Ice and ocean sediment cores from the polar regions indicate that temperatures at the poles during previous epochs when sea level was tens of meters higher is not too far removed from the temperatures Earth could reach this century on a "business as usual" trajectory.
"We don't have a substantial cushion between today's climate and dangerous warming," Hansen said. "Earth is poised to experience strong amplifying feedbacks in response to moderate additional global warming."
Detailed considerations of a new warming target and how to get there are beyond the scope of this research, Hansen said. But this research is consistent with Hansen's earlier findings that carbon dioxide in the atmosphere would need to be rolled back from about 390 parts per million in the atmosphere today to 350 parts per million in order to stabilize the climate in the long term. While leaders continue to discuss a framework for reducing emissions, global carbon dioxide emissions have remained stable or increased in recent years.
Hansen and others noted that while the paleoclimate evidence paints a clear picture of what Earth's earlier climate looked like, but that using it to predict precisely how the climate might change on much smaller timescales in response to human-induced rather than natural climate change remains difficult. But, Hansen noted, the Earth system is already showing signs of responding, even in the cases of "slow feedbacks" such as ice sheet changes.
The human-caused release of increased carbon dioxide into the atmosphere also presents climate scientists with something they've never seen in the 65 million year record of carbon dioxide levels a drastic rate of increase that makes it difficult to predict how rapidly the Earth will respond. In periods when carbon diox
|Contact: Patrick Lynch|
NASA/Goddard Space Flight Center