estuvieron disminuyendo
-they/you were reducing
Pretérito progresivo para el sujetoellos/ellas/ustedesdel verbodisminuir.

disminuir

Hay buena evidencia que las temperaturas globales han estado ascendiendo lentamente durante los cuatro siglos pasados y estuvieron disminuyendo lentamente durante muchos siglos antes de eso.
There is good evidence that global temperatures have been slowly climbing for the past four centuries and were slowly declining for many centuries prior to that.
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