Original sentence: Thousands of climate researchers around the world use climate models to understand the climate system, and publish thousands of papers about this in peer reviewed journals - and a part of this research is work improving the models
Edited sentence: Improvement has been difficult, and progress has sometimes led to discovering new uncertainties.There are thousands of papers published about model-based studies in peer reviewed journals - and a part of this research is work improving the models.Thousands of climate researchers around the world use climate models to understand the climate system, because we don't yet understand climate