Cambodia is suffering disproportionately from the impacts of greenhouse gas emissions from more developed nations, according to a new study published in the journal Nature on Friday.

The study, conducted by University of Queensland and the Wildlife Conservation Society, found that the top 20 emitters, including China, Australia and the US are “free riders” – enjoying polluting industries’ contribution to their GDPs, but suffering low climate impacts relative to the size of their economy. Meanwhile, countries that don’t produce much greenhouse gases are choking on the emissions.

According to the study, Cambodia is one of 36 countries “severely” affected by global climate change, as of 2010. If current trends continue, Cambodia’s vulnerability will downgrade slightly to “acute” by 2030.

“This is like a non-smoker getting cancer from second-hand smoke, while the heavy smokers continue to puff away.

Essentially, we are calling for the smokers to pay for the health care of the non-smokers they are directly harming,” study co-author James Watson, of University of Queensland, said in a statement.

Climate change’s threat to Cambodia is well-established by organisations ranging from the UN’s Food and Agriculture Organization to Standard & Poor’s credit agency, both of which ranked the Kingdom as one of the most vulnerable countries in the past few years.

Nop Polin, Cambodia’s civil society delegate to the recent COP21 climate talks in Paris, said that Cambodia’s vulnerability is expressed in the “low adaptive capacity” of its farmers, who comprise most of the population.

If their crops are wiped out by extreme weather, most of them have no alternative but to starve or go deep into debt.

Furthermore, Cambodia’s health system is vulnerable to disease outbreaks that accelerate in hot weather, said Polin.

Polin said that while Cambodia’s government and civil society can do a lot to improve their coordination and commitment to fighting climate change, the Kingdom is largely at the mercy of the larger players. The Paris agreement is “important” for Cambodia, he said.

However, authors of the Nature study said that current targets for greenhouse gas emissions are “unlikely” to limit warming to below 2 degrees Celsius, and there is no clear indication of how successful the Paris agreement will be.

“The historic commitment to [greenhouse gas] emissions reduction by key free riders has been slow,” they wrote.