Climate Change Panel Foresees Longer, Dryer Droughts

by Meghan Sittler, NDMC Research & Outreach Specialist

Drought is likely to intensify in both duration and severity, according to the recently released ”Summary for Policymakers” of the Intergovernmental Panel on Climate Change (IPCC) report: Climate Change 2007: the Physical Science Basis. Using language such as “virtually certain, extremely likely, very likely,“ and “likely,” the report’s authors conclude that human activities such as emission of greenhouse gases and land use practices are having a significant impact on the global climate.

The report highlights paleoclimatic, historic and more recent trends to validate the claim that the global climate is changing at an unprecedented rate. The following observed phenomena are believed to have been “likely” or “more likely than not” to have occurred in the past because of human activities:

• Intensified droughts have occurred over wider geographical areas, especially the tropics and sub-tropics, since 1970. The severity of drought as measured by the Palmer Drought Severity Index (PDSI) rapidly increased from 1980 through 2002.
• Droughts have also been influenced by increased sea surface temperatures, changed and strengthened wind patterns particularly in the mid-latitudes and decreased snow pack and snow cover.
• There have been widespread changes in extreme temperatures with an increased number of hot days, hot nights and heat waves.
• Increased global surface temperatures.
• Increased drying (or evapotranspiration) as a result of the increased temperatures and decreased precipitation.
• A decrease in the total area of seasonally frozen ground in the Northern Hemisphere and increased temperature of the permafrost layer in the Arctic since the 1980s.

From the Intergovernmental Panel on Climate Change

So what can we expect to see in the next 100 years? Unfortunately, we can expect to see many of the above trends continue or accelerate unless technological and social initiatives are carried out to curb emissions, provide more sustainable land and resource use, and increase economic security throughout the regions of the world. The IPCC used a variety of scenarios to project future impacts and trends. The scenarios differ in the assumed rate of population growth and expansion, rate of implementation of cleaner and more efficient energy, and levels of economic development. The scenarios also factor whether the loci of control for the implementation of the social, economic and environmental policies are global, regional, or local.

For example, a scenario with a peak in global population at mid-century and then an ensuing decline, with a global introduction of “clean and resource efficient technologies,” reduced material consumption and a focus on global solutions, resulted in a “best estimate” projected surface temperature change of 1.8 degrees by the last decade of this century. An alternative scenario that maintained the intensity of use of fossil fuels, with mid-century achievement of maximum global population and ensuing decline, rapid economic growth and increased social and cultural interaction and capacity building could result in a “best estimate” increase of 4.0 degrees by 2090.

Regardless of the specific scenario, IPCC projects that many of the observed trends are likely to continue. Specific projections related to drought include:

• Decreased precipitation in tropical and subtropical land regions.
• Increased hot nights, hot days and heat waves.
• Increased evapotranspiration as a result of increased temperature and decreased precipitation.
• Significant decrease in precipitation in the Sahel, Mediterranean, Southern Africa and Southern Asia.
• Decline in mountain glaciers, snowpack and snow cover, particularly in the Northern Hemisphere.
• Continued decrease in the total area of seasonally frozen ground.
• A pole-ward movement of extratropical storm tracks resulting in continued changes in wind, temperature and precipitation patterns.

The IPCC’s projections demonstrate the need for actions to be taken on all levels to offset and mitigate the impacts of climate change. The panel projected more widespread and intense droughts in regions where the world is currently seeing high levels of population growth, economic development and social conflict, which will jeopardize food security, access to safe drinking water and economic stability for a high percentage of the world’s population.

The National Drought Mitigation Center anticipates that the newly acknowledged danger of climate change will prompt vigorous, constructive dialog between scientists, policy makers and communities about the appropriate technologies and strategies that are needed to meet these challenges. Dialogue about desalinization, water banking, alternative energy sources, “cap and trade” emission policies, and many other issues has already begun. Whatever the outcome of the scientific and political debate, the NDMC anticipates planning and preparedness being more essential now than ever.

To read the Summary for Policymakers visit: http://www.ipcc.ch/. The second volume of the IPCC report, "Impacts, Adaptation and Vulnerability," is expected to be released on April 6, 2007 in Brussels.

Back to DroughtScape Spring 2007