Increasing temperatures, and in some areas reduced rainfall, will stress native Pacific Island plants and animals, especially in high-elevation ecosystems with increasing exposure to invasive species, increasing the risk of extinctions.

This finding is from chapter 23 of Climate Change Impacts in the United States: The Third National Climate Assessment.

Process for developing key messages: A central component of the assessment process was convening three focus area workshops as part of the Pacific Islands Regional Climate Assessment (PIRCA). The PIRCA is a collaborative effort aimed at assessing the state of climate knowledge, impacts, and adaptive capacity in Hawai‘i and the U.S. Affiliated Pacific Islands. These workshops included representatives from the U.S. federal agencies, universities, as well as international participants from other national agencies and regional organizations. The workshops led to the formulation of a foundational Technical Input Report (TIR).7350d7b3-6e95-4375-ba23-26756b441fc2 The report consists of nearly 140 pages, with almost 300 references, and was organized into 5 chapters by 11 authors. The chapter author team engaged in multiple technical discussions via regular teleconferences that permitted a careful review of the foundational TIR7350d7b3-6e95-4375-ba23-26756b441fc2 and of approximately 23 additional technical inputs provided by the public, as well as the other published literature, and professional judgment. These discussions included a face-to-face meeting held on July 9, 2012. These discussions were supported by targeted consultation among the lead and contributing authors of each message. There were several iterations of review and comment on draft key messages and associated content.

Description of evidence base: In Hawai‘i and the Central North Pacific (CNP), projected annual surface air temperature increases are 1.0°F to 2.5°F by 2035, relative to 1971-2000.634424c9-14a9-4133-9ed6-8948faa0b11e eff5ce0d-c403-455b-9358-98be45351c7b In the Western North Pacific (WNP), the projected increases are 2.0°F to 2.3°F by 2030, 6.1°F to 8.5°F by 2055, and 4.9°F to 9.2°F by 2090.a639a8f6-3355-43d7-ab21-ef29364db75a In the Central South Pacific (CSP), projected annual surface air temperature increases are 1.1°F to 1.3°F by 2030, 1.8°F to 2.5°F by 2055, and 2.5°F to 4.9°F by 2090.a639a8f6-3355-43d7-ab21-ef29364db75a In Hawai‘i the rate of increase has been greater at high elevations.c70e33c2-49f5-499b-ac5a-a63cbf83b698 (Please note that the islands that comprise the U.S. Pacific Islands Region are shown in Figure 23.1). In Hawai‘i mean precipitation, average stream discharge, and stream baseflow have been trending downward for nearly a century, especially in recent decades and with high ENSO and PDO-related variability.8e3247e0-fd15-4c29-8ed4-4aafd9c8660f 9a5c2112-9d46-45f0-b97a-64a8a8c574b1 a7bc5b58-4952-4499-9285-af61da992262 692a84a8-b5db-4ab2-82bf-e5244a63402a Projects based on statistical downscaling2aea4790-7e38-4922-bc92-d20c06d23b7d suggest the most likely precipitation scenario for Hawai‘i for the 21st century to be a 5% to 10% reduction for the wet season and a 5% increase in the dry season. On high islands like Hawai‘i, decreases in precipitation and baseflowa7bc5b58-4952-4499-9285-af61da992262 are already indicating that there will be impacts on freshwater ecosystems and aquatic species, and on water-intensive sectors such as agriculture and tourism. Hawaiian high-elevation alpine ecosystems on Hawai‘i and Maui islands are already beginning to show strong signs of increased drought and warmer temperatures.d1588faa-2aa9-4cdd-ba04-489c464fca3f Demographic data for the Haleakalā silversword, a unique (endemic to upper Haleakalā volcano) and integral component of the alpine ecosystem in Haleakalā National Park, Maui, have recorded a severe decline in plant numbers over the past two decades.04621537-01f9-459c-ac49-b531db72c3f2 Many of Hawai‘i’s endemic forest birds, marvels of evolution largely limited to high-elevation forests by predation and disease, are increasingly vulnerable as rising temperatures allow the disease-vectoring mosquitoes to thrive upslope and thereby reduce the extent of safe bird habitat.85ce98bb-ac2b-47a8-acf9-75007bcde4b9 73af9d00-a709-4b04-975e-e3f90431695a

New information and remaining uncertainties: Climate change impacts in the Pacific Islands region will vary because of differing island size and height. The impacts will also vary because of natural phase variability (for example, El Niño-Southern Oscillation and Pacific Decadal Oscillation) in precipitation and storminess (tropical and extra-tropical storms) as well as long-term trends, both strongly influenced by geographic location. Climate model simulations produce conflicting assessments as to how the tropical Pacific atmospheric circulation will respond in the future to climate change.7350d7b3-6e95-4375-ba23-26756b441fc2 a639a8f6-3355-43d7-ab21-ef29364db75a Climate change ecosystem response is poorly understood.7350d7b3-6e95-4375-ba23-26756b441fc2

Assessment of confidence based on evidence: Terrestrial and marine ecosystems are already being impacted by local stressors, such as coastal development, land-based sources of pollution, and invasive species.7350d7b3-6e95-4375-ba23-26756b441fc2 3d9112b9-6aa1-4614-9599-6966c9591ef9 There is abundant and definitive evidence that air temperature has increased and will continue to increase. Historical observations show strong evidence of a decreasing trend for rainfall in Hawai‘i and many other Pacific Islands.7350d7b3-6e95-4375-ba23-26756b441fc2 Given the evidence base and remaining uncertainties, confidence is high in this key message.