The big red button: Which world leaders have access to nuclear codes?

Following the storming of US Capitol Hill on Wednesday, US President Donald Trump could be impeached for the second time for his role in encouraging crowds of his supporters that stormed the sitting place of the US federal government's legislative branch.

There have been calls for taking away the nuclear warhead access codes from Trump as well given his recent behavior. Speaker of the United States House of Representatives Pelosi on Friday revealed in a letter that she had spoken to the top United States military commander Mark Milley about taking precautions to ensure Republican President Donald Trump cannot initiate hostilities or order a nuclear attack in his remaining 12 days in office.

Pelosi said in the letter she discussed "available precautions for preventing an unstable president from initiating military hostilities or accessing the launch codes and ordering a nuclear strike" with Gen. Milley.

"The situation of this unhinged president could not be more dangerous, and we must do everything that we can to protect the American people from his unbalanced assault on our country and our democracy," Pelosi said.

According to the Federation of American Scientists (FAS) presently there are an estimated 13,410 nuclear warheads in the world, with the US and Russia accounting for nearly 90% of the world's nuclear arsenal.

It would take just three nuclear warheads to destroy one of the planet's 4,500 cities. If all the nukes in the world are put together and detonated, it would unleash an explosion with the force of 3 billion tons of TNT - equivalent to 15 Krakatoa 1883 eruptions, the most powerful volcanic eruption on record.

The massive explosion would trigger a 50-kilometer fireball that would destroy all within a 3,000-kilometer radius of the blast. This would generate a series of pressure waves that would circle the world in the following weeks. Meanwhile, a mushroom cloud would extend to the upper levels of the Earth's atmosphere and millions of tons of incinerated material would be catapulted into the skies.

Nuclear attack by any country would be met with serious retaliation – triggering a chain of events that may very well turn into a world war, and millions dead within moments, taking the dead count to billions within a few days. Therefore, for a person like Donald Trump and given his recent behavior, to have nuke codes can be devastating.

During his tenure as the US president, Trump has boasted about nuclear power and his easy access to it. The concern from the US lawmakers regarding Trump's access to Gold Codes is understandable. The Gold Codes are the launch codes for nuclear weapons provided to the Presidents of the United States in their role as Commander-in-Chief of the United States armed forces.

This raises the question, which world-leaders have access to codes to initiate a nuclear strike.

US

US President Donald Trump can currently order a nuclear missile launch without consulting Congress.

When the US president's Twitter rants over North Korea's nuclear arsenal escalated, senators debated this during a meeting of the Senate Foreign Relations Committee.

While some senators argued that the "military does not blindly follow orders," including those of a military nature.

Another said: "No one human being should have the power to unilaterally unleash the most destructive forces ever devised by humankind."

The US has an estimated total of 5,800 nuclear warheads.

Russia

In Russia, Putin can decide to use the country's nuclear arsenal.

Little information exists on specific details of the country's nuclear weapons programme, but open sources say Putin carries a "Cheget" (nuclear briefcase) with him, weighing nearly 11 kg along with the Minister of Defense and the Chief of the General Staff.

In the event of a nuclear attack in the country, the three Cheget would alert their owners simultaneously.

They are connected to a communications system code-named "Kavkaz" which allows communication between senior government officials if they needed to make a decision whether to use nuclear weapons.

Russia also has a backup system in place called "Perimeter," known in the US and Western Europe as the "Dead Hand", which means a retaliatory strike with the full power of the Russian Strategic Missile Forces would be provided in the event that Chegetov carriers and command posts were disabled.

Totaling 6,372, Russia is said to have the most number of nuclear warheads in the world.

United Kingdom

 The UK's nuclear deterrent is called "Trident" and dictates that the final decision on firing the missiles is the responsibility of the prime minister or of a nominated deputy while if they are out of the country.

When a new PM takes office they write four identical "letters of last resort," that are then stored securely on board Vanguard submarines, nuclear-powered ballistic missile submarines, which make up part of the UK's nuclear arsenal.

If the vessel loses contact with the UK and its commanding officer believes that the country has suffered an overwhelming attack, they must follow directions on the letter, which can include: Retaliate with nuclear weapons – Do not retaliate – Putting the submarine under the command of an ally.

The letters' contents are top secret and are destroyed, without being read, upon the election of a new prime minister.

It is estimated the UK has a total of 195 nuclear warheads in its arsenal.

France

The decision to launch a nuclear attack also rests solely in the hands of the French president. They alone can decide to order a strike if "the independence of the nation, the integrity of its land are seriously and imminently threatened," according to article 16 of the Constitution.

If the government feels that the president is "politically failing" it can ask the Constitutional Council to legally block the president, an action which automatically triggers a new presidential election.

France is said to have a total of 290 nuclear warheads.

China

Little is publicly known about China's nuclear launch protocol. However, a 2004 Chinese military text, translated by the Union of Concerned Scientists, suggested that the Central Military Commission, or just its chair, holds the authority to command a launch.

The Commission's 11 members are senior generals and senior party officials and its chair is China's president. It's also possible that recent reforms have changed this process.

China is estimated to have 320 nuclear warheads in its arsenal.

India

Indian Prime Minister Narendra Modi currently has the ability to "push the country's nuclear button". As the prime minister, he chairs the Nuclear Command Authority's (NCA) "political council," which is the sole body that can authorise a nuclear strike against an adversary in retaliation.

The final call rests with the prime minister.

India's niclear arsenal is estimated to be 150.

Pakistan

Prime Minister of Pakistan Imran Khan is chairman of the Nuclear Command Authority (NCA) and therefore has the right to launch a nuclear attack.

The country operates a three-tier activation structure involving: the National Command Authority, the Strategic Plans Division Force (SPD) and the Services' Strategic Forces Command (SSFC).

The NCA's strategic operational policy guidelines dictate a decision to launch a nuclear strike would be made by consensus within the NCA, with the chairman casting the final vote.

The other organisations would communicate decisions and implement the command.

Pakistan's nuclear warhead number is estimated to be 160.

Israel

Information on Israel's nuclear policies is scarce, but multiple experts have suggested that the country's arsenal isn't controlled by a single person, but "subject to a system of tight civilian control".

Israel has never officially denied nor admitted having nuclear weapons.

The country is estimated to have 90 nuclear warheads.

North Korea

Very little is known about North Korea's nuclear launch procedure, but it might be assumed that Kim Jong-un holds the power to press the big red button.

It is estimated that the country has about 35 nuclear warheads.

Iran

Iran started its nuclear programme in the 1950s and has always insisted its nuclear energy programme is peaceful.

According to the BBC, there have been suspicions it was being used as a cover to develop nuclear weapons, which prompted the UN Security Council, US and EU to impose crippling sanctions from 2010.

And after the escalating tensions between Iran and the US this year, President Trump has pledged that as long as he is president, Iran will not be allowed to have nuclear weapons.

After increased tensions over the killing of Iranian General Qasem Soleimani by the US in Baghdad, Iran has said it's not going to follow the restrictions imposed by the deal anymore.