The occurrence and scale of major fires has been increasing worldwide over the past few decades. In 2016, nearly 565,000 acres of land burned in California alone, and US federal spending on fire suppression in California reached nearly $2 billion. Additionally, burning of forests accounts for about 12% of carbon dioxide emissions and further reduces the potential for forests to uptake carbon dioxide via photosynthesis. The world is struggling to mitigate damage from wildfires, and seemingly contradictory concerns complicate solutions. On the one hand, fire management practices should prevent fires from reaching populated areas because fires destroy infrastructure and crops and even result in loss of life. On the other hand, wildfires are a natural part of the Earth system; they cannot be perfectly contained and often serve an essential restorative function for particular ecosystems. Good fire management balances the immediate risk fires pose to humans against a better understanding of wildfire systems as a whole. A smart approach to fire management ensures that immediate suppression efforts today do not exacerbate future systems (as they did during the US Fire Suppression period from the 1920s to the 1980s). Good fire management necessitates the study of paleofire records to understand what characterizes natural cycles of wildfire and how humans are altering fire regimes. Fires leave behind evidence of their existence in the form of charcoal, the carbon-based residue of a burn. Charcoal from the distant past can be found fossilized within rocks, whereas more recent charcoal is often preserved in loose sediments. By analyzing the quantity and age of charcoal within sediment cores, we can see how fire activity has changed over time. Our class discussed two papers: Bowman et al. (2009) and Marlon et al. (2013), both of which report on fire activity throughout Earth’s history. Since large-scale fires require significant fuel on land and sufficient oxygen in the atmosphere to drive combustion, it is not surprising that fossil charcoal records indicate wildfires started soon after the emergence of terrestrial plants (~ 420 million years ago). Fire activity also depends on local climate. Despite high levels of heat and dryness, deserts tend to have insufficient vegetation for large fires, whereas the most heavily vegetated areas tend to be too humid to promote large fires. As a result, fires are most likely to occur in intermediate conditions, with savannas (e.g., US oak savannas) being ideal ecosystems. The Holocene (11,700 years ago to present) is a particularly illuminating epoch. Extensive charcoal records span this time, and scientists can compare recent fire history to known events in early human history to explore human impacts to the fire system. Several trends emerge from these data. First, human activities (i.e., the growth of organized civilizations and development of agriculture) caused minor increases in fire activity throughout the Holocene, and global and regional climate are generally the dominant drivers of fire. We know this because proxies for ocean temperature, ice sheet extent, and ENSO events are better predictors for overall fire variability than human activities. Even though humans cause about 85% of today’s wildfires, global and regional climate controls the frequency and intensity of fires. Despite improved human capacity to suppress large fires, the past couple of centuries have experienced an unprecedented rapid increase in fire activity. Yet, for the past couple of centuries, humans have been altering the climate beyond natural variation and progression. Climate change caused by increased human carbon dioxide emissions is altering global conditions in dramatic and unpredictable ways, and we are likely to see increased fire activity and damage in spite of our best efforts to take more personal responsibility and directly suppress fires. Effective fire management means not only perfecting our techniques for fighting dangerous fires, but also learning how to adapt to a new climate regime where increased fire may be unavoidable. Comments are closed.
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ArchiveSea Levels: Past, Present and Future
How has El Niño changed in the past? Lessons from paleoclimate archives Paleoclimate into Policy: is there a bright future for learning from the past AuthorsWritten by the members of UC Davis GEL 232: K. Barclay, R. Banker, P. Edwards, C. Fish, K. Hewett, T. Hill, G. Hollyday, C. Livsey, H. Palmer, P. Shukla, D. Vasey. Categories
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