Climate Change and Biodiversity in Melanesia - The Indo-Pacific Conservation Alliance -

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Preliminary Results Announced in Melanesia Climate Change Study

Bishop Museum’s V.P. for Science and IPCA Chairman Dr. Allen Allison announced initial findings in the MacArthur Foundation-funded study, Climate Change and Biodiversity in Melanesia (CCBM) at the 8th Pacific Islands Conference on Nature Conservation and Protected Areas, held in Milne Bay province in Papua New Guinea in October 2007.

Previous projections on future climate scenarios for the Pacific region have been unclear at best. Analyses by the U.N. Inter-Governmental Panel on Climate Change (IPCC), the world’s preeminent body on climate science, lack precision on specifically how climate change will affect the Pacific because current computer climate models do not yet have a sufficiently fine-scale resolution to “see” islands. An additional complication is the inherent uncertainty of different possible future global carbon emissions scenarios. Because of these uncertainties, the CCBM study is important to determine how projected broad-scale climate pattern changes will specifically impact the Melanesia region.

The CCBM project convened a multidisciplinary expert workshop in Hawai’i in September 2007 to assess the best scientific understanding of climate change impacts on Melanesia, and develop a series of White Papers that summarize current knowledge. All information and reports are organized and presented on the CCBM project website. While many ambiguities remain about what climate change in the Pacific will look like, the CCBM study found several consistent patterns, These include:

WARMING AND EL NIÑO

It is likely that warming in the western tropical Pacific will closely follow the projected global average warming rate of 1.8° to 4.0° C (3.2° to 7.2° F) by the year 2099. El Niño/La Niña cycles (known as ENSO) are known to have major effects on the climate of Melanesia, but how global warming will affect the intensity or variability of the ENSO cycle is currently unknown. In Melanesia, El Niño generally results in hotter and drier land conditions, but paradoxically, relatively cool sea temperatures. Conversely, La Niña conditions in Melanesia mean relatively wet conditions on land (which implies cloudiness that tends to suppress temperatures),but far hotter sea surface temperatures, which results in more frequent and intense coral bleaching.

The CCBM study found that large-scale changes in ocean circulation patterns in the Pacific are a highly plausible result of global warming, but it is not yet possible to accurately predict exactly how, where, and what these circulation changes may be. Increased temperature, changes in rainfall, wind speed and direction, sea level rise, and increased intensity of tropical cyclones are likely scenarios for Melanesia. However, since regional climates in the Pacific region are strongly affected by ENSO and ocean circulation (factors that heavily influence such events) it is not yet possible to precisely estimate to what degree these changes will happen, or how they vary from one island to another in the western tropical Pacific.

SSTs AND CORAL BLEACHING

The CCBM study found that sea surface temperatures (SSTs) are warming fastest near the equator and less quickly towards the higher latitudes (both north and south of the equator). While all of Melanesia’s reefs and oceans will become warmer, resulting in an increase in coral bleaching events, northern Melanesia is likely to experience more frequent and prolonged coral bleaching events before southern areas of the region. However, Dr. Steve Coles of the Bishop Museum noted that reef ecosystems and species may have more resilience to such bleaching than previously thought. The CCBM study concludes that with careful design and management of marine protected areas (MPAs), and through the use of other conservation measures, coral reef ecosystems may exhibit some resilience in the face of increased SSTs.

SEA-LEVEL RISE

Dr. Axel Timmerman of the International Pacific Research Center (IPRC) at the University of Hawaii indicated that sea-levels in the northern Melanesia area have been rising faster than the global mean sea-level rise, and indications are that they will continue to rise faster than the global average, which is currently projected by the IPCC to be around one-half to one meter by 2100. Looking at sea-level rise in isolation from other factors such as bleaching and acidification, and coastal flooding, coral reef accretion can probably keep pace with rising seas. Melanesia also has some of the world’s largest remaining stands of coastal mangrove habitat, which is highly affected to sea-level rise impacts. However, Dr. Geoff Hope from the Australian National University noted in the workshop that mangroves have the capacity to adapt to sea-level rise by (a) trapping sediment and thereby raising their base level, and (b) by migrating (through reproduction) in-land as sea-levels rise. However, structures such as seawalls or roads could limit coastal resilience by preventing mangroves from migrating inland as sea-level rises. Atolls and some other coastal areas will be particularly hard-hit by sea-level rise, but projections are not necessarily straight-forward. Dr. Hope concluded that mangrove forests such as those in southwestern New Guinea may protect some low-lying areas from complete inundation by capturing and redistributing sediment.

