Role Of Anthropogenic Forcing Research Articles

The 2022 Record-Breaking Heat Event over the Middle and Lower Reaches of the Yangtze River: The Role of Anthropogenic Forcing and Atmospheric Circulation

Abstract The anthropogenic forcing and anomalous atmospheric circulation have increased the occurrence probability of 2022-like extreme heat by approximately 62.0 and 2.6 times, respectively.

Role of anthropogenic forcing and atmospheric circulation in a low-temperature event in February 2022 in eastern China

In February 2022, eastern China experienced prolonged low temperatures, with significant impacts on agriculture, transportation, and power supply. The regional average temperature anomaly for February 2022 was −0.65 °C, making it the third coldest February from 2000 to 2022. Understanding the influence of anthropogenic forcing and atmospheric circulation on low-temperature events is important for climate change adaptation and mitigation in the region. This study used observational and model data from the Coupled Model Intercomparison Project Phase 6 to conduct an extreme event attribution study. The results showed that anthropogenic forcing led to a 1.5-fold decrease in the probability of 2022-like events, with anthropogenic greenhouse gases being the primary contributors to this reduction. Conversely, aerosols slightly increased the likelihood of such events. To evaluate the role of atmospheric circulation in this event, we chose Siberian High as the key circulation system and employed circulation similarity, intensity classification, and regression methods to estimate the impacts of circulation patterns, circulation intensity, and human-induced circulation change. The results demonstrated that under the influence of the same anthropogenic forcing, the presence of an anomalous Siberian High and anomalously enhanced intensity of the Siberian High both increased the likelihood of such a cold event occurrence. However, anthropogenic forcing exerts a negligible effect on such cold events via anomalous circulation.

The Role of Anthropogenic Forcings on the Regional Climate of Summertime Diurnal Variations over North China

Abstract Anthropogenic greenhouse gases (GHG) and anthropogenic aerosols (AA) have changed radiation balance and regulated the regional climate at seasonal or longer time scales. Based on station observations, reanalyses, and satellite observations, this study examines how anthropogenic forcings affect surface temperature and strongly regulate the regional climate at a diurnal time scale over the North China plains (NCP) in July and August. As AA cooling is dominant in the daytime over low-lying plains, it leads to a cooler day–warmer night temperature trend that decreases the diurnal temperature range over NCP but increases the thermal contrast between NCP and its west highlands. In response to the daytime cooling, the weakened vertical thermal contrast decreases the boundary layer turbulent mixing in the daytime and reduces friction to low-level winds, which leads to anomalous southerlies at 2000 LST over NCP. In contrast, nighttime warming results in anomalous northerlies at 0200 LST. On the other hand, in response to the enlarged horizontal thermal contrast, the stronger mountain–plain circulation helps to intensify low-level ascent over the plains at 0200 LST. These human-induced changes in the diurnal variation of regional circulations are conducive to the increased moisture convergence at 2000 and 0200 LST over NCP. The nighttime proportion of precipitation accordingly exhibits an increasing trend over NCP, though the seasonal precipitation decreases because of the weakened monsoon background. These findings highlight that the diurnal cycle of regional circulations can express a strong dynamic response to the radiation effect of anthropogenic forcings and thus affect the long-term change in regional climate.

The Role of Anthropogenic Forcing in Western United States Hydroclimate Extremes

AbstractDespite lower‐than‐average total precipitation in the western states of the U.S., the 2021 “precipitation roller coaster” defined as large precipitation swings has pointed to a strong hydroclimatic intensity (HYINT). Here we examine the 2021 HYINT using an index—a product of the average precipitation intensity (INT) and dry spell length (DSL). HYINT exhibited an extremely high value in the western U.S. in 2021. INT and DSL contribute differently to the 2021 HYINT, with large spatial variability. Overall, the 2021 extreme HYINT in central California and Utah is tied more to large INT, than to DSL. Meanwhile, the historical trends in INT and DSL may have contributed to the extreme 2021 HYINT event. The fraction of attributable risk framework reveals that the 2021 extreme HYINT is more likely to occur with anthropogenic forcing (e.g., 7.3 times more likely for HYINT exceeding 1.3) than natural forcing alone.

