In December 2015, 176 nations around the world signed the Paris Agreement, pledging to mitigate climate change by decreasing greenhouse gas emissions and fostering climate resilience. The stated goal of the Paris Agreement is “keeping the increase in global average temperature to well below 2°C above pre-industrial levels,” ideally limiting the increase to 1.5°C.
In a new study, Sanderson et al. reviewed potential global climate trajectories to determine what it would take to achieve the Paris temperature targets.
Although the Paris Agreement has not yet entered into force (and will not until 55 countries accounting for at least 55% of global emissions have officially ratified the agreement), many of the parties have begun working on their official mitigation goals: Intended Nationally Determined Contributions, or INDCs. According to the authors, if short-term emissions are in line with INDCs, net negative emissions would be required later in the century to keep temperature rise under 2°C, even though the technology to remove the necessary amount of greenhouse gases may not be realized by then.
To achieve a stable climate, a balance will likely need to be reached between emissions and carbon dioxide removal, but the need for negative emissions later can be dramatically reduced through rapid emissions reductions in the near future. If the mitigation process begins in earnest in 2020, the researchers found that net emissions would need to reach zero by 2060 to limit global temperature increase to 2°C or by 2043 to limit it to 1.5°C. Allowing 50 extra years for Earth’s temperature to exceed goals and then cool back down increases planning flexibility, but even in an overshoot scenario, rapid mitigation in the near term remains necessary. The later mitigation begins, the fewer plausible scenarios exist that avoid 2°C of warming worldwide, let alone stick to the 1.5°C goal. Every year spent following the limited guidelines currently in place decreases the likelihood of a 1.5°C world. (Geophysical Research Letters, doi:10.1002/2016GL069563, 2016)
—Leah Crane, Freelance Writer