Climate Basics - Frequently Asked Questions


Education Modules


The CCRC is developing an educational program to provide accessible information on climate change science. Three comprehensive education modules are being created using curriculum developed by the Forest Service.

Complete the first module on Climate Change Science and Modeling by selecting the tab above.

Modules are based on the best available science and have many interactive features, allowing users to take control of their learning experience. There are also opportunities to choose to explore detailed information. Each module has an activity at the end that will let users demonstrate their knowledge, and a certificate will be generated upon completion.

These education modules can be used to satisfy the Forest Service Climate Change Performance Scorecard Element One requirement for all-employee education. To learn more about the Climate Change Performance Scorecard, click here.

The cover of the document Responding to a Changing Climate and its Effects on Forests and Grasslands

The modules are based on a curriculum developed by the Forest Service Climate Change Advisor’s Office, Climate Change Education and Training Team.Responding to a Changing Climate and its Effects on Forests and Grasslandsis an instructional package that can be used by National Forest Service units to implement education and training for all employees.

The first education module,Climate Change Science and Modeling: What You Need to Know, is available on a hard-copy CD-ROM. To order a CD copy of the module, please email or fill out the Pacific Northwest Research Station onlinePublication Request Form and ask for PNW-GTR-902. Anyone is welcome to order copies.

How to Use this Module

Here is some important information before beginning the module:

  • The module progresses through a series of Next buttons. These buttons do not appear until after the animation and narration is completed for the section.
  • Navigation is enabled through the Table of Contents on the left-hand side of the screen. However, the Table of Contents only makes it possible to revisit previously viewed slides, not skip forward to new, unseen, material. Viewed slides are indicated by checkmarks.
  • Clicking on links within the module will open up a new tab or window.
  • If you are unable to finish the module in one session and need to exit during runtime, then the module does bookmark your place. This makes it possible for you to resume the module in the same section, but only if you restart it on your original viewing device. The module bookmarks your place without using cookies or saving any Personally Identifiable Information (PII).
  • If you would like to see a text version of the narration, then click on the Closed Caption (CC) button on the module playbar.
  • The module generates a personalized certificate upon completion of the activity. This certificate can be printed by clicking on the Print button on the module playbar.

Information, Documentation, and Support

Climate Change Science and Modeling: What You Need to Know, Module 1:

Accessibility Features (pdf)

Narration Script (pdf)

Narration Script with Captioned Screenshots (pdf)

List of Hyperlinks (pdf)

If you would like more information on accessibility features or need other accessibility resources, please contact us at

Climate Change Science and Modeling


Climate Change Science and Modeling: What You Need to Know is the first education module in a series of three. It gives a brief overview of the climate system, greenhouse gases, climate models, current climate change impacts, and future projections. There is a 14-question activity at the end of the module, and users who complete the activity will receive a printable certificate with their name and the date completed. The expected time commitment for this module is about 20 minutes, plus the activity. Time spent exploring the many outward links and interactive features within the module will be at the user's discretion.

Click here to begin the module.

Click to begin


The first education module, Climate Change Science and Modeling: What You Need to Know, is available on a hard-copy CD-ROM. To order a CD copy of the module, please email or fill out the Pacific Northwest Research Station online Publication Request Form and ask for PNW-GTR-902. Anyone is welcome to order copies.


Learning Objectives

By the end of the climate change science and modeling education module, users should know:

  • The difference between weather and climate
  • Main greenhouse gases contributing to climate change
  • How the greenhouse effect works
  • The flow of carbon through the carbon cycle
  • Examples of climate change impacts by region
  • The components of climate models and the uncertainty associated with models
  • Emissions scenarios storylines and representative concentration pathways
  • Examples of projected future climate impacts

The climate change science and modeling activity will help users identify:

  • Historic temperature changes in their region
  • Projected temperature changes by mid-century and the end of the century for their region
  • Current and projected impacts in their region
  • General differences between high and low emissions scenario projections


Information, Documentation, and Support

Climate Change Science and Modeling: What You Need to Know, Module 1:

Accessibility Features (pdf)

Narration Script (pdf)

Narration Script with Captioned Screenshots (pdf)

List of Hyperlinks (pdf)

If you would like more information on accessibility features or need other accessibility resources, please contact us at

Education Resources

(Click any question for details.)

What is climate?

Climate refers to the average meteorological conditions and patterns in a region over a long time period (classically 30 years according to the World Meteorological Organization). These meteorological conditions include measurements such as temperature, precipitation, and wind.

