Bill Gates published a blog post in which he reflected on the last 12 months and shared his thoughts about the year to come.

In the post, Gates said he believes the US must spend more on nuclear energy research in order to regain its global leadership leadership in that area.

Burning fossil fuels causes global temperatures to rise. Renewable energy sources don't emit the same heat-trapping gases, but Gates said breakthroughs in solar and wind energy won't be enough.

Gates and other billionaires lead a fund called Breakthrough Energy Ventures that invests in startups focusing on clean energy.

Bill Gates is urging the United States to invest in nuclear power research.

In his annual year-in-review Gates Notes blog post, Gates noted that, despite the consequences of climate change that people face around the globe, "global emissions of greenhouse gases went up in 2018."

Because burning fossil fuels (oil, coal, and natural gas) releases carbon dioxide and other heat-trapping gases into the atmosphere, Gates wrote that we need breakthroughs in clean energy in order to curb the rise of global temperatures. Generating energy from sunlight and wind does not emit CO2; the same goes for nuclear energy.

"The world needs to be working on lots of solutions to stop climate change," Gates wrote. "Advanced nuclear is one, and I hope to persuade US leaders to get into the game."

According to the Intergovernmental Panel on Climate Change, the world will face catastrophic effects of climate change if global temperatures climb to 1.5 degrees Celsius above pre-industrial levels. We are on track to hit that 1.5-degree threshold by 2040, though the IPCC said a huge shift in global energy and economic systems could still reverse the trend.

Read more: The scariest parts of the new climate change report: The goals the world set are inadequate, and the track we're on is disastrous

Solar and wind energy are becoming much cheaper — which Gates said he was "glad to see" — but he wrote that these energy sources alone are not enough. That's because solar and wind energy are not viable when the sun doesn't shine or the wind doesn't blow. Nuclear power, on the other hand, is available 24 hours a day.

This is not the first time Gates has sought to improve the world's energy options. Gates, along with Amazon CEO Jeff Bezos and other billionaires, leads a fund called Breakthrough Energy Ventures that invests in startups that focus on renewable energy. In 2018, the group announced the first companies to get that funding.

"The companies we chose are run by brilliant people and show a lot of promise for taking innovative clean-energy ideas out of the lab and getting them to market," Gates wrote in his end-of-year note.

As far as nuclear power is concerned, Gates said he is confident that further innovation can eliminate concerns about the risk of accidents.

"The United States is uniquely suited to create these advances with its world-class scientists, entrepreneurs, and investment capital," he wrote. "Unfortunately, America is no longer the global leader on nuclear energy that it was 50 years ago. To regain this position, it will need to commit new funding, update regulations, and show investors that it’s serious."

As an example of a promising approach to nuclear energy, Gates pointed to the company TerraPower that he started 10 years ago. TerraPower is working on creating a traveling-wave reactor, which Gates said is safe, produces minimal waste, and can't be used in nuclear weapon production.

A TerraPower facility. TerraPower

TerraPower was trying to building a pilot project in China, Gates wrote, but recent moves by the Trump administration have "made that unlikely."

Gates said there may be a chance for the project to move forward in the US. But regardless, he plans to continue drawing more attention to energy issues in 2019.

"Next year I will speak out more about how the US needs to regain its leading role in nuclear power research," Gates wrote.