Knowledge of historical fire activity tends to be focused at local to landscape scales with few attempts to examine how local patterns of fire activity scale to global patterns. Generally, fire activity varied globally and continuously since the last glacial maximum (LGM) in response to long-term changes in global climate and shorter-term regional changes in climate, vegetation, and human land use. We have synthesised sedimentary charcoal records of biomass burning since the LGM and present global maps showing changes in fire activity for time slices during the past 21,000 years (as differences in charcoal accumulation values compared to pre-industrial). There is strong broad-scale coherence in fire activity after the LGM, but spatial heterogeneity in the signals increases thereafter. In eastern and western North America and western Europe and southern South America, charcoal records indicate less-than-present fire activity from 21,000 to ~11,000 cal yr BP. In contrast, the tropical latitudes of South America and Africa show greaterthan-present fire activity from ~19,000 to ~17,000 cal yr BP whereas most sites from Indochina and Australia show greater-than-present fire activity from 16,000 to ~13,000 cal yr BP. Many sites indicate greater-than-present or near-present activity during the Holocene with the exception of eastern North America and eastern Asia from 8000 to ~2000 cal yr BP, Indonesia from 11,000 to 4000 cal yr BP, and southern South America from 6000 to 3000 cal yr BP where fire activity was less than present. Regional coherence in the patterns of change in fire activity was evident throughout the postglacial period. These complex patterns can be explained in terms of large-scale climate controls modulated by local changes in vegetation and fuel load.

A mid- to late-Holocene synthesis of fire activity from the Mediterranean basin explores the linkages among fire, climate variability and seasonality through several climatic and ecological transitions. Regional fire histories were created from 36 radiocarbon-dated sedimentary charcoal records, available from the Global Charcoal Database. During the mid-Holocene 'Thermal Maximum' around 7500-4500 cal. BP, charcoal records from the northern Mediterranean suggest an increase in fire while records from the southern Mediterranean indicate a decrease associated with wetter-than-present summers. A North-South partition between 40 degrees and 43 degrees N latitude is apparent in the central and western Mediterranean. Relatively abrupt changes in fire activity are observed c. 5500-5000 cal. BP. Records of Holocene fire activity appear sensitive to both orbitally forced climate changes and shorter-lived excursions which may be related to North Atlantic cold events, possibly modulated by an NAO-like climate mechanism. In cases where human-fire interactions have been documented, the regional coherency between fire occurrence and climate forcing suggests a dominant fire-climate relationship during the early-mid Holocene. The human influence on regional fire activity became increasingly important after c. 4000-3000 cal. BP. Results also suggest that: (1) teleconnections between the Mediterranean area and other climatic regions, in particular the North Atlantic and the low latitudes monsoon areas, influenced past fire activity; (2) gradual forcing, such as changes in orbital parameters, may have triggered abrupt shifts in fire activity; (3) regional fire reconstructions contradict former notions of a gradual (mid-to late-Holocene) aridification of the entire region due to climate and/or human activities and the importance of shorter-term events; (4) Mediterranean fire activity appears hightly sensitive to climate dynamics and thus could be considerably impacted by future climate changes

Summary 1The Early Holocene sediment of a lake at tree line (Gouillé Rion, 2343 m a.s.l.) in the Swiss Central Alps was sampled for plant macrofossils. Thin (0.5 cm) slices, representing time intervals of c . 50 years each from 11 800 to 7800 cal. year  , were analysed and the data compared with independent palaeoclimatic proxies to study vegetational responses to environmental change. 2 Alpine plant communities (e.g. with Salix herbacea ) were established at 11 600-11 500 cal. year  , when oxygen-isotope records showed that temperatures increased by c . 3-4 ° C within decades. Larix decidua trees reached the site at c . 11 350 cal. year  , probably in response to further warming by 1-2 ° C. Forests dominated by L. decidua persisted until 9600 cal. year  , when Pinus cembra became more important. 3 The dominance of Larix decidua for two millennia is explained by dry summer conditions, and possibly low winter temperatures, which favoured it over the late-successional Pinus cembra . Environmental conditions were a result of variations in the earth's orbit, leading to a maximum of summer and a minimum of winter solar radiation. Other heliophilous and drought-adapted species, such as Dryas octopetala and Juniperus nana , could persist in the open L. decidua forests, but were out-competed when the shade-tolerant P. cembra expanded. 4 The relative importance of Larix decidua decreased during periods of diminished solar radiation at 11 100, 10 100 and 9400 cal. year  . Stable concentrations of L. decidua indicate that these percentage oscillations were caused by temporary increases of Pinus cembra , Dryas octopetala and Juniperus nana that can be explained by increases in moisture and/or decreases in summer temperature. 5 The final collapse of Larix decidua at 8400 cal. year  was possibly related to abrupt climatic cooling as a consequence of a large meltwater input to the North Atlantic. Similarly, the temporary exclusion of Pinus cembra from tree line at 10 600-10 200 cal. year  may be related to slowing down of thermohaline circulation at 10 700-10 300 cal. year  . 6 Our results show that tree line vegetation was in dynamic equilibrium with climate, even during periods of extraordinarily rapid climatic change. They also imply that forecasted global warming may trigger rapid upslope movements of the tree line of up to 800 m within a few decades or centuries at most, probably inducing large-scale displacements of plant species as well as irrecoverable biodiversity losses.

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