On October 29, 2025, just minutes before his meeting with Chinese President Xi Jinping in Busan, South Korea, U.S. President Donald Trump said the U.S. would “start testing our nuclear weapons on an equal basis with other nations”. While returning to Washington, Mr. Trump told reporters, aboard Air Force One, “We have halted it for years – many years. But with others doing testing, I think it’s appropriate that we also do.” Back in the U.S., Mr. Trump repeated his claims in an interview. “Russia is testing; China is testing, but they don’t talk about it… And certainly North Korea has been testing. Pakistan has been testing.”

Mr. Trump is correct about North Korea, which has tested multiple nuclear weapons in the new century. But other nuclear powers, including the U.S., China and Russia, have maintained a moratorium on weapons testing since the 1990s. They, however, have tested weapons that can carry nuclear warheads. Mr. Trump’s announcement came immediately after Russia announced that it successfully tested a nuclear-powered cruise missile (Burevestnik) and an undersea torpedo (Poseidon). Both are designed to overcome American missile defence systems and can carry nuclear warheads. But those were not nuclear detonation tests.

Age of tests

The last time Russia tested a nuclear weapon was in 1990, when the Soviet Union was still alive. The last American nuclear bomb test was held in 1992, and the last Chinese test was in 1996. In 1996, the Comprehensive Test Ban Treaty (CTBT) banned all nuclear tests, but it never came into force as the required number of countries did not ratify it. The U.S. and China have signed the treaty but never ratified it. Russia had signed and ratified it, but in 2023, amid mounting tensions with the U.S., it decided to de-ratify it.

Russia remains the world’s largest nuclear power with an inventory of 4,309 warheads, according to the Federation of American Scientists. The U.S. comes second with 3,700 weapons, while China, which is ramping up its nuclear arsenals, is believed to have more than 1,000 warheads. Historically, the U.S. has carried out the most number of nuclear tests — 1,030 detonations, followed by the Soviet Union (715) and the French (210). China has conducted more than 45 nuclear tests. In total, there have been 2,056 nuclear tests since ‘Trinity’, the first nuclear detonation by the U.S.

Debate in the U.S.

In the U.S., the debate on whether the country should resume nuclear tests has been raging for some time. Last year, Robert C. O’Brien, a National Security Adviser under Mr. Trump’s first term as President, wrote in Foreign Affairs magazine that the U.S. should restart nuclear testing to address Russia’s and China’s “growing and modernising” arsenals”. ‘Project 2025’, a political initiative published by the pro-Trump Heritage Foundation in 2023, called resuming or at least preparing to resume nuclear testing. Those who support tests argue that it is important to bolster the country’s nuclear deterrent-tests can prove that nuclear arsenals actually work, and provide critical data allowing countries to build more powerful, compact and specialised warheads.

On November 2, U.S. Secretary of Energy Chris Wright said the U.S. would not resume nuclear weapons tests but would conduct “subcritical tests”. A subcritical test uses conventional explosives to compress fissile material (Plutonium 239), without triggering nuclear chain reaction or explosion. In other words, subcritical tests are not a violation of the CTBT. But Mr. Trump, in another interview, clearly said, ‘We are going to test nuclear weapons like other countries do”.

Devastating effects

The 1963 Partial Test Ban Treaty, signed by the Soviet Union, the U.S. and the U.K., banned all nuclear test detonations in the atmosphere, outer space and underwater. Since then most tests were conducted underground. (Now, CTBT bans all tests, including underground detonations). Even subterranean tests, experts say, could cause devastating environmental damages, including total destruction of ecosystems at test sites and contamination of soil, air and water. Radioactive contamination could affect vast areas for hundreds of years.

If the U.S. breaks the moratorium and starts testing weapons, it could cause a domino effect on other nuclear powers. There were reports that China had made preparations at Lop Nur, where Mao detonated China’s first bomb in 1964, in case it decides to resume testing. For now, China has called on the U.S. to maintain the moratorium. Russia was unambiguous in its reaction. “If they begin testing, naturally we will do the same,” Russia’s Security Council chief Sergey Shoygu said on October 31, 2025. If the U.S. and Russia resume tests, China, which hasn’t carried out as many tests as its nuclear peers, could do the same. And if China does it, India will come under internal pressure to start testing its weapons. Then Pakistan may not stand out. A new phase of nuclear arms race would begin, with long-term consequences for humanity.

Published – November 06, 2025 11:48 am IST

For billions of years, the carbon cycle has been nature’s solution to removing excess carbon from the atmosphere.

In nature, volcanic eruptions and life forms vent carbon dioxide (CO₂) into the atmosphere. Plants and trees then draw in and store this CO₂ during photosynthesis.

Of late, the carbon cycle has been a focus area in climate mitigation. Plants’ ability to lock away carbon produced by burning fossil fuels can offer respite. Both fossil-fuel corporations and governments have subscribed to this idea as they look for ways to offset their still-rising carbon footprints.

