The term "primary driver of climate" refers to a factor or set of factors that have the most significant impact on the overall state and changes in Earth's climate. In other words, it is the main force behind the current trends and variations observed in global temperature, precipitation patterns, and other climatic variables.
The primary drivers of climate can vary over time due to natural fluctuations or human activities that alter the composition of the atmosphere, such as greenhouse gas emissions from burning fossil fuels. Currently, the most significant driver of climate change is the increase in atmospheric concentrations of carbon dioxide and other heat-trapping gases, which are largely a result of human activity.
Other factors that can influence climate include changes in solar radiation, volcanic eruptions, variations in Earth's orbit, and natural cycles such as El Niño Southern Oscillation (ENSO). However, these factors typically have less impact on the overall state of the climate compared to greenhouse gas emissions.
In summary, the "primary driver of climate" refers to the main force or forces that are currently driving significant changes in Earth's climate, with human-caused greenhouse gas emissions being the most important factor today.