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This paper has reviewed many of the studies on fire and climate interactions in the past few decades. The major findings from these studies include:
Wildfire emissions can have remarkable impacts on radiative forcing. Smoke particles reduce overall solar radiation absorbed by the earth-atmosphere at local and/or regional scales during individual fire events or burning seasons. Fire emissions of CO2, on the other hand, are one of the important atmospheric CO2 sources and contribute substantially to the global greenhouse effect.
The radiative forcing of smoke particles can generate significant regional climate effects. It leads to a reduction in surface temperature. Smoke particles mostly suppress cloud and precipitation. Fire events could enhance climate anomalies such as droughts.
Black carbon in smoke particles plays some different roles in affecting radiation and climate. BC could lead to warming in the middle and lower atmosphere, leading to a more stable atmosphere. BC also plays a key role in the smoke-snow feedback mechanism.
Interannual variability in area burned is often related to ENSO and various teleconnection patterns. Unfortunately, climate models are limited in their ability to provide information on potential changes regarding ENSO variability and its interaction
with various teleconnections in North America, which limits our ability to discuss future shifts in fire potential beyond just changes in the mean potential. However, the models are improving in this area and useful seasonal to multi-year projections of ENSO, AMO, etc., are probable in the next few years, which will improve prediction of interannual fire variability. Fires are expected to increase in many regions of the globe
under a changing climate due to the greenhouse effect. Fire potential levels in the US are likely to increase in the Rockies all year long and in the Southeast during summer and fall seasons. Burned areas in the western US could increase by more than 50% by the middle of this century. Many issues remain, which lead to uncertainties in our understanding
of fire-climate interactions. Further studies are needed to begin to reduce these uncertainties. For fire particle emissions, a global picture of all kinds of radiative forcing is needed. It is a challenge considering the significant variability in both space and time scales that characterize smoke emissions, along with the evolution of optical properties as smoke ages, and interactions with atmospheric dynamics and cloud microphysics. Smoke plume height and vertical profiles are important properties for impacts of smoke particles on the atmosphere, including locations of warming layers, stability structure, clouds, and smoke transport. Many simulation studies have been conducted based on assumed profiles. Some recent techniques such as the Multi-angle Imaging SpectroRadiometer (MISR) (e.g., Kahn et al., 2008) could be useful tools to determine these smoke plume properties. BC has received increased attention recently. BC emissions from fires, including emission factors from different fuels, need to be improved. In addition, BC and OC have different optical properties and climate effects. New techniques for measurement, analysis, and modeling are required to help investigate their separate and combined roles. Work remains to be done on the assessment of the greenhouse effects and climate change deriving from fire CO2 emissions. Unlike atmospheric total CO2 concentrations, which have increased relatively steadily since the industrial revolution, fires have significant temporal variability. Fire regimes of a specific region may change dramatically as a result of changes in both climate and human activities. The variability can occur also over a short period. For example, the global carbon emissions in 1998 were 0.8 Pg C yr1 more than the average, but by 2001 they had dropped to 0.4 Pg C yr1 below the average (van der Werf et al., 2010). Thus, it is hard to estimate historical fire CO2 emissions and their impacts. Furthermore, the contribution of wildfire emissions to global atmospheric CO2 increase is more significant over a short period because regrowth of burned lands over a long period will remove some CO2 from the atmosphere. Many indices have been developed to measure fire risk, which is one of the factors for fore occurrence and spread, which is most closely related to climate change. More efforts are needed to build quantitative relationships with actual fire properties such as burned area. Although wildfires occur at local or regional scales,current climate models do not have the capacity to provide consistent and reliable simulation of climate variability at these scales, in particular for precipitation. The risk from mega-fires, which are small probability events and involve complex atmospheric, fuel,and human processes, would become larger under the projected warming climate. Many statistical climate–fire relations and vegetation models have very limited prediction skills for mega-fires. Fuel conditions such as type, loading, and moisture could change at a specific location in response to climate change. They will be also affected by human factors such as urbanization. Comprehensive approaches combining natural and social factors are needed for improving future fire projections. While the strong relationships among atmospheric teleconnection/ SST patterns and wildfire activity are useful for seasonal forecasting applications, their application to climate change scenarios is problematic. Joseph and Nigam (2006) revealed that the climate models used in the IPCC’s Fourth Assessment report currently do a poor job simulating many features of ENSO variability and its interaction with various teleconnections in North America. ENSO-fire relations are valuable for seasonal fire predictions. USDA Forest Service and US National Oceanic and Atmospheric Administration joined research forces recently to develop plans and tools to improve fire weather and climate prediction skills, including exploring the SST-fire relations.
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