Aim The summits of mountain ranges at mid‐latitude in the Northern Hemisphere share many ecological properties with the Arctic, including comparable climates and similar flora. We hypothesize that the orogeny during the Oligocene‐Miocene combined with global cooling led to the origin and early diversification of cold‐adapted plant lineages in these regions. Before the establishment of the Arctic cryosphere, adaptation and speciation in high elevation areas of these mountain ranges may have led to higher species richness compared to the Arctic. Subsequent colonization from mid‐latitude mountain ranges to the Arctic may explain similar but poorer flora. Location Arctic‐Alpine regions of the Northern Hemisphere. Methods We mapped the cold climate in the Northern Hemisphere for most of the Cenozoic (60 Ma until present) based on paleoclimate proxies coupled with paleoelevations. We generated species distribution maps from occurrences and regional atlases for 5,464 plant species from 756 genera occupying cold climates. We fitted a generalized linear model to evaluate the association between cold‐adapted plant species richness and environmental, as well as geographic variables. Finally, we performed a meta‐analysis of studies which inferred and dated the ancestral geographic origin of cold‐adapted lineages using phylogenies. Results We found that the subalpine‐alpine areas of the mid‐latitude mountain ranges comprise higher cold‐adapted plant species richness than the Palearctic and Nearctic polar regions. The topo‐climatic reconstructions indicate that the cold climatic niche appeared in mid‐latitude mountain ranges (42–38 Ma), specifically in the Himalayan region, and only later in the Arctic (22–18 Ma). The meta‐analysis of the dating of the origin of cold‐adapted lineages indicates that most clades originated in central Asia between 39–7 Ma. Main conclusions Our results support the hypothesis that the orogeny and progressive cooling in the Oligocene‐Miocene generated cold climates in mid‐latitude mountain ranges before the appearance of cold climates in most of the Arctic. Early cold mountainous regions likely allowed for the evolution and diversification of cold‐adapted plant lineages followed by the subsequent colonization of the Arctic. Our results follow Humboldt's vision of integrating biological and geological context in order to better understand the processes underlying the origin of arctic‐alpine plant assemblages.

<p>Human societies rely on the existence of functioning global ecosystems, which are threatened by a combination of gradual changes and extreme events. Among the latter, natural hazards such as wildfires or floods can play a *functional* role for ecosystems, with plant and animal species requiring regular disturbance in their life-cycle in order to thrive, but beyond a threshold, the extreme events might cause ecosystem degradation.</p> <p>Here we map and project the risk of tropical cyclones on coastal ecosystems worldwide, using the probabilistic risk model CLIMADA to describe the vulnerability of global terrestrial ecosystems to tropical cyclones. First, a baseline for the current climate conditions is used to determine whether ecosystems are resilient, dependent, or vulnerable to tropical cyclones. We show that most ecosystems in the tropics are at least resilient to lower-intensity storms, but only a few ecosystems are not vulnerable to high-intensity storms. Second, the changes in tropical cyclone frequency under the high-emission scenario RCP8.5 in 2050 are used to determine which ecosystems are at risk. We show that while the global increase in the frequency of strong storms is the most threatening effect, several ecosystems with a dependency relationship are also at risk of locally decreasing frequency of low to middle-intensity storms.</p> <p>Our study paves the way for a better understanding of the functional and vital relationship between extreme weather events and ecosystems at a global scale, and how regime shifts under climate change might threaten them. This can prove useful to improve ecosystem management and design appropriate nature-based protection measures in a rapidly changing climate.  </p>

<p>Ultimately, human societies rely on the existence of functioning global ecosystems. Thus, avoiding the collapse of global ecosystems should be among the highest priorities of climate mitigation and adaptation efforts. However, "protecting" ecosystems is a challenge much more complex than avoiding adverse effects on human infrastructures, societies, economies or lives. For instance, natural hazards such as wildfires or floods can play a *functional* role for ecosystems, with species requiring those events in their life-cycle. Therefore simply trying to avoid the at-first-sight devastating effects of natural hazards on ecosystems can be counter-productive, and even be damaging.  </p><p>Here we present a statistical study made with the open-source, probabilistic risk model CLIMADA [1] about the frequency and magnitude distribution of several natural hazards affecting global terrestrial ecosystems. The hazard modelling is based on historical data augmented with probabilistic methods, and thus can be interpreted as providing a snap-shot of "current conditions". This can then be used as a baseline to be contrasted with future projections of climate change and socio-economic development. Further, this baseline can inform studies on the functional and vital relationship between natural hazards and ecosystems, which are necessary to design appropriate protection measures.</p><p>CLIMADA: https://github.com/CLIMADA-project/climada_python </p><p>[1] Aznar-Siguan, G. et al., GEOSCI MODEL DEV. 12, 7 (2019) 3085–97</p>