Climate change and disruptions to global fire activity

May combine two claims.

By the end of the century, the magnitude and the agreement in direction of change are projected to increase substantially.

“By the end of the century, the magnitude and the agreement in direction of change are projected to increase substantially.”

May combine two claims.

In the near term, decreases in fire activity are less pronounced and concentrated primarily in a few tropical and subtropical biomes.

“In the near term, the most consistent increases in fire activity occur in biomes with already somewhat warm climates; decreases are less pronounced and concentrated primarily in a few tropical and subtropical biomes.”

May combine two claims.

Precipitation of the driest month (16.9%), temperature seasonality (16.8%), and the mean temperature of the warmest month (15.9%) are other important variables in the 'Climate + Baseline NPP' models.

“Precipitation of the driest month (16.9%), temperature seasonality (16.8%), and the mean temperature of the warmest month (15.9%) are other important variables in these models.”

May combine two claims.

The magnitude of change and the degree of agreement among GCMs grows substantially through time.

“However, the magnitude of change and the degree of agreement among GCMs grows substantially through time.”

May combine two claims.

Most of the predicted increase in fire occurs in the higher northern latitudes, although in some regions of central Europe and central North America such changes are projected to be relatively minor.

“Most of the predicted increase occurs in the higher northern latitudes, although in some regions of central Europe and central North America such changes are projected to be relatively minor.”

May combine two claims.

The paper's results suggest a striking increase in fire activity for boreal ecosystems in the more distant future, coherent with other temperature-driven projections.

“Our results suggest a striking increase in fire activity for boreal ecosystems in the more distant future, which is coherent with other temperature-driven projections (Stocks et al. 1998, Flannigan et al. 2005, Balshi et al. 2009).”

• cites Stocks et al. 1998Not checked yet

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• cites Flannigan et al. 2005Not checked yet

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• cites Balshi et al. 2009Not checked yet

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May combine two claims.

In the 'Climate only' models, the mean temperature of the warmest month (27.6%) and annual precipitation (24.0%) are the dominant variables; however, all remaining climatic variables also play a significant role.

“In the ''Climate only'' models, the mean temperature of the warmest month (27.6%) and annual precipitation (24.0%) are the dominant variables; however, all remaining climatic variables also play a significant role.”

May combine two claims.

The modeled global fire probability for the baseline period of 1971-2000 shows complex spatial patterns of fire activity and is largely consistent with observed fire patterns.

“The modeled global fire probability for the baseline period of 1971-2000 shows complex spatial patterns of fire activity (Fig. 4) and is largely consistent with observed fire patterns (Fig. 2A).”

May combine two claims.

The approximated prevalence of fire in this study is 0.56, which equates to a maximum achievable AUC of 0.72.

“The approximated prevalence of fire in this study is 0.56, which equates to a maximum achievable AUC of 0.72.”

May combine two claims.

The uncorrected AUC, averaged for the 100 model replicates and then for the 16 climate models, is 0.67 for the 'Climate + Baseline NPP' models and 0.66 for the 'Climate only' models.

“The uncorrected AUC, averaged for the 100 model replicates and then for the 16 climate models, is 0.67 for the ''Climate þ Baseline NPP'' models and 0.66 for the ''Climate only'' models.”

May combine two claims.

Decreases in fire activity are most extensively projected for the tropical and subtropical savannas of the world, which eventually show agreement for higher temperatures in both warmest and wettest months, increasing temperature seasonality, and less precipitation in the driest month, likely causing greater water stress and lower biomass productivity.

“Decreases in fire activity are most extensively projected for the tropical and subtropical savannas of the world, which eventually show agreement for higher temperatures in both warmest and wettest months, increasing temperature seasonality, and less precipitation in the driest month, likely causing greater water stress and lower biomass productivity.”

May combine two claims.

The world's decreasing fire activity is centered on the equatorial regions, a trend that is amplified through the end of the century.

“In contrast, the world's decreasing fire activity is centered on the equatorial regions, a trend that is amplified through the end of the century.”

May combine two claims.

