Causes and Evidence of Global Warming

Before presenting the main evidence for global warming and discussing its probable effects on our specific arguments - behavior and geographic distribution changes of arthropods of forensic interest under climate change - we introduce some of the

Department of Biology, University of Padova, Italy f Prof. Margherita Turchetto deceased on July 25th 2009.

J. Amendt et al. (eds.), Current Concepts in Forensic Entomology, 327

DOI 10.1007/978-1-4020-9684-6_15, © Springer Science + Business Media B.V. 2010

most quoted theories on this subject. Global warming is undoubtedly a process that is truly underway; and the theory of the "greenhouse effect," based on knowledge and study of a single big phenomenon, can be a valid approach to study and can aid our predictions of trends in global climate changes.

A planet's climate is decided by its mass, its distance from the sun, and the composition of its atmosphere. The phenomena that mainly affect the changes of the Earth's climate can be classified under the following categories:

• Astronomic effects

• Geological variations

• Human contribution

The effect of these causes, leading to a global warming, can be stated as:

• Increased atmospheric gas content (CO2, methane, and N2O)

• Warming of the troposphere

• Increased global average surface heart temperature of about 0.6°C (~1°F) during the twentieth century

• Increased ocean water temperature, especially in tropical areas (+1-2°C) over the past 100 years but also in closed seas and freshwater basins

• Rise in ocean and sea levels and the drift of streams

• Increased precipitation over tropical and Northern Hemisphere areas

• Significant weather events, such as the El Niño/southern oscillation (ENSO), monsoons, hurricanes, and typhoons

The best sources of scientific information on global warming are the Intergovernmental Panel on Climate Change (IPCC) reports. In 1988, the IPCC was set up by the United Nations Environmental Program and the World Meteorological Organization to examine the most current scientific knowledge on climate change. More than 2,500 scientists from about 100 countries have been involved in the program. Scientists, economists, and risk experts along with other interest groups have reviewed all the previous data and scientific information from the last few years to assess what is actually known about the climate: if global warming is already happening; how and why it will predominantly affect the world; what it will mean for people and the environment; and exactly what can be done about it.

The last IPCC reports (Climate Change 2001: The Third Assessment Report and Climate Change 2007: The Fourth Assessment Report) are the most comprehensive and revised evaluations of global climate change. IPCC reports testify that global warming is occurring on the basis of current climatic, physical, and ecological changes, some of the most important of which are as follows:

• Melting of snow cover, sea ice extent, polar ice caps, and mountain glacier retreat, along with thawing of permafrost

• Extended dry climate and desertification

• Shift of plants and animals toward poles or higher altitudes

• Decline of some plant and animal species; reduction of species' geographic areas, sometimes to niche species: loss of biodiversity

• Migration of nonnative species to new biota and altered composition of previous ecological communities, in both marine and terrestrial environments

• Modification of primary and secondary marine production, affecting planktonic organisms, fish larvae, and large fish and, consequently, the migration of pelagic fish and marine mammals

• Changes in the timing of holoartic species' spring activities, such as earlier shooting and flowering of plants, earlier arrival of migrant animals, earlier breeding and egg-laying of birds, and earlier emergence of insects

Even though these listed effects confirm that changes in the climate system are trending upward, leading to an increase in the average world temperature, it is impossible to foresee how they can interact and modify both weather and climate together in single regions and in such a short time frame.

The alteration of the Earth's physical conditions along with the other abiotic factors that have a variety of effects on local climates may affect environmental assessments and organisms' lives, starting from the vegetal composition and distribution and extending to animal biodiversity in the sea and on land. Consequently, human life and health could also be affected by the altered distribution of organisms, mainly in terms of food availability and vector-borne diseases.

Fossil evidence clearly demonstrates that Earth's climate has repeatedly shifted abruptly in the past and that a dramatic climate change that happened within a decade can have persisted for centuries. The climate shifts do not necessary have global effects: even as the Earth as a whole continues to warm gradually, large regions may experience a precipitous and dramatic shift into a colder climate. The dynamics of the climate has more than one mode of operating, and each mode produces different climate patterns. Earth's history shows that a climate system has a sensitive threshold. Pushed past the threshold, the system can jump quickly from one stable operating mode to a complete different one, as stated by the U.S. National Academy of Sciences report (US National Academy of Sciences 2002).

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