Climate change effects abrupt, studies warn

Scientists sounded alarms Tuesday with a pair of studies challenging the idea that climate change is occurring gradually over the century and that its worst effects can be avoided by keeping emissions below a critical threshold.

A National Research Council report says the planet is warming so quickly that the world should expect abrupt and unpredictable consequences in a matter of years or a few decades. Among the changes already underway are the sudden decline in Arctic sea ice as well as climbing extinction rates, the report found.

Scientists based their findings, in part, on the study of climate history as recorded in tree rings, ocean sediment and ice cores. They found the timeline punctuated by big, sudden changes, including ocean circulation shifts and mass extinctions.

As a result of the burning of fossil fuels, industrial activity and deforestation, the amount of carbon dioxide and other heat-trapping greenhouse gases in the atmosphere has soared to levels not seen in millions of years, with global temperatures rising by about 1.5 degrees. The scientists say the accelerating gas levels increase the risk of reaching various “tipping points,” leaving nature and society little time to react.

“To willfully ignore the threat of abrupt change could lead to more costs, loss of life, suffering and environmental degradation,” said the council, an arm of the National Academies that produces reports for the U.S. government.

Even slow and steady changes in climate can have sudden repercussions, the report says. A slight increase in sea level could be enough to overtop a levee during a storm, and a tiny rise in ocean acidity from carbon dioxide could make seawater inhospitable to coral.

The scientists also call for an early warning system to anticipate sudden climate shifts. They envision a network of satellites and land-based monitors tracking ocean temperatures near polar ice sheets and methane levels in the Arctic. Those monitors would work alongside existing networks for drought, famine and groundwater depletion.

A separate study published Tuesday challenges a widely held view that the world can avoid the most dangerous consequences of climate change by limiting emissions to 1 trillion metric tons of carbon since preindustrial times. Staying below that ceiling would keep global temperatures from rising more than 3.6 degrees, a threshold the United Nations-backed Intergovernmental Panel on Climate Change has endorsed.

An international group of scientists, health experts, legal scholars and economists under the auspices of Columbia University says the cap is too high. Fossil fuel emissions must be kept to half that and global warming held to about 1.8 degrees to avert disastrous consequences, they say, including many feet of sea level rise and irreversible ecological harm.

“If we don’t get on a downward emissions pathway this decade, young people are likely to inherit a climate system with dramatic consequences out of their control,” said James Hansen, the climate scientist who led the study.

Stabilizing Earth’s climate would also require restoring 100 billion metric tons of carbon to forests and soils through better management, the authors say. Going beyond typical research papers, they call for a global tax on carbon to facilitate a transition to nuclear and renewable energy.