Some catastrophic changes to the climate can still be headed off
The most comprehensive report yet on climate change looks at potentially irreversible climate dangers, from sea level rise to ocean circulation slowdowns, that can still be avoided with strong climate action.
Climate change has already touched every corner of the planet and will continue to reshape the human experience for centuries to come, its impacts intensifying as warming grows, scientists warn.
The 2.0 degrees Fahrenheit (1.1 degrees Celsius) the planet has warmed since the preindustrial period has pushed Earth toward irreversible change, some of which is unavoidable. But decisive action to cut emissions quickly and thoroughly—keeping total temperature rise as low as possible—can greatly reduce the risks of crossing further dangerous thresholds that would put the planet even more at risk, according to a massive new Intergovernmental Panel on Climate Change (IPCC).
“In order to stabilize climate, we have to stop emitting immediately, full stop,” says Charles Koven, one of the report authors and a climate scientist at the Lawrence Berkeley National Laboratory in California.
Risk of irreversible change have become clearer
Earth’s temperatures have increased more or less steadily for decades, neatly in tandem with rising greenhouse gases. The basic rule of thumb is simple: the more carbon dioxide emitted, the warmer it gets, and that relationship will continue, the report says.
But scientists have known for over 30 years that there are thresholds in the climate system which, if crossed, could drastically reshape the world as we know it—causing changes that are irreversible on human timescales. Pushing ice sheets in Greenland and Antarctica past certain points, for example, can drive them into self-reinforcing declines that would continue even if emissions stopped tomorrow.
"We play Russian roulette with climate [and] no one knows what lies in the active chamber of the gun," groundbreaking climate scientist Wally Broecker wrote in 1987.
Since then, reams of research have shown that many of these outcomes could occur at lower global temperature changes than anyone expected and that some may have already begun. Though the exact thresholds are still uncertain, some could be triggered within the 1.5 to 2°C warming range, the warming limits suggested in the 2015 Paris Agreement.
The new report says the planet could warm by about 2.5°F (1.4°C) above preindustrial temperatures by 2100 under the most ambitious pathway to reduce emissions, or more than 7.2°F (4°C) in the least ambitious.
Even at the low end of that range, shifts that can’t be taken back could occur in all corners of the planet: the icy parts, the oceans, the land, and the atmosphere. But the risks become much greater and harder to escape with more warming.