This chapter assesses long-term projections of climate change for the end of the 21st century and beyond, where the forced signal depends on the scenario and is typically larger than the internal variability of the climate system. Changes are expressed with respect to a baseline period of 1986-2005, unless otherwise stated.

Chapter 12 - Long-term climate change: Projections, commitments and irreversibility

. Landslides are a ubiquitous hazard in terrestrial environments with slopes,
incurring human fatalities in urban settlements, along transport corridors
and at sites of rural industry. Assessment of landslide risk requires
high-quality landslide databases. Recently, global landslide databases have
shown the extent to which landslides impact on society and identified areas
most at risk. Previous global analysis has focused on rainfall-triggered
landslides over short ∼  5-year observation periods. This paper presents
spatiotemporal analysis of a global dataset of fatal non-seismic landslides,
covering the period from January 2004 to December 2016. The data show that in
total 55 997 people were killed in
4862 distinct landslide events. The spatial distribution of landslides
is heterogeneous, with Asia representing the dominant geographical area.
There are high levels of interannual variation in the occurrence of
landslides. Although more active years coincide with recognised patterns of
regional rainfall driven by climate anomalies, climate modes (such as El
Nino–Southern Oscillation) cannot yet be related to landsliding,
requiring a landslide dataset of 30 + years. Our analysis demonstrates that
landslide occurrence triggered by human activity is increasing, in particular
in relation to construction, illegal mining and hill cutting. This supports
notions that human disturbance may be more detrimental to future landslide
incidence than climate.

/pdf/global-fatal-landslide-occurrence-from-2004-to-2016-1to3ljrrt3.pdf

Global fatal landslide occurrence from 2004 to 2016

This Review looks at the state of knowledge on the El Nino/Southern Oscillation (ENSO), a natural climate phenomenon. It discusses recent advances and insights into how climate change will affect this natural climate varibility cycle. The El Nino/Southern Oscillation (ENSO) is the dominant climate phenomenon affecting extreme weather conditions worldwide. Its response to greenhouse warming has challenged scientists for decades, despite model agreement on projected changes in mean state. Recent studies have provided new insights into the elusive links between changes in ENSO and in the mean state of the Pacific climate. The projected slow-down in Walker circulation is expected to weaken equatorial Pacific Ocean currents, boosting the occurrences of eastward-propagating warm surface anomalies that characterize observed extreme El Nino events. Accelerated equatorial Pacific warming, particularly in the east, is expected to induce extreme rainfall in the eastern equatorial Pacific and extreme equatorward swings of the Pacific convergence zones, both of which are features of extreme El Nino. The frequency of extreme La Nina is also expected to increase in response to more extreme El Ninos, an accelerated maritime continent warming and surface-intensified ocean warming. ENSO-related catastrophic weather events are thus likely to occur more frequently with unabated greenhouse-gas emissions. But model biases and recent observed strengthening of the Walker circulation highlight the need for further testing as new models, observations and insights become available.

/pdf/enso-and-greenhouse-warming-28s15qbi7a.pdf

ENSO and greenhouse warming

El Nino events are characterized by surface warming of the tropical Pacific Ocean and weakening of equatorial trade winds that occur every few years Such conditions are accompanied by changes in atmospheric and oceanic circulation, affecting global climate, marine and terrestrial ecosystems, fisheries and human activities The alternation of warm El Nino and cold La Nina conditions, referred to as the El Nino–Southern Oscillation (ENSO), represents the strongest year-to-year fluctuation of the global climate system Here we provide a synopsis of our current understanding of the spatio-temporal complexity of this important climate mode and its influence on the Earth system

/pdf/el-nino-southern-oscillation-complexity-5alyl3svf7.pdf

El Niño–Southern Oscillation complexity

We analyse the ability of CMIP3 and CMIP5 coupled ocean–atmosphere general circulation models (CGCMs) to simulate the tropical Pacific mean state and El Nino-Southern Oscillation (ENSO). The CMIP5 multi-model ensemble displays an encouraging 30 % reduction of the pervasive cold bias in the western Pacific, but no quantum leap in ENSO performance compared to CMIP3. CMIP3 and CMIP5 can thus be considered as one large ensemble (CMIP3 + CMIP5) for multi-model ENSO analysis. The too large diversity in CMIP3 ENSO amplitude is however reduced by a factor of two in CMIP5 and the ENSO life cycle (location of surface temperature anomalies, seasonal phase locking) is modestly improved. Other fundamental ENSO characteristics such as central Pacific precipitation anomalies however remain poorly represented. The sea surface temperature (SST)-latent heat flux feedback is slightly improved in the CMIP5 ensemble but the wind-SST feedback is still underestimated by 20–50 % and the shortwave-SST feedbacks remain underestimated by a factor of two. The improvement in ENSO amplitudes might therefore result from error compensations. The ability of CMIP models to simulate the SST-shortwave feedback, a major source of erroneous ENSO in CGCMs, is further detailed. In observations, this feedback is strongly nonlinear because the real atmosphere switches from subsident (positive feedback) to convective (negative feedback) regimes under the effect of seasonal and interannual variations. Only one-third of CMIP3 + CMIP5 models reproduce this regime shift, with the other models remaining locked in one of the two regimes. The modelled shortwave feedback nonlinearity increases with ENSO amplitude and the amplitude of this feedback in the spring strongly relates with the models ability to simulate ENSO phase locking. In a final stage, a subset of metrics is proposed in order to synthesize the ability of each CMIP3 and CMIP5 models to simulate ENSO main characteristics and key atmospheric feedbacks.

