North American birds require mitigation and adaptation to reduce vulnerability to climate change

In an emerging climate crisis, effective conservation requires both adaptation and mitigation to improve the resilience of species. The currently pledged emissions reductions outlined in the Paris Agreement framework would still lead to a +3.2°C increase in global mean temperature by the end of this century. In this context, we assess the vulnerability of 604 North American bird species and identify the species and locations most at risk under climate change. We do this based on species distribution models for both the breeding and nonbreeding seasons, projected under two global warming scenarios (an optimistic mitigation scenario 1.5°C and an unmitigated 3.0°C scenario). We evaluate vulnerability under each season and scenario by assessing sensitivity and adaptive capacity based on modeled range loss and range gain, respectively, and based on species specific dispersal abilities. Our study, the first of its magnitude, finds that over two-thirds of North American birds are moderately or highly vulnerable to climate change under a 3.0°C scenario. Of these climate-vulnerable species, 76% would have reduced vulnerability and 38% of those would be considered nonvulnerable if warming were stabilized at 1.5°C. Thus, the current pledge in greenhouse gas reductions set by the Paris Agreement is inadequate to reduce vulnerability to North American birds. Additionally, if climate change proceeds on its current trajectory, arctic birds, waterbirds, and boreal and western forest birds will be highly vulnerable to climate change, groups that are currently not considered of high conservation concern. There is an urgent need for both (a) policies to mitigate emissions and (b) prioritization to identify where to focus adaptation actions to protect birds in a changing climate.