The economy of Pakistan is agrarian. The production system is predominantly irrigated that uses 90% of the available river-water and provides over 80% of agricultural produce. The productive resources of land and water, which are the base for food production, are limited, rather dwindling due, inter alia, to the changing climate. The climate change is exerting pressure on these resources, both directly (e.g. through increased glacier-melt, increased evapotranspiration, increased land-degradation, etc) and indirectly (e.g. via enhancing soil processes, such as, denitrification leading to emission of greenhouse gases, and unavailability of plant-nutrients, increasing crop-water requirements, etc). Not only this, but the frequency and intensity of extreme climate events of floods, drought, cyclones, etc., is on the increase with serious consequences for the standing crops apart from immeasurable damage to life and property. These changes are expected to have significant impacts on food security of the country. Global assessment (projections) of the impact of climate change on agriculture suggests-losses in crop yields, reduction of growing-season length, increased water requirements of crops and decreased irrigation watersupplies as a result of warmer temperatures. This paper presents results of some studies carried out at GCISC with the help of DSSAT-based crop-simulation models (CERES-Wheat and CERES-Rice) on impacts of climate change on the productivity of two major food crops, wheat and rice, of Pakistan. The paper also discusses food-security prospects of Pakistan towards the end of this century in the light of the abovementioned analyses.