In other words, climate can be described as the 'average weather'. Although weather can change rapidly from day to day and can be difficult to predict, climate is much more predictable. For example, the weather where we live dictates what we wear each day, which can change dramatically from one day to the next. However, the climate influences the type of clothes we have in our closet, which is
generally consistent from year to year.

For more details, see the following resources:

What Factors Determine Earth's Climate? (IPCC 2007, WG1, FAQ 1.1)
What is the Relationship between Climate Change and Weather? (IPCC 2007, WG1, FAQ 1.2)
If You Cannot Predict the Weather Next Month, How Can You Predict Climate for the Coming Decade? ( IPCC 2013, WG1, FAQ 11.1)

What has caused the climate to change in the past?

Climate and climate variability are determined by three main factors (Chapin et al. 2002):

  1. The amount solar energy that reaches Earth. This is affected by changes in the Earth's orbit around the Sun and in the Sun's brightness.
  2. The chemical composition of the atmosphere. For example, changes in the amount of carbon dioxide and other greenhouse gases in the atmosphere affect how much energy (initially received as solar radiation) is trapped by the atmosphere. Energy that is not trapped is re-emitted into space.
  3. The reflectivity of Earth's surface and atmosphere. Surface features, such as ice sheets, increase the amount of solar radiation that is reflected back into space.

These factors and ways that they interact with one another have all contributed to the climate patterns and variability we see in earth's history.

Figure 1 - Changes in Carbon Dioxide and Temperature (US EPA)

However, the fact that climate has changed without human influence in the past does not mean that current climate change is following 'natural' patterns. The factor that best explains the observed global warming over the last century is the increase of CO2 and other greenhouse gases in the atmosphere, largely caused by the burning of fossil fuels and other human activity (IPCC 2013).

For more details, see the following resources:

What Factors Determine Earth's Climate? (IPCC 2007, WG1, FAQ 1.1)
What Caused the Ice Ages and Other Important Climate Changes Before the Industrial Era? (IPCC 2007, WG1, FAQ 6.1)
Is the Current Climate Change Unusual Compared to Earlier Changes in Earth's History? (IPCC 2007, WG1, FAQ 6.2)
Climate is Always Changing, How Do We Determine the Causes of Observed Changes? (IPCC 2013, WG1, FAQ 10.1)
Is Current Warming Natural? (NASA Earth Observatory)

How do we know what climate was like in the past?

The factors that make up climate (such as temperature and precipitation) have been measured directly since the 1860's. However to understand what climate was like before this, scientists have to use 'proxies', or indirect measurements that have a well-defined relationship to temperature or other climatic variables. Some common proxies include:

  1. Ice cores - The ratio of oxygen isotopes in the ice can indicate the temperature at the time the ice was formed. Air bubbles trapped in ice can show what the greenhouse gas concentration of the atmosphere was at the time of formation.
  2. Ocean sediment cores - The remains of small hard-shelled creatures (foramnifera) are preserved in ocean sediments. The composition of their shells can reveal ocean temperatures at the time of their formation.
  3. Pollen records - Fossilized pollen grains can indicate what types of plants were present at the time the fossils were formed.
  4. Tree rings - The width of annual tree rings in temperate climates depend in part on soil moisture and temperature, and can therefore reveal information about these variables.

Past climate is often 'reconstructed' by looking at many of these measurements together. More
examples can be found at the following websites:

NOAA Paleoclimatology - proxy data
National Institute of Water and Atmospheric Research (NZ) - common questions

How do human activities affect climate?

Humans are affecting the climate by increasing the amount of greenhouse gases present in the atmosphere and by changing the surface characteristics of the land (see discussion about "albedo"). Activities such as fossil fuel burning, land-use change (e.g. deforestation), animal husbandry, and practicing fertilizer-dependent agriculture lead to increases in greenhouse gases including carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O). These 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 since 1750 as a result of human activities, and now far exceed pre- industrial values (IPCC 2007, WG1, Ch. 2).

For more details, see the following resources:

How do Human Activities Contribute to Climate Change and How do They Compare with Natural Influences? (IPCC 2007, WG1, FAQ 2.1)
Are the Increases in Atmospheric Carbon Dioxide and Other Greenhouse Gases During the Industrial Era Caused by Human Activities? (IPCC 2007, WG1, FAQ 7.1)

What is the greenhouse effect and what are the major greenhouse gases?

The greenhouse effect is the process by which certain gases in the atmosphere absorb and re-emit energy that would otherwise be lost into space (IPCC 2007, WG1, Ch. 1).

The Earth's transparent atmosphere lets sunlight through to warm the ground and the oceans (more when it is clear, less when it is cloudy). The Earth's warmed surface releases some of that heat in the form of infrared radiation, a form of light, but invisible to human eyes. Greenhouse gases in the atmosphere like carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O), and water vapor, absorb this infrared radiation and keep it from passing out into space. This energy is then reradiated in all directions, and the energy that is directed back toward the Earth's surface warms the planet.

