This paper examines the potential for hydrogen to address the long-term challenges of global climate change by reducing the accelerating increase of CO2 and other greenhouse gases in the earth's atmosphere. A long-term analysis (through the year 2095) was conducted to evaluate the potential development pathways for hydrogen-based systems and related infrastructure and the dynamics of deployment within an integrated global energy system. The potential impacts on greenhouse gas emissions over time for alternative deployment pathways were then compared. The analysis was conducted using the PNNL integrated assessment modeling system (MiniCAM), a long-term, global, market equilibrium model of energy, agriculture, land-use, and economy interactions. The MiniCAM draws on a variety of scientific disciplines to assess various climate change policies and technology strategies and impacts over long time scales, and provides the ability to evaluate alternatives for hydrogen production, storage and distribution, and end use within the context of competing energy options (eg, fossil fuels). Because the biggest impact of hydrogen system research will be experienced in the long-term (the next 25 to 50 or more years) it is important that an analysis of this emerging technology base be conducted within the context of a long-term model that can effectively address the dynamics of technological evolution and economic shifts over decades. The results of our research quantify the potential impacts of hydrogen on greenhouse gas emissions both in the long term and over a transitional period of deployment. We find that the competitive deployment of hydrogen systems and their influence on greenhouse gas emissions in the atmosphere are highly dependent on the success of R&D investments being made today and in the next few decades on hydrogen system technologies ranging from production to transport to storage to end-use.