XEAST-WESTCENTERThe East-West Center promotes better relations and understanding among the people and nations of the United States, the Pacific, and Asia through cooperative study, research, and dialogue. Established by the US Congress in 1960, the Center serves as a resource for information and analysis on critical issues of common concern, bringing people together to exchange views, build expertise, and develop policy options.The Centers 21-acre Honolulu campus, adjacent to the University of Hawaii at Manoa, is located midway between Asia and the US mainland and features research, residential, and international conference facilities. The Centers Washington, DC, office focuses on preparing the United States for an era of growing Asia Pacific prominence.The East-West Center hosts the core office of the Pacific RISA grant, providing administrative and research capabilities for the program. The Pacific RISA is one of the 11 National Oceanic and Atmospheric Administration (NOAA) Regional Integrated Sciences and Assessments (RISA) teams that conduct research that builds the nations capacity to prepare for and adapt to climate variability and change. This work is supported by funding from NOAA. The Pacific RISA provided primary oversight of this and the 2012 PIRCA report.EastWestCenter.orgPacificRISA.orgISBN: 978-1-932728-95-8 (print)ISBN: 978-1-932728-81-1 (electronic)DOI: 10.5281/zenodo,41242592020 East-West CenterRecommended Citation:Miles, W., Z. Grecni, E. Matsutaro, P. Colin, V. Keener, Y. Golbuu, et al., 2020: Climate Change in Palau: Indicators and Considerations for Key Sectors. Report for the Pacific Islands Regional Climate Assessment. Honolulu, HI: East-West Center, https:/www.eastwestcenter.org/PIRCA-Palau.Global Climate Change: Causes and Indicators Global Climate Change: Causes and IndicatorsThe causes of climate changeScientists have investigated the physical science of climate change for almost two centuries. Carbon dioxide and other greenhouse gases in the atmosphere capture some of the heat from the Suns energy that radiates from Earths surface, preventing it from escaping back into space (USGCRP 2018, Ch. 1, Overview). Known as the /zgreenhouse effect/7 this process keeps Earth habitable for life. However, human activities have emitted an increasing amount of greenhouse gases into the atmosphere since the late 1800s through burning fossil fuels (such as oil, gas, and coal) and, to a lesser extent, through changes in land-use and global deforestation. As a result, the greenhouse effect has intensified and driven an increase in global surface temperatures and other widespread changes in climate. These changes are now happening faster than at any point in the history of modern civilization (USGCRP 2018, Ch. 1, Overview;USGCRP 201Z Ch. 2, Physical Drivers of Climate Change; IPCC 2014, SPM.1.2).Although natural climate cycles and other factors affect temperatures and weather patterns at regional scales, especially in the short term, the long-term warming trend in global average temperature documented over the last century cannot be explained by natural factors alone (USGCRP 2018, Ch. 2, Key Message 1). Human activities, especially emissions of greenhouse gases, are the only factors that can account for the amount of warming observed over the past century (USGCRP 2018, Ch. 2, Key Message 1; IPCC 2014, SPM.1.2). The largest contributor to human-caused warming has been carbon dioxide emissions. Natural factors alone would have actually had a slight cooling effect on climate over the past 50 years (USGCRP 2018, Ch. 2, Key Message 1).How is climate changing?Long-term scientific observations show the effects of increasing greenhouse gas concentrations in the atmosphere on the climate system. The factors observed to be changing are known as indicators of change. Data collected from around the world show, for example: Globally, the Earth has experienced a warming trend over the last century. Oceanias five warmest years in the past century have occurred since 2005, with the warmest year on record being 2019 (NOAA 2020a). Seas are rising, warming, and becoming more acidic. Some ocean species are moving toward cooler waters. Ice sheets and sea ice are decreasing, and glaciers and snow cover are shrinking.These and many other changes are well- documented and are clear signs of a warming world (USGCRP 2018, Chi, Overview, Fig. 1.2, and Ch. 2, Key Messages 3-7; IPCC 2014, SPM.1.1; also see USGCRP Indicators and EPA Indicators websites.)CLIMATE INDICATORST J Extreme Events ChangingCarbon Dioxide Concentrations RisingT Rainfall ChangingT More Intense and Changing Tropical StormsT Surface Air Temperature RisingSea Level RisingT Ocean Heat Content RisingOcean Chemistry ChangingT J Winds and Waves Changing TSea Surface Temperature RisingHabitats and Species Distributions Changingin Stream