Climate Change and Implications

Climate has changed in the past and will continue to change in the future. Climate change is a part of Earth's history. The issue is whether or not humans are significantly altering the natural progression of climate change, and if so, will these changes be detrimental to life on Earth, including human life. The figure below shows measured changes in temperature and precipitation over the United States from 1900-1996. The label "Present" is about 8 years old. Although this figure is rather old, I present it here because it shows that even though the global average surface temperature increased by about 0.5°C over this period, there is quite a bit of variation in the temperature and precipitation changes at individual reporting stations.

Climate has changed during the past century. Below is a list of some of the changes that have occurred. Note that these are observed changes, so they have happened. However, we cannot say with certainty that all of these observed changes resulted from human activity.

• Global mean temperature has increased by about 1°F
• Minimum temperatures have increased more than maximum temperatures. Note this is what would be expected if the increase in temperatures is due to a stronger greenhouse effect (more noticeable effect at night rather than during the day). However, this cannot be used as absolute proof that all of the temperature increase is due to the additional greenhouse gases in the atmosphere.
• The frost-free season in much of the northern hemisphere middle and high latitudes has lengthened.
• Global sea level has risen 4-10 inches
• Global precipitation has increased by about 1%
• Most of increase in middle and high latitude areas
• Slight decrease in subtropical regions (20-35)°Latitude
• (2-4)% increase in the frequency of heavy rain events in northern hemisphere middle and high latitude regions.
• (10-15)% decrease in arctic sea ice in the spring and summer seasons
• Most continental and alpine glaciers have decreased in size
• Northern hemisphere snow cover has decreased by about 10%
• No conclusive change in severe weather events (such as tornadoes and hurricanes). Some reasearch groups are claiming that hurricanes are becoming more intense, while other groups dispute this claim.
• Limited observational evidence shows that some biological systems have already been affected by climate change
• Lengthening of middle and high latitude growing seasons
• Poleward and altitudinal shifts of plant and animal ranges
• Earlier flowering of trees, emergence of insects, and egg-laying in birds.

Climate is expected to continue to change in the future. The following list is based on climate model projected changes due to addition of greenhouse gases. Because this list is based on climate model projections, these changes are by no means certain, but they are the best estimates we can make at this time.

• Projected temperature increases of (1.8-6.3°F) by 2010.
• Projected sea level rise of 20 inches by 2100 (range: 6-38 inches)
• Likely increase in precipitation intensity. More heavy rain events and more severe droughts.
• Continued reduction in areal coverage of snow, glaciers, and sea ice.
• Continued changes in biological systems

Potential Impacts of Climate Change

• Human health, natural ecological systems, and socioeconomic systems are all sensitive to both the magnitude and the rate of climate change
• Many physical and ecological systems will be simultaneously affected
• The ability of natural ecological systems to migrate appears to be much slower than the predicted rate of climate change
• Climate change can add to existing environmental stresses

Health Impacts	Water Resources Impacts	Forest Impacts
Coastal Areas	Species and Natural Areas	Agriculture Impacts