One of the most striking ongoing changes in the Arctic is the rapid melting of sea ice. Some climate models predict that, sometime during the first half of the 21st century, summer sea ice will vanish from the Arctic Ocean. An absence of summer ice would amplify the existing warming trend in Arctic tundra regions as well as in regions beyond the tundra, because sea ice reflects sunlight much more readily than the open ocean and, thus, has a cooling effect on the atmosphere. In addition, research indicates that the retreat of sea ice would enhance the productivity of tundra vegetation, and the resulting buildup of plant biomass might lead to more extreme events such as large tundra fires. Finally, an ice-free Arctic Ocean would improve access to high northern latitudes for recreational and industrial activities; this would likely place additional stress on tundra plants and animals as well as compromise the resilience of the tundra ecosystem itself. In alpine tundras too, climate warming could encourage more human activity and increase damage to plant and animal populations there.
The fate of permafrost in a warmer world is a particularly important issue. Together, tundra and taiga account for approximately one-third of global carbon storage in soil, and a large portion of this carbon is tied up in permafrost in the form of dead organic matter. Some of this organic matter has been preserved for many thousands of years, not because it is inherently difficult to break down but because the land has remained frozen. Thawing of the permafrost would expose the organic material to microbial decomposition, which would release carbon into the atmosphere in the form of CO2 and methane (CH4). Rates of microbial decomposition are much lower under anaerobic conditions, which release CH4, than under aerobic conditions, which produce CO2; however, CH4 has roughly 25 times the greenhouse warming potential of CO2. The Arctic has been a net sink (or repository) of atmospheric CO2 since the end of the last ice age. At the same time, however, the region has been a net source of atmospheric CH4, primarily because of the abundance of wetlands in the region.
the eastern and western deserts prevented invaders from the east and west. The deserts were a hard climate to travel through. Therefore, nobody could walk across to conquer Egypt. Furthermore, the cataracts in the Nile to the south protected the Egyptians from lands below them.
The global carbon dioxide levels increase the temperature when higher, and lower the temperature when lower.
Explanation:
The carbon dioxide is the most abundant and most important greenhouse gas. This gas has the property to trap and keep heat, thus instead of the heat going back into space, it is retained in the atmosphere. To put is simple, the more abundant the carbon dioxide is in the atmosphere, the higher the temperatures are, the lower the levels of the carbon dioxide, the lower the temperatures.
In recent times, the global carbon dioxide levels are experiencing an increase. While this is mostly due to the natural processes, the humans have been having bigger and bigger influence because of their activities. With the constant rise of carbon dioxide levels in the atmosphere, the temperatures have been gradually rising, and if the current trends continue it is expected that the global temperatures may rise by several C degrees.
The countries that contribute the most to the carbon dioxide emissions are:
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