The new findings show that earlier assumptions, used to build the Kyoto agreement between industrialised nations limiting carbon dioxide and other emissions, were too optimistic.
Instead, the sophisticated new computer models, devised to examine how well non-atmospheric sources could absorb the gases produced by the burning of fossil fuels, indicate that, in time, neither the oceans nor forests will be able to "fix" gases which contribute to the warming of the planet.
The findings, published today in two papers in the science journal Nature, show that earlier hopes - that the sea, in particular, might be able to act as a huge "sink" for atmospheric carbon dioxide - were exaggerated.
Those expectations were built in to the work of the Intergovernmental Panel on Climate Change (IPCC). Commenting on the latest work, David Schimel, of the National Center for Atmospheric Research in Colorado, said the differences from the IPCC's baseline estimates "has serious implications for policy designed to stabilise the concentration of trace gases in the atmosphere".
A team at Princeton University in New Jersey found that as the ocean began to absorb more carbon dioxide from the atmosphere (becoming more acidic in the process), it would also become more "stratified" - so that there would be less mixing between the top and lower layers.
The topmost layers, which are most exposed to higher atmospheric levels of greenhouse gases, would reach a point where they could not absorb any more gases more quickly. That means the ocean would stop acting as a brake on atmospheric global warming.
In the atmosphere, carbon dioxide acts to absorb radiation from the sun, making the temperature higher. While some global warming is essential to life, too much change too quickly could cause catastrophic "climate change" - which some scientists say has already begun.
Another paper by a team at the University of Sheffield, investigating land-based systems' reaction to higher carbon dioxide levels, discovered that while the gas helps vegetation for a while (because plants use it for photosynthesis), "this response will decline".