Climate Basics

Climate Change and...

Frequently Asked Questions

Climate Science Basics

Ecosystem Impacts

Management Options



* Q: What is climate?

* A: In the Glossary of Terms used in the Intergovernmental Panel on Climate Change (IPCC) Fourth Assessment Report, the definition of climate is:

Climate in a narrow sense is usually defined as the “average weather,” or more rigorously, as the statistical description in terms of the mean and variability of relevant quantities over a period of time ranging from months to thousands or millions of years. The classical period is 30 years, as defined by the World Meteorological Organization (WMO). These quantities are most often surface variables such as temperature, precipitation, and wind. Climate in a wider sense is the state, including a statistical description, of the climate system.

* Q: What is natural climate variability?

* A: Natural climate variability refers to variations, owing to natural internal processes in the climate system or natural external forcing, in the mean state and other statistics of the climate on all spatial and temporal scales beyond that of individual weather events (IPCC 2007).

* Q: What mechanisms cause climate to change naturally?

* A: Climate and climate variability are determined by the amount of incoming solar radiation, the chemical composition and dynamics of the atmosphere, and the surface characteristics of the Earth. The circulation of the atmosphere and oceans influences the transfer of heat and moisture around the planet and thus strongly influences climate patterns and their variability in space and time (Chapin et al. 2002).

* Q: How do human activities affect climate?

* A: Human activities such as fossil fuel burning, industrial activities, land-use change, animal husbandry, and fertilized and irrigated agriculture lead to increases in greenhouse gases, including carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O), which contribute to the greenhouse effect and cause the surface temperature of the Earth to increase. Global atmospheric concentrations of CO2, CH4 and N2O have increased markedly as a result of human activities since 1750 and now far exceed pre-industrial values (IPCC 2007).

* Q: What is the “greenhouse effect” and what are the major greenhouse gases?

* A: About 30 percent of solar radiation that reaches Earth is reflected back into space by clouds, air molecules, dust, haze, and the Earth’s surface. Another 20 percent of incoming solar radiation is absorbed by the atmosphere. The remaining solar radiation reaches the Earth’s surface and is absorbed. The Earth’s surface radiates this energy back to the atmosphere in the form of infrared radiation. Most (90 percent) of this infrared radiation is trapped in the atmosphere by greenhouse gases. The energy absorbed by the greenhouse gases is reradiated in all directions. The energy that is directed back toward the Earth’s surface contributes to the warming of the planet. This phenomenon is called the greenhouse effect.

Gases that absorb infrared radiation and contribute to the greenhouse effect include carbon dioxide (CO2), methane (CH4), chlorofluorocarbons (CFCs) and nitrous oxide (N2O).

* Q: What is “albedo” and “feedback,” and how does land use affect climate?

* A: Albedo is the reflectance of a surface. Absorbed radiation warms the surface, whereas, reflected radiation does not. Feedback is a general term that encompasses all of the different forms of energy exchange between the land surface and the atmosphere. Positive feedbacks enhance land surface warming; negative feedbacks enhance land surface cooling. Albedo is one component of this energy feedback. Different land covers have varied albedo. Thus, land use change can influence albedo and whether a land surface has a warming or cooling effect. For example, snow has a very high albedo and thus has a cooling effect (negative feedback). Melting of snow or coverage of snow with vegetation or black carbon (from air pollution) results in a higher surface albedo and has a warming effect (positive feedback) (IPCC 2007).

* Q: If climate varied naturally in the past, how do we know that humans are disrupting climate now?

* A: General Circulation Models (GCM) of the atmosphere are now being coupled with those of the oceans (AOGCM), ice, and the Earth’s terrestrial biosphere. These models have been under development for many decades. They spontaneously exhibit interannual and interdecadal oscillations not unlike those observed in the real Earth System. They are run under different starting conditions and using different amounts of solar, volcanic, and greenhouse gas "forcing" of the atmospheric dynamics. Using this "ensemble" approach, various AOGCMs have successfully simulated the Earth’s climate over the past 1,000 years. However, they cannot capture the rapid increase in global temperature of the past half century without including greenhouse gas forcing (IPCC 2007). Similarly, the models are able to simulate the warming of the upper 700 meters of all the major oceans of the world over the past 40 years, but only if they include the greenhouse gas emissions of the industrial age (IPCC 2007).

* Q: Is the rate of climate change greater now than the rate of natural climate change in the past?

* A: According to the Intergovernmental Panel on Climate Change (IPCC), the linear warming trend of 0.13 °C per decade over the 50 years 1956-2005 is nearly twice that for the 100 years 1906-2005. Eleven of the last 12 years (1995-2006) rank among the 12 warmest years in the instrumental record of global surface temperature (since 1850).

