气候变化科学方面的几个最新认知

IPCC第六次评估报告(AR6)第一工作组报告主要从以下几个方面的进展提升了我们对气候系统变化、气候变化原因以及预估未来气候系统变化等方面的认知,对过去气候变化及其与人类活动的关系有了更加清晰、可靠的认识。综合多重证据评估指出,全球气候正经历着前所未有的变化;包括极端事件在内的归因进展已把人类活动对气候系统影响的认识从大气圈扩展到水圈、冰冻圈和生物圈,进一步强化了人类活动影响全球和区域气候的认识;有关区域气候变化信息的内容更加丰富,与各行业和敏感地区的气候变化影响联系更加紧密,使这些信息能更好地为气候变化风险评估和气候变化区域适应提供支持;气候模式和约束预估方法的发展以及对气候敏感度认识的深化,减少了未来不同排放情景下全球地表温度(Global Surface Temperature,GST)、海平面上升和海洋热含量的变化预估的不确定性。这份最新报告对我国提升气候变化研究水平和防灾减灾应对能力具有十分重要的指导意义。

对基于土地应对气候变化的新认知

2019年8月7日IPCC《气候变化与土地特别报告》决策者摘要获得通过,报告涉及对基于土地应对气候变化不同措施的评估,取得一些新的认知,包括定量评估基于土地的40种综合措施对提高气候变化减缓和适应能力、防治荒漠化和土地退化、增强粮食安全、保护生物多样性和水资源及促进可持续发展的效益,提出在防治荒漠化和土地退化及保障粮食安全过程中提高气候变化适应和减缓能力的措施,评估了实施不同措施的风险、限制、障碍和保障政策等。在措施的分类、气候变化适应的主体对象,以及风险和政策分析等方面还存在一些不足。评估报告结论将对我国建立基于土地的应对气候变化的对策,促进把应对气候变化与防治荒漠化和土地退化、保护生态环境与增强粮食安全工作结合,制定相关政策等方面都具有重要的启示意义。

Changes in persistent and non-persistent extreme precipitation in Chinafrom 1961 to 2016

In this study, based on daily gage precipitation data of 2480 stations from 1961 to 2016, the summer （JuneeAugust） extreme precipitationevent was defined using the 95th percentile, and the changes in persistent （last for at least 2 d） and non-persistent （1 d） extreme precipitation inChina were analyzed. The results indicate that under global warming, the contribution of extreme precipitation to total summer precipitationincreased in most areas of China, but it decreased in the central part of Inner Mongolia and the Sichuan Basin. In North and Southwest China,both persistent and non-persistent extreme precipitation decreased; the decreasing trend of persistent extreme precipitation was more prominent;thus, extreme precipitation event occurred more as non-persistent event. Meanwhile, in the Yangtze River Basin and South China, both types ofextreme precipitation increased particularly the persistent extreme precipitation; persistent extreme precipitation occurred more compared withnon-persistent events.

Changes in classified precipitation in the urban, suburban, and mountain areas of Beijing

In this paper, based on hourly precipitation observations in 1977e2013 in the Beijing area, China, hourly precipitation in summer (June?August) is classified into three categories: light (below the 50th percentile values), moderate (the 50th to 95th percentile values), and heavy (above the 95th percentile values). Results reveal that both light and moderate precipitation decreased significantly during the research period and thereby caused the decrease in summer totals. By contrast, pronounced trends failed to be detected in the heavy category. Since 2004, the contribution of heavy rainfall to the summer total precipitation in the urban area increased as compared to the suburban area, which is opposite to light rainfall. There are obvious differences in the diurnal variations of classified precipitation. Light precipitation shows a double peak structure in the early morning and at night, while moderate and heavy rainfall show a single peak at night. Light precipitation at the early morning peak time decreased significantly in the whole Beijing area. Compared with the suburban area, light precipitation in the urban area occurred less frequently whereas heavy precipitation occurred more frequently at evening peak time after 2004. The asymmetry of the rainfall is obvious, especially, for heavy precipitation. The asymmetry of heavy precipitation events in the urban area exhibits a significant increasing trend.

