scholarly journals Exploring the Interplay between Natural Decadal Variability and Anthropogenic Climate Change in Summer Rainfall over China. Part I: Observational Evidence

2011 ◽  
Vol 24 (17) ◽  
pp. 4584-4599 ◽  
Author(s):  
Yonghui Lei ◽  
Brian Hoskins ◽  
Julia Slingo
Keyword(s):  
Climate Change ◽  
Decadal Variability ◽  
Daily Rainfall ◽  
Summer Rainfall ◽  
Internal Variability ◽  
Anthropogenic Climate Change ◽  
Light Rain ◽  
The North ◽  
Recent Trends ◽  
Summer Rainfall Over China

Summer rainfall over China has experienced substantial variability on longer time scales during the last century, and the question remains whether this is due to natural, internal variability or is part of the emerging signal of anthropogenic climate change. Using the best available observations over China, the decadal variability and recent trends in summer rainfall are investigated with the emphasis on changes in the seasonal evolution and on the temporal characteristics of daily rainfall. The possible relationships with global warming are reassessed. Substantial decadal variability in summer rainfall has been confirmed during the period 1958–2008; this is not unique to this period but is also seen in the earlier decades of the twentieth century. Two dominant patterns of decadal variability have been identified that contribute substantially to the recent trend of southern flooding and northern drought. Natural decadal variability appears to dominate in general but in the cases of rainfall intensity and the frequency of rainfall days, particularly light rain days, then the dominant EOFs have a rather different character, being of one sign over most of China, and having principal components (PCs) that appear more trendlike. The increasing intensity of rainfall throughout China and the decrease in light rainfall days, particularly in the north, could at least partially be of anthropogenic origin, both global and regional, linked to increased greenhouse gases and increased aerosols.

scholarly journals Fluctuating reproductive rates in Hawaii's humpback whales, Megaptera novaeangliae , reflect recent climate anomalies in the North Pacific

2019 ◽  
Vol 6 (3) ◽  
pp. 181463 ◽  
Author(s):  
R. Cartwright ◽  
A. Venema ◽  
V. Hernandez ◽  
C. Wyels ◽  
J. Cesere ◽  
...  
Keyword(s):  
Climate Change ◽  
North Pacific ◽  
Megaptera Novaeangliae ◽  
Anthropogenic Climate Change ◽  
Humpback Whales ◽  
Encounter Rates ◽  
The North ◽  
The Impact ◽  
The North Pacific ◽  
Population Segment

Alongside changing ocean temperatures and ocean chemistry, anthropogenic climate change is now impacting the fundamental processes that support marine systems. However, where natural climate aberrations mask or amplify the impacts of anthropogenic climate change, identifying key detrimental changes is challenging. In these situations, long-term, systematic field studies allow the consequences of anthropogenically driven climate change to be distinguished from the expected fluctuations in natural resources. In this study, we describe fluctuations in encounter rates for humpback whales, Megaptera novaeangliae , between 2008 and 2018. Encounter rates were assessed during transect surveys of the Au'Au Channel, Maui, Hawaii. Initially, rates increased, tracking projected growth rates for this population segment. Rates reached a peak in 2013, then declined through 2018. Specifically, between 2013 and 2018, mother–calf encounter rates dropped by 76.5%, suggesting a rapid reduction in the reproductive rate of the newly designated Hawaii Distinct Population Segment of humpback whales during this time. As this decline coincided with changes in the Pacific decadal oscillation, the development of the NE Pacific marine heat wave and the evolution of the 2016 El Niño, this may be another example of the impact of this potent trifecta of climatic events within the North Pacific.

