Of Climate Change in Mesoamerica
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Technical Series Technical Report No. 383 ABC of Climate Change in Mesoamerica Miguel Cifuentes Jara Tropical Agriculture Research and Higher Education Center (CATIE) Climate Change Program Turrialba, Costa Rica, 2010 The Tropical Agricultural Research and Higher Education Center (CATIE) is a regional center dedicated to research and graduate education in agriculture and the management, conservation and sustainable use of natural resources. Its members include the Inter-American Institute for Cooperation on Agriculture (IICA), Belize, Bolivia, Colombia, Costa Rica, the Dominican Republic, El Salvador, Guatemala, Honduras, Mexico, Nicaragua, Panama, Paraguay, Venezuela and Spain. © Tropical Agriculture Research and higher Education Center, CATIE, 2010 ISBN 978-9977-57-529-2 Credits Technical editors Editor Enric Aguilar, Ph.D. Elizabeth Mora Climate Change Research Group Geography Department Copy editors University Rovira i Virgili de Tarragona Joselyne Hoffmann Av. Catalunya, 35 Cynthia Mora 43002, Tarragona Spain Designer Rocío Jiménez Salas Víctor Orlando Magaña Rueda, Ph.D. Center for Atmospheric Sciences Translator Universidad Nacional Autónoma de México Christina Feeny Ciudad Universitaria Mexico City 04510 Mexico Contents Introduction . 5 Key concepts of global climate change . 7 Climate and the greenhouse effect . 7 Climate change . 8 Natural climate variability . 9 Planetary movements . 9 Solar radiation . 10. Volcanic eruptions . .11 Human influence on climate . .11 Greenhouse gases (GHG) . .11 Aerosols . 13. The unequivocal human action . 14. Evidence of climate change . 16. Temperature . 16. Precipitation . 17. Changes in the oceans . 18. Ice and snow cover . 19. Extreme events . 19. Climate scenarios . 21. IPCC carbon emissions scenarios . 22. The importance of considering several scenarios . 24. Projections of future climate change . 24. Areas of uncertainty in the predictions . 26. Climate in Mesoamerica . 29. Historical climate patterns . 29. Precipitation . 29. 3 ABC of Climate Change in Mesoamerica Temperature . 31. Changes observed in climate variables . 31. Climate scenarios for Mesoamerica . 35. Expected changes in temperature and precipitation . 36. Effects of climate change on Mesoamerica . 41. Water resources . 44. Biodiversity . 45. Climate change severity index . 48. Terrestrial ecosystems . 49. Aquatic ecosystems . 52. Freshwater systems . 52. Mangrove forests and coral reefs . 53. Coastal zones . 54. Fisheries . 55. Agriculture and cattle ranching . 56. Generalities of the sector . 56. Changes in production . 57. Human health . 59. Disasters . 60. Other sectors . 62. Bibliography . 63. Annex 1 . 73. Annex 2 . 80. 4 Introduction Introduction Human activities have brought about changes in the natural func- tioning of the Earth’s climate system. Potential effects are varied and affect all areas of human endeavor. The scale of the changes and a limited capacity for response make Mesoamerica the region most vulnerable to climate change in the entire tropical region. In the face of this threat, it is essential to have access to high quality informa- tion to better understand the scope of the potential effects of climate change and design strategies to address them. The purpose of this document is to provide up-to-date scientific information to support the formulation of the Regional Strategy on Climate Change for Central America and the Dominican Republic. The strategy aims to guide the actions of different sectors, institutions and organizations (governmental, private and civil society) to respond more effectively to the impacts and challenges of climate change. It will also help the countries of the region to position themselves in the global process of discussion and negotiation on climate change. This document consists of three main parts. The first contains a detailed description of the processes that generate climate on Earth, the role played by human activities in influencing climate, the scientific evi- dence related to climate change and an analysis of climate scenarios. The second part of the document contains a summary of historical cli- mate patterns in the region, the changes observed in recent decades and the predictions for future climate. The third section offers a synthe- sis of the potential impacts of climate change on those sectors of society which, according to the Intergovernmental Panel on Climate Change (IPCC), would be most affected by climate change. 