But a study recently published in the journal Science by an international team of researchers suggests plants absorb more CO₂ from the atmosphere than expected and also store it for a shorter duration than expected, before releasing it into their surroundings.

To establish their findings, the researchers investigated the remains of nuclear bomb tests the U.S. and the Soviet Union conducted in the 1960s using climate models.

Relics of the Cold War

The dozens of nuclear bomb tests during the Cold War in the second half of the 20th century maintained an atmosphere of trepidation worldwide and, scientists later found, an opportunity for climate research.

“As terrible as they were, they’ve been quite useful to scientists,” Heather Graven, a climate physicist at Imperial College London and the study’s lead author, said.

The explosions sprayed radioactive material around the planet, including a lot of it in the atmosphere. One of them was carbon-14, an isotope also called radiocarbon. Its atom’s nucleus has two neutrons more than in the nucleus of the more common carbon-12. Radiocarbon is naturally found in minute quantities but the nuclear bomb tests steadily deposited more and more of it in the atmosphere.

In 1963, Cold War powers signed the Limited Test Ban Treaty (LTBT) that prohibited nuclear testing over land, air, and under water. The atmospheric radiocarbon concentration stopped increasing beyond this year. Dr. Graven and her team used models to track the change in this level between 1963 and 1967 and found that it dropped steadily.

Often, radiocarbon bonds with oxygen to form CO₂. Plants, trees, and other vegetation absorb this CO₂ during photosynthesis to produce food and ultimately energy. The researchers found that the models suggested the radiocarbon was moving into vegetation from the atmosphere.

‘The whole system is cycling faster’

Plants need food to survive and they make it themselves. They absorb CO₂ from the atmosphere during photosynthesis and use it to make glucose. A plant consumes some of the glucose and some it stores as starch in its leaves. In this process, some carbon is also lost when the plant exhales CO₂ as it respirates.

Scientists don’t have a direct way to measure the rates at which vegetation loses and gains carbon. But they have been able to use satellite data to estimate how much carbon vegetation around the world hosts.

The researchers behind the new study used climate models to estimate the amount of carbon stored in vegetation around the planet in a year. Previous studies had shown this value to be at least 43-76 billion tonnes of carbon per year worldwide. But the study team said it could be around 80 billion tonnes per year, with most of the carbon being stored in leaves and finer roots, i.e. the non-woody parts of the plant.

If the higher value is accurate, plants must also be shedding their carbon sooner than thought. Otherwise, the researchers figured, they would have more carbon than estimated based on satellite data.

The findings also shed light on how quickly carbon is exchanged between vegetation and the atmosphere. “The whole system is kind of cycling faster than what we thought before,” Dr. Graven said.

But Raghu Murtugudde, a climate scientist at IIT Bombay who wasn’t involved in the study, advised caution. “To say what the actual impact on the carbon cycle is would be a challenge,” he told The Hindu. “Theoretically you want to include all the details [in the models] but there are missing understandings and lack of data and irreducible uncertainties.”

He said the models simulating carbon stored in vegetation in the study make assumptions that, if tweaked, could change the results significantly.

The study’s co-author Will Wieder, a climate scientist with the U.S. National Center for Atmospheric Research, said Dr. Murtugudde’s statement was “accurate” but also “short-sighted”.

Radioactive representation

In 1995, the World Climate Research Program set up the Coupled Model Intercomparison Project (CMIP), which prepares climate projections that inform the U.N.’s climate reports.

For the CMIP, scientific institutions in several countries pool their individual climate models together to produce better projections. But most of these models haven’t been tested with radiocarbon data.

It’s not difficult to input this data, according to Dr. Graven. “Some of them haven’t really bothered to do so.”

In fact, only one model, the ‘Community Earth System Model 2’ developed by the U.S. University Corporation for Atmospheric Research, accounted for radiocarbon in its simulations — but it also predicted plants had absorbed much less radiocarbon than Dr Graven & co. found they should. 

Climate models have always had uncertainties.

“They are not wrong. They are imperfect,” Dr. Murtugudde said. “It’s like a car that pulls to one side but it can be driven. So it needs to be looked at by a mechanic to make sure it eventually drives straight.”

The CMIP models used in the study included some of the latest versions (5 and 6). The short-falls highlighted in the study are more of a stepping stone for future research into climate modelling, according to Dr. Wieder. “This kind of information is critical as we work to improve the models for CMIP 7 and beyond.”

This said, all these climate scientists agreed radiocarbon needs to be represented better in climate predictions. So far, radiocarbon inclusion has been plagued by “limited resources, both funding and effort, available for model development and observational research,” Govindasamy Bala, a climate physicist at the Indian Institute of Science, Bengaluru not involved in the study, told The Hindu.

“Representation of isotopes, ice sheet dynamics, permafrost, etc. in models is likely to gain momentum in the future,” he added.

Karthik Vinod is a freelance science journalist and co-founder of Ed Publica. He has masters’ degrees in astrophysics and science, technology and society.