Pacific Islands Climate Change Monitor 2021

This report describes variability and change in Pacific Island climates, drawing on the latest meteorological and oceanographic data, information, and analyses. The report primarily focuses on observed changes across the Pacific Islands region in general and includes some country-specific information. It also includes some information about projections and the social, environmental, and economic impacts of rapid climate change. This information is intended to facilitate communication among, and inform decisions of, a broad spectrum of public and private sector stakeholders. Historical observations and climate modeling paint a consistent picture of ongoing human-forced climate change interacting with underlying natural variability.

Discernible trends are found in measures of atmospheric greenhouse gases, surface air temperatures, sea level, sea surface temperature, and ocean acidification. Most areas are experiencing increased, positive rates of change in all these parameters, while ocean chlorophyll concentration in surface waters is decreasing.

• Over the last 60 years, the concentration of carbon dioxide (CO2) in the atmosphere measured at NOAA’s Mauna Loa Observatory increased by more than 100 ppm (parts per million), to an annual average value over 414 ppm in 2020.

• The combined impact of the greenhouse gases carbon dioxide, methane (CH4), nitrous oxide (N2O), and halogenated compounds (mainly CFCs) in December 2020 is equivalent to a CO2 concentration of 504 ppm.

• The Pacific Islands mean temperature over land has increased by 1.1°C (2°F) since 1951.

• Since the start of the satellite record in 1993, mean sea level has risen approximately 10–15 cm (4–6 in) in much of the western tropical Pacific and approximately 5–10 cm (2–4 in) in much of the central tropical Pacific.

• Rising mean sea levels have already resulted in (in some cases dramatic) increases in the frequency of minor flooding.

• Over the past few decades mean sea surface temperature across most of the Pacific has warmed by a few tenths of a degree per decade, with an overall warming of approximately 0.9°C (1.6°F) since 1982.

• From the 1980s to 2000s the duration of marine heat waves tended to be 5–16 days. This increased significantly in the 2010s over most of the Pacific to 8–20 days or longer.

• Over the period 1981 to 2018 subsurface oceanic heat content increased in most locations in the Western Warm Pool (WWP) region and in the northern and southern sub-tropics.

• Oceanic pH measurements since 1988 at Station ALOHA near Hawai‘i show that the ocean became 12% more acidic over this time.

• Significant declines in phytoplankton size since 1998 are detectable across major portions of the Pacific Islands region.

Natural variability in rainfall, tropical cyclone (TC) properties and surface winds is high, and no statistically significant trends are apparent.

• Over the last 70 years, there has been little change in annual total rainfall and annual consecutive dry days at most of the Pacific Islands observation sites. Evidence for change in heavy rainfall across the Pacific Islands is mixed.

• No robust trends in the frequency or magnitude of TCs since the 1980s are evident.

The lack of high quality, long-term observational records, particularly with respect to in-situ stations, contributes to difficulties in discerning trends. To maintain and enhance our ability to assess environmental change, attention needs to be given to robust and sustained monitoring.