A COMMENT ON ...
Volcanoes in a Changing Global Climate
Jessica F. Larsen
It seems that everyone these days is talking about climate change. Volcanologists, too, are involved in the discussion, as we examine how and where volcanoes fit into the climate change picture.
Volcanic eruptions can trigger climate cooling through the injection of sulfate aerosols into the stratosphere. For example, the 1815 eruption of Tambora in Indonesia created a cooling effect that lasted more than a year, causing the 1816 “year without a summer.” More recently, the 1991 eruption of Mount Pinatubo in the Philippines contributed a global cooling of approximately 1 degree Celsius, which lasted from less than one to several years, depending on different observations.
In the recent report by the Intergovernmental Panel on Climate Change (IPCC) — which outlines evidence indicating that anthropogenic contributions are likely a significant factor producing the observed pattern of global warming since the late 19th century — researchers did consider the contribution of volcanic aerosols to climate cooling to be a dampening effect, reducing the amount of warming observed up to the present time. IPCC did not consider, however, potential contributions from volcanic eruptions to future global climate patterns, because volcanoes erupt episodically, making it difficult to predict how much they will influence climate cooling in the future.
The degree to which volcanic eruptions could further dampen the predicted warming outlined in the IPCC report — which suggests a rise in temperature of 2 to 4.5 degrees Celsius, and a rise in sea level of 0.2 to 0.6 meters over the next century, not including potentially large contributions from the Greenland ice sheet — remains to be seen. Ongoing efforts by volcanologists and atmospheric scientists to better quantify the effects of volcanic eruptions on global climate will remain a critical avenue of research during the 21st century.
Volcanoes can also be linked with climate change in other ways. Recent observations and modeling of ocean temperatures indicate that atmospheric cooling from volcanic aerosols substantially cools the oceans, ultimately resulting in a relative drop in sea levels. This effect can last for years, and could substantially reduce the effect of sea-level rise from anthropogenic sources, according to an article by P.J. Gleckler and colleagues in Nature on Feb. 9, 2006. This presents an interesting conundrum: Could volcanic eruptions over the coming decades sufficiently mitigate sea-level rise, thus reducing the numbers of people potentially displaced? Or could sea-level rise caused by a warming climate effectively increase the risk associated with violent volcanic eruptions, by pushing people inland, closer to major volcanoes?
Nations located on volcanically active islands could be particularly susceptible to changing risk from volcanic hazards in the coming decades. Scientists are now modeling the numbers of people at risk for displacement from sea-level rise, and a recent study published in Environment and Urbanization lists Asia, and large coastal cities such as Jakarta, as particularly vulnerable. In the coming decades, it is likely that some Southeast Asians will be displaced by rising sea levels, probably forcing them to move closer to inland active volcanic centers. As it is generally easier and more profitable to inhabit flat-lying, fertile stream and river valleys, that’s likely where people will settle. Yet deadly pyroclastic density currents and mudflows (called lahars) triggered by volcanic activity and heavy rainfall also typically follow valleys as they travel downslope. Thus, more people could be at risk, ultimately as a consequence of sea-level rise.
Examining different models of sea-level rise will thus be important. Integrating those models at a regional scale with volcanic hazards assessments could provide a way to help prevent people from relocating into the most dangerous zones around active volcanoes.
Hydrological changes also increase the volcanic risk to people. Lahars are a potentially deadly phenomenon associated with volcanic eruptions on snow and ice covered volcanoes, or heavy rainfall on volcanic slopes in tropical climates. A significant increase in precipitation in a lahar-prone region could lead to an increase in the number and volume of lahars occurring on the slopes of a volcano, whether triggered directly by an eruption or not.
Southwestern Asia and the Western, Central and North Pacific — all volcanically active areas — may experience a relative increase in precipitation during the summers, according to the IPCC, which may increase the lahar risk. Meanwhile, models suggest that the Caribbean, Central America and southern Chile could experience decreased rain and snowfall all year, which might actually lower the lahar risk in these volcanically active areas. Models and observations of changing precipitation around lahar-prone volcanoes could provide volcanologists with a valuable tool to assess significant changes in the associated hazards.
It is highly speculative at present to predict how global climate change will transform the science of volcanology. Yet it is important that we begin to anticipate how the impacts of volcanoes will change, as population and precipitation patterns adjust to climate change during the 21st century. Volcanologists should continue to be involved in climate change discussions. We should examine both the potential of volcanoes to mitigate climate warming and sea-level rise, and the possibility that hazards will change significantly based on how changes in sea level and precipitation unfold in volcanically active regions of the world.