United States
Environmental Protection
£% mA United States
Environmental Protection
What Climate Change
Means for QUam
August 2016
EPA 430-F-16-062
In the coming decades, changes in the earth's atmosphere are
likely to alter several aspects of life in Guam. The air and ocean are
warming, sea level is rising, and the ocean is becoming more acidic.
These changes are likely to damage or destroy much of Guam's coral
reef ecosystems, increase damages from flooding and typhoons,
reduce the availability of fresh water during the dry season, and make
air temperatures uncomfortably hot more often than they are today.
Our planet is warming and the climate is changing. People have
increased the amount of carbon dioxide in the air by 40 percent
since the late 1700s. Other heat-trapping greenhouse gases are also
increasing. These gases have warmed the surface and lower atmo-
sphere of the earth about one degree (F) during the last 50 years.
Evaporation increases as the atmosphere warms, which increases
humidity, average rainfall, and the frequency of heavy rainstorms in
many places—but contributes to drought in others.
Greenhouse gases are also changing the world's oceans and ice
cover. Carbon dioxide reacts with water to form carbonic acid, so
the oceans are becoming more acidic. Worldwide, the surface of
the ocean has warmed about one degree during the last 80 years.
Mountain glaciers are retreating and even the great ice sheets on
Greenland and Antarctica are shrinking. Thus the sea is rising at an
increasing rate.
Climate Change and Coral Loss
Warming waters are likely to damage much of the coral around Guam.
Average water temperatures around Guam have risen more than one
degree over the last century, in addition to the year-to-year changes
associated with the El Nino-Southern Oscillation ("El Nino"). Rising water
temperatures harm the algae that live inside corals and provide food for
them. The loss of algae weakens corals and can eventually kill them. This
process is commonly known as "coral bleaching" because the loss of the
algae also causes the corals to turn white. Coral bleaching is becoming
more common around Guam, including record-breaking bleaching that
has occurred throughout the western Pacific since 2013. Elevated water
temperatures also cause outbreaks of diseases that can harm or kill corals.
Increasing ocean acidity also damages corals. By changing the balance
of minerals in sea water, higher acidity decreases the ability of corals
to produce calcium carbonate, which is the primary component of their
skeletons. The Pacific Ocean has become about 25 percent more acidic in
the past three centuries, and acidity is likely to increase another
40 to 50 percent by 2100. Over the next 50 to 60 years, warming and
acidification are likely to harm coral reefs around Guam and throughout the
world, and widespread loss of coral is likely.
Warming and acidification could result in widespread damage to marine
ecosystems. Guam is home to a diverse array of fish species. Sharks, rays,
grouper, snapper, and hundreds of other fish species rely on healthy coral
reefs for habitat. Reefs also protect nearshore fish nurseries and feeding
grounds. A significant fraction of reef-dwelling fish are likely to lose their
habitats by 2100. Increasing acidity would also reduce populations of
shellfish and other organisms that depend on minerals in the water to build
their skeletons and shells.
Change in sea surface temperature (°F)
1 1.5 2
~ Insufficient data
Rising sea surface temperatures since 1901. The waters around Guam have
warmed by more than one degree. Source: EPA. Climate Change Indicators in
the United States.
Bleached corals in the Tumon Bay Marine Preserve in 2007. Credit: Dave Burdick.

Tropical Storms
As the climate changes, typhoons may cause more damage. Guam lies
in one of the world's most active regions for tropical storms. In 2002,
Typhoon Pongsona caused $700 million in damages, destroyed 1,300
homes, and left the island without power, in just the last few years,
neighboring islands have suffered from some of the strongest and most
damaging tropical cyclones ever recorded, including Super Typhoons
Haiyan (2013), Maysak (2015), and Soudelor (2015). Although warming
oceans provide typhoons with more potential energy, scientists are not
yet sure whether typhoons have become stronger or more frequent.
Nevertheless, wind speeds and rainfall rates during typhoons are likely to
increase as the climate continues to warm. Higher wind speeds and the
resulting damages can make insurance for wind damage more expensive
or difficult to obtain.
Damage caused by Typhoon Pongsona in 2002. Credit Andrea Booher, FEMA.