Trends, Variability and Predictive Skill of the Ocean Heat Content in North Atlantic: An Analysis with the EC-Earth3 Model

2021 ◽  
Author(s):  
Teresa Carmo-Costa ◽  
Roberto Bilbao ◽  
Pablo Ortega ◽  
Ana Teles-Machado ◽  
Emanuel Dutra
Keyword(s):  
North Atlantic ◽  
Climate Model ◽  
Decadal Variability ◽  
Heat Content ◽  
Internal Variability ◽  
Ocean Heat Content ◽  
Internal Climate Variability ◽  
The North ◽  
Predictive Skill ◽  
Modeling Uncertainties

Abstract This study investigates trends, variability and predictive skill of the upper ocean heat content (OHC) in the North Atlantic basin. This is a region where strong decadal variability superimposes the externally forced trends, introducing important differences in the local warming rates, and leading in the case of the Central Subpolar North Atlantic to an overall long-term cooling. Our analysis aims to better understand these regional differences, by investigating how internal and forced variability contribute to local trends, exploring also their role on the local prediction skill. The analysis combines the study of three ocean reanalyses to document the uncertainties related to observations, with two sets of CMIP6 experiments performed with the global coupled climate model EC-Earth3: a historical ensemble to characterise the forced signals; and a retrospective decadal prediction system, to additionally characterise the contributions from internal climate variability. Our results show that internal variability is essential to understand the spatial pattern of North Atlantic OHC trends, contributing decisively to the local trends and providing high levels of predictive skill in the Eastern Subpolar North Atlantic and the Irminger and Iceland Seas, and to a lesser extent in the Labrador Sea. Skill and trends in other areas like the Subtropical North Atlantic, or the Gulf Stream Extension are mostly externally forced. Large observational and modeling uncertainties affect the trends and interannual variability in the Central Subpolar North Atlantic, the only region exhibiting a cooling during the study period, uncertainties that might explain the very poor local predictive skill.

Simulation of Late-Twenty-First-Century Changes in Wintertime Atmospheric Circulation over Europe Due to Anthropogenic Causes

2004 ◽  
Vol 17 (24) ◽  
pp. 4630-4635 ◽  
Author(s):  
Laurent Terray ◽  
Marie-Estelle Demory ◽  
Michel Déqué ◽  
Gaelle de Coetlogon ◽  
Eric Maisonnave
Keyword(s):  
Climate Change ◽  
North Atlantic ◽  
General Circulation ◽  
Circulation Model ◽  
Horizontal Resolution ◽  
Anthropogenic Climate Change ◽  
Strong Increase ◽  
Climate Change Scenarios ◽  
The North ◽  
The North Atlantic

Abstract Evidence is presented, based on an ensemble of climate change scenarios performed with a global general circulation model of the atmosphere with high horizontal resolution over Europe, to suggest that the end-of-century anthropogenic climate change over the North Atlantic–European region strongly projects onto the positive phase of the North Atlantic Oscillation during wintertime. It is reflected in a doubling of the residence frequency of the climate system in the associated circulation regime, in agreement with the nonlinear climate perspective. The strong increase in the amplitude of the response, compared to coarse-resolution coupled model studies, suggests that improved model representation of regional climate is needed to achieve more reliable projections of anthropogenic climate change on European climate.

scholarly journals The Impact of Natural and Anthropogenic Climate Change on Western North Pacific Tropical Cyclone Tracks*

2015 ◽  
Vol 28 (5) ◽  
pp. 1806-1823 ◽  
Author(s):  
Angela J. Colbert ◽  
Brian J. Soden ◽  
Ben P. Kirtman
Keyword(s):  
Climate Change ◽  
North Atlantic ◽  
North Pacific ◽  
Western North Pacific ◽  
Large Scale ◽  
Anthropogenic Climate Change ◽  
The North ◽  
Steering Flow ◽  
The North Atlantic ◽  
The Impact

