The leading culprit for carbon emissions in the travel sector is the shipping and freight industry. We could have a fission reactor that is relatively safe on every boat like the military does with subs, but you'd need a highly trained nuclear physicist on each boat to handle that correctly.

According to this awesome chart, it's quite clear that it is the energy sector producing the largest amount of CO2. If Fusion reactors are a required means of producing grid energy, then our travel emissions will be easily balanced out naturally, especially if we can require reactors on freighters and large ocean transport since I believe that is about 3% of total world emissions and a good chunk of travel emissions.

Plus with battery cars like Tesla getting more popular, consumer emissions will continue to shrink.

The problem with fission reactors is that while they are safe, people don't want them in their backyard and a lot of regulations get in their way. They also need extra cost fortification when compared to other power sources and startup is difficult. Plus with Fukushima, almost everyone has realized that the "Black swan" phenomenon is not so unlikely. They also have a long term cost of radioactive waste and storage or recycling.

Fusion byproducts are not very dangerous. It's only bottlenecks will be dealing with corporate interests that are not aligned with companies producing fusion (and increase cost of startup or bad press, etc.) and scalability/distribution of the reactors. 10 years to get to market another 5 or ten to scale and we have reduced all our carbon emissions form the energy sector. This is one reason why I'm not worried about global warming. It is not a doomsday scenario at all.