Zickfeld Kirsten, Solomon Susan, Gilford Daniel M
Department of Geography, Simon Fraser University, Burnaby, BC, Canada V5A 1S6;
Department of Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, MA 02139-4307
Proc Natl Acad Sci U S A. 2017 Jan 24;114(4):657-662. doi: 10.1073/pnas.1612066114. Epub 2017 Jan 9.
Mitigation of anthropogenic greenhouse gases with short lifetimes (order of a year to decades) can contribute to limiting warming, but less attention has been paid to their impacts on longer-term sea-level rise. We show that short-lived greenhouse gases contribute to sea-level rise through thermal expansion (TSLR) over much longer time scales than their atmospheric lifetimes. For example, at least half of the TSLR due to increases in methane is expected to remain present for more than 200 y, even if anthropogenic emissions cease altogether, despite the 10-y atmospheric lifetime of this gas. Chlorofluorocarbons and hydrochlorofluorocarbons have already been phased out under the Montreal Protocol due to concerns about ozone depletion and provide an illustration of how emission reductions avoid multiple centuries of future TSLR. We examine the "world avoided" by the Montreal Protocol by showing that if these gases had instead been eliminated in 2050, additional TSLR of up to about 14 cm would be expected in the 21st century, with continuing contributions lasting more than 500 y. Emissions of the hydrofluorocarbon substitutes in the next half-century would also contribute to centuries of future TSLR. Consideration of the time scales of reversibility of TSLR due to short-lived substances provides insights into physical processes: sea-level rise is often assumed to follow air temperature, but this assumption holds only for TSLR when temperatures are increasing. We present a more complete formulation that is accurate even when atmospheric temperatures are stable or decreasing due to reductions in short-lived gases or net radiative forcing.
减少寿命较短（从一年到几十年不等）的人为温室气体排放有助于限制气候变暖，但人们对其对长期海平面上升的影响关注较少。我们发现，短寿命温室气体通过热膨胀导致海平面上升（热膨胀海平面上升），其影响的时间尺度比这些气体在大气中的寿命长得多。例如，即使人为甲烷排放完全停止，由于甲烷增加导致的热膨胀海平面上升中至少一半预计仍将持续200多年，尽管这种气体在大气中的寿命仅为10年。由于担心臭氧层损耗，氯氟烃和氢氯氟烃已根据《蒙特利尔议定书》逐步淘汰，这说明了减排如何避免未来多个世纪的热膨胀海平面上升。我们通过表明如果这些气体在2050年才被淘汰，21世纪预计额外的热膨胀海平面上升将高达约14厘米，且持续影响将持续超过500年，来研究《蒙特利尔议定书》所避免的情况。未来半个世纪氢氟烃替代品的排放也将导致未来几个世纪的热膨胀海平面上升。考虑短寿命物质导致的热膨胀海平面上升的可逆时间尺度，有助于深入了解物理过程：人们通常认为海平面上升与气温变化同步，但这种假设仅在气温上升时的热膨胀海平面上升中成立。我们提出了一个更完整的公式，即使在由于短寿命气体减少或净辐射强迫导致大气温度稳定或下降时，该公式也能准确适用。