The greenhouse effect is necessary for human survival, since without it the Earth's average temperature would be about 0 C (Swanston et al. 2011). However current concentrations of greenhouse gases are higher now than they have been for the past 800,000 years encompassing the history of human development, and are enhancing the greenhouse effect.

The 'greenhouse effect' gets its name from the fact that a fairly similar process takes place in a greenhouse. The glass panes on a greenhouse let incoming sunlight pass through them, but intercept some of the infrared light on its way back out, warming the interior (Climate Central 2009).

Figure 2 - The Greenhouse Effect: Natural vs. Human Enhanced (Center for Climate and Energy Solutions)

For more details, see the following resources:

What is the Greenhouse Effect? (IPCC 2007, WG1, FAQ 1.3)

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

The factor that best explains the warming trend over the last century is the increase of greenhouse gases in the atmosphere, which are caused by human activity. Scientists have examined many other potential causes of recent warming, such the Sun's variations in brightness, however, the magnitude of these effects is not sufficient to explain actual temperature observations on Earth. Human disruption is simply the only current explanation we have that fits the data (Lean 2009).

Figure 3 - Only Human Influence can Explain Recent Warming (National Climate Assessment, 2014)

Climate models are an important tool for studying all of the various influences on the Earth's climate. These models are constructed to include many different measurements that could affect temperature, including solar output, volcanic emissions, and the effects of greenhouse gas concentrations in the atmosphere. When the effects of increasing levels of greenhouse gases are included in the models, as well as natural external factors, the models produce good simulations of the warming that has occurred over the past century. The models fail to reproduce the observed warming when run using only natural factors (IPCC 2007).

For more details, see the following resources:

How do Human Activities Contribute to Climate Change and How do They Compare with Natural Influences? (IPCC 2007, WG1, FAQ 2.1)
Can the Warming of the 20th Century be Explained by Natural Variability? (IPCC 2007, WG1, FAQ 9.1)
Climate is Always Changing, How Do We Determine the Causes of Observed Changes? (IPCC 2011, WG1, FAQ 10.1)
Is Current Warming Natural? (NASA Earth Observatory)

How is Today's Warming Different from the Past? (NASA Earth Observatory)

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

Global average temperatures are currently increasing at greater rates than those that have occurred over the last million years of Earth's history. Global average temperatures started rapidly rising during the 1900's as the industrial revolution was accelerating and as humans started relying more heavily on burning fossil fuels for energy (see Figure 4).

Figure 4 - Annual Mean Temperature Change (NASA, Goddard Institute for Space Studies)

For the past 100 years, we have clear records of the increasing rate of global temperature change. The decade beginning January 2000 and ending December 2009 was the warmest decade in the modern record (since 1880), with 2010 tied with 2005 as the warmest year on record (NASA 2011). From the 1910s to the 1940s, global average temperatures increased by 0.35 °C, and for an equivalent time period from the 1970s to 2006, global average temperatures increased by 0.55 °C (IPCC 2007), reflecting an increasing rate of change.

The Earth's temperature has undergone some large changes in the past; according to proxy data, global average temperatures did change by as much as 4°C to 7°C between ice ages and warm interglacial periods. However, this change took approximately 5,000 years (IPCC 2007). Current rapid rates of global climate change are clearly very unusual in the context of past changes. More abrupt shifts may have occurred in the past at smaller, regional scales due to ocean heat transport, but did not likely affect the global mean temperature (IPCC 2007).

For more details, see the following resources:

How Are Temperatures on Earth Changing?
Is the Current Climate Change Unusual Compared to Earlier Changes in Earth's History?

How is Today's Warming Different from the Past?

What are albedo and feedback, and how does the Earth's surface affect climate?

Albedo is the reflectance of a surface, such as the earth's surface. Different earth land covers have very different albedo; for example, ice and snow are highly reflective (high albedo) while darker surfaces like vegetation do not reflect as much radiation (low albedo). Albedo plays an important role in global temperature change, since absorbed solar radiation warms the Earth's 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. In the context of global warming, positive feedbacks enhance land surface warming; negative feedbacks enhance land surface cooling.

Albedo is one component of this energy feedback. Since different land covers have varied albedo, land use change can influence albedo and whether a land surface has a warming or cooling effect. As mentioned, snow has a very high albedo because it reflects more sunlight, and thus has a cooling effect on global temperatures (negative feedback). However, if snow melts and is replaced by darker vegetation, more sunlight is absorbed, which will add to a warming effect (positive feedback - IPCC 2007).

