Microscopic charcoal preserved in lake and swamp sediments from 10 sites in Indonesia and Papua New Guinea and from 5 sites in Central and South America have been used to reconstruct long-term fire histories for these two regions. Comparison of these records demonstrates that fire is promoted during periods of rapid climate change and high climate variability, regardless of the presence or absence of humans. Broad synchrony of changes in corrected charcoal values in each region supports an atmospheric transmission of the climate signal via the dominant large-scale atmospheric circulation systems (Walker Circulation) that appears to have persisted since 16,000 cal yr B.P. Altered climate boundary conditions under the influence of changing El Niño-related variability, insolation, sea level, and sea surface temperature all influenced the strength of this connection. Correlation of biomass burning records between the regions tends to increase in the Holocene. The main period of inverse correlation occurs during the Younger Dryas Stade, when extratropical climate most affected the tropics. The strongest correlation between the two regions postdates 5000 cal yr B.P., when El Niño-related variability intensified. Fluctuations in tropical biomass burning are at least partly controlled by orbital forcing (precession), although extratropical climate influences and human activity are also important.