ENSO representation in climate models: from CMIP3 to CMIP5

[1] El Nino-Southern Oscillation (ENSO), which dominates variability on interannual timescale in the climate system, is known to exhibit various spatio-temporal characteristics. Recent studies show that in additional to a canonical El Nino with its major center of sea surface temperatures (SST) anomalies in the equatorial Pacific cold-tongue region, a different type of El Nino with its major action center shifted to the warm-pool edge has emerged and become more common during the past two decades. Because the SST patterns of these two types of El Nino events are highly correlated, neither of the traditional Nino3 and Nino4 SST indices alone is effective in representing the new-type El Nino. Through a simple transformation of the Nino3 and Nino4 indices, we devised two new indices that separately identify the two types of ENSO events. Unlike the Nino3 and Nino4 indices, the two new indices are of little simultaneous correlation. The SST patterns associated with these new indices capture SST characteristics of the two types of ENSO. Their running lagged-correlations capture different ENSO-phase propagations and ENSO regime changes associated with the climate shift in 1976/77.

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/2010GL046031

Niño indices for two types of ENSO

The development and termination of El Nino events seem to be coupled with the seasonal cycle. Statistical analyses suggest that this link reflects the presence of a combination climate mode with periods of 10 and 15 months.

/pdf/a-combination-mode-of-the-annual-cycle-and-the-el-nino-3s02kuue3c.pdf

A combination mode of the annual cycle and the El Niño/Southern Oscillation

The El Ni~ Oscillation (ENSO) tends to behave arguably as two different ‘‘types’’ or ‘‘flavors’’ in recent decades. One is the canonical cold-tongue-type ENSO with major sea surface temperature anomalies(SSTA)positionedoverthe easternPacific.Theotheris awarm-pool-typeENSOwith SSTAcenteredin the central Pacific near the edge of the warm pool. In this study, the basic features and main feedback processes of these two types of ENSO are examined. It is shown that the interannual variability of upper-ocean heat content exhibits recharge‐discharge processes throughout the life cycles of both the cold tongue (CT) and warm pool (WP) ENSO types. Through a heat budget analysis with focus on the interannual frequency band, the authors further demonstrate that the thermocline feedback plays a dominant role in contributing to the growth and phase transitions of both ENSO types, whereas the zonal advective feedback contributes mainly to their phase transitions. The westward shift of the SSTA center of the WP ENSO and the presence of significant surface easterly wind anomalies over the far eastern equatorial Pacific during its mature warm phase are the two main factors that lead to a reduced positive feedback for the eastern Pacific SSTA. Nevertheless, both the WP and CT ENSO can be understood to a large extent by the recharge oscillator mechanism.

https://journals.ametsoc.org/doi/pdf/10.1175/JCLI-D-12-00601.1

Recharge Oscillator Mechanisms in Two Types of ENSO

This work contrasts the climatic impacts of so-called warm-pool (WP) and cold-tongue (CT) El Nino on the atmospheric circulation over the western North Pacific (WNP). It is found that the anomalous atmospheric circulation over the WNP is nearly opposite in response to these two types of El Nino events in developing autumn. A weak anomalous anticyclone appears over the WNP during CT El Nino, whereas a weak anomalous cyclone emerges in the same region during WP El Nino. These nearly opposite autumn responses of atmospheric circulation have a significant impact on East Asian climate, and southern China autumn rainfall in particular, although this contrast tends to diminish as El Nino events enter their mature phase.

Contrasting Impacts of Two-Type El Niño over the Western North Pacific during Boreal Autumn

An interdecadal shift in the variability and mean state of the tropical Pacific Ocean is investigated within the context of changes in El Nino–Southern Oscillation (ENSO). Compared with 1979–99, the interannual variability in the tropical Pacific was significantly weaker in 2000–11, and this shift can be seen by coherent changes in both the tropical atmosphere and ocean. For example, the equatorial thermocline tilt became steeper during 2000–11, which was consistent with positive (negative) sea surface temperature anomalies, increased (decreased) precipitation, and enhanced (suppressed) convection in the western (central and eastern) tropical Pacific, which reflected an intensification of the Walker circulation.The combination of a steeper thermocline slope with stronger surface trade winds is proposed to have hampered the eastward migration of the warm water along the equatorial Pacific. As a consequence, the variability of the warm water volume was reduced and thus ENSO amplitude also decreased....

Hong-Li Ren

Papers

Niño indices for two types of ENSO

A combination mode of the annual cycle and the El Niño/Southern Oscillation

Recharge Oscillator Mechanisms in Two Types of ENSO

Contrasting Impacts of Two-Type El Niño over the Western North Pacific during Boreal Autumn

Weakened Interannual Variability in the Tropical Pacific Ocean since 2000