Hydrogen production doesn't generate greenhouse gas emissions.

 Burning hydrogen can produce nitrogen oxides (NOx), which are hazardous air pollutants: 

Nitrogen oxides

NOx is created when air is exposed to high temperatures, which can happen during the combustion of hydrogen. NOx can include nitric oxide (NO) and nitrogen dioxide (NO2). 

Health impacts

NOx is linked to smog, acid rain, and health issues like asthma and respiratory infections. 

Emissions per unit of heat

Hydrogen can produce more NOx per unit of heat generated than most fossil fuels. 

Comparison to methane

Burning hydrogen can produce up to six times more NO than methane. 

However, there are ways to reduce NOx emissions from hydrogen combustion, including: 

Using a higher ratio of air to fuel 

Lowering the temperature at which the hydrogen is burned 

Using existing exhaust aftertreatment technologies 

Hydrogen has some benefits over hydrocarbon fuels like gasoline, diesel, and ethanol: It produces lower emissions of particulate matter and It eliminates carbon monoxide. 

Hydrogen production doesn't generate greenhouse gas emissions.