Recent wildfire outbreaks around the world have prompted concern that climate change is increasing fire incidence, threatening human livelihood and biodiversity, and perpetuating climate change. Here, we review current understanding of the impacts of climate change on fire weather (weather conditions conducive to the ignition and spread of wildfires) and the consequences for regional fire activity as mediated by a range of other bioclimatic factors (including vegetation biogeography, productivity and lightning) and human factors (including ignition, suppression, and land use). Through supplemental analyses, we present a stocktake of regional trends in fire weather and burned area (BA) during recent decades, and we examine how fire activity relates to its bioclimatic and human drivers. Fire weather controls the annual timing of fires in most world regions and also drives inter-annual variability in BA in the Mediterranean, the Pacific US and high latitude forests. Increases in the frequency and extremity of fire weather have been globally pervasive due to climate change during 1979–2019, meaning that landscapes are primed to burn more frequently. Correspondingly, increases in BA of ∼50% or higher have been seen in some extratropical forest ecoregions including in the Pacific US and high-latitude forests during 2001–2019, though interannual variability remains large in these regions. Nonetheless, other bioclimatic and human factors can override the relationship between BA and fire weather. For example, BA in savannahs relates more strongly to patterns of fuel production or to the fragmentation of naturally fire-prone landscapes by agriculture. Similarly, BA trends in tropical forests relate more strongly to deforestation rates and forest degradation than to changing fire weather. Overall, BA has reduced by 27% globally in the past two decades, due in large part to a decline in BA in African savannahs. According to climate models, the prevalence and extremity of fire weather has already emerged beyond its pre-industrial variability in the Mediterranean due to climate change, and emergence will become increasingly widespread at additional levels of warming. Moreover, several of the major wildfires experienced in recent years, including the Australian bushfires of 2019/2020, have occurred amidst fire weather conditions that were considerably more likely due to climate change. Current fire models incompletely reproduce the observed spatial patterns of BA based on their existing representations of the relationships between fire and its bioclimatic and human controls, and historical trends in BA also vary considerably across models. Advances in the observation of fire and understanding of its controlling factors are supporting the addition or optimization of a range of processes in models. Overall, climate change is exerting a pervasive upwards pressure on fire globally by increasing the frequency and intensity of fire weather, and this upwards pressure will escalate with each increment of global warming. Improvements to fire models and a better understanding of the interactions between climate, climate extremes, humans and fire are required to predict future fire activity and to mitigate against its consequences.

中文翻译：

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气候变化下的全球和区域趋势及火灾驱动因素

最近在世界各地爆发的野火引发了人们的担忧，即气候变化正在增加火灾发生率，威胁人类生计和生物多样性，并使气候变化长期存在。在这里，我们回顾了目前对气候变化对火灾天气（有利于野火点燃和蔓延的天气条件）的影响以及由一系列其他生物气候因素（包括植被生物地理、生产力和闪电）和人为因素（包括点火、抑制和土地利用）。通过补充分析，我们对近几十年来火灾天气和烧毁面积 (BA) 的区域趋势进行了盘点，并研究了火灾活动与其生物气候和人类驱动因素之间的关系。火灾天气控制着世界上大多数地区的年度火灾发生时间，也推动了地中海、美国太平洋和高纬度森林中 BA 的年际变化。由于 1979 年至 2019 年期间的气候变化，火灾天气的频率和极端程度的增加在全球普遍存在，这意味着景观已经准备好更频繁地燃烧。相应地，在 2001-2019 年期间，包括美国太平洋和高纬度森林在内的一些温带森林生态区的 BA 增加了约 50% 或更高，尽管这些地区的年际变化仍然很大。尽管如此，其他生物气候和人为因素可以超越 BA 与火灾天气之间的关系。例如，稀树草原的 BA 与燃料生产模式或农业对自然易着火景观的分割更密切相关。同样，热带森林的 BA 趋势与森林砍伐率和森林退化有关，而不是与火灾天气的变化有关。总体而言，过去 20 年全球 BA 减少了 27%，这在很大程度上是由于非洲大草原的 BA 下降。根据气候模型，由于气候变化，火灾天气的普遍性和极端性已经超出了其在地中海的工业化前可变性，并且在进一步变暖的情况下，火灾天气的出现将变得越来越普遍。此外，近年来发生的几场主要野火，包括 2019/2020 年的澳大利亚丛林大火，发生在火灾天气条件下，这更有可能是由于气候变化造成的。当前的火灾模型基于现有的火灾与其生物气候和人类控制之间关系的表示，无法完全再现观察到的 BA 空间模式，并且 BA 的历史趋势在不同模型之间也存在很大差异。对火灾的观察和对其控制因素的理解的进步正在支持在模型中添加或优化一系列过程。总体而言，气候变化通过增加火灾天气的频率和强度，对全球火灾产生普遍的上行压力，而这种上行压力将随着全球变暖的每一次增加而升级。改进火灾模型，更好地理解气候、极端气候、