Last week, politicians and leaders gathered in Glasgow for COP26 to work out policies to address the climate crisis. Because the need for energy is fueling the crisis, it may be tempting to look at the burning sun and wonder if we, too, could achieve nuclear fusion.

For decades, scientists have been attempting to achieve fusion. However, doing so necessitates overcoming a massive number of logistical challenges. Although fusion is a slow-moving science, scientists are getting closer to realizing their dream.

They are focusing their efforts on two types of fusion reactors. One method goes big, attempting to trigger fusion in a room-sized chamber. The other goes small, attempting to do the same in a pin-size pellet. But, in the end, both attempt to replicate what happens in the sun.

Our star generates its immense heat and blinding light by fusing hydrogen atoms, which collide to form helium and an enormous amount of energy. That is what fusion researchers ultimately hope to achieve: if we could create even a pale shadow of a star on Earth, we would have access to enormous amounts of clean energy.

These two approaches appear to be the most promising.

Because of the infernal conditions in its core, the sun can easily fuse hydrogen atoms. Atoms overcome the electromagnetic forces that keep them apart at temperatures of tens of millions of degrees. They combine. This reaction emits no greenhouse gases.

At such temperatures, the atoms lose their electrons and condensate into a scalding soup of electrically charged particles known as plasma. Scientists can manipulate and stir this soup by using electric and magnetic fields.

It is possible to create plasma on Earth. However, this is only the first step. The plasma must then be compressed to sufficiently high densities by physicists. One method is to confine the plasma in a harsh magnetic cage. This is known as magnetic confinement fusion.

The tokamak is the most well-known vessel for this method: a doughnut-shaped chamber about the size of a medium-sized room. The walls of the chamber are lined with powerful magnets that help keep the plasma contained until it reaches the densities required for fusion to begin.

The long-sought goal of fusion is a threshold known as “ignition,” which occurs when the reactor produces more energy than is required to start it—a necessary benchmark to make a fusion power plant viable. Despite the fact that magnetic confinement fusion has been around since the 1950s, no such reactor has come close to that mark thus far.

However, scientists believe that date is approaching. The International Thermonuclear Experimental Reactor, or ITER, is currently under construction in the hills of southern France. It is the world’s largest and most powerful tokamak. Its tokamak will be ten times larger than the largest on the market today. ITER, which has been in the works for more than a decade, hopes to begin operations in 2025. It has been dubbed the most expensive scientific experiment ever.

Another type of reaction was taking place in August 2021, halfway around the world from France. Scientists announced at the National Ignition Facility (NIF) at Lawrence Livermore National Laboratory in California that they had conducted fusion at such a high efficiency that it nearly reached ignition.

In NIF’s successful experiment, there is no tokamak. Instead, NIF employs a reaction known as inertial confinement fusion. This works by jolting a tiny pellet of hydrogen fuel, typically the size of a pinhead, with powerful shockwaves. As the shockwaves pass over the pellet, they compress and broil the hydrogen inside, bringing it to pressures and temperatures high enough to start fusion.

Fusion reactors promise near-limitless power, but they are far from a quick fix for the climate crisis. The August experiment at NIF, for example, relied on a laser that can pulse every few hours. However, Larson believes that in order for an inertial confinement fusion power plant to be commercially viable, the laser must fire every few seconds. NIF intends to upgrade the laser.

ITER, the massive tokamak under construction in France, is only a first step toward making fusion power a reality. Its designers hope that the knowledge gained from ITER will help to improve the next generation of fusion reactors, known as the Demonstration Fusion Power Plant, or DEMO. DEMO, they hope, might be what brings fusion to the people. Those power plants won’t start construction until the 2030s.