The paper projects long-term decreases in fire for tropical rainforests due to increasing precipitation, which is notable given that concern in these regions tends to be on future fire increases, particularly through intentional deforestation fires.

“Our projected long-term decreases in fire for tropical rainforests, due to increasing precipitation, are notable given that concern in these regions tends to be on future fire increases, particularly through intentional deforestation fires (e.g., Cochrane et al. 1999, van der Werf et al. 2008, Le Page et al. 2010).”

• cites Cochrane et al. 1999Not checked yet

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• cites van der Werf et al. 2008Not checked yet

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• cites Le Page et al. 2010Not checked yet

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May combine two claims.

Large areas of the globe are expected to experience relatively small near-term changes in fire probability, whereas predicted changes become much more pronounced in the 2070-2099 time period.

“Large areas of the globe are expected to experience relatively small near-term changes in fire probability (yellow areas in Fig. 6A), whereas predicted changes become much more pronounced in the 2070-2099 time period (Fig. 6C).”

May combine two claims.

This general trend is projected to strengthen by the end of the century, with agreement emerging for decreased fire in most other tropical and subtropical biomes.

“This general trend is projected to strengthen by the end of the century, with agreement emerging for decreased fire in most other tropical and subtropical biomes.”

May combine two claims.

Fire data are spatially clustered at the 10% sampling fraction and random below the 1-5% fraction, with the value varying by continent.

“We first divide our point pattern analysis up into continents because of the spatial pattern associated with these landmasses, finding that fire data are spatially clustered at the 10% fraction and random below the 1-5% fraction, with the value varying by continent.”

May combine two claims.

The projections reported here highlight the potential for rapid disruptions in future fire activity, and consensus on such alterations strengthens through time.

“Projections reported here highlight the potential for rapid disruptions in future fire activity, and consensus on such alterations strengthens through time.”

Probably not a substantial claim: may not pass S3 (load-bearing).

The paper's results are most similar to Krawchuk et al. (2009), especially when comparing patterns for the single GCM in their study, which used a different statistical approach but functionally similar variables.

“Our results are most similar to Krawchuk et al. (2009), especially when comparing patterns for the single GCM in their study, which used a different statistical approach but functionally similar variables.”

• cites Krawchuk et al. (2009)Not checked yet

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Probably not a substantial claim: may not pass S3 (load-bearing). May combine two claims.

The B1 scenario represents a lower emissions future, wherein multi-model GCM projections show a median of roughly 1.8°C global surface warming from 2000 levels by 2100.

“The B1 scenario represents a lower emissions future (Nakicenovic et al. 2000), wherein multi-model GCM projections show a median of roughly 1.88C global surface warming from 2000 levels by 2100.”

• cites Nakicenovic et al. 2000Not checked yet

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Classified as probably not a substantial claim. May combine two claims.

Our models are designed to project fire probabilities over a given time period, results that are directly representative of fire frequencies.

“Of the parameters important for characterizing fire regimes-fire sizes, frequencies, intensities, and seasonalityour models are designed to project fire probabilities over a given time period, results that are directly representative of fire frequencies.”

May combine two claims.

The A2 scenario is a mid-to-high emissions future wherein projections show a median increase closer to 3.5°C.

“The A2 scenario is a mid-to-high emissions future wherein projections show a median increase closer to 3.58C.”

• cites Nakicenovic et al. 2000Not checked yet

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May combine two claims.

The fire dataset used in this study spans a shorter time period than the GCM reference period and did not completely overlap.

“The fire dataset used in this study spans a shorter time period (1996)(1997)(1998)(1999)(2000)(2001)(2002)(2003)(2004)(2005)(2006)(2007) than the GCM reference period and did not completely overlap.”

May combine two claims.

Ongoing fire activity requires biomass resources to burn, atmospheric conditions conducive to combustion, and ignitions.

“Ongoing fire activity requires biomass resources to burn, atmospheric conditions conducive to combustion (i.e., dry, hot, and/or windy periods), and ignitions (Bond and van Wilgen 1996, Moritz et al. 2005, Bradstock 2010).”