5 Key concepts of global climate change 1 Key concepts of global climate change Climate and the greenhouse effect Climate is defined as the set of states and changes in atmospheric conditions observed in a given area over a period of at least 30 years. Average conditions, together with their variability, and extreme events of precipitation, temperature, wind, atmospheric pressure, etc. are all expressions of a region’s climate. The climate of an area is a dynamic phenomenon subject to variability and change. Solar radiation is the main source of energy for the planet’s climate system. More specifically, the balance (known as “radiative balance”) between the energy received by our planet from the sun, and energy that it re-emits, is the main mechanism that determines the Earth’s climate. To balance the amount of incoming energy absorbed, the Earth must radiate approximately the same amount of energy back to space. This occurs in the form of long wave energy, also known as thermal radiation. Approximately 30% of the solar energy reaching our planet is reflected directly back into space by the highest layers of the atmosphere and by surfaces with a high albedo1, such as those covered with ice and snow. The remaining two-thirds of the incident energy are absorbed by Earth’s surface and by the atmosphere. Some trace gases in the atmosphere (carbon dioxide, methane, among others) absorb a large amount of thermal radiation emitted by the surface of the planet and radiate it back to Earth again. This natural 1 Albedo is a fraction of solar radiation reflected by a surface or an object, often expressed as a percentage. 7 ABC of Climate Change in Mesoamerica phenomenon is known as the “greenhouse effect” and results in the warming of the planet’s surface (Figure 1). If the natural greenhouse effect were not in place, the temperature of Earth’s surface would be -18 ºC and would fluctuate widely between day and night. Therefore, the natural greenhouse effect makes life as we know it possible on Earth. Atmospheric trace gases that directly contribute to the greenhouse effect are commonly known as “greenhouse gases” or “GHG”. The main greenhouses gases that contribute to global warming are water vapor and carbon dioxide (CO2). Other important GHG are methane (CH4), nitrous oxide (N2O), ozone (O3), among others. Human activi- ties have increased the concentrations of carbon dioxide, methane, chlorofluorocarbons, etc. in the atmosphere, further intensifying the greenhouse effect and thereby increasing Earth’s surface temperature. Climate change The climate system changes over time under the influence of its own internal mechanisms (such as El Niño/Southern Oscillation) and also because of external factors known as natural drivers or “forcings”. Some of the most important external natural forcings affecting cli- mate are variations in solar activity, planetary movements, volcanic eruptions and changes in the composition of the atmosphere. Recently, scientists have determined that human activities—more specifically, increases in concentrations of greenhouse gases in the atmosphere—have become a dominant external forcing on the cli- mate, being responsible for most of the warming observed in the last 50 years. This phenomenon, is popularly known as “global warming”, or more broadly as “climate change” when other effects are considered. The IPCC definition of “climate change” does not distinguish between natural and anthropogenic causes of climate change, whereas the 8 Key concepts of global climate change Figure 1. Idealized model of the greenhouse effect. From Solomon et al. (2007). definition of the United Nations Framework Convention on Climate Change (1992) describes this process as “a change of climate which is attributed directly or indirectly to human activity that alters the com- position of the global atmosphere and which is in addition to natural climate variability over comparable time periods.” Natural climate variability Planetary movements Long before human presence on Earth, the planet’s energy balance, and therefore its climate, was affected by various natural causes. For example, there is strong evidence showing that ice ages occur peri- odically and that these are linked to variations in Earth’s orbit. These changes are known as “Milankovitch cycles” (Figure 2), which are regular variations (in the order of hundreds of thousands of years) in the eccentricity of Earth’s orbit around the Sun, and changes in 9 ABC of Climate Change in Mesoamerica Earth’s obliquity2 and precession3. Such variations in the planet’s movements alter the amount of incoming solar radiation received by the planet at different latitudes, producing drastic changes in the global climate. Solar radiation Another likely cause of climate change is the variation in the amount of energy produced by the Sun. For example, sunspot observations as well as data from isotopes generated by cosmic radiation, show that solar radiation varies (by nearly 0.1%) in short 11-year cycles and also over much longer periods. Figure 2. Diagram of Earth’s orbital changes (Milankovitch