Abstract The impact of natural and anthropogenic climate change on tropical cyclone (TC) tracks in the western North Pacific (WNP) is examined using a beta and advection model (BAM) to isolate the influence of changes in the large-scale steering flow from changes in genesis location. The BAM captures many of the observed changes in TC tracks due to El Niño–Southern Oscillation (ENSO), while little change is noted for the Pacific decadal oscillation and all-India monsoon rainfall in either observations or BAM simulations. Analysis with the BAM suggests that the observed shifts in the average track between the phases of ENSO are primarily due to changes in the large-scale steering flow, with changes in genesis location playing a secondary role. Potential changes in TC tracks over the WNP due to anthropogenic climate change are also assessed. Ensemble mean projections are downscaled from 17 CMIP3 models and 26 CMIP5 models. Statistically significant decreases [~(4%–6%)] in westward moving TCs and increases [~(5%–7%)] in recurving ocean TCs are found. These correspond to projected decreases of 3–5 TCs per decade over the Philippines and increases of 1–3 TCs per decade over the central WNP. The projected changes are primarily caused by a reduction in the easterlies. This slows the storm movement, allowing more time for the beta drift to carry the storm northward and recurve. A previous study found similar results in the North Atlantic. Taken together, these results suggest that a weakening of the mean atmospheric circulation in response to anthropogenic warming will lead to fewer landfalling storms over the North Atlantic and WNP.

scholarly journals Characteristics of North American Summertime Rainfall with Emphasis on the Monsoon

2008 ◽  
Vol 21 (6) ◽  
pp. 1277-1294 ◽  
Author(s):  
Brant Liebmann ◽  
Ileana Bladé ◽  
Nicholas A. Bond ◽  
David Gochis ◽  
Dave Allured ◽  
...  
Keyword(s):  
North American ◽  
Rain Rate ◽  
Daily Rainfall ◽  
Summer Rainfall ◽  
Wet Season ◽  
Southern Mexico ◽  
The North ◽  
Sierra Madre ◽  
Grid Points ◽  
Northwestern Mexico

Abstract The core region of the North American summer monsoon is examined using spatially averaged daily rainfall observations obtained from gauges, with the objective of improving understanding of its climatology and variability. At most grid points, composite and interannual variations of the onset and end of the wet season are well defined, although, among individual stations that make up a grid average, variability is large. The trigger for monsoon onset in southern and eastern Mexico appears to be related to a change in vertical velocity, while for northwestern Mexico, Arizona, and New Mexico it is related to a reduction in stability, as indicated by a decrease in the lifted index. The wet-season rain rate is a combination of the wet-day rain rate, which decreases with distance from the coast, and the wet-day frequency, which is largest over the Sierra Madre Occidental. Thus the maximum total rate lies slightly to the west of the highest orography. As has been previously noted, onset is not always well correlated with total seasonal precipitation, so in these areas, variations of wet-day frequency and wet-day rain rate must be important. Correlations are small between the wet-day frequency and the wet-day rate, and the former is better correlated than the latter with the seasonal rain rate. Summer rainfall in central to southern Mexico exhibits moderate negative correlations with the leading pattern of sea surface temperature (SST) anomalies in the equatorial Pacific, which projects strongly onto El Niño. The influence of equatorial SSTs on southern Mexico rainfall seems to operate mainly through variability of the wet-day frequency, rather than through variations of the wet-day rain rate.

scholarly journals Midlatitude atmospheric circulation responses under 1.5 °C and 2.0 °C warming and implications for regional impacts

2017 ◽  
Author(s):  
Camille Li ◽  
Clio Michel ◽  
Lise Seland Graff ◽  
Ingo Bethke ◽  
Giuseppe Zappa ◽  
...  
Keyword(s):  
Climate Change ◽  
Atmospheric Circulation ◽  
North Atlantic ◽  
North American ◽  
Storm Track ◽  
Internal Variability ◽  
The North ◽  
Regional Impacts ◽  
The North Atlantic ◽  
The Mediterranean