The 2020 Record-Breaking Mei-yu in the Yangtze River Valley of China: The Role of Anthropogenic Forcing and Atmospheric Circulation

© 2022 American Meteorological Society. For information regarding reuse of this content and general copyright information, consult the AMS Copyright Policy (www.ametsoc.org/PUBSReuseLicenses).CORRESPONDING AUTHOR: Ying Sun, sunying@cma.gov.cnA supplement to this article is available online (10.1175/BAMS-D-21-0161.2)

The Alaskan Summer 2019 Extreme Heat Event: The Role of Anthropogenic Forcing, and Projections of the Increasing Risk of Occurrence

AbstractExtreme heat occurred over Alaska in June–July 2019, posing risks to infrastructure, ecosystem, and human health. It is vital to improve our understanding of the causes of such events and the extent to which anthropogenic forcing may alter their likelihood and magnitude. Here, we use multiple large ensembles of climate models, comprising thousands of simulated years, to investigate these issues. Our results suggest that the presence of anthropogenic radiative forcing increased the likelihood of the 2019 extreme heat event by as much as 6%. Further we show the rate of occurrence of such an extreme heat event is likely to substantially increase in the future with increasing levels of atmospheric greenhouse gases. While uncertainty in projected climate risk from model choice leads to a broad range of future extreme heat event probabilities, some models project that with rapidly increasing levels of greenhouse gases the likelihood of such events would exceed 75% by 2090.

Record‐breaking daily rainfall in the United Kingdom and the role of anthropogenic forcings

AbstractThe breaking of the United Kingdom's daily rainfall record in October 2020 made a striking addition to the list of recent heavy precipitation events in the country. Mounting evidence from attribution research suggests that such extremes become more frequent and intense in a warming climate. Although most studies consider extreme events in specific months or seasons, here we investigate for the first time how extremes of the wettest day of the year may be influenced by anthropogenic forcings. Data from large multimodel ensembles indicate that the moderate historical trend towards wetter conditions will emerge more strongly in coming decades, while a notable anthropogenic influence on the variability of the wettest day may be identified as early as the 1900s. Experiments with different forcings are employed to estimate the changing probability of extremes due to anthropogenic climate change in a risk‐based attribution framework. We introduce a new methodology of estimating probabilities of extremes in the present and future that calibrates data from long simulations of the preindustrial climate to the mean state and variability of the reference climatic period. The new approach utilises larger samples of rainfall data than alternative methods, which is a major advantage when analysing extremely rare events. The record rainfall of the wettest day in year 2020 is estimated to have become about 2.5 times more likely because of human influence, while its return time, currently about 100 years, will decrease to only about 30 years by 2100. Compared to a hypothetical natural climate, we estimate a 10‐fold increase in the chances of such extreme rainfall events in the United Kingdom by the end of this century, which underlines the need for effective adaptation planning.

Indian summer monsoon: Extreme events, historical changes, and role of anthropogenic forcings

The South Asian summer monsoon is a complex coupled human‐natural system that poses unique challenges for understanding its evolution alongside increasing anthropogenic activities. Rapid and substantial changes in land‐use, land‐management and industrial activities over the subcontinent, and warming in the Indian Ocean, have influenced the South Asian summer monsoon. These might continue to be significant drivers in the near‐term along with rising global greenhouse gas emissions. Deciphering the region's vulnerability to climate change requires an understanding of how these anthropogenic activities, acting on a range of spatial scales, have shaped the monsoon spatially and temporally. This review summarizes historical changes in monsoon rainfall characteristics, associated mechanisms, and the role of anthropogenic forcings, focusing on subseasonal variability and extreme events. Several studies have found intensified subseasonal extremes across parts of India and an increase in spatial variability of rainfall despite an overall weakening of seasonal rainfall in the monsoon core. However, understanding these changes remains challenging because of uncertainties in observations and climate models. The mechanisms and relative influences of various anthropogenic activities, particularly on subseasonal extremes, remain relatively underexplored. Large biases in the representation of relevant processes in global climate models limit the ability to attribute historical changes and make reliable projections. Nevertheless, recent advances in modeling these processes using higher‐resolution modeling frameworks provide new tools to investigate the Indian summer monsoon's response to various anthropogenic forcings. There is an urgent need to understand how these forcings interact to shape climate variability and change in this vulnerable region.This article is categorized under: Paleoclimates and Current Trends > Earth System Behavior

