Daybreak and Mount Pinatubo bursts angrily into life again.

It happened on June 15th, 1991 in the north-west of the Philippines.

It was so powerful it produced a gas cloud that reached the stratosphere.

The explosion caused a lot of damage locally, but the cloud itself did something extraordinary.

It lowered the Earth's temperature for four years.

Sulphur dioxide in the cloud created particles which spread around the Earth.

These then reflected some of the sun's rays into space.

Scientists are looking to mimic the effects of this phenomenon to counter global warming.

It's a highly controversial concept known as solar geoengineering.

Climate change is probably the biggest problem humanity faces today.

In the past 25 years the global average temperature has risen by around 0.5°C.

The accumulation of carbon in the atmosphere is warming the Earth up, making more intense hurricanes, rains, higher temperatures.

So far governments have focused on policies for cutting emissions but they keep rising.

The concentration of carbon dioxide in the atmosphere has risen 15% since 1994.

The Paris Agreement, signed by 175 parties in 2016, was a sign that countries were willing to work together to cut emissions.

But not every world leader is on board.

The Paris Climate Accord is simply the latest example of Washington entering into an agreement that disadvantages the United States.

If emissions aren't reduced, what next?

Theoretically solar geoengineering could cool the entire planet.

It's actually potentially incredibly simple because all you need to do is inject a bunch of particles into the stratosphere and there's a number of ways you could do that.

Recently a study out of Yale and Harvard looked at the details of how this would be done.

In that Harvard and Yale study, they imagined building a fleet of planes.

Up to 95 of them.

That would make 60,000 flights a year.

The fleet would spread hundreds of thousands of tonnes of sulphur dioxide into the stratosphere every year.

After 15 years they reckon the world would cool by 0.3°C.

But there are reasons not to do this.

One of the biggest concerns is that it could make governments complacent.

The big worry is that it will be exploited to argue against emissions cuts.

Geoengineering is a supplement to cutting emissions, not a substitute for cutting emissions.

It would also be politically messy.

If the plan is to put a thermostat on the Earth, deciding who has their hand on the dial won't be easy.

For it to have a global effect, you're going to need all governments on board, and that is going to be extremely difficult.

If a country went alone and decided to do it on its own then obviously because the impacts are going to be regional or global, you could create a lot of international tension.

A Swiss proposal to study geoengineering and how it should be regulated was recently put forward at the UN Environment Assembly.

But America and Saudi Arabia opposed the motion.

Possibly because they don't want international regulation of geoengineering.

As things stand, not enough is known about how it could impact the climate or the chemistry of the atmosphere.

There could be unexpected consequences.

You can affect rain patterns and you might cause a region that is already suffering from drought to have even less water.

A lot more basic research both into how we would do it but also what the consequences of it would be if we did it in one way or in another way is needed.

But of course, if we don't do it, there's deep uncertainty about how much climate change we get for a given amount of CO₂ in the air.

Both of those are risky, both are uncertain, the question is which has higher risk?

The politics of solar geoengineering are so complex that it might never happen.

That said, as the world continues to warm the case for exploring radical measures grows stronger.