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. On this page we will examine the recent observed changes in temperture and climate as well as some of the impacts of those changes. We will then briefly discuss the IPCC 2007 report's estimation of what caused the recent observed changes. Finally, we will take a look at what could happen in the future if current climate trends continue.

Climate has changed during the past century. Below is a list of some of the changes that have occurred based on information contained in Climate Change 2007: The Physical Science Basis. Note that these are observed changes, so they have happened. However, we are unable to absolutely determine how much influence the increases in greenhouse gases have had on these changes.

• Global mean surface temperature has increased by about 0.75°C (1.4°F) since 1850
• 11 of the last 12 years (1995-2006) rank among the 12 warmest years of the instrumental temperature record (since 1850).
• Observations since 1961 show that the average temperature of the global ocean has increased to depths of at least 3000 m and that the ocean has been absorbing more than 80% of the heat added to the climate system.
• Widespread changes in extreme temperture have been observed over the last 50 years. Cold days, cold nights, and frost have become less frequent, while hot days, hot nights, and heat waves have become more frequent (see Table SPM-2, IPCC 2007). Instructors note: I have some question about the ability to prove these conclusions.
• Global sea level has risen 0.12-0.22 meters (4.7-9.0 inches) since 1900.
• Widespread decreases in glaciers and icecaps (not including Greenland and Antarctica) have contributed to sea level rise
• The remaining sea level rise due to thermal expansion of oceans.
• Global precipitation patterns have changed
• General increase over eastern parts of North and South America and nothern Europe and Asia
• Slight decrease in many subtropical regions (20-35)°Latitude
• Increase in the frequency of heavy rain events over many land areas
• More intense and longer droughts now more likely in tropics and subtropics
• Significant decrease in arctic sea ice, particularly in the spring and summer seasons
• 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.

Attributing Observed Climate Changes to Human Activities

The most recent IPCC report (2007) is now more forceful in its statement concerning the anthropogenic influence on observed climate changes: "Most of the observed increase in globally averaged tempertures since the mid-20th century is very likely due to the observed increase in greenhouse gas concentrations." This is different from the previous statement "most of the observed warming over the last 50 years is likely to have been due to the increase in greenhouse gas concentrations." The new assessment considers longer and improved records and observations of climate change, as well as improvements in climate model simulations. Instructor's note: I wonder if they are putting too much faith in the ability of climate models.

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 (1.1-6.4°F) by 2010.
• Projected sea level rise of 0.18 to 0.59 meters (7 - 23 inches) by 2100
• 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

Some Issues specific to the Southwest

• Population is growing. Arizona was the fastest growing state in the US last year
• Mountain snowpack is critical to life in the Southwest. However, the portion of the season when snowpack forms will likely shorten with regional warming predicted by models. This will result in less snowpack and earlier runoff. So adjustments will have to be made.
• There are indications that manmade aerosols may be reducing the amount of precipitation in the mountains. Increasing the number of aerosols, increases the number of cloud droplets which tends to reduce the volume of each droplet which reduces the number of droplets that become large enough to fall out as precipitation. This effect may be as large as a 20% reduction in precipitation rates in the Sierra Nevada in California.
• Southwest dust bowl?
  Climate models generally predict the North American Southwest is going to get warmer and drier. Caveat: The models do not capture the summer monsoon well. It seems that the predicted wintertime reduction in precipitation due to the storm tracks moving further north is reasonable and likely to occur. However, as the desert Southwest gets warmer(with global warming) and the ocean temperatures lag behind, it will cause the pressure gradient that drives the summertime monsoon to become stronger causing the monsoonal winds to become stronger bringing more moisture in from the south creating more moisture convergence and rainfall at least in the southern part of Arizona and New Mexico. So the wintertime part of the prediction seems reasonable but the summertime part of the prediction is more questionable, at least in the southern part of the Southwest.