New perspectives on ‘warming-wetting’ trend in Xinjiang, China

Recently,a hot topic about warmer and wetter climate change in the arid region of Northwest China,especially in Xinjiang,has attracted much attention by general public and scientific community.This study revisits this topic especially for Xinjiang in the Eurasian continental context from multiple perspectives based on most updated CRU high-resolution grid data and China's homogenized station data in 1961–2019.We conclude that such‘warming-wetting’trend is not a regional phenomenon for Xinjiang but has much larger spatial scale.Regions having experienced both temperature and precipitation increases reflecting‘warming-wetting’trend account for more than half of the Eurasian continent since 1961.Nevertheless,the‘warming-wetting’trend in Xinjiang suggests some unique regional features in response to the global warming.Although drought seems to have relieved to some extent,especially in the mountainous regions in western Xinjiang,the nature of arid and semi-arid climate regime has not changed.Noticeably,the interannual variability of precipitation has enlarged and the increase in extreme precipitation events has a major contribution.These findings suggest that‘warming-wetting’trend in Xinjiang is asymmetric regarding warming and wetting in seasons and intensifying interannual variability and increasing contribution of extreme precipitation to the total.Thus,the current‘warming-wetting’trend in Xinjiang possibly brings us some beneficial impacts for the ecosystem but also increases challenges for water resources utilization and risk management.

Achieving Paris Agreement temperature goals requires carbon neutrality by middle century with far-reaching transitions in the whole society

The concept of carbon neutrality is much emphasized in IPCC Spatial Report on Global Warming of 1.5C in order to achieve the long-termtemperature goals as reflected in Paris Agreement.To keep these goals within reach,peaking the global carbon emissions as soon as possible andachieving carbon neutrality are urgently needed.However,global CO_(2)emissions continued to grow up to a record high of 43.1 Gt CO_(2)during2019,with fossil CO_(2)emissions of 36.5 Gt CO_(2)and land-use change emissions of 6.6 Gt CO_(2).In such case,the global carbon emissions mustdrop 32 Gt CO_(2)(7.6%per year)from 2020 to 2030 for the 1.5C warming limit,which is even larger than the COVID-induced reduction(6.4%)in global CO_(2)emissions during 2020.Recently,China has announced scaling up its national commitments,aiming to peak its CO_(2)emissionsbefore 2030 and achieve carbon neutrality before 2060.Achieving these goals requires rapid and far-reaching transitions in the whole society.Onthe one hand,deeper emissions reduction in all sectors includes decarbonization of energy,electrification,increasing share of renewables,energyefficiency,sustainable land management,decarbonization of transport,reducing food loss and waste,as well as behavior and lifestyles changes.On the other hand,possible actions by removing CO_(2)from the atmosphere involves enlarging land and ocean net carbon sink,CO_(2)removaltechnologies(such as Bioenergy with carbon capture and storage),and CO_(2)capture,utilization and storage technologies,but should be cautionfor their scales and tradeoffs.

Change in drought conditions and its impacts on vegetation growth over the Tibetan Plateau

Understanding climate change as well as its impacts on vegetation growth over the Tibetan Plateau has important implication for ecosystems.This study investigated changes in drought conditions and their impacts on vegetation growth over the Tibetan Plateau.The results reveal that the precipitation in growing season(May-September)shows a significant increase over most parts of the central and eastern Tibetan Plateau during 1961—2019.Consequently,drought conditions have generally relieved except in the south and northeast where precipitation has decreased.Combining analyses of gridded-dataset-derived drought indices with vegetation indices during 1982—2015,vegetation improvement in most regions of the Plateau is mainly due to lessened drought conditions.Noticeably,vegetation degradation is also found in part of southern Tibetan Plateau mainly resulting from drought enhancement.This study is expected to provide scientific basis for understanding of change in drought condition and its impacts on vegetation over different regions of TP under global warming background.