• cites Bond and van Wilgen 1996Not checked yet

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• cites Moritz et al. 2005Not checked yet

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• cites Bradstock 2010Not checked yet

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Probably not a substantial claim: may not pass S3 (load-bearing). May combine two claims.

Not all fires are detected by ATSR and MODIS sensors; for example, smoldering fires in peatland soils may evade detection.

“Note that not all fires are detected by these sensors; for example, smoldering fires in peatland soils may evade detection.”

May combine two claims.

More precipitation in some warm grasslands and shrublands can lead to higher productivity and increased fire activity during the dry season, whereas in more mesic areas the same precipitation increase could diminish fire activity.

“There is growing evidence that more precipitation in some warm grasslands and shrublands can lead to higher productivity and increased fire activity during the dry season, whereas in more mesic areas the same precipitation increase could diminish fire activity (Meyn et al. 2007, van der Werf et al. 2008, Littell et al. 2009, Krawchuk and Moritz 2011).”

• cites Meyn et al. 2007Not checked yet

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• cites van der Werf et al. 2008Not checked yet

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• cites Littell et al. 2009Not checked yet

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Probably not a substantial claim: may not pass S3 (load-bearing).

Despite screening, some non-vegetation fires are reported in the datasets.

“Conversely, despite the screening, some non-vegetation fires are reported in the datasets.”

May combine two claims.

Warmer and drier weather may increase fire activity in biomass-rich areas, but have the opposite effect in moisture-stressed biomes, as increased evaporative demand decreases growth of biomass necessary to carry fire.

“Warmer and drier weather may therefore increase fire activity in biomass-rich areas, but have the opposite effect in moisturestressed biomes, as increased evaporative de-mand decreases growth of biomass necessary to carry fire (Fig. 1B).”

Probably not a substantial claim: may not pass S3 (load-bearing).

There remains a lack of understanding about how variations among GCMs affect future fire projections versus differences in the modeling approaches themselves.

“Furthermore, because most of these global studies used different GCMs, there remains a lack of understanding about how variations among GCMs affect future fire projections versus differences in the modeling approaches themselves (Littell et al. 2011).”

• cites Littell et al. 2011Not checked yet

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May combine two claims.

With warmer temperatures, substantial tundra areas may become more conducive to plant growth within the next century, and thus fire could rapidly become a novel disturbance there.

“With warmer temperatures, substantial tundra areas may become more conducive to plant growth within this next century, and thus fire could rapidly become a novel disturbance there.”

Classified as probably not a substantial claim. May combine two claims.

The modeling approach is designed to evaluate the strength of chronic environmental constraints on fire's long-term geographic distribution, not specific sets of conditions that lead to a particular fire in a given year.

“The modeling approach is thus not designed to evaluate specific sets of conditions that lead to a particular fire in a given year, but instead to evaluate the strength of chronic environmental constraints on fire's long-term geographic distribution.”

May combine two claims. The quote only partly states this claim.

The settings used (all feature types, default regularization, 10,000 background samples) produced models that represented the observed global fire patterns well but minimized overfitting of the data.

“These settings, in conjunction with the sampling scheme described below, produced models that represented the observed global fire patterns well but minimized overfitting of the data.”

Probably not a substantial claim: may not pass S3 (load-bearing). May combine two claims.

To the authors' knowledge, the potential for widespread climate-driven decreases in future tropical and subtropical fire probabilities is not reported in the published literature, although some studies have shown less extensive but still generally decreasing fire activity for many of these same regions.

“To our knowledge, the potential for widespread climate-driven decreases in future tropical and subtropical fire probabilities is not reported in the published literature, although some studies (e.g., Scholze et al. 2006) have shown less extensive but still generally decreasing fire activity for many of these same regions.”

• cites Scholze et al. 2006Not checked yet

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May combine two claims.

Some areas where fire is not observed in the fire dataset have high predicted fire probabilities, suggesting that they do in fact represent fire-prone environments.

“Some areas where fire is not observed in the fire dataset have high predicted fire probabilities, suggesting that they do in fact represent fire-prone environments.”