Anthropogenic influence on global warming for effective cost-benefit analysis: a machine learning perspective

In the climate domain, attribution is the process of determining the external forcings which are more likely to be responsible of the climate change which, in turn, affects global economic growth. These factors influence the climatic system by altering its properties including, for instance, the radiative balance. In this context, investigating the role of anthropogenic forcings toward natural factors in the global warming of the last decades is of paramount importance. Global climate models (GCMs) applied to attribution studies showed that the temperature increase in the second half of the twentieth century can be mainly imputable to the emissions of anthropogenic greenhouse gases. In this study we resort to a data-driven approach based on machine learning with the aim of analyzing the relationship between global temperature anomalies and natural and anthropogenic forcings. Our empirical findings fully agree with the results of GCMs attribution studies, and further shed light on the natural and anthropogenic drivers that, on a multivariate basis, exert the major influence on the global temperature.

Role of Anthropogenic Forcing in 2014 Hot Spring in Northern China

Role of Anthropogenic Forcing in 2014 Hot Spring in Northern China

Role of Anthropogenic Forcing in 2014 Hot Spring in Northern China

Role of Anthropogenic Forcing in 2014 Hot Spring in Northern China

Sea levels changing in response to natural variations

Scientists have widely accepted that sea levels have been rising since the end of the 19th century due to human activities that warm the planet and melt land‐locked ice. Models of future sea level rise suggest that sea levels will continue to increase at an accelerating rate if emissions of greenhouse gases continue at the current rate. This has motivated a number of scientists to search for already existing accelerations in global and regional sea level during the past 2 decades. However, Dangendorf et al. note that current attempts to detect a significant acceleration in sea level rise might have overestimated the role of anthropogenic forcing.

Probabilistic estimates of recent changes in temperature: a multi-scale attribution analysis

The role of anthropogenic forcings in temperature changes during recent decades is investigated over a range of spatial scales. Changes in the annual mean surface temperature and also in the warmest night of the year, which has implications for human health, are considered. Distributions of regional trends with and without the effect of human activity are produced, using constraints from a global optimal detection analysis. Anthropogenic forcings are estimated to have more than doubled the likelihood of mean warming in all regions considered except central North America, where results are more model dependent. The likelihood of warming of the warmest night has also increased, but the estimated change is more uncertain. Inferences on sub-continental scales are indicative rather than definitive because of the absence of locally important forcings and processes in model simulations, as well as model biases. As model inconsistencies may impact regional analyses, a multi-model approach is essential.

Highly variable Northern Hemisphere temperatures reconstructed from low- and high-resolution proxy data

A number of reconstructions of millennial-scale climate variability have been carried out in order to understand patterns of natural climate variability, on decade to century timescales, and the role of anthropogenic forcing. These reconstructions have mainly used tree-ring data and other data sets of annual to decadal resolution. Lake and ocean sediments have a lower time resolution, but provide climate information at multicentennial timescales that may not be captured by tree-ring data. Here we reconstruct Northern Hemisphere temperatures for the past 2,000 years by combining low-resolution proxies with tree-ring data, using a wavelet transform technique to achieve timescale-dependent processing of the data. Our reconstruction shows larger multicentennial variability than most previous multi-proxy reconstructions, but agrees well with temperatures reconstructed from borehole measurements and with temperatures obtained with a general circulation model. According to our reconstruction, high temperatures--similar to those observed in the twentieth century before 1990--occurred around ad 1000 to 1100, and minimum temperatures that are about 0.7 K below the average of 1961-90 occurred around ad 1600. This large natural variability in the past suggests an important role of natural multicentennial variability that is likely to continue.