What causes sea level rise?

The two major causes of global mean sea level rise are the expansion of ocean water as it warms (thermal expansion) and the added water from land-based ice (e.g., mountain glaciers and ice sheets) as it melts. Both of these processes are driven by increased global temperatures that are associated with greenhouse gas emissions from human activities. At a local level, any vertical land motion that may be occurring — from either natural or anthropogenic factors — can cause changes in ‘relative sea level.’

For more details, see the Global Sea Level Rise section of Sea Level 101.