May combine two claims.

Any future increases in annual precipitation could exacerbate the trend of increasing fire in some deserts, although some desert areas may also have novel climates in which temperature increases outweigh precipitation increases, leading ultimately to lower productivity and less fire.

“It appears that any future increases in annual precipitation could exacerbate this trend, although some of these desert areas may also have novel climates in which temperature increases will outweigh precipitation increases, leading ultimately to lower productivity and less fire.”

Classified as probably not a substantial claim.

Where fuels are sufficient and atmospheric conditions are conducive to combustion, the potential for ignition during the period of record exists, either by lightning or human causes.

“This implies that, where fuels are sufficient and atmospheric conditions are conducive to combustion, the potential for ignition during the period of record exists, either by lightning or human causes.”

• AssumptionThe authors state this as an assumption: Ignitions do not limit fire activity at the study's coarse spatial and temporal resolution.

Probably not a substantial claim: may not pass S3 (load-bearing). May combine two claims.

It is questionable whether the single variable temperature seasonality is really limiting in the vast savannas of Africa, indicating that MaxEnt MLF results may reflect a surrogate for more precipitation-related constraints there.

“It is questionable, however, whether the single variable temperature seasonality is really ''limiting'' in the vast savannas of Africa, indicating that MaxEnt MLF results may somehow reflect a surrogate for more precipitationrelated constraints there (e.g., Archibald et al. 2009).”

• cites Archibald et al. 2009Not checked yet

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Probably not a substantial claim: may not pass S4 (based).

Removing highly correlated variables greatly enhances the ability to interpret each variable's effect on fire probabilities.

“Removing highly correlated variables also greatly enhances the ability to interpret each variable's effect on fire probabilities.”

May combine two claims.

Although productivity is mainly constrained by precipitation at a global scale, temperature is the dominant control on biomass in many parts of the world.

“Although productivity is mainly constrained by precipitation at a global scale, temperature is the dominant control on biomass in many parts of the world (Beer et al. 2010), a limitation that emerges when NPP is not included in our models.”

• cites Beer et al. 2010Not checked yet

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Classified as probably not a substantial claim.

The final set of five climate variables captures annual trends, seasonality and extreme environmental conditions that provide meaningful approximations of water and energy balances that determine the amount and dryness of biomass and thus fire occurrence.

“These climate metrics capture annual trends, seasonality and extreme environmental conditions that provide meaningful approximations of water and energy balances that determine the amount and dryness of biomass and thus fire occurrence.”

Probably not a substantial claim: may not pass S4 (based).

The coarse spatial scale of the analysis and the use of only one cross-over variable (temperature of the wettest month) should minimize any challenges that future monthly shifts in this variable may pose.

“The coarse spatial scale of our analysis and the use of only one such variable (temperature of the wettest month) should minimize any challenges that future monthly shifts in this variable may pose.”

Probably not a substantial claim: may not pass S3 (load-bearing).

MaxEnt has the flexibility to fit non-linear relationships between fire and independent variables, so that resulting models can encapsulate complex relationships.

“MaxEnt has the flexibility to fit non-linear relationships between response variables (fire) and independent variables (climate and NPP), so that resulting models have the ability to encapsulate complex relationships.”

May combine two claims.

The 2010-2039 'Climate + Baseline NPP' models explicitly specify the current distribution of biomass and are therefore more appropriate for near-term projections in which vegetation patterns are not likely to shift substantially across the 0.5° study cells.

“These ''Climate þ Baseline NPP'' models explicitly specify the current distribution of biomass and are therefore more appropriate for near-term projections in which vegetation patterns are not likely to shift substantially across the 0.58 study cells.”

Probably not a substantial claim: may not pass S3 (load-bearing). May combine two claims.

Although the paper's models achieve high classification accuracies, it has yet to be determined whether incorporating interannual variation would lead to large global improvements or marginal refinements in specific locations.

“Although our models achieve high classification accuracies, it has yet to be determined whether incorporating interannual variation would lead to large global improvements or marginal refinements in specific locations (e.g., Zimmermann et al. 2009).”

