Human activities including fossil fuel burning are currently altering the global climate system at rates faster than ever recorded in geologic time. Biomass burning causes carbon dioxide emissions equal to 50% of those from fossil-fuel combustion and so are highly likely to influence future climate change. However, aerosols continue to be one of the least understood aspects of the modern climate system and even less is known about their past influence.
Humans impact fire regimes by changing fire ignition rates, fuels, and land cover. Although fire regimes dramatically alter interactions between the land surface, biosphere and atmosphere, the impact of these fires on the climate system is not clear. Anthropogenic aerosols may have altered the global climate system for thousands of years as suggested by comparing late-Holocene greenhouse-gas (GHG) concentrations in ice cores to those from previous interglacials. The decrease in the spatial extent of forests beginning ~7000 years BP and at ~5000 years BP may be related to early agricultural activity including forest clearance through burning which should leave a quantifiable signal in climate proxies.
We aim to quantify the temporal and spatial changes in Holocene biomass burning in ice and lake core records from seven continents which correspond with centres of the origin of agriculture.
My research group has pioneered a ground-breaking technique for measuring a globally present molecular marker of biomass burning (levoglucosan, 1,6-anhydro-β-D-glucopyranose) in ice cores and lake sediments. We will supplement pyrochemical analyses (levoglucosan, oxalate and PAHs) with palynological evidence of the impact of past fire regimes.
The combination of ice and sediment cores are the only scientific approach to fire history that provides data across all possible time scales and types of information on fire, yet this combination has never been utilized. These fire histories can provide essential insight into the interplay between climate and human activity as well as the role of aerosols through time.
Table 1: The typical spatial and temporal reach of chemical markers and palynological evidence for past fire regimes (modified from Conedera et al., 2009). The orange markers depict high reliability and the yellow markers indicate intermediate reliability. Time periods are: Paleozoic (250-540 Myr); Mesozoic (85-250 Myr); Tertiary (2-65 Myr); Quaternary (15,000 – 2 Myr); Historical period (0-2000 yr).
Figure 1: Locations of ice and lake core records to be analyzed for past biomass burning and evidence of early anthropogenic influence on the climate system. Modified from Diamond, Nature, 2003.