The position of the northern boundary of the tropical belt affects the hydroclimate of many arid and semi-arid regions in the Northern Hemisphere. Widening of the tropical belt since the 1970s has largely been attributed to anthropogenic forcing. However, the relative influence of natural drivers of tropical belt expansion and contraction before this time is poorly understood. Here we use data on tree-ring widths from five mid-latitude regions in the Northern Hemisphere to reconstruct the movement of the northern boundary of the early spring tropical belt over the past 800 years (ad 1203–2003). Our reconstruction explains 45% of the interannual variance in the latitudinal extent of the Hadley circulation, a metric of the position of the tropical belt boundary. We find that the tropical belt contracted (expanded) during positive (negative) phases of the El Niño Southern Oscillation and Pacific North American teleconnection patterns. The tropical belt also contracted significantly following major volcanic events that injected sulfur into the stratosphere. The longest period of persistent tropical belt expansion occurred in the late sixteenth century, during one of the coldest periods of the Little Ice Age. Our results warn of potential socio-economic consequences of future variations in tropical belt width driven by natural climate variability or stratospheric aerosol injections, whether volcanic or artificial.

热带带北部边界的位置影响北半球许多干旱和半干旱地区的水文气候。自1970年代以来热带带的扩大在很大程度上归因于人为强迫。然而，在此之前，热带带扩张和收缩的自然驱动因素的相对影响知之甚少。在这里，我们使用来自北半球五个中纬度地区的年轮宽度数据，重建了过去800年中早春热带带北边界的运动（ad1203–2003年）。我们的重建解释了Hadley环流纬度范围内年际变化的45％，这是热带带边界位置的度量。我们发现，热带海带在厄尔尼诺南部涛动和太平洋北美遥相关型的正（负）阶段收缩（扩展）。在发生重大火山事件并将硫注入平流层后，热带带也显着收缩。持续性热带带扩张的最长时期发生在十六世纪末期，当时是小冰期最冷的时期之一。我们的结果警告了自然气候变化或平流层气溶胶注入（无论是火山的还是人工的）驱动的热带带宽度未来变化的潜在社会经济后果。