Quantifying the Human Cost of Global Warming (Data)

<strong>The costs of climate change are often estimated in monetary terms but this raises ethical issues. Here we express them in terms of numbers of people left outside the ‘human climate niche’ – defined as the historically highly-conserved distribution of relative human population density with respect to mean annual temperature (MAT). We show that climate change has already put ~9% of people (&gt;600 million) outside this niche. By end-of-century (2080-2100),</strong> <strong>current policies leading to around 2.7 °C global warming could leave one third (22-39%) of people outside the niche. Reducing global warming from 2.7 to 1.5 °C results in a ~5-fold decrease in the population exposed to unprecedented heat (MAT ≥29 °C). The lifetime emissions of ~3.5 global average citizens today (or ~1.2 average US citizens) expose 1 future person to unprecedented heat by end-of-century. That person comes from a place where emissions today are around half of the global average. These results highlight the need for more decisive policy action to limit the human costs and inequities of climate change.</strong>气候变化的代价通常以货币形式进行估算，但这一做法引发了诸多伦理争议。本研究以脱离「人类气候生态位（human climate niche）」的人口数量来衡量气候变化代价——该生态位被定义为历史上高度稳定的、对应年平均气温（mean annual temperature, MAT）的相对人口密度分布格局。研究表明，气候变化已使约9%的人口（超过6亿人）脱离该生态位。到本世纪末（2080-2100年），若维持当前政策路径，全球升温幅度将达到约2.7℃，届时将有三分之一（22%~39%）的人口脱离该生态位。若将全球升温幅度从2.7℃降至1.5℃，暴露于史无前例高温（年平均气温≥29℃，MAT≥29℃）中的人口数量将减少约5倍。当前，每3.5名全球人均排放水平的公民一生的总排放量，将使到本世纪末的1名未来人口暴露于史无前例的高温环境中；若以美国人均排放水平计算，则仅需1.2名公民即可达到同等效果。该未来人口所处区域的当前排放量约为全球平均水平的一半。上述研究结果凸显了采取更果断政策行动的必要性，以遏制气候变化带来的人类代价与不公平现象。