perturbation
3743
for about a century (Stenchikov et al., 2009; Delworth et al., 2005). Gregory et al. (2013)
3744
indicated the importance of the pre-industrial volcanic forcing to predict future climate
3745
correctly. The prolonged volcanic activity could be a reason for a long-term climate cooling as
3746
it had arguably happened during the medieval Little Ice Age in 1300-1850 (Free and Robock,
3747
1999) when in the middle of this period the cooling was enhanced by the Maunder Minimum
3748
in Solar Irradiance (Eddy, 1976).
3749 3750
In addition, the differential heating/cooling due to volcanic aerosols affect atmospheric
3751
circulation. It is believed these circulation responses could cause a positive phase of the
3752
Arctic oscillation and winter warming in high northern latitudes (Ramaswamy et al., 2006;
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Shindell et al., 2003, 2004; Stenchikov et al., 2002, 2004, 2006; Perlwitz and Graf, 2001;
3754
Toohey et al., 2014;), prolong or even initiate El Nino (Adams et al., 2003; Pausata et al.,
3755
2015; Predybaylo et al., 2017; McGregor et al., 2011; Ohba et al., 2013), or damp monsoon
3756
circulations (Trenberth and Dai, 2007; Anchukaitis et al., 2010; Iles et al., 2013; Schneider et
3757
al., 2009). There are still large discrepancies between the models on the magnitude and the
3758
leading mechanism that forces those dynamic responses, and observations are not long
3759
enough to provide empirical proof of a concept. E.g., (Polvani et al., 2019) argued that the
3760
positive phase of Arctic Oscillation in winter of 1991/1992 was not casually forced by the
3761
1991 Pinatubo eruption, as it was not associated with the strong northern polar vortex.
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However, one has to take precaution making a far-reaching conclusion from their analysis as
3763
the authors only considered one volcanic winter that does not exhibit a statistically
3764
significant climate signal.
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One robust finding in terms of dynamical response to high latitude eruptions that
3767
preferentially load one hemisphere relative to the other, is that tropical precipitation
3768
associated with the Inter-Tropical Convergence Zone is shifted towards the unperturbed
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hemisphere in both observations and global climate models (Oman et al., 2006 Haywood et al.,
3770
2013). Thus, significant high latitude ruptions in the northern hemisphere (e.g., Katmai which
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erupted in 1913) can lead to drought in sub-Saharan Africa and cause the North Atlantic
3772
hurricane frequency to dramatically reduce in years subsequent to the eruptions (Evan, 2012;
Jones et al., 2017). These impacts are relatively well understood from theoretical constraints
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on cross equatorial energy and moisture transport (e.g. Bischoff and Schneider, 2014; 2016).
3775
Equatorial eruptions also can affect the position of African rain-belt by the combined effect
3776
of the preferential hemispheric summer cooling and damping of Indian Monsoon (Dogar et
3777 al., 2017). 3778 3779 9.7 Summary 3780 3781 3782
Stratospheric aerosols exert a substantial, albeit transient, impact on climate after the Junge
3783
layer is replenished by strong volcanic injections. For the equatorial eruptions, the radiative
3784
forcing peaks in about a half a year after a volcanic explosion and relaxes with the e-folding
3785
time of one-two years. For the high-latitude eruptions, the e-folding time is shorter than for
3786
tropical ones. Despite the transient nature of the volcanic forcing, the global ocean integrates
3787
the cooling from multiple eruptions extending the climate response to decades and even
3788
centuries (Delworth et al., 2005; Stenchikov et al., 2009).
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Our understanding of the effect of stratospheric aerosols has grown substantially over the last
3791
century, from descriptive and intuitive knowledge base to the full-scale first-principle
3792
modeling supported by ground-based and satellite observations. Despite this progress, the
3793
error bars in volcanic radiative forcing probably remain larger than 20-30%. Because we
3794
have a limited ability to reconstruct volcanic forcing in the past, it is extremely important to
3795
further develop models that could interactively simulate volcanic plume development and its
3796
radiative effect. The best models so far demonstrate a sizable discrepancy with available
observations that also may bear a significant uncertainty. One important bottle-neck is
3798
aerosol particle size distribution that is controlled by fine-scale microphysical processes.
3799
Particle sizes are important as they define both radiative effects of aerosols and their
3800
lifetime with respect to gravitational settling. The accumulation of the effect of small
3801
volcanic eruptions has to be better understood as it contradicts the expectation of a smaller
3802
lifetime of above-tropopause emissions. The pre-calculated, based on observations, aerosol
3803
datasets have their value in helping to better calibrate simulated climate
3804
responses to volcanic forcing.
3805 3806
It is important to consider radiative forcing and climate responses in combination, as this
3807
gives important feedback on how well a model reproduces the observed climate variations.
3808
The climate models are capable of calculating the thermodynamic responses to the volcanic
3809
aerosols forcing, but fail to consistently reproduce the circulation anomalies forced by
3810
volcanic eruptions. Further development of model capabilities and stratospheric aerosol
3811
monitoring are necessary to reduce uncertainties in past and future climate simulations
3812 3813 3814 3815
3816 Figure captions 3817 3818 Figure 9.1 3819
Global mean optical depth of stratospheric sulfate aerosols for 0.55 um calculated using
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CMIP6, Sato et al. (1993) with (Schmidt et al., 2011) corrections, and Amman et al.
3821 (2003) data sets 3822 3823 Figure 9.2. 3824
Global mean radiative forcing (clear-sky and all-sky) at top of the atmosphere after the
3825
1991 Pinatubo eruption as a function of time calculated using different volcanic aerosol
3826 datasets 3827 3828 Figure 9.3. 3829
Zonal mean SW (top row) and LW (bottom row) Heating Rates after the 1991 Pinatubo
3830
eruption calculated using CMIP6 (left column), Sato1.8 (middle column), and Sato2
3831
(right column) datasets averaged over the equatorial belt of 5S-5N as a function of time
3832
and pressure.
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3836 3837 3838 3839 3840 3841 3842 3843 3844 3845 3846 3847 3848 3849 3850 3851
3852 Figure 9.1 3853 3854 3855 3856 3857 Figure 9.2. 3858 . 3859 3860 3861 Figure 9.3. 3862 3863 3864
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