An emerging topic of interest related to albedo and feedback is the deposition of black carbon. Black carbon is a component of air pollution and is produced by combustion. It absorbs solar radiation and can greatly lower surface albedo if deposited on snow or ice. Black carbon is now thought to have played a major role in warming in the arctic, mainly by changing albedo and causing a positive warming feedback (Shindell & Faluvegi, 2009).

For a more details, see the following resources

NASA Earth Observatory:

How Much More Will Earth Warm?

Pew Center on Global Climate Change:

What is Black Carbon?

What are examples of climate changes that have occurred over the past century?

Global average surface temperatures have increased by about 0.74°C (1.33°F) between 1906 and 2005 (IPCC 2007), although the rate and magnitude of change differs with location and the period examined. While 0.74°C may not seem like a large temperature change, on a global scale this has huge implications for many of the earth's processes that effect ecosystems and humans. Even with this relatively modest temperature change, clear effects have been observed.

For example, in concurrence with observed temperature changes, in the 20th century there has been a nearly worldwide reduction in glacial mass and extent, a decrease in snow cover in many Northern Hemisphere regions, a decrease in Arctic sea ice thickness and extent, a decrease in the length of river and lake ice seasons, warmer ocean temperatures, and rising sea levels (IPCC 2007).

From 1900 to 2005, long-term changes in precipitation trends have also been observed, leading to wetter conditions in some areas (eastern North and South America, northern Europe, northern and central Asia) and drier in others (the Sahel, southern Africa, the Mediterranean, southern Asia). Widespread increases in heavy precipitation events have been observed, even in places where total precipitation amounts have decreased (IPCC 2007).

See the 'Ecosystem Effects' section of the FAQ's to read more about the implications of these changes.

For more details, see the following resources:

IPCC FAQs (2007):

How are temperatures on earth changing?
How is precipitation changing?
Is the amount of snow and ice on earth decreasing?
Is sea level rising?

US Global Change Research Program:

National Climate Assessment
Regional Factsheets

What do projections suggest for climate changes in the 21st century?

Average global surface temperatures are projected to increase by 1.1 to 6.4°C (2 to 11.5°F) by the end of the 21st century, relative to 1980-1990, with a best estimate of 1.8 to 4.0°C (3.2 to 7.2°F) (IPCC 2007). This large range in projections is due in part to the fact that we do not know whether greenhouse gas emissions will continue at their current levels, increase, or decrease. Temperature projections do vary regionally, with the highest projected warming taking place near the poles (USGCRP 2009). These temperature changes will continue to have effects on ice extent, snow cover, sea level, and many other factors. See the 'Ecosystem Effects' section of the FAQs for more detail.

Precipitation changes over the next century are more complex and uncertain, and differ within regions and subregions. Current models indicate that precipitation will generally increase in higher latitudes and in the tropical Pacific during the monsoon (rainy) seasons, and decrease in the subtropical dry belt. In the U.S. the Southwest is expected to become drier while northern regions may see an increase in precipitation (USGCRP 2009). Overall, the frequency and intensity of extreme weather events, such as heat waves, droughts, storms, heavy downpours, and heavy snowfall are projected to increase.

For more details, see the following resources:

IPCC FAQs (2007):

Do Projected Changes in Climate Vary from Region to Region?

US Global Change Research Program:

National Climate Assessment
Regional Factsheets

How does climate change affect the water cycle (snow, rain, runoff)?

Changing climates affect the water cycle by influencing factors such as surface temperatures & 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). Precipitation patterns are expected to change in ways that are very regionally specific. In the United States, overall precipitation is projected to increase in the north and decrease in the south, while the number of heavy downpours is expected to increase everywhere (USGCRP 2009). In parts of the Midwestern and eastern U.S., earlier snowmelt combined with changing precipitation patterns is expected to produce increased spring flooding and lower summer water levels in rivers, lakes and wetlands (USGCRP 2009).

For more details, see the following resources:


Water Resources and Climate Change
Climate change presentations on Water & Fish management

US Global Change Research Program:

Climate Change Impacts by Sector - Water Resources Sector

How does climate change affect flooding, drought, and severe weather events?

