GISS scientists have determined that the Earth's current temperatures are now reaching a level that has not been reached in thousands of years. According to NASA global warming expert, Dr. James E. Hansen, based on a joint study conducted by NASA GISS, Columbia University, Sigma Space Partners, Inc., and the University of California at Santa Barbara, the Earth is surpassing the warmest levels it has seen since the last ice age, which ended about 12,000 years ago. Careful calculations have shown that for the past three decades, the Earth has been warming about 0.36°F (0.2°C) per decade. Although this may not seem to be a lot, it is. It is already causing many species of plants and animals to move toward the polar regions. They must do this because they can tolerate only certain temperature ranges. If their habitat becomes too warm, they need to move to a cooler area in order to stay in their comfort range, which means they must move poleward.
According to Dr. Hansen, head of GISS, "This evidence implies that we are getting close to dangerous levels of human-made (anthropogenic) pollution. In recent decades, human-made greenhouses (GHGs) have become the dominant climate change factor." One major obstacle, however, is that it may not be possible to migrate. For instance, animals cannot migrate if a city is in the way. Plants may not be able to migrate if the right kind of soil or moisture is not available. When one part of an ecosystem is disrupted, it causes a ripple effect and can destroy entire food chains and habitats.
According to Dr. Hansen, a study conducted in 2003 that appeared in Nature determined that 1,700 plant, animal, and insect species had moved poleward at a rate of 4 miles (6 km) each decade from 1950 to the present. With current global warming trends, however, the temperature zones have migrated 25 miles (40 km) per decade from 1975 to the present, meaning that species cannot keep up with the rate of change under global warming. Wildlife species that cannot keep up will face extinction.
The same threat exists for species that live in mountain habitats. When temperatures become warmer, species that live in the lower elevations may try to migrate to higher elevations, where it is cooler.
This may or may not be possible, especially for the species that already inhabited the highest elevations. They may be displaced with nowhere else to go.
According to Dr. Hansen, over the past 30 years, the increase in temperature—current global warming—is due primarily to humanmade greenhouse gases. The area where the largest increases in temperature are occurring are the high latitudes of the Northern Hemisphere (the polar regions), and the temperature increase is greater over land than over the oceans. The reason polar areas are affected the most is due to the behavior of polar ice and snow. Snow and ice have a high albedo—they reflect most of the light they receive. As the Earth warms, however, it causes the snow and ice to melt, which exposes the darker surface of the ground beneath the ice. Because dark surfaces absorb light and convert it to heat energy, this causes accelerated melting of snow and ice in a chain reaction called positive feedback. The ocean does not heat as rapidly because water has a higher heat capacity—it can hold huge amounts of heat at extreme depths before it starts to warm significantly.
Based on research Dr. Hansen conducted with David Lea and Martin Medina-Elizade, they determined that the western equatorial Pacific and Indian Oceans are now as warm or warmer than at any time during the past 12,000 years. This conclusion was based on proxy data from the magnesium content found in the shells of microscopic sea-surface animals contained in ocean sediments. This is especially important because temperature change in these two oceans indicates overall global temperature change. The western Pacific serves as a major source of heat for the world's oceans and for the global atmosphere. In addition, the Earth's recent rapid warming has brought global temperatures to within 1.8°F (1°C) of the maximum estimated temperature during the past million years. In contrast, the eastern Pacific has not shown the same amount of warming. Hansen believes this is due to the effects of El Niño.
Based on the results of this study, Hansen concluded that if warming increases another 1.8°F (1°C), the Earth's atmosphere will reach a critical level. If temperatures stay below that level, the situation may remain manageable. If temperatures increase 3.3 to 5°F (2-3°C), how ever, the Earth will become a very different environment than what humans are presently used to. The last time the atmosphere was that warm (approximately 3 million years ago, during the Pliocene), sea level was 80 feet (25 m) higher than it is today. If that situation were to occur again today, it would flood coastal areas worldwide, causing serious disruption, damage, destruction, and death.
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