Long-term changes in other aspects of climate have also been observed. From 1900 to 2005, precipitation increased significantly in eastern parts of North and South America, northern Europe and northern and central Asia, whereas precipitation declined in the Sahel, the Mediterranean, southern Africa and parts of southern Asia (IPCC 2007).

* Q: What are westwide examples of climate change that occurred over the past century?

* A: From 1916 to 2003, there have been increases in both cool season and warm season temperatures over almost the entire Western United States (Hamlet et al. 2006; Mote et al. 2005). Although the rate of change differs with location and the period examined, the warming has been on the order of 1 ºC per century from 1916 to 2003 (Hamlet et al. 2006). The rate of increase from 1947 to 2003 is roughly double that of the longer period from 1916 to 2003; much of the observed warming has occurred from about 1975 to present.

* Q: What do westwide simulations suggest for climate changes in the 21st century?

* A: Simulated temperatures across the West by the end of the 21st century range from increases of 2 to 3 ºC at the low end of the uncertainty range, and as high as 5 to 6 ºC at the upper end of the uncertainty range (IPCC 2007). Precipitation changes in the West over the next century are more complex and uncertain, however, and differ within subregions. As both the Subtropical Jetstream and the Bermuda High intensify, the summer rains in the Southwest may intensify and shift to the north. Winter rains might decrease in the Southwest but increase in the northern half of the West (Salathé 2006). Interannual and interdecadal variability via El Niño-La Niña cycles may intensify (Timmermann et al. 1999), producing extreme winter events in both the Southwest and the Northwest.

Ecosystem Effects

* Q: How do changing climates affect the water cycle (snow, rain, runoff)?

* A: Changing climates influence the water cycle by influencing factors such as surface temperatures and evapotranspiration rates, precipitation patterns, proportions of precipitation received as rain versus snow, and amount and timing of runoff. Increased temperatures lead to more precipitation falling as rain rather than snow, earlier snowmelt and snowmelt-driven streamflow, and reduced spring snowpack. For the mountainous regions of the Western United States, snowmelt provides approximately 70 percent of annual streamflow. Thus, reduced spring snowpack leads to reduced summer streamflow in these regions. (Mote 2003, Mote et al. 2005, Mote et al. 2008, Stewart et al. 2005).

* Q: Does climate change affect flood and drought severity and frequency?

* A: Warmer temperatures and higher rates of evapotranspiration with climate change in some areas, such as the Southwest United States, will likely lead to increased drought frequency and severity. Overall, drought-affected areas are projected to increase in extent. Although increased temperatures will likely lead to decreased runoff in some areas, increased frequency of heavy precipitation events will likely lead to increased flood risk in many regions. Earlier snowmelt and runoff due to increased temperatures could also lead to increased winter and spring flooding. (IPCC 2007).

* Q: What is the relationship of climate change to fire intensity and frequency?

* A: Widespread fire years and fire extent are associated with warmer and drier spring and summer conditions in the Western United States Warmer spring and summer conditions lead to relatively early snowmelt, and lower summer soil and fuel moisture, and thus longer fire seasons. Increased temperatures and drought occurrence in some locations owing to global warming will likely lead to increased fire frequency and extent. Intensity of fires may also increase in some areas if higher temperatures interact with fuel characteristics to increase fire intensity. (Heyerdahl et al. 2008, McKenzie et al. 2004, Taylor et al. 2008, Westerling et al. 2006).

* Q: What are primary ecological effects of climate change?

* A: Climate controls ecosystem structure and processes such as species distribution and abundance, regeneration, vegetation productivity and growth, and disturbance, including insects and fire. Increasing temperatures and changes in precipitation with climate change will impact both ecosystem structure and ecosystem processes. For example, regeneration of tree species will be influenced by changes in snowpack, length of growing season, and moisture availability. Forest productivity may decrease in lower elevation forest ecosystems because of water limitations. Insects and disease outbreaks may become more frequent and widespread because warmer temperatures may accelerate their life cycles. Fire extent and frequency will likely increase with increased temperatures and longer fire seasons. Species distributions are likely to shift, and invasive species may become more of a problem owing to positive response to increased carbon dioxide levels. Increased disturbances may also create opportunities for invasive species to become established. (Logan and Powell 2001, McKenzie et al. 2004, Westerling et al. 2006).

* Q: How did plants and animals adapt to past natural variability?