Both Floods and droughts are likely to become more common and more intense as regional and seasonal precipitation patterns change, and rainfall becomes more concentrated into heavy downpours (with longer, hotter dry periods in between) (USGCRP 2009). Changing precipitation patterns, warmer temperatures and higher rates of evapotranspiration are expected in areas such as the Southwestern United States, and will likely lead to increased drought frequency and severity. Overall, the range and extent of drought-affected areas are projected to increase. In addition, an increase in the total frequency of heavy precipitation events is expected to cause more flooding in many areas. Earlier snowmelt and runoff due to warmer temperatures could also lead to increased winter and spring flooding (IPCC 2007, USGCRP 2009). Seasonal temperatures, storms and high winds, and precipitation events may become more extreme and variable than they have been in the past (USGCRP 2009). This could have consequences for species and ecosystems that are not able to recover from the level or frequency of extreme events.

For more details, see the following resources:


Water Resources and Climate Change

IPCC FAQ's (2007):

Are Extreme Events, Like Heat Waves, Droughts or Floods, Expected to Change as the Earth's Climate Changes?

US Global Change Research Program:

Climate Change Impacts by Sector - Water Resources Sector

How does climate change affect fire intensity and frequency?

Warmer and drier spring and summer conditions are currently associated with more numerous fires, greater fire extent, and a longer fire season especially in the Western United States. Warmer spring and summer conditions lead to relatively early snowmelt, lower summer soil and fuel moisture, and thus longer fire seasons; in some areas, the window of time for high fire risk is expected to increase by 10-30% (McKenzie et al. 2011). Increased fire frequency and severity are more difficult to predict, but the interaction of higher temperatures and drier fuels could potentially produce these outcomes. In general, we can expect more large and severe fires at broad scales. (Heyerdahl et al. 2008, McKenzie et al. 2004, Taylor et al. 2008, Westerling et al. 2006).

For more details, see the following resources:


Wildland Fire and Climate Change

Fire Science Digest:

The Fire-Climate Connection [pdf]

What are primary ecological effects of climate change?

Climate is a major determinant of ecosystem structure and processes such as species distribution and abundance, regeneration, vegetation productivity and growth, the timing of biological events (phenology), and disturbances (e.g. insects and fire). With climate change, increasing temperatures and changes in precipitation 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. This effect could be positive for some species, negative for others. Species distributions are likely to shift and ranges may expand for some species and contract for others. Plant and wildlife reproduction will be affected by changes in the timing of flowering, pollinating and breeding events (Parmesan, 2006). Insects and disease outbreaks may become more frequent and widespread because warmer temperatures may accelerate their life cycles (Logan and Powell 2001). Fire extent and frequency will likely increase with higher temperatures and longer fire seasons (McKenzie et al. 2004, Westerling et al. 2006). Increased disturbances may create opportunities for invasive species to become established, and invasive species may also show positive response to increased carbon dioxide levels. In addition to these disruptive effects, forest productivity may increase in some areas due to higher levels of CO2 (CO2 fertilization) as long as water remains available. The duration of the CO2 fertilization effect on ecosystems is not well known; it's effect on individual trees is short-term, since trees acclimatize to CO2 levels over time.

For more details on how climate change will affect specific ecosystem components, see the CCRC collection of Topic Pages.

How did plants and animals respond to climate changes in the past?

Plant and animal species responded to historical climate variability through shifts in geographic range (migration). Evolution, made possible through genetic diversity, also helped species become more adapted to new climates over many generations.

Genetic mechanisms that have allowed species to adapt to historical climate changes include mutation, natural selection, changes in gene flow and breeding patterns, and genetic drift (that is, random effects resulting from changes in population size, isolation, and fragmentation). Over time, species survived where genetic changes resulted in increased adaptation to new climate conditions; others suffered loss of fitness, population extirpation (loss of a population but not entire species), and species extinction.

Plant 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 collectively result in shifts of the species' distribution range. (Davis and Shaw 2001, Delcourt and Delcourt 1991)

The unprecedented rates of climate changes occurring now, combined with habitat fragmentation and land use changes that impede gene flow, pose serious problems for the ability of plants and animals to respond to current climate changes as they have in the past, through evolution and migration (Davis and Shaw 2001).

For more details, see the following resource (CCRC):

Landscape Analysis and Climate Change

How do patterns of land use affect the ability of plants and animals to adapt to climate
change now?

Current land-use patterns, including fragmentation, extensive urban and suburban development, altered fire regimes, vegetation management, and introduction of invasive species, often impede the ability of species to respond to climate change adaptively. 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. 2008). Many land-use changes impose physical barriers that impede species' migration to favorable new environments (e.g. expanded suburban development). However some land-use patterns (e.g. roads, powerline rights-of-way) may assist migration for certain species that can tolerate these environments.

What are examples of responses that U.S. plant and animal species have had to 20th-
century climate change?

Hundreds of studies in the U.S. have already documented species responses to climate change, including changes in phenology (the timing of cyclical changes), range shifts, local extirpations and even some genetic response.

