Cumulonimbus Clouds (IMAGE) DOE/Pacific Northwest National Laboratory Caption Under certain conditions, pollution can either strengthen or weaken thunderstorm clouds. PNNL researchers have figured out how to factor the effect into climate models. Credit UCAR/Carlyle Calvin Usage Restrictions Only for noncommercial use, per UCAR's copyright restrictions. License Licensed content Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.