In the 21st century, critical thinking skills play an important role in facing the challenges of globalization in the world of education; in Indonesia, students' critical thinking skills are still in the low category. Therefore, it is necessary to conduct an initial study to find out an overview of students' essential level of thinking skills. The subjects in this study involved 192 students of class X phase E independent curriculum who were available and willing to be studied, divided into five schools in South Sumatra. Critical thinking skills data uses Ennis indicators packaged as a questionnaire. The data collected were analyzed using descriptive qualitative methods per indicator and the overall average of the indicators. The results of this study show that only one of the five indicators of students' thinking skills shows a high category. For the average critical thinking skills in each school, namely for the first school, the average percentage is 85.30% with a high category; in the second school, the average percentage is 47.38% with a medium category; in the third school, the average percentage is 37.78% with a medium category, the fourth school, the average percentage is 36.66% with a medium category and the fifth school, the average percentage is 29.44% with a low category. Following up on the findings in this study, the critical thinking skills of grade X high school students in South Sumatra on global warming material must be improved. Some solutions to improve students' critical thinking skills are using learning models, learning methods, teaching materials, LKPD, and appropriate technology in the learning process.