Climate change has altered the phenology of plant and animal species on nearly every continent, meaning that the timing of regular annual species events has changed due to longer and/or earlier growing and breeding seasons. Documented examples include earlier dates observed for plant flowering and bud break, animal emergence from hibernation, breeding, and egg laying for certain species (Parmesan 2006, Cayan 2001). In some cases, changes in phenology lead to a mismatch between species that interact with or depend on one another. For example, in Colorado, marmots have been emerging earlier from hibernation most likely in response to increased air temperatures, but without a corresponding emergence of flowering plants that the marmots need as food (Inouye 2000).

Species distributions have also shifted in response to climate change in the United States. Both animal species such as birds and butterflies (Rodenhouse et al. 2009, Crozier 2004) and plant species (Woodall et al. 2009) have exhibited range shifts northward or the northward movement of their species boundaries. Range constrictions have occurred for some polar and high-elevation species (Parmesan
2006). This has been accompanied by extirpations (local population extinctions) for some species that are dependent on cooler climates, for example pika populations in the mountainous western U.S. (Beever et. Al. 2003).

Although often difficult to separate from other factors, some evolutionary responses to climate change have been documented. These have principally occurred in fast-reproducing insect species, however there is little evidence that genetic shifts will be of the magnitude necessary to avoid extinctions (Parmesan 2006).

For more details on how climate change is affecting specific ecosystem components, see the CCRC collection of Topic Pages.

What are some ways that climate change might affect vegetation in the United States?

It is well understood that changes in climate will affect vegetation productivity and distribution (Ryan et al. 2008). However, site-specific vegetation responses to current climate change are extremely complex and difficult to forecast. Responses will depend primarily on factors that limit plant growth at a particular site, namely temperature and precipitation.

Temperature: With increasing temperatures, species that are limited to lower latitudes or elevations may expand their ranges northward or upward in elevation. In turn, species that are dependent on colder temperatures (e.g. alpine vegetation) may decline or be out-competed. Warmer winters, earlier spring snowmelt, and changing freeze-thaw patterns could each have negative effects on certain plant species. However, increased temperatures can result in longer growing seasons, which have been associated with increased annual productivity. Increases in forest primary productivity can occur with higher temperatures, however this is highly dependent on the availability of water during the proper time in a tree's growing cycle (USGCRP 2009).

Precipitation: Climate change is expected to cause increases in precipitation in some areas and decreases in others. Vegetation responses are complex and depend on both the amount and timing of this precipitation, and how precipitation interacts with increased temperatures. For example, an increase in precipitation during a plant's growing season may have positive implications for plant growth. However increased winter precipitation combined with lower summer precipitation might lead to water stress. Increases in water availability may also be offset by higher temperatures that increase evaporative demand. Though it is difficult to summarize an overall effect on vegetation given these varied complicating factors, a recent report notes:

"If existing trends in precipitation continue, forest productivity will likely decrease in the Interior West, the Southwest, eastern portions of the Southeast, and Alaska. Forest productivity will likely increase in the northeastern United States, the Lake States, and in western portions of the Southeast. An increase in drought events will very likely reduce forest productivity wherever these events occur." (USGCRP 2009)

Disturbances: Disturbances to vegetation and forested ecosystems are expected to increase with climate change. Warmer and drier conditions could lead to increased incidence and severity of wildfire in some areas. Warmer winters can also allow the spread of damaging insect pests (e.g. the bark beetle) that were previously kept in check by consistent cold winter temperatures. An increase in severe weather events would also have strong implications for vegetation distribution and productivity.

What are adaptation and mitigation in a management context?

Adaptation refers to all approaches taken to adjust, prepare for, and accommodate new conditions that are created by changing climates. Adaptations may be cultural and societal, for instance families deciding to purchase flood, fire, or windstorm insurance. For natural-resource managers, adaptation strategies also include actions taken to assist natural resources (species, habitats, forest plantations, watersheds) in accommodating the changes and new conditions imposed by climate (Millar et al. 2008).

In the context of climate change, mitigation is a human intervention or action designed to reduce and reverse the human influence on the climate system, primarily through increased removal of greenhouse gases from the atmosphere, the reduction of greenhouse gas emissions, and the reduction of feedbacks that might enhance warming (Millar et al. 2008).

For more details, see the following resources:

Managing lands under climate change (CCRC)
Adapting to Climate Change: A Short Course for Land Managers (CCRC)

What are examples of adaptation strategies for ecosystems?