• cites Zimmermann et al. 2009Not checked yet

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May combine two claims.

In the only study that used a sizeable ensemble of GCMs to estimate future fire probabilities, the DGVM-based models of Scholze et al. (2006) yielded some predictions (e.g., decreasing fire in some tropical areas) that broadly concur with ours and other patterns (e.g., decreasing fire in boreal regions) that differ considerably.

“In the only study that used a sizeable ensemble of GCMs to estimate future fire probabilities, the DGVM-based models of Scholze et al. (2006) yielded some predictions (e.g., decreasing fire in some tropical areas) that broadly concur with ours and other patterns (e.g., decreasing fire in boreal regions) that differ considerably.”

• cites Scholze et al. (2006)Not checked yet

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Probably not a substantial claim: may not pass S3 (load-bearing).

Some tropical rainforests appear to be less sensitive to such climate fluctuations than others.

“Some tropical rainforests, however, appear to be less sensitive to such climate fluctuations than others (van der Werf et al. 2008).”

• cites van der Werf et al. 2008Not checked yet

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Probably not a substantial claim: may not pass S4 (based).

A key difference in DGVMs is their bottom-up generation of global fire patterns by iteratively simulating fire-climate-vegetation feedbacks that may occur as climates change.

“A key difference in DGVMs is their bottom-up generation of global fire patterns by iteratively simulating fireÀclimateÀvegetation feedbacks that may occur as climates change.”

Probably not a substantial claim: may not pass S3 (load-bearing). May combine two claims.

Model agreement on disruptions to future fire is no guarantee that the majority of GCMs are correct for any given location, but it is encouraging that these GCM-driven predictions show some consensus across large tracts of the globe.

“Model agreement on disruptions to future fire is therefore no guarantee-the majority of GCMs could of course be wrong for any given location-but it is encouraging that these GCM-driven predictions show some consensus across large tracts of the globe.”

Classified as probably not a substantial claim.

Localized human activities such as fire suppression and land development are not explicitly addressed in the paper's study.

“The influence of localized human activities such as fire suppression and land development varies across the globe (Whitlock et al. 2010, Aldersley et al. 2011, Bowman et al. 2011), and these factors are not explicitly addressed in our study.”

Probably not a substantial claim: may not pass S3 (load-bearing). May combine two claims.

The types of variables chosen for modeling future fire activity are affected by global data availability and constrained by the GCMs themselves.

“The types of variables chosen for modeling future fire activity are affected by global data availability and constrained by the GCMs themselves.”

Probably not a substantial claim: may not pass S3 (load-bearing). May combine two claims.

Another DGVM-based study by Gonzalez et al. (2010) used three GCMs and showed yet another outcome: increasing fire across much of the tropics and decreasing fire in many higher latitudes.

“Another DGVM-based study by Gonzalez et al. (2010) used three GCMs and showed yet another outcome: increasing fire across much of the tropics and decreasing fire in many higher latitudes.”

• cites Gonzalez et al. (2010)Not checked yet

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Classified as probably not a substantial claim. May combine two claims.

The paper does not model 'natural' global fire activity, but rather modern fire-with its many human influences-as it currently occurs on Earth and how this may be altered by changing climates.

“We do not model ''natural'' global fire activity, but rather modern fire-with its many human influences-as it currently occurs on Earth and how this may be altered by changing climates.”

May combine two claims.

Abrupt changes in fire will stress native flora and fauna as they adjust to climate change and threaten biodiversity in many conservation areas.

“In addition to impacting terrestrial carbon stocks and human livelihoods, abrupt changes in fire will stress native flora and fauna as they adjust to climate change (Loarie et al. 2009) and threaten biodiversity in many conservation areas (Myers 2006, Nelson andChomitz 2009).”

• cites Loarie et al. 2009Not checked yet

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• cites Myers 2006Not checked yet

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• cites Nelson andChomitz 2009Not checked yet

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Probably not a substantial claim: may not pass S3 (load-bearing).