OCEAN ACIDIFICATION

Oceans naturally absorb CO₂, but the scale of recent human-produced carbon emissions is so large that it is changing the chemistry of the Earth’s oceans. Carbonic acid forms when oceans absorb CO₂, and global ocean surface waters have become more acidic in recent decades, resulting in a drop of 0.1 pH. (The pH scale is a measure of acidity and alkalinity ranging from 0 to 14, with 7 being neutral: A 0.1 unit decrease means that acidity has increased by 30%.) Depending on the path of future global carbon emissions, ocean surface pH could decrease by an additional 0.3 to 0.7 pH units by 2100. Such changes have not occurred on the planet for millions of years, and never on such a rapid timeframe.

Acidification of ocean waters reduces the availability of calcium carbonate required by organisms such as corals, sea urchins, clams, and zooplankton. Acidification also interferes with respiratory processes in fish, and may also negatively impact their food supply. IPCA Executive Director John Burke Burnett notes that “the most recent scientific projections are that calcium carbonate levels in the world’s equatorial regions will become marginal by 2070, and even sooner in the higher latitudes.” This will result in the slowing or even reversal of reef formation and shell formation, possibly resulting in major disruptions to marine food webs. He also noted that “It appears likely that ocean acidification will result in fundamental changes in marine community structures in both coastal and pelagic areas, and that this will quite possibly result in very serious negative impacts on both near-shore and deep water fisheries, ecosystem services such as provision of food sources, and storm protection provided by coral reefs.”

CLIMATE CHANGE AND TERRESTRIAL BIODIVERSITY

Melanesia ’s terrestrial animal and plant species are especially vulnerable to climate change because of high levels of endemicity in the region. Species that are most threatened by climate change are: 1. those found near the tree line at higher elevations; 2. those found in isolated or outlying mountain ranges; 3. small island mammals; and 4. larger mammals. It is possible that species could shift their ranges along both latitudinal and elevational gradients, but this depends on other factors that are highly uncertain, such as cloud formation and conditions as well as other ecological interactions such as changes in inter-species competition and predation, seeding and fruiting patterns, and future land-use changes.

Dr. Geoff Hope pointed out that species and ecosystems have adapted to past climate changes. However, he underscored that during those past periods of climate change the ecosystems most at risk were healthier than they currently are. In today’s world most ecosystems are already under pressure from other human-based threats such as over-hunting, over-fishing, and forest cover changes. The effects of climate change add yet one more stress factor to these ecosystems, and in some cases may become the “straw that breaks the camel’s back.”

RECOMMENDATIONS: ADAPTING TO GLOBAL WARMING

Regardless of future carbon emission scenarios, climate change is already with us, according to the latest IPCC report. While it is critical to reduce greenhouse gas emissions, it is equally important for island communities to take steps to mitigate the projected impacts of global warming on their livelihoods, economies, and biodiversity. Islands and marine ecosystems are already under particular pressure from a range of threats including over-harvesting of natural resources, loss of habitat, and marine pollution.

Workshop participants agreed that establishing effective networks of marine protected areas is one of the critical tools that can assist in protecting both vulnerable habitats as well as critical ecosystem processes, and thereby enhance resilience to climate change impacts. Likewise, preserving terrestrial habitat is critical in order to buffer global warming’s effects on island ecosystems. For example, preserving intact forest protects hydrological processes that generate cloud cover, which will then reduce temperature and maintain adequate rainfall.

The workshop participants concluded that climate change by itself isn’t likely to be the main driver of plant and animal biodiversity losses, but rather climate change in combination with existing stresses, such as habitat loss, overuse of resources, and invasive species that will amplify and accelerate these losses. The Earth is committed to some degree of climate change because of increased anthropogenic CO₂ that is already “in the system”, but early and deep reductions in future carbon emissions are critical to limit the degree of future warming. But the critical message of the CCBM study is that much can still be done to increase the resilience of biota to adapt to climate change. “One of the key messages from the Bishop/SPREP vulnerability study is that maintaining healthy ecosystems through good management practices will enhance resilience to future climate impacts,” said Dominique Benzaken from the Pacific Regional Environment Programme (SPREP).

It was also agreed that there is currently a significant dearth of several kinds of data for Melanesia that are important to understand climate change and how to adapt to it. Such data gaps include information on baseline rainfall, temperatures, biogeographical patterns, species physiology and ecological requirements of most marine and terrestrial species. This information is necessary to build better climate models that will allow more accurate regional projections and forecast potential impacts on biota and ecosystem services. The workshop further identified two additional priorities: the need to strengthen in-country capacity of local scientists to conduct research, and for scientists from outside Melanesia to return information to local stakeholders so that they can better understand climate change-related factors and how best to respond and adapt.