A new study argues that a singular focus on planting trees will not help in keeping global warming to well below two degrees celsius above the pre-industrial levels. To ensure that global temperature remains under this safe limit, the signatories to the Paris Climate Accord will need to undertake aggressive mitigation measures to reduce emission of greenhouse gases.
The study titled “The limits to global-warming mitigation by terrestrial carbon removal” has been published in Earth’s Future, a journal of the American Geophysical Union.
In a report issued by the Potsdam Institute for Climate Impact Research (PIK), Germany, Lena Boysen, the lead author of the study, has been quoted as saying, “If we continue burning coal and oil the way we do today, the amount of greenhouse gas we need to take out of the atmosphere in order to stabilize the climate will in due time be too huge to manage.”
Plants suck carbon dioxide out of the atmosphere, but this low-tech terrestrial carbon dioxide removal method, the study argues, will need to be combined with high-tech carbon storage mechanisms to ensure that global temperature stay within permissible limits.
The study analyzed the feasibility of a negative emissions approach using biomass plantations and of carbon dioxide removal using global dynamic vegetation computer simulations. Based on their results, they calculate that the number of trees that will need to be planted will be so large that they will eliminate most natural ecosystems around the world or reduce food production to dangerously low levels. The study estimates that more than a quarter of land used for agriculture at present will have to be converted into biomass plantations. This will place global food security at risk.
“Even if we were able to use productive plants such as poplar trees or switchgrass and store 50 percent of the carbon contained in their biomass,” says Boysen in the PIK report, “the business-as-usual scenario of continued, unconstrained fossil fuel use will cause devastating environmental consequences.”
However, the study says that growing biomass soon in well-selected places with increased irrigation or fertilization can support climate policies of rapid and strong emission cuts to achieve climate stabilization below two degrees celsius. “As scientists, we are looking at all possible futures, not just the positive ones,” says Wolfgang Lucht, a co-author of the study. “What happens in the worst case, a widespread disruption and failure of mitigation policies? Will plants allow us to still stabilize climate in emergency mode? The answer is: no. There is no alternative for successful mitigation. Plants can potentially play a limited – but important – role if managed well.”
Even in a scenario of aggressive climate stabilization, the study says, we will need high inputs of water and fertilizer, and a globally applied high-tech carbon-storage machinery that captures more than 75 percent of extracted carbon dioxide to limit warming to around 2°C by 2100. The authors contend that technologies minimizing carbon emissions from cultivation, harvest, transport, conversion of biomass, and the long-term carbon capture and storage (CCS) will be needed to improve at globally to achieve this end.
“So this is a positive message: We know what to do – rapidly ending fossil fuel use complemented by a great variety of CO2 removal techniques. We know when to do it – now. And if we do it, we find it is still possible to avoid the bulk of climate risks by limiting temperature rise to below two degrees celsius,” says Hans Joachim Schellnhuber, the PIK director.