Hydrogens use adds heat to the environment and its oxide is the most important greenhouse gas.
Global warming is at least in part a consequence of our increased conversion of carbon and hydrogen to their oxides and our concerns need be with both.
Our appliances/processes add heat to the environment, whether operated from carbon, hydrogen, or photovoltaics.
The work we seek as an aid adds heat to the environment. Power plants, including nuclear power plants, add large quantities of heat to the local environment, often significantly affecting local waters. We're taking water from the ground and putting it into the atmosphere and don't know what the effects will be. Less groundwater for agriculture is one effect.
Water is the most important greenhouse gas and removing it from the atmosphere and storing it in plants and earth can reduce global warming. See solaculture.com