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The tropical peat swamp forests of South‐East Asia are being rapidly converted to agricultural plantations of oil palm and Acacia creating a significant global "hot‐spot" for CO2 emissions. However, the effect of this major perturbation has yet to be quantified in terms of global warming potential (GWP) and the Earth's radiative budget. We used a GWP analysis and an impulse‐response model of radiative forcing to quantify the climate forcing of this shift from a long‐term carbon sink to a net source of greenhouse gases (CO2 and CH4). In the GWP analysis, five tropical peatlands were sinks in terms of their CO2 equivalent fluxes while they remained undisturbed. However, their drainage and conversion to oil palm and Acacia plantations produced a dramatic shift to very strong net CO2‐equivalent sources. The induced losses of peat carbon are ~20× greater than the natural CO2 sequestration rates. In contrast, a radiative forcing model indicates that the magnitude of this shift from a net cooling to warming effect is ultimately related to the size of an individual peatland's carbon pool. The continuous accumulation of carbon in pristine tropical peatlands produced a progressively negative radiative forcing (i.e., cooling) that ranged from −2.1 to −6.7 nW/m2 per hectare peatland by 2010 CE, referenced to zero at the time of peat initiation. Peatland conversion to plantations leads to an immediate shift from negative to positive trend in radiative forcing (i.e., warming). If drainage persists, peak warming ranges from +3.3 to +8.7 nW/m2 per hectare of drained peatland. More importantly, this net warming impact on the Earth's radiation budget will persist for centuries to millennia after all the peat has been oxidized to CO2. This previously unreported and undesirable impact on the Earth's radiative balance provides a scientific rationale for conserving tropical peatlands in their pristine state. Tropical peatlands in South‐East Asia store large amounts of carbon in their peat soils. Widespread conversion of tropical peatlands to agricultural oil palm and pulp plantations entails draining water from the peat soils. These drier soil conditions lead to peat carbon being rapidly released to the atmosphere as carbon dioxide. We calculated the effect of these significant greenhouse gas emissions on the global climate and found that they will contribute to climate warming for several centuries. Reducing drainage of tropical peatlands and restoring drained peatlands will reduce this climate warming impact. [ABSTRACT FROM AUTHOR]

Peatlands have been recognised as globally important carbon sinks over long timescales that produced a global, net-climatic cooling effect over the Holocene. However, little is known about the role of tropical peatlands in the global carbon cycle. We therefore determine the past rates of carbon storage and release in the Indonesian peatlands of Kalimantan and Sumatra - the largest global concentration of tropical peatlands - since 20 ka (kiloannum before present). Using a novel GIS (geographic information system) approach we provide a spatially-explicit reconstruction of peatland expansion in a series of paleogeographic maps. Sea-level change is identified as the principal driver for peatland formation and expansion in western Indonesia as it controls both atmospheric moisture supply and the hydrological gradient on the islands. Initiation of inland peatlands in Kalimantan was coupled to periods of rapid deglacial sea-level rise with rates of over 10 mm yr-1 whereas coastal peatlands could only form after 7 ka when the rate of sea-level rise had slowed to 2.4 mm yr-1. Falling sea levels after 5 ka led to rapid peatland expansion in coastal lowlands and a doubling of the total peatland area in western Indonesia to 131,500 km² between 2.3 ka and 0 ka. As a result of slow peatland expansion from 15 to 6 ka and rapid expansion afterwards the rate of annual carbon storage of all western Indonesian peatlands remained <1 Tg C yr-1 until 6 ka and then increased to 7.2 Tg C yr-1 by 0 ka. Associated with this rise in carbon storage was an exponential growth of the peat carbon pool from 0.01 Pg C by 15 ka to 23.2 Pg C at present, of which 70% is stored in coastal peatlands. In inland Kalimantan peatlands, falling sea levels together with increased El Niño activity induced an annual carbon release of 0.15 Tg C yr-1 from aerobic peat decay since 2 ka. Cumulative carbon losses from anaerobic decomposition do not seem to limit peat bog growth in the tropical peatlands of Indonesia. Carbon losses from Holocene peat fires are only known from the Kutai basin since 4.4 ka with an associated release of 0.1-3.6 Tg C per fire event, which never surpassed the contemporaneous annual C storage. The peatlands of western Indonesia were thus a persistent carbon sink since 15 ka but this sink was of global importance only over the past 2000 years when it likely contributed to a slower growth in atmospheric CO2 concentrations. Currently, annual losses of carbon from peat drainage and fires are on average 28 times higher than the pre-disturbance rate of uptake implying that this carbon reservoir has recently switched from being a net carbon sink to a significant source of atmospheric carbon and is currently in danger of eradication. [ABSTRACT FROM AUTHOR]

Summary Peatlands are the dominant landscape element in many northern watersheds where they can have an important influence on the hydrology of streams. However, the capacity of peatlands to moderate stream flow during critical dry periods remains uncertain partly due to the difficulty of estimating discharge from extensive peat deposits. We therefore used two different approaches to quantify diffuse pore water contributions from peatlands to a creek within a small watershed in Southcentral Alaska. A sensitivity analysis of a water budget for a representative peatland within this watershed showed that a substantial surplus of pore water may remain available for subsequent discharge during a dry period after accounting for water losses to evapotranspiration. These findings were supported by end member mixing analysis (EMMA), which indicated that 55% of the stream flow during a dry period originated from the near-surface layers of peatlands within the watershed. Contributions from peatlands to stream flow in northern coastal regions may therefore provide an important buffer against the potentially harmful effects of changing climatic conditions on commercially important fish species. [ABSTRACT FROM AUTHOR]