* A: Plants and animal species responded to historical climate variability through changes in genetic diversity (evolution) and shifts in geographic range (migration). Genetic diversity is affected as a result of climate-driven changes in natural selection, gene flow and breeding patterns, genetic drift (that is, random effects resulting from changes in population size, isolation, and fragmentation), and changes in mutation rates. Evolutionary change in the past commonly increased adaptation in species, but in other situations resulted in decreased adaptation such as loss of fitness, population extirpation (loss of a population but not entire species), and species extinction.

Plants and animal species also responded to past climate change by migrating to favorable environments. For animals, this happens through individuals moving to new locations for breeding and home ranges. For plants, geographic shifts (migration) usually take place through seed and pollen transport. Mortality and population extirpation in parts of a species’ former range often occur. Over time, extirpation and colonization events cumulatively result in shifts of the species’ distribution range. (Davis and Shaw 2001, Delcourt and Delcourt 1991)

* Q: How do changes in land use affect the ability of plants and animals to adapt to climate change now?

* A: Land-use changes, including fragmentation, urban development, altered fire regimes, vegetation management, and introduction of invasive species, often impede the ability of species to respond to climate change adaptively. For instance, many land-use changes impose barriers to species’ migration to favorable new environments; small population sizes and isolation of populations as a result of land-use impede gene flow; invasive species disrupt opportunities for migration; and altered fire regimes destroy corridors for movement and habitat for breeding. (Joyce et al., in press.)

* Q: What are examples of responses that western plant and animal species have had to 20th-century climate change?

* A: Climate change has altered phenology of some western species. For example, a study in central California showed that 70 percent of 23 species of butterfly have advanced their first flight dates by an average of 24 days over a 31-year period. Climate variables explained 85 percent of the variation in this study, with warmer, drier winters leading to early flight. Honeysuckle (Lonicera tatarica & L. korolkowii) in the Western United States has shown earlier mean flowering dates by 3.8 days per decade. In response to a 1.4 ºC rise in local temperatures at the Rocky Mountain Biological Laboratory in Colorado between 1975 and 1999, yellow-bellied marmots (Marmota flaviventris) emerged from hibernation 23 days earlier. However, the flowering plant phenology did not shift in that time period. Thus, the change in marmot behavior shifted the relative phenology of marmots and their food plants.

Species distributions have changed in response to climate change in the Western United States. For example, the northern boundary of the sachem skipper butterfly (Atalopedes campestris Boisduval) has moved from California to Washington State (420 miles) over a 35-year period. Studies showed that winter cold extremes determine the northern range limit.

Climate change in the Western United States has also resulted in population extinctions. In the Great Basin, since being recorded in the 1930s, 7 out of 25 re-censused populations of the pika (Ochotona princeps) were extinct. There is little human disturbance in the high-elevation pika habitat. It was observed that extinct populations were at significantly lower elevations than populations still present. Other experiments showed that adult pikas were killed within 30 minutes at more than 31 ºC. (Beever et al. 2003; Cayan et al. 2001; Crozier 2003, 2004; Forister and Shapiro 2003; Inouye et al. 2000; Parmesan and Galbraith 2004; Smith 1974).

* Q: What are some changes that might occur in western vegetation over the 21st century?

* A: Likely vegetation responses to climate change in the West are extremely complex and difficult to forecast. They can best be understood if considered from the perspective of the two fundamental constraints on vegetation distribution: thermal and water constraints.

The highest and coldest zones, the Alpine (Tundra) zones will contract significantly and in many areas will be pushed entirely off the tops of the mountains. The Boreal and Temperate Forest zones (primarily conifer dominated) will shift up in elevation helping to squeeze the high elevation Alpine (treeless) and Krummholz transitional (stunted tree) zones into smaller domains. Winter minimum and nighttime temperatures are forecast to increase faster than maximum temperatures through the 21st century. This release of winter constraints is already occurring and has allowed bark beetles to invade higher elevations and latitudes where it was previously excluded by winter cold. Thus, many forests that have historically never experienced these infestations are being decimated or severely threatened now and will be more so in the future. The frost-sensitive vegetation of the subtropical zone, including oaks and other woody and ephemeral species, will also expand up in elevation and north. This expansion of southern species could result in a contraction of the Great Basin shrublands.

