A long-term assessment of the sensitivity of hundreds of tropical forest plots to increasing temperatures brings encouraging news: in the long run, Earth's tropical forests may be more resilient to a moderately warming world than short-term predictions have suggested. According to the new biome-wide study, tropical forests worldwide and their carbon storage capacities are likely to remain intact in moderate climate warming scenarios - so long as they're not further impacted by other human disturbances such as clearance, logging or fires. As plants and trees grow, they convert inorganic carbon into biomass, effectively storing vast amounts of atmospheric carbon dioxide into terrestrial flora. Understanding the land-atmosphere carbon flux of tropical forests - where nearly 40% of the world's carbon-hoarding vegetation resides - is particularly important to understanding potential climate change scenarios. However, the long-term sensitivity of tropical forests to climate warming, as well as how increased temperatures might affect carbon fluxes, are poorly constrained, representing some of the greatest sources of uncertainty in global climate change predictions. Long-term thermal sensitivity of tropical forests is often derived through short-term and inter-annual observations. However, the sensitivity of these scales may lead to overestimations in longer-term responses to climate change. To assess long-term climate controls on tropical forests directly, Martin Sullivan and colleagues measured biomass carbon and carbon flux in 590 globally distributed, permanent tropical forest plots. The results identify maximum temperature as the most important predictor of overall biomass; it depresses growth rates and reduces carbon storage by killing trees under hot, dry conditions. These adverse effects were most prominent when daytime high temperatures exceeded 32.2 °Celsius (C). Stabilizing global temperatures at 2 °C would push 71% of tropical forests beyond this threshold. Nevertheless, Sullivan et al. reveal greater long-term thermal resilience during moderate warming conditions than previous studies have implied, though, they say, this thermal adaptation potential may not be fully realized in all forests' future responses because of factors including the speed of temperature rises exceeding species' adaptive capabilities. The authors also emphasize that achieving the biome-wide climate resilience potential they document depends on both limiting heating and on large-scale conservation and restoration in forests.
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