A new study on the relationship between people and the planet shows that climate change is only one of many inter-related threats to the Earth's capacity to support human life.

An international group of distinguished scientists, including five members of the National Academies, has argued that there are critical components missing from current climate models used by experts and political decision makers to inform environmental, climate, and economic policies. They say that current models are underestimating the threats posed by climate change.

Reporting in the National Science Review this week, the group outlined how the recent growth in resource use, land-use change, emissions, and pollution has made humanity the dominant driver of change in most of the Earth's natural systems, and how these changes, in turn, have important feedback effects on humans with costly and serious consequences. They also pointed to the impacts of unbridled consumption, population growth and inequality which have all risen since the middle of the last century.

They said these last few factors (human demographics, inequality, economic growth, and migration) aren’t factored into models of climate change, which means the models don’t reflect the real-world situation and may therefore be generating recommendations for unexpected or counterintuitive outcomes. They said some models used to inform policy will be downright unreliable.

They gave the United Nations’ projections as an example; the UN’s predictions of a relatively stable population for the whole of the developed world depend on dramatic, and the researchers say highly unlikely, declines projected in a few key countries. Japan, for example, must decline by 34%, Germany by 31% and Russia by about 30% for the projected stability in total developed country population to be born out. However, populations in countries that are frequently highlighted for their low birth rates, like Italy and Spain, are not projected to decline by even 1% for decades.

The US-based group said models need to be made more detailed still, and must reflect real world scenarios, to ensure that their findings influence good decision making by world leaders.

"Current models are likely to miss critical feedbacks in the combined Earth-Human system," said University of Maryland professor and co-author of the report, Eugenia Kalnay. "It would be like trying to predict El Niño with a sophisticated atmospheric model but with the Sea Surface Temperatures taken from external, independent projections by, for example, the United Nations. Without including the real feedbacks, predictions for coupled systems cannot work; the model can get away from reality very quickly."