Submitted to: Rangeland Ecology and Management
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/14/2013
Publication Date: 9/23/2013
Citation: Polley, H.W., Briske, D.D., Morgan, J.A., Wolter, K., Bailey, D.W., Brown, J.R. 2013. Climate change and North American rangelands: Trends, projections, and implications. Rangeland Ecology and Management. 66(5):493-511. Interpretive Summary: Atmospheric science projects that increasing concentrations of certain trace gases in the atmosphere, referred to as greenhouse gases (GHGs), will cause warming and greater climatic variability, expressed as more frequent or severe droughts and storms. GHGs, which include carbon dioxide (CO2), warm Earth by reducing the emission of thermal infrared radiation from Earth’s atmosphere. Climate change, which included CO2 enrichment, warming, and precipitation modification, will affect the vegetation and productive potential of all ecosystems, including the grasslands and shrublands (rangelands) that occupy most of the western U.S. and upon which millions of humans depend for animal products, livelihoods, and other goods and services. Climate change effects likely will differ geographically, but often will be determined by their impact on soil water availability. Elevated CO2 increases water availability by reducing transpiration, whereas warming reduces soil water content by increasing water loss. Wetter winter seasons are anticipated in the northern US and Canada. Drier conditions are predicted for the southwest. CO2 enrichment, warming, and reduced precipitation may lessen forage quality. Warming may reduce livestock production in southern areas by depressing animal metabolic function and reproduction and increasing parasite infestations. The social and ecological consequences of climate change will vary by regions, but potentially are enormous. We suggest that recent evidence of change together with projected trends compel the rangeland profession to devise strategies to increase preparedness for climate change.
Technical Abstract: A climate change footprint has emerged over the past 50 years that is consistent with projections of climate change science. Increasing concentrations of greenhouse gases (GHGs), including carbon dioxide (CO2), are widely acknowledged as the driver of these changes. GHG concentrations are projected to increase well into the future. Consequences of this ‘greenhouse effect’ include atmospheric warming and modification to the annual amount and intra-annual pattern of precipitation. Atmospheric temperature has increased by 1°C since industrialization and is anticipated to increase by 2°C by mid-century, with the greatest increases at high latitudes. Projections are less certain for precipitation than warming or GHG concentrations. The current consensus is for a general drying of the western US, especially the southwest and southern plains, in response to a reduction in mean annual precipitation, delivered in fewer, but more intense events, and increase in evapotranspiration because of warming. Wetter winter seasons are anticipated in the northern US and Canada. Rising CO2 may off-set desiccating effects of climate change by increasing plant water use efficiency, but the CO2 effect is mediated by climatic conditions and will vary regionally. Ecosystem responses to climate change, including CO2 enrichment, are even less certain given their greater complexity, but likely will vary geographically and include positive as well as negative outcomes. For example, precipitation delivery as fewer, larger events is anticipated to increase net primary production in arid and semiarid regions, but decrease production in mesic regions. Forage quality will pose an increasing constraint on livestock production because climate changes will reduce forage crude protein content and digestibility. Warming will increase animal stress and ecotoparasite loads, especially in southern areas. The existing footprint of climate change and anticipated consequences of future change compel the rangeland profession to devise strategies to enhance preparedness for an altered climate.