Water constraints in the West are far more complex. Where as the thermal constraints tend to limit northern and upper elevational distributions, water constraints tend to limit southern and lower elevational distributions. However, water limitations have at least four confounding factors. Variations in precipitation, both winter and summer, will exhibit very complex spatial patterns in the West. Regional increases in precipitation could be more than offset by dramatic increases in evaporative demand, which increases exponentially with increasing temperature. However, elevated CO2 concentrations confer some drought resistance via increases in water-use-efficiency (WUE). The situation is even further complicated by the nearly ubiquitous prevalence of fire as a major disturbance mechanism throughout the West. A way to sort out all these conflicting processes is through the use of complex ecosystem models that simulate these processes directly. Most simulations shift the water-limited boundaries, such as between closed forest and open tree-savanna, further down in elevation in the northern half of the West (north of the Oregon-California border) (Bachelet et al. 2001). Other water-limited vegetation in these same regions, such as pine and juniper woodlands, is expected to expand (Bachelet et al. 2001). In the Southwest, winter precipitation may decrease, but summer precipitation might increase. With the benefit of increased WUE from elevated CO2 concentrations, lower ecotones might shift down the mountains, or perhaps stay about the same. At the lower elevations, the reduction in winter precipitation may limit woody vegetation. Increased summer precipitation would benefit the summer grasslands.


* Q: What is “adaptation” in a management context?

* A: Adaptation is defined as an adjustment in ecological, social, or economic systems in response to climate stimuli and their effects. More specifically, adaptation refers to “a process, action, or outcome in a system (household, community, [organization], sector, region, country) in order for the system to better cope with, manage or adjust to some changing condition, stress, hazard, risk or opportunity”. (McCarthy et al. 2001, Smit and Wandel 2006).

