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Unit 12: Earth's Changing Climate // Section 7: Observed Impacts of Climate Change


Human-induced climate change has already had many impacts. As noted above, global average surface temperatures rose by 0.6°C +/- 0.2°C and sea levels rose by 0.12 to 0.22 meters during the 20th century. Other observed changes in Earth systems that are consistent with anthropogenic climate change include:

Arctic sea ice coverage, 1979 and 2003

Figure 12. Arctic sea ice coverage, 1979 and 2003
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Source: © National Aeronautics and Space Administration.

The Earth is not warming uniformly. Notably, climate change is expected to affect the polar regions more severely. Melting snow and ice expose darker land and ocean surfaces to the sun, and retreating sea ice increases the release of solar heat from oceans to the atmosphere in winter. Trends have been mixed in Antarctica, but the Arctic is warming nearly twice as rapidly as the rest of the world; winter temperatures in Alaska and western Canada have risen by up to 3–4°C in the past 50 years, and Arctic precipitation has increased by about 8 percent over the past century (mostly as rain) (footnote 12).

Observed climate change impacts are already affecting Earth's physical and biological systems. Many natural ecosystems are vulnerable to climate change impacts, especially systems that grow and adapt slowly. For example, coral reefs are under serious stress from rapid ocean warming. Recent coral bleaching events in the Caribbean and Pacific oceans have been correlated with rising sea surface temperatures over the past century (footnote 13). Some natural systems are more mobile. For example, tree species in New England such as hemlock, white pine, maple, beech, and hickory have migrated hundreds of meters per year in response to warming and cooling phases over the past 8,000 years (footnote 14). But species may not survive simply by changing their ranges if other important factors such as soil conditions are unsuitable in their new locations.

Insects, plants, and animals may respond to climate change in many ways, including shifts in range, alterations of their hibernation, migrating, or breeding cycles, and changes in physical structure and behavior as temperature and moisture conditions alter their immediate environments. A recent review of more than 40 studies that assessed the impacts of climate change on U.S. ecosystems found broad impacts on plants, animals, and natural ecosystem processes. Important trends included:

Because many natural ecosystems are smaller, more isolated, and less genetically diverse today than in the past, it may be increasingly difficult for them to adapt to climate change by migrating or evolving, the review's authors concluded (footnote 15). This is especially true if climate shifts happen abruptly so that species have less response time, or if species are adapted to unique environments (Fig. 13).

Polar bear hunting on Arctic sea ice

Figure 13. Polar bear hunting on Arctic sea ice
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Source: © Greenpeace/Beltra.

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