There are many adaptation options for managing ecosystems to help them cope with the negative effects of climate change. These can be broadly grouped into three categories:

  1. One set of options promotes resistance to the effects of climate change and strives to improve the defenses of the forest against anticipated changes.
  2. Resilience options accommodate gradual change, usually returning to a prior condition after disturbance.
  3. Options for response intentionally accommodate change and enable ecosystems to adaptively respond and adjust to future conditions.

Management actions for adaptation vary widely, which provides flexibility in tailoring actions tomeet specific management and conservation goals. Having a number of options available in the management "toolbox" can help managers use a combination of traditional management approaches and new practices to improve the ability of ecosystems to adapt to new and often uncertain conditions (Millar et al. 2007).

For more details, see the following resources:

Managing lands under climate change (CCRC)
Adapting to Climate Change: A Short Course for Land Managers (CCRC)
Climate change presentations - Adaptation (CCRC)
Preliminary review of adaptation options for climate-sensitive ecosystems and resources (Climate Change Science Program)
Climate change and forests of the future: Managing in the face of uncertainty (Millar et al. 2007)
Responding to Climate Change: A Toolbox of Management Strategies (Millar 2010)

What are examples of mitigation strategies in forest management?

In a forest management context, examples of mitigation actions can generally be placed into three categories: emissions avoidance, sequestration, and substitution.

  1. Emissions avoidance focuses on maintaining existing carbon storage in trees by avoiding deforestation and reducing potential impacts from catastrophic disturbances, such as wildfire.
  2. Enhancing sequestration encompasses actions such as afforestation (planting trees) and managing forests to increase the amount of carbon stored relative to 'business as usual'.
  3. Substitution describes actions that reduce greenhouse gas emissions by using forest products in the place of fossil fuel intensive products. This would include using renewable forest-derived biofuels for energy instead of fossil fuels, and using wood that will store carbon long-term (e.g., lumber for wood houses) in place of materials that may be more energy-intensive to produce. (Maness 2009)

For more details, see the following resources:

Greenhouse Gas Mitigation Potential in U.S. Forestry and Agriculture (US Environmental Protection Agency)
Forest Management Solutions for Mitigating Climate Change in the United States (Society of American Foresters)
A Synthesis of the Science on Forests and Carbon for U.S. Forests (Ryan et al. 2010)

Are adaptation and mitigation approaches complementary?

Adaptation and mitigation strategies are often considered joint paths - they are optimally combined and integrated (Millar et al. 2008). For example, a fuel-reduction treatment to reduce severe wildfire could be conducted for complementary adaptation and mitigation goals: reducing wildfire protects certain habitats and also averts excess greenhouse gas emissions.

However conflicts between adaptation and mitigation can also occur in forest and ecosystem management situations (Klein et al. 2007). Mitigation options may have negative ecological consequences, and adaptation options may have associated carbon effects; for this reason it is important to assess potential tradeoffs between the two approaches and try to seek strategies that may be complementary (Joyce et al. 2008).

For more details, see the following resources:

Managing lands under climate change (CCRC)
Preliminary review of adaptation options for climate-sensitive ecosystems and resources - see Chapter 3 on National Forests (Climate Change Science Program)

Why should humans help ecosystems adapt rather than allowing them to adapt on their own?

Forests and other ecosystems provide many direct and indirect services for humans and other species, including the provision of wood and fuel, food, temperature and flood regulation, erosion control, recreational and aesthetic value, and species habitat. These ecosystems are facing many cumulative threats due to climate change, which will affect how they function and whether they are able to provide these environmental benefits.

Many ecosystems may be able to survive and adjust to climate changes on their own. However, this is unlikely to happen without severe near-term consequences for current ecosystem structure and the species that depend on this structure, including humans. In the past, plant and animal species have migrated and undergone genetic changes in response to climate change. These responses are now more difficult because of human alteration of the landscape and the rapid rate of climate change. For example, tree migration may not be able keep pace with the current and future rates of climate change (Mohan et al. 2009). Forests could convert to other ecosystems as tree species fail to survive and regenerate, or they could convert to forest types that are less economically, socially, or ecologically valuable than they were before.

Actively assisting in adaptation to climate change may help to maintain the benefits society receives from ecosystems. By doing this, we could avoid future costs and risks that might arise from reacting to climate changes instead of considering them ahead of time (Joyce et al. 2008). Deciding NOT to actively manage an ecosystem is also an option, but one that should be reached after considering the vulnerabilities of an ecosystem and the variety of options available.

A coherent adaptation strategy can help guide forests along a trajectory that will hopefully continue to provide the services that societies consider valuable.

For more details, see the following resources:

Preliminary review of adaptation options for climate-sensitive ecosystems and resources - see Chapter 3 on National Forests (Climate Change Science Program)
Climate Change 101: Adaptation Pew Center Report (Center for Climate and Energy Solutions)

What is assisted migration?

