Why Drought Turns Forests from Carbon Sinks into Carbon Sources: The Water-CO2 Tradeoff

Forests are often counted on to absorb about a quarter of human CO2 emissions, but that capacity is not guaranteed. This article from The Conversation explains the biological mechanics behind drought-induced forest carbon losses. When water is scarce, trees close their stomata to conserve moisture, which halts photosynthesis and can lead to embolism, leaf death, and ultimately turning a forest from a net carbon sink into a net carbon source. The piece highlights the 'currency' of water in carbon capture, noting that for every CO2 molecule absorbed, roughly 400 water molecules are lost. It also discusses species-specific drought tolerance and the risk of more frequent droughts under climate change, which could undermine the effectiveness of forest-based climate mitigation strategies. Understanding these dynamics is crucial for accurate carbon accounting and for designing realistic climate policies that do not over-rely on forests as permanent carbon offsets.