Abstract. This study investigates the global response of the midlatitude atmospheric circulation to 1.5 °C and 2.0 °C of warming using the HAPPI Half a degree Additional warming, Projections, Prognosis and Impacts ensemble, with a focus on the winter season. Characterizing and understanding this response is critical for accurately assessing the near-term regional impacts of climate change and the benefits of limiting warming to the 1.5 °C above pre-industrial levels, as advocated by the Paris Agreement of the United Nations Framework Convention on Climate Change (UNFCCC). The HAPPI experimental design allows an assessment of uncertainty in the circulation response due to model dependence and internal variability. Internal variability is found to dominate the multi-model mean response of the jet streams, storm tracks and stationary waves across most of the midlatitudes; larger signals in these features are mostly consistent with those seen in more strongly forced warming scenarios. Signals that emerge in the 1.5 °C experiment are a weakening of storm activity over North America, an inland shift of the North American stationary ridge, an equatorward shift of the North Pacific jet exit, and an equatorward intensification of the South Pacific jet. Signals that emerge under an additional 0.5 °C of warming include a poleward shift of the North Atlantic jet exit, an eastward extension of the North Atlantic storm track, and an intensification on the flanks of the Southern Hemisphere storm track. Case studies explore the implications of these circulation responses for precipitation impacts in the Mediterranean, western Europe and the North American west coast, paying particular attention to possible outcomes at the tails of the response distributions. For example, the projected weakening of the Mediterranean storm track emerges in the 2.0 °C world, though the ensemble spread still allows for both wetting and drying responses.

scholarly journals Robust detection of forced warming in the presence of potentially large climate variability

2021 ◽  
Author(s):  
Sebastian Sippel ◽  
Nicolai Meinshausen ◽  
Eniko Székely ◽  
Erich Fischer ◽  
Angeline G. Pendergrass ◽  
...  
Keyword(s):  
Climate Change ◽  
Climate Variability ◽  
Climate Models ◽  
Climate Model ◽  
Decadal Variability ◽  
Internal Variability ◽  
Warming Trend ◽  
Robust Detection ◽  
Internal Climate Variability ◽  
Detection And Attribution

<p>Warming of the climate system is unequivocal and substantially exceeds unforced internal climate variability. Detection and attribution (D&A) employs spatio-temporal fingerprints of the externally forced climate response to assess the magnitude of a climate signal, such as the multi-decadal global temperature trend, while internal variability is often estimated from unforced (“control”) segments of climate model simulations (e.g. Santer et al. 2019). Estimates of the exact magnitude of decadal-scale internal variability, however, remain uncertain and are limited by relatively short observed records, their entanglement with the forced response, and considerable spread of simulated variability across climate models. Hence, a limitation of D&A is that robustness and confidence levels depend on the ability of climate models to correctly simulate internal variability (Bindoff et al., 2013).</p><p>For example, the large spread in simulated internal variability across climate models implies that the observed 40-year global mean temperature trend of about 0.76°C (1980-2019) would exceed the standard deviation of internally generated variability of a set of `low variability' models by far (> 5σ), corresponding to vanishingly small probabilities if taken at face value. But the observed trend would exceed the standard deviation of a few `high-variability' climate models `only' by a factor of about two, thus unlikely to be internally generated but not practically impossible given unavoidable climate system and observational uncertainties. This illustrates the key role of model uncertainty in the simulation of internal variability for D&A confidence estimates.</p><p>Here we use a novel statistical learning method to extract a fingerprint of climate change that is robust towards model differences and internal variability, even of large amplitude. We demonstrate that externally forced warming is distinct from internal variability and detectable with high confidence on any state-of-the-art climate model, even those that simulate the largest magnitude of unforced multi-decadal variability. Based on the median of all models, it is extremely likely that more than 85% of the observed warming trend over the last 40 years is externally driven. Detection remains robust even if their main modes of decadal variability would be scaled by a factor of two. It is extremely likely that at least 55% of the observed warming trend over the last 40 years cannot be explained by internal variability irrespective of which climate model’s natural variability estimates are used.</p><p>Our analysis helps to address this limitation in attributing warming to external forcing and provides a novel perspective for quantifying the magnitude of forced climate change even under uncertain but potentially large multi-decadal internal climate variability. This opens new opportunities to make D&A fingerprints robust in the presence of poorly quantified yet important features inextricably linked to model structural uncertainty, and the methodology may contribute to more robust detection and attribution of climate change to its various drivers.</p><p> </p><p>Bindoff, N.L., et al., 2013. Detection and attribution of climate change: from global to regional. IPCC AR5, WG1, Chapter 10.</p><p>Santer, B.D., et al., 2019. Celebrating the anniversary of three key events in climate change science. <em>Nat Clim Change</em> <strong>9</strong>(3), pp. 180-182.</p>

