## 5 Tropical Deforestation and Carbon Emissions  
Tropical forests are great carbon sinks. Around 10% of the global carbon emissions are added through the degradation and deforestation of tropical forests [114] and a net loss of 1.0 PgC stock per year from 2000 to 2010 [105]. It is important to understand the changes in the AGB of tropical forests for their significant role in climate change mitigation policies to increase net carbon sink under REDD+ initiatives. The Intergovernmental Panel on Climate Change (IPCC) has devised a default rate of change in AGB in tropics, which is based on the outcome from several studies. This net rate of change in AGB does not account for the age of forests considered given that, in tropical areas, the forest is re-growing and much of the tropical forests can be classified as secondary forest. The authors of [155] have updated the estimates of the rate of change in AGB in tropical countries using field inventory data from 176 plots in secondary and 536 plots in primary tropical forests. However, these rates are spatially constrained and do not imply across the tropics. Therefore, remote-sensing-based upscaled and spatially continuous estimates of carbon density changes in tropical forests are required for the monitoring and understanding of gains and losses in the AGB. Conventional remote sensing approaches rely on forest cover change integrated with forest density. For example, [PERSON] et al. [4] used forestry inventory data and country-level remote-sensing-based ecosystem carbon studies, for 1999 to 2007, to estimate annual rates of net carbon emission (2.9 PgC) and sink (2.8 PgC) from tropical forests. A similar rate of emission, 1.0 Pg carbon stock per year from 2000 to 2010, is reported by [PERSON] et al. [105] due to deforestation and degradation in tropical areas. In another study, the gross rate of carbon emission from tropical areas is estimated to be 0.81 PgC during 2000 to 2005, using a combination of field plot data and multi-sensor remote sensing images of MODIS, Landsat ETM+ and LiDAR [92]. In recent years, a combination of optical and airborne LiDAR datasets has emerged as a common practice among scientists to estimate aboveground carbon stocks in tropical forests. Many other significant studies applied remote sensing techniques to estimate pan-tropical carbon losses and gains [156; 157; 158; 155]. Recently, a pan-tropical quantification of the net change in carbon density of tropical woody vegetation has been made [159]. Primarily, this study is based on field inventory data, LiDAR measurements and pan-tropical MODIS images spanning over 12 years (from2003 to 2014). It is revealed that the tropical forests are a source of CO\({}_{2}\) with an annual release rate of 0.425 PgC. Moreover, 30 m Landsat-based maps of tree cover percentage [67] were used to distinguish carbon losses from forest cover loss and degradation/deforestation. Overall, carbon is sequestrated at an annual rate of 0.436 Pg, while deforestation and degradation of tropical forests have released 0.861 Pg of carbon per year. In contrast to this, a few studies found that the tropical forest is a net sink of carbon, absorbing carbon at a net annual rate of 1.4 PgC [7]. A recent study by [PERSON] et al. (2020) [160] found asynchronous patterns of carbon sinks in the tropics. The African tropical forest and Amazonian forest both showed an unparallel increase in carbon loses. Carbon sinks in intact African tropical forests have been stable for the past three decades, until 2015, as compared to a continuous decline in Amazonian forests' carbon sink. This difference is largely due to the increasing tree mortality in Amazon forests. Both continents showed an increase in tree growth. However, since 2010, an increase in carbon losses in African forests has been observed, indicating saturation of the carbon sink potential of intact old-growth tropical forests in Africa. An overall global carbon sink is increasing with a greater increase in the Northern Hemisphere [160].