Both nuclear and renewable energy are needed in the global energy mix to help fight climate change. 

In order to cut down on the share of fossil fuels in the world energy mix, nuclear is necessary. A total of WELL OVER 40% of the world's energy mix for renewable and nuclear energies combined is needed to reach significant greenhouse gas emission reduction targets. Over 40% is not a final goal, but represents a realistic initial goal on the path towards the target of over 70% clean, zero-emission global energy generation.

To achieve a significant GHG emissions reduction target for the planet, the world needs nuclear energy. Nuclear energy is going to have to augment truly environmentally-friendly, renewable energy in the effort to dramatically reduce fossil fuel use.

How much of the world's energy is nuclear?

Nuclear reactors provided 10% of the world's total energy sources, on average annually, during the last decade. 13 countries get at least 1/4 of their energy from nuclear, including France (which gets around 3/4 from nuclear), Belgium, Sweden, Switzerland, and Finland.

Nuclear energy is also put to great use in the US, France, China, Russia, and South Korea, among other countries. Now is probably as good of a time as any in this article to mention a couple of major drawbacks (to put it mildly) of nuclear energy.

Namely the danger- catastrophic disasters due to large-scale accidents like the one at Fukushima, Japan, enrichment of uranium in order to create nuclear weapons, and the difficult, expensive process of securely managing the disposal of nuclear waste.

The former major problems mentioned (and less waste generated by the nuclear process - Gen IV theoretically can just run on spent uranium) are resolved in the 4th generation nuclear reactor designs, discussed below.

Current reactors, mostly Gen I & II nuclear plants, along with several operational Gen III plants, rely on uranium and water (to cool the plants). Therefore, these nuclear plants still deplete water supplies, create nuclear waste, use a fuel source that can be enriched to convert the material into a bomb, and represent a source of potential danger.

The largest nuclear disaster in history was the Chernobyl disaster (although the risk of nuclear disaster is dramatically minimized in a Gen III plant, and eliminated in Gen IV nuclear. Some Gen IV designs dramatically cut the need for water to cool plants, as well).

Here's a brief snippet from the World Nuclear Association summarizing nuclear energy's current role in the global energy mix:

• The first commercial nuclear power stations started operation in the 1950s.
• Nuclear energy now provides about 10% of the world's electricity from about 440 power reactors.
• Nuclear is the world's second largest source of low-carbon power (29% of the total in 2018). 
• Over 50 countries utilise nuclear energy in about 220 research reactors. In addition to research, these reactors are used for the production of medical and industrial isotopes, as well as for training.  FROM  -  https://www.world-nuclear.org/information-library/current-and-future-generation/nuclear-power-in-the-world-today.aspx

Advanced nuclear reactors

Safer, cheaper, still energy abundant and emissions-free designs that use relatively benign energy sources (thorium or depleted uranium), and much less water for cooling the reactor than previous designs and current operational nuclear plants, are being envisioned in 4th generation nuclear, and are currently available in a few 3rd generation nuclear power plant designs.

Using a small fraction of the water as previous designs, Gen IV nuclear plant designs, are safe, cost-effective, environmentally friendly, and still offer tremendous potential for energy production. Molten salt reactors using depleted uranium, nuclear waste from other plants, or thorium as a complete replacement of uranium, are being planned in Gen IV nuclear plant designs. 4th generation designs (and many 3rd generation plants, both planned and operational) are autonomous, smart plants, with heightened safety measures.

Thorium is being looked at as a fuel source for new nuclear reactors, as it is abundant, much less radioactive than uranium, and creates by-products from burning the fuel source that can be used again in the reactor. There is a higher level of thorium than uranium on the planet.

Thorium, as well as depleted uranium, are being designed with relatively lower up-front capital costs. Little manpower is needed to run and maintain future, advanced 4th generation nuclear plants, due to the autonomous computer technology set to be deployed in the plants.

Summation of the benefits of advanced nuclear reactors

Nuclear reactors designed to run on thorium, and depleted uranium, have a very low chance of being used to develop nuclear weapons, produce less radioactive waste, are abundant fuel sources; and are safer, more cost-efficient in addition to being energy-efficient, and cleaner vis-a-vis energy generation compared to current widely deployed nuclear reactors.

Thorium, in particular, is being looked at by developing nations like China and India because of the relatively low cost, increased safety, an abundance of the material, and tremendous energy potential of this energy source. The U.S. has huge amounts of thorium, in places like Kentucky and Idaho (as well as depleted uranium); and there are large quantities in countries like India, Australia, and Brazil.

The U.S., Europe, and even some of the aforementioned developing countries, also have large stockpiles of depleted uranium. More depleted uranium is being produced every day, which would work in many of the 4th generation designs. A few 3rd generation nuclear plants are already operating, and some more are projected to be developed and ready for operation by 2025. 4th Gen nuclear promises to produce abundant, low-cost energy safely, and with little environmental impact.

In order to meet increased demand for low-emission, safer, lower up-front capital investment, high-efficiency energy sources, there has also been an increased global interest in light water small modular nuclear reactors (SMRs). Benefits of nuclear SMRs include-

Small modular reactors offer a lower initial capital investment, greater scalability, and siting flexibility for locations unable to accommodate more traditional larger reactors.  They also have the potential for enhanced safety and security compared to earlier designs. Deployment of advanced SMRs can help drive economic growth. From- USDOE Office of Nuclear Energy

For a comprehensive guide on public policy that increases nuclear energy globally, in order to help fight anthropogenic climate change, please see: Public policy proposal to stabilize greenhouse gas emissions

Please also see:

Renewable energy overview