Symptoms and Effects of Climate Change

Air Temperatures

Globally measured surface temperatures have increased rapidly since 1979. Generally, the temperature increases are more severe at higher latitudes, as the atmosphere moves excess energy poleward. The warmest years in the instrumental record (extending back to 1850) are 2005, 2007, 1998, 2002, 2003, and 2006. However, temperature increases are not uniform, because of changes in atmospheric circulation and localized effects such as urbanization. These local processes are accounted for in global temperature change calculations and are not the cause of the documented global temperature increase.

Warming air leads to greater occurrence of heat waves; this trend is most pronounced in the polar regions (averaging twice the rate of lower latitudes) and becomes less evident toward the equator. Extreme high temperatures affect older or stressed organisms because the cardiovascular system must work so much harder to regulate temperature. While warmer winter temperatures have led to reduced death rates during the colder months, the increase in summer deaths far outweighs that reduction. These trends have been documented in human populations across the world and in multiple animal species as well. Warmer winter and nighttime average temperatures also mean decreased frost risk, changes in snowfall, and changes in the length of the growing season.

Ocean Changes

Global sea level has risen by more than 3 millimeters per year in the past decade, and it is uncertain if this rate will remain constant or increase. Sea-level rise is caused by oceanic thermal expansion and the melting of the world's ice caps and glaciers. As the majority of the world's surface is covered by water, warmer air temperatures are warming the ocean as well. However, due to the high heat capacity of water and the layered nature of the ocean, with little mixing of surface and deep water, ocean warming is a slow process that will occur over the next century-to-millennia time-frame. If temperatures stabilized today, the ocean [Page 2771]would continue warming for hundreds of years as deep-water mixing slowly occurs. Deep-ocean measurements have measured steady temperature increases throughout the world's ocean basins.

Warmer water is less dense than cold water, and thermal expansion of water has led to increasing sea-level rise. An increase in water temperature also lowers the ability of water to retain dissolved oxygen and carbon dioxide (CO2), so that biological systems are stressed due to less oxygen for fish and other organisms and warm water releases even more CO2 into the atmosphere. However, increased freshwater flow from melting glaciers in Greenland and other locations will lower ocean salinity in the high latitudes at areas of ocean multilevel mixing. Lower salinity allows water to absorb more CO2. This may be sufficient to offset CO2 release from ocean warming in other areas but will lead to increased acidification of the oceans.

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