Assisted migration is a 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 are 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 responses and interactions (McLachlan et al. 2007).

How do forests sequester carbon?

Carbon sequestration is the process by which carbon dioxide from the atmosphere is absorbed by trees and plants through photosynthesis, then stored as carbon in biomass such as tree boles, branches, roots, and foliage. Both live and dead plants (e.g., dead wood) contain carbon and are important for carbon sequestration. Significant amounts of carbon are stored belowground in plant roots and in soil. These various components are often referred to as carbon 'pools'. Forests in particular have a strong influence on atmospheric levels of carbon dioxide because trees are long-lived plants and contain significant amounts of biomass compared to other plants.

The rate at which a forest can sequester carbon depends on many factors, including forest age; a young, fast-growing forest may sequester carbon more quickly than an old-growth forest dominated by mature trees. In contrast, an old-growth forest represents an immense amount of stored carbon that is being kept out of the atmosphere despite its slower sequestration rate.

Carbon sequestered in trees and soils can be released back to the atmosphere through processes such as respiration, decomposition, and wildfire.

For more details, see the following resources:

Forests and Carbon Storage (CCRC)
Carbon short course (CCRC)

What are sinks and sources?

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 release over a specified period. Carbon sources release more carbon than they absorb over a specified period. Forests can act as sources or sinks at different times.

How can management increase the amount of carbon sequestered in ecosystems?

Forest management practices can affect both the total carbon storage and 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. In general, certain actions, such as tree planting and keeping forest productivity high, can increase carbon sequestration. Thinning forests may delay large carbon dioxide emissions by reducing the chance of severe wildfire for a certain period of time, but will cause some emissions in the short-term. Other important forest management practices that may affect carbon sequestration include rotation length and fertilization; however, the effects of these activities are not well understood for all forest types.

Management actions that promote increased sequestration may not necessarily be the same strategies that promote carbon storage; it is important to consider each of these within the context of other land management goals. For example, management activities that favor larger, older trees may favor the ongoing storage of carbon contained in those mature trees as opposed to an actual increase in the rate of carbon sequestered.

For more details, see the following resources:

Forests and Carbon Storage(CCRC)
Forest Management Solutions for Mitigating Climate Change in the United States (Society of American Foresters)
A Synthesis of the Science on Forests and Carbon for U.S. Forests (Ryan et al. 2010)

What should land managers be doing to respond to climate change?

Because goals and circumstances across ecosystems are so different, there is no single management solution to climate change. Meeting the diverse challenges that climate change is imposing on National Forests and other environments requires many approaches, and specific responses will depend heavily on the management goals for a particular resource. For this reason, adaptation options can be thought of as tools that are available in a well-supplied toolbox. Each option, or tool, will be selected based on the user's situation, goals, and needs. For example, 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 toolbox from which the manager can choose the best approach to fit the situation at hand (Millar et al. 2007).

For more details, see the following resources:

Managing lands under climate change (CCRC)
Adapting to Climate Change: A Short Course for Land Managers (CCRC)
Climate change presentations - Adaptation (CCRC)
Climate change and forests of the future: Managing in the face of uncertainty (Millar et al. 2007)
Responding to Climate Change: A Toolbox of Management Strategies (Millar 2010)

How can climate change be addressed at scales applicable to current forest management?

This question remains largely unresolved; however, this is a huge area of interest in which new developments occur regularly. Most current information on the effects of climate change is available only for large spatial scales (e.g., global, regional, and subregional), and must be used cautiously when applied to smaller area, such as the forest and stand levels (Janowiak et al. 2011). In addition, uncertainty about future conditions increases at finer spatial scales, and this uncertainty must be considered in the management planning process.

Addressing climate change can be easier to envision 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).

Forest management planning can take deliberate steps to incorporate climate change. Management targets based on historical references (e.g., historical range of variation) and equilibrium conditions (e.g. plant association groups, potential natural vegetation), though traditionally used, will be less relevant as the climate changes. Management approaches and performance standards will need to be adjusted as change occurs (Millar et al. 2007). Planning is more likely to result in successful outcomes if it is consistently based on adaptive management; that is, management by experiment where resource monitoring provides feedback for decision making. Large disturbances and options for post-disturbance management should be included as a normal part of the planning process.

For more details, see the following resources:

Managing lands under climate change (CCRC)
Adapting to Climate Change: A Short Course for Land Managers (CCRC)
Climate change presentations - Adaptation (CCRC)
CCRC collection of Topic Pages (for more details on management options related to specific natural resource issues)
Climate Change Land Management and Project Planning (US Forest Service)


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