* Q: What are examples of adaptation strategies in western wildlands?
* A: The following are potential adaptation approaches. Not all recommendations listed are appropriate to all situations; methods must be carefully evaluated to fit the case in hand.
  1. Increase landscape and watershed resiliance and diversity
    • Increase resilience at large spatial scales--Treatments and spatial configurations that minimize loss of large number of structural and functional groups
    • Increase size of management units--Much larger treatments and age/structural classes. Plan and manage by watersheds and basins where appropriate.
    • Maintain connectivity
  2. Maintain biological diversity
    • Modify genetic guidelines
    • Experiment with mixed species and mixed genotypes
    • Implement species triage
    • Assist colonization and establish neo-native species
    • Identify species, populations, and communities that are sensitive to increased disturbance
  3. Plan for postdisturbance management
    • Treat fire and other ecological disturbance as normal, periodic occurrences
    • Incorporate fire management options directly in general planning process
  4. Implement early detection/rapid response
    • Eliminate or control exotic species
    • Monitor postdisturbance conditions and reduce fire-enhancing species (e.g., cheatgrass [Bromus tectorum L.])
  5. Manage for realistic outcomes
    • Identify key thresholds for species and functions
    • Determine which thresholds will be exceeded (e.g., Pacific salmon)
    • Prioritize projects with high probability of success; abandon hopeless causes
    • Identify those species and vegetation structures tolerant of increased disturbance
  6. Incorporate climate change in restoration
    • Reduce emphasis on historical references
    • Reduce emphasis on guidelines based on static relationships (e.g., plant associations, habitat types)
    • Develop performance standards appropriate for accomplishing realistic restoration trajectories
    • Develop performance standards appropriate for increased fire (e.g., lower stand densities)
  7. Develop climate-smart regulations, policies
    • Address regulatory barriers
    • Address policy barriers
    • Address process barriers
    • Work with legislators and policymakers to revise regulations and policy; work more closely with local stakeholders from onset of projects
  8. Anticipate big surprises
    • Expect mega droughts, larger fires, system collapses, species extirpations, etc.
    • Incorporate these phenomena in planning
* Q: What is “assisted migration”?
* A: Assisted migration is a new management approach whereby resource managers physically move species (individuals, seeds, etc.) to new locations assessed suitable for survival under changed climate conditions. Assisted migration recognizes that suitable habitat will change as climate changes and that species need to move to survive. Under conditions of rapid climate change, however, species may not be able to move fast enough on their own. Land-use changes further impede natural dispersal. For both of these reasons, intervention may be appropriate. Decisions on where to move species would be based on projections about future conditions; for instance, species might be moved from current warm environments (e.g., lowlands) to higher elevations. Assisted migration is a controversial topic, as it assumes a secure understanding of local climate change and an understanding of biotic and ecologic response (McLachlan et al. 2007).
* Q: What is “mitigation” in a management context?
* A: In the context of climate change, mitigation is a human intervention or action designed to lower the level of greenhouse gases in the atmosphere or enhance greenhouse gas “sinks” or carbon storage. Mitigation is one way to characterize the human response to global climate change and climate variability. In a forest management context, examples of actions include those that will avoid emissions by maintaining existing carbon storage in trees, increasing carbon storage by planting trees, using forest-derived biofuels for energy instead of fossil fuels that generate greater quantities of carbon dioxide, and using cut trees for products (e.g., lumber for wood houses) that will store carbon for the long term.
* Q: How do forests sequester carbon?
* A: Carbon sequestration is the process through which carbon dioxide from the atmosphere is absorbed by trees, plants, and crops through photosynthesis, and stored as carbon in biomass (tree boles, branches, foliage, etc.). Both live and dead sources of carbon (e.g., dead wood) are important for carbon sequestration. Sequestered carbon can be thought of as “carbon you can see.” But significant amounts of carbon are also stored belowground in plant roots and in soil. Forests and forest soils have an important influence on atmospheric levels of carbon dioxide because trees are long-lived plants and they have significant amounts of biomass compared to other plants. Carbon sequestered in trees and soils can be released back to the atmosphere (e.g., through decomposition or wildfire), and carbon sequestration eventually reaches a saturation point.
* Q: What are “sinks” and “sources”?
* A: Forests, as well as soils, oceans, and the atmosphere, have the ability to store carbon. A carbon sink occurs when carbon sequestration is greater than carbon releases over some period. Carbon sources release more carbon than they absorb over some period. Forests can act as sources or sinks at different times.
* Q: How does vegetation management affect carbon sequestration?
* A: Forest management practices affect the rate of carbon sequestration in forest ecosystem. The effect of vegetation management on carbon sequestration is a complex issue and must be examined within a specific timeframe and include all components of the carbon life cycle. It can be difficult to assess the actual effect that vegetation management may have on carbon sequestration. In general, certain actions, such as tree planting and keeping forest productivity high, can increase carbon sequestration. Thinning forests may delay carbon dioxide emissions by reducing the chance of severe wildfire for a certain period of time. Other important forest management practices that may affect carbon sequestration include rotation length and fertilization; however, the effect of these activities are not well understood for all forest types.
* Q: Are mitigation and adaptation approaches complementary?
* A: Conceptually, many situations can be envisioned whereby mitigation and adaptation practices complement each other. For instance, certain fuel-reduction treatments to reduce severe wildfire could be conducted for complementary adaptation and mitigation goals: reducing wildfire protects habitats and also averts excess greenhouse gas emissions. Conflicts between adaptation and mitigation are also likely. For instance, other types of fuel-reduction treatments can be envisioned, such as extreme and uniform thinning over large areas, that have the potential to reduce adaptive responses even though they are effective mitigation practices. Because the situation is so complex and our knowledge yet untested, it is very difficult to evaluate what situations would be complementary or conflicting, and how to effectively integrate these approaches. (Klein et al. 2007)
* Q: What is a “toolkit approach” to managing for climate?
* A: Because situations, issues, and concerns across western national forest are so different, there is no single solution to climate change for management. Meeting the diverse challenges that climate change is imposing on national forest environments requires many approaches. Further, some issues need to be addressed urgently whereas others are longer-term concerns—these require different tools and strategies for planning. In some cases quantitative planning and analytical models (climate and climate impacts models) need to be used; in other cases; conceptual processes (e.g., based on uncertainty) will be favored. Case studies and demonstrations will also become useful for considering alternative strategies. Collectively these strategies compose a toolkit from which the manager can choose the best approach to fit the situation at hand (Millar et al. 2007) .
* Q: How can climate be addressed in planning and plan revision at project to forest scales?'

* A: Most current information on the effects of climate change is available only for large spatial scales (regional to subregional), and must be downscaled cautiously to smaller spatial scales. In addition, uncertainty about those effects must be estimated and considered in the planning process. Historical references (e.g., historical range of variation) and management targets based on equilibrium conditions (e.g., plant association groups, potential natural vegetation) will be less relevant in the future, requiring that performance standards be adjusted for a warmer climate (Millar et al. 2007). Simulation modeling may be helpful in quantifying future distribution and abundance of species, providing a biogeographic template for management decisions.

For the time being, climate will be easier to address across large landscapes where more options for management, vegetation structure, and natural resource conditions exist. For individual projects, it will be critical to consider how small-scale activities contribute to much larger patterns of landscape diversity, habitat, and resilience to fire and other disturbances over decades to centuries (Joyce et al. 2008). Planning is more likely to result in successful outcomes if it is consistently based on adaptive management; that is, management by experiment with resource monitoring providing feedback to decisionmaking. Large disturbances and options for postdisturbance management must be included as a normal part of the planning process.


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