This second in a series of four articles examines mitigation of climate change, excerpted from the Intergovernmental Panel on Climate Change's fifth assessment report.

In recent decades, changes in climate have caused impacts on natural and human systems on all continents and across the oceans.

Changing precipitation or melting snow and ice are altering hydrological systems, affecting water resources in terms of quantity and quality. Negative impacts of climate change on crop yields have been more common than positive impacts.

Impacts from heat waves, droughts, floods, cyclones and wildfires reveal significant vulnerability of some ecosystems and many human systems to climate variability.

Responding to climate-related risks involves decision making in a changing world, with uncertainty about the severity and timing of climate-change impacts. Adaptation and mitigation choices in the near term will affect the risks of climate change throughout the 21st century.

Uncertainties about interlinked human and natural systems are large. This motivates exploration of a wide range of socioeconomic futures in assessments of risks. A first step toward adaptation to future climate change is reducing exposure to present climate variability. Greater rates and magnitude of climate change increase the likelihood of exceeding adaptation limits.

Climate change is projected to amplify existing climate-related risks and create new risks for natural and human systems. Some of these risks will be limited to a particular sector or region In the Southwest. These risks include:

Wildfire-induced loss of ecosystem integrity, property loss, human morbidity, and mortality as a result of increased drying trend and temperature.

Snowpack and streamflow amounts are projected to decline in parts of the Southwest, decreasing surface water supply reliability for cities, agriculture, and ecosystems.

The Southwest produces more than half of the nation's high-value specialty crops, which are irrigation-dependent and particularly vulnerable to extremes of moisture, cold, and heat. Reduced yields from increasing temperatures and increasing competition for scarce water supplies will displace jobs in some rural communities.

Increased warming, drought, and insect outbreaks, all caused by or linked to climate change, have increased wildfires and impacts to people and ecosystems. Fire models project more wildfire and increased risks to communities across extensive areas.

Projected regional temperature increases, combined with the way cities amplify heat, will pose increased threats and costs to public health in southwestern cities, which are home to more than 90% of the region's population. Disruptions to urban electricity and water supplies will exacerbate these health problems.

Chip Tuthill is a longtime resident of Mancos. Sources for this column: www.climatechange2013.org and www.globalchange.gov/.