A coal "renaissance" in poor and developing countries has led to the fossil fuel becoming the dominant source of carbon emissions once again.
Scientists from the Mercator Research Institute for Global Commons and Climate Change in Berlin have found the low price of coal compared with gas and oil has led to a surge in consumption since the end of the 1990s.
This has mainly been seen in poor and developing countries, with these economies relying on inexpensive coal to meet their energy demands.
Publishing their findings in the journal PNAS, the authors said the trend is not restricted to just a few countries such as China, but that the world is "witnessing a global renaissance of coal majorly driven by poor, fast-growing countries".
"Because coal is the most carbon-intensive fossil fuel, such a development would have serious implications for climate change-mitigation strategies," the authors wrote. "The observation that numerous countries, such as China and India, seem to meet their growing appetite for energy to a large part with coal raises serious concerns about whether current development trajectories are compatible with climate change mitigation."
In their report, the researchers systematically analysed the main drivers and impacts of carbon-intensity increases focusing on coal. Findings showed the acceleration of coal use can be attributed by low prices compared to other energy sources, with coal-fired power plants also having relatively low capital costs.
They said developing countries should be looked to in terms of climate change mitigation, as the trend towards higher carbon intensity will cancel out the effect of decreases in industrialised countries.
"If the future economic convergence of poor countries is fuelled to a major extent by coal, ie, if current trends continue, ambitious mitigation targets likely will become infeasible," they said.
"Furthermore, building new coal power plants, mining operations, and transport networks for long-distance coal trade arguably would result in further lock-in of this highly carbon-intensive energy carrier and would make future emission reductions even more difficult to achieve."
To avoid an increase in high-carbon technologies, they say international climate policy should found ways to make the use of coal unattractive – either through raising the price or lowering the cost of low-carbon alternatives – without hampering development.
Concluding, they said: "The [relatively] low coal prices are an important reason countries choose coal to satisfy their energy needs. This result underlines the importance of cheaply available energy for economic growth and suggests that viable alternatives to cheap coal will be required to ensure the participation of developing countries in global climate change mitigation."