Rising Sea Level and Coastal Flooding
Sea level has risen by about four inches relative to Guam's shoreline since
1993. If the oceans and atmosphere continue to warm, sea level around
Guam is likely to rise one to three feet in the next century. Sea level rise
submerges low-lying areas, erodes beaches, and exacerbates coastal
flooding from typhoons and tsunamis. Coastal homes and infrastructure
will flood more often as sea level rises because storm surges will become
higher as well. Homes, businesses, roads, and the Port of Guam are
vulnerable to the impacts of storms and sea level rise.
The loss of coral reefs compounds this problem because reefs help
protect the shore from waves and storm damage. As reefs die, they lose
their structural integrity and provide less protection to the shore. If larger
waves strike the shore, beaches will erode more rapidly.
Rainfall and Water Supplies
Average rainfall in Guam has increased slightly since 1950, but scientists
are not sure whether totai rainfall here will increase in the future. Never-
theless, Guam's wet season may become wetter, while dry periods may
become drier. Warmer temperatures tend to make both rainstorms and
droughts more intense. Moreover, Guam's climate tends to be dry during
El Nino years and wet during La Nina years, and scientists generally
expect the differences between El Nino and La Nina years to become
greater in most places.
Inland flooding in Guam may increase as the climate changes. Heavy
rainstorms occasionally overwhelm Guam's rivers, streams, and urban
storm drains, leading to damaging floods. Flooding is most common in the
southern part of Guam, where the local bedrock is less permeable than
the limestone in the north. This means that rainfall in the south runs off
into rivers and streams instead of filtering into the ground. Flooding during
the wet season could become worse as rainstorms become more intense.
Conversely, water may be less available in the dry season. Less rainfall
occurs during El Nino years, such as during the drought that affected the
island in 2015-2016. Thus, if the El Nino cycle becomes more intense,
less rain might fall during the dry season. Moreover, rising temperatures
increase the rate at which water evaporates (or transpires) into the air
from soils, plants, and reservoirs, which would further exacerbate drought
During droughts, rising sea level could make fresh water less available—
particularly groundwater, which provides 80 percent of Guam's water
supply. Most of Guam's fresh water comes from the northern part of the
island, which has a "lens" of fresh groundwater floating on top of the
heavier, saltier water. Some wells already produce salty water during dry
periods when the freshwater lens becomes thinner; prolonged drought
could make more of Guam's wells salty. Rising sea level could also cause
salt water to infiltrate farther into the island's groundwater.
Inland Plants and Animals
Warmer temperatures and changes in rainfall could expand, shrink, or
shift the ranges of various plants and animals in Guam's forests, depend-
ing on the conditions that each species requires. Many tropical plants
and animals could be threatened by warming, as they are accustomed to
the temperatures that currently prevail in Guam, which are fairly steady
year-round. It is unclear whether species could tolerate the weather often
being warmer than it ever is today. Some native species could be crowded
out by invasive species better adapted to the changing climate, and some
could face extinction.
Human Health
Hot days can be unhealthy—even dangerous. Rising temperatures will in-
crease the frequency of hot days and warm nights. High air temperatures
can cause heat stroke and dehydration and affect people's cardiovascular
and nervous systems. Warm nights are especially dangerous because
they prevent the human body from cooling off after a hot day. Certain peo-
ple are especially vulnerable, including children, the elderly, the sick, and
the poor. Military personnel also face a higher risk of heat-related illness
because they perform intense physical activities outdoors, they often wear
layers of protective equipment, and many are from cooler climates and not
acclimated to Guam's warm and humid climate.
The sources of information about climate ana the impacts of climate change in this publication are: the national climate assessments by the U.S. Global Change Research
Program, synthesis and assessment products by the U.S. Climate Change Science Program, assessment reports by the Intergovernmental Panel on Climate Change, and EPA's
Climate Change Indicators in the United States. Mention of a particular season, location, species, or any other aspect of an impact does not imply anything about the likelihood or
importance of aspects that are not mentioned. For more information about climate change science, impacts, responses, and what you can do, visit EPA's Climate Change website
at www.epa.aov/ciimatechanae.