Simulating present and future climates of southern Africa using general circulation models

1997 ◽  
Vol 21 (1) ◽  
pp. 51-78 ◽  
Author(s):  
A.M. Joubert ◽  
B.C. Hewitson
Keyword(s):  
Climate Change ◽  
Southern Africa ◽  
General Circulation ◽  
Regional Climate ◽  
Daily Rainfall ◽  
Regional Climate Change ◽  
Summer Rainfall ◽  
General Circulation Models ◽  
Empirical Downscaling ◽  
Projected Changes

The current state of regional climate and climate change modelling using GCMs is reviewed for southern Africa, and several approaches to regional climate change prediction which have been applied to southern Africa are assessed. Confidence in projected regional changes is based on the ability of a range of models to simulate present regional climate, and is greatest where intermodel consensus in terms of the nature of projected changes is highest. Both equil ibrium and transient climate change projections for southern Africa are considered. Warming projected over southern Africa is within the range of globally averaged estimates. Uncertainties associated with the parameterization of convection ensure that projected changes in rainfall at GCM grid scales remain unreliable. However, empirical downscaling approaches produce rainfall changes consistent with synoptic-scale circulation. Both downscaling and grid-scale approaches indicate a 10-15% decrease in summer rainfall over the central interior which may have important implications for surface hydrology. Climate change may be manifested as a change in variability, and not in mean climate. Over southern Africa, increases in the variability and intensity of daily rainfall events are indicated.

Variability of Tropical Cyclone Track Density in the North Atlantic: Observations and High-Resolution Simulations

2014 ◽  
Vol 27 (13) ◽  
pp. 4797-4814 ◽  
Author(s):  
Wei Mei ◽  
Shang-Ping Xie ◽  
Ming Zhao
Keyword(s):  
High Resolution ◽  
Tropical Cyclone ◽  
Time Scales ◽  
North Atlantic ◽  
Decadal Variability ◽  
Internal Variability ◽  
Track Density ◽  
The North ◽  
The North Atlantic ◽  
The U.S

Interannual–decadal variability of tropical cyclone (TC) track density over the North Atlantic (NA) between 1979 and 2008 is studied using observations and simulations with a 25-km-resolution version of the High Resolution Atmospheric Model (HiRAM) forced by observed sea surface temperatures (SSTs). The variability on decadal and interannual time scales is examined separately. On both time scales, a basinwide mode dominates, with the time series being related to variations in seasonal TC counts. On decadal time scales, this mode relates to SST contrasts between the tropical NA and the tropical northeast Pacific as well as the tropical South Atlantic, whereas on interannual time scales it is controlled by SSTs over the central–eastern equatorial Pacific and those over the tropical NA. The temporal evolution of the spatial distribution of track density is further investigated by normalizing the track density with seasonal TC counts. On decadal time scales, two modes emerge: one is an oscillation between track density over the U.S. East Coast and midlatitude ocean and that over the Gulf of Mexico and the Caribbean Sea and the other oscillates between low and middle latitudes. They might be driven by the preceding winter North Atlantic Oscillation and concurrent Atlantic meridional mode, respectively. On interannual time scales, two similar modes are present in observations but are not well separated in HiRAM simulations. Finally, the internal variability and predictability of TC track density are explored and discussed using HiRAM ensemble simulations. The results suggest that basinwide total TC counts/days are much more predictable than local TC occurrence, posing a serious challenge to the prediction and projection of regional TC threats, especially the U.S. landfall hurricanes.

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