Abstract:Aims Assessment of the sensitivity and vulnerability of terrestrial ecosystem to climate change is one of the most important aspects of global change research. Our objective was to develop a new approach to assessing the vulnerability of terrestrial ecosystem using a process-based ecosystem model. Methods We developed a new quantitative approach to assess vulnerability of terrestrial ecosystems based on an ecosystem process model with two aspects: vegetation changes and ecosystem function changes. In accordance with the definition of vulnerability used by the Intergovernmental Panel on Climate Change (IPCC), we used change times and changing direction of vegetation as key indicators of sensitivity and adaptation of vegetation responses to climate change. We also used the function’s annual variability and its trend as indicators of sensitivity and adaptation of ecosystem functions response to climate change, respectively. Based on these indicators, the integrated vulnerability was determined, including assessment under the contemporary climate condition and future climate change scenarios. Important findings The more vulnerable ecosystems were found in the north and west areas of China, with less vulnerable ecosystems mostly in the south and east . The vulnerability of ecosystems would increase with climate change, but the pattern of vulnerability would be little changed by the end of this century, depending on the scenarios. The percentage of non- vulnerable ecosystems would be reduced by about 22%, and the highly and exceedingly vulnerable ecosystems would be reduced by about 1.3% and 0.4%, respectively. Most highly vulnerable ecosystems are distributed in northwestern China, Inner Mongolia, south of the Tibet Plateau and some areas of northern and northeastern China, both under contemporary climate condition and the future climate change scenarios, and they were mainly scattered in transition eco-zones and grassland-desert ecosystems in northwestern China. When investigated regionally, the vulnerability would increase in southern, central, northwestern and southwestern China, but vulnerability would decrease in northern and northeastern China and Inner Mongolia of China.