The influence of localized human activities such as fire suppression and land development varies across the globe.

“The influence of localized human activities such as fire suppression and land development varies across the globe (Whitlock et al. 2010, Aldersley et al. 2011, Bowman et al. 2011), and these factors are not explicitly addressed in our study.”

• cites Whitlock et al. 2010Not checked yet

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• cites Aldersley et al. 2011Not checked yet

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• cites Bowman et al. 2011Not checked yet

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May combine two claims.

There is great uncertainty in the ability of GCMs to represent key modes of interannual variability, and even predicting future climate variability at decadal scales can pose substantial challenges.

“There is great uncertainty in the ability of GCMs to represent key modes of interannual variability (Stoner et al. 2009, Yeh et al. 2009), and even predicting future climate variability at decadal scales can pose substantial challenges (Solomon et al. 2011).”

• cites Stoner et al. 2009Not checked yet

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• cites Yeh et al. 2009Not checked yet

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• cites Solomon et al. 2011Not checked yet

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Probably not a substantial claim: may not pass S3 (load-bearing), S4 (based). May combine two claims.

Humans are not minor players with respect to global fire activity, and their influence on global fire regimes is more than likely to increase in the future through population growth and more accelerated land cover change.

“Humans are not minor players with respect to global fire activity: their influence on global fire regimes is more than likely to increase in the future through population growth and more accelerated land cover change.”

Probably not a substantial claim: may not pass S3 (load-bearing), S4 (based).

Divergent projections may also be due to differences in the environmental variables chosen to drive fire activity now and in the future.

“Divergent projections may also be due to differences in the environmental variables chosen to drive fire activity now and in the future.”

May combine two claims.

Liu et al. (2010) used four GCMs and characterized drought-driven effects on the severity of the fire season, predicting almost opposite fire patterns to those reported here.

“In contrast, Liu et al. (2010) used four GCMs and characterized drought-driven effects on the severity of the fire season, predicting almost opposite fire patterns to those reported here.”

• cites Liu et al. (2010)Not checked yet

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Probably not a substantial claim: may not pass S3 (load-bearing).

The predicted future fire activity from Pechony and Shindell (2010), who used one GCM and a process-based fire module suitable for use in a DGVM, broadly agree with those of the paper's study.

“Interestingly, the predicted future fire activity from Pechony and Shindell (2010), who used one GCM and a process-based fire module suitable for use in a DGVM, broadly agree with those of our study.”

• cites Pechony and Shindell (2010)Not checked yet

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Probably not a substantial claim: may not pass S3 (load-bearing), S4 (based).

Based on the few global projections published to date, it is difficult to attribute differences among future fire predictions primarily to modeling strategies, variable types, prediction resolution, or choice of GCMs.

“Based on the few global projections published to date, it is difficult to attribute differences among future fire predictions primarily to modeling strategies, variable types, prediction resolution, or choice of GCMs.”

Probably not a substantial claim: may not pass S3 (load-bearing), S4 (based). May combine two claims.

Greater climatic extremes, especially precipitation fluctuations, can promote increased fire activity in chronically wet locations (e.g., drought in tropical rainforests) and chronically dry locations (e.g., precipitation pulses in deserts).

“Greater climatic extremes, especially precipitation fluctuations, can promote increased fire activity in chronically wet locations (e.g., drought in tropical rainforests) and chronically dry locations (e.g., precipitation pulses in deserts) (Fig. 1B).”

May combine two claims.

Reductions in fire as a key ecological disturbance may have important trickle-down effects in many fire-prone regions, and longer fire intervals could conceivably make some areas more vulnerable to catastrophic wildfires over time.

“Although sharp decreases in fire activity are less likely to capture our attention, reductions in this key ecological disturbance may have important trickle-down effects in many fire-prone regions (Bond andvan Wilgen 1996, Krawchuk et al. 2009), and longer fire intervals could conceivably make some areas more vulnerable to catastrophic wildfires over time.”

• cites Bond andvan Wilgen 1996Not checked yet

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• cites Krawchuk et al. 2009Not checked yet

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