In its starkest warning yet, the United Nations' Intergovernmental Panel on Climate Change declared that we need to drop carbon emissions down to zero by the end of this century if we're to have a decent chance of keeping global temperatures below dangerous levels.
The report — the fifth and final volume of the UN panel — made it clear that climate change is happening, that it's most assuredly our fault, and that we need to reduce greenhouse gas emissions to zero.
"Science has spoken. There is no ambiguity in their message. Leaders must act. Time is not on our side," stated UN Secretary General Ban Ki-moon at the report's launch in Copenhagen.
According to the report, failure to eliminate fossil fuel emissions by 2100 would lock the world onto a trajectory with "irreversible" impacts on people and the environment. At the same time, it would force us to deploy unproven and risky geoengineering schemes (namely technologies that remove greenhouse gases out of the atmosphere).
The 45-page summary for policymakers found that:
- Evidence of global warming is "unequivocal, and many of the observed changes are unprecedented [in recent history]".
- Human influence on the climate is clear, and "extremely likely" to be the cause of warming since the mid 20th century.
- The Earth's weather is already changing because of human influence, and the 21st century will "very likely" see more and longer heatwaves, more and fiercer storms and more acidic and higher seas.
- The Earth's urban areas, climate change will increase the risk of "heat stress, storms and extreme precipitation, inland and coastal flooding, landslides, air pollution, drought, water scarcity, sea-level rise and storm surges".
Some of the worst effect will likely be felt by disadvantaged people and communities; driving poverty and economic shock is set to increase the risk of violent conflict.
Should climate change not be tackled, the Earth is expected to be 4 degrees warmer by 2100, accompanied by "substantial species extinction, [and] global and regional food insecurity".
But the report also offered hope. Its primary injunctions include a breaking of our reliance the oil, coal, and gas that's powering the global energy system while polluting the atmosphere with heat-trapping CO2.
"We have the means to limit climate change," IPCC chairman Rajendra Pachauri said. "The solutions are many and allow for continued economic and human development. All we need is the will to change, which we trust will be motivated by knowledge and an understanding of the science of climate change."
But the situation could be more dire than this.
"The headline across many media outlets is that we have to zero out fossil fuel use by 2100," said Ramez Naam to io9. "The scarier thing is that we have to do most of that now, cutting emissions by 40-70% over the next 36 years. Every year we wait, we get closer to the cliff, and the turn we have to make looks more like a hairpin."
Naam, the author of The Infinite Resource: The Power of Ideas on a Finite Planet, says the IPCC has underestimated a lot of warming effects.
"They didn't expect anything like the melt of arctic sea ice we've seen to date," he says. "The arctic is melting at least 50 years and maybe as much as 100 years ahead of schedule. And that, I turn, could accelerate warming in ways the IPCC doesn't take into account."
The one ray of hope is that clean tech has also improved radically faster than the IPCC predicted, he says.
"Solar, wind, and battery prices have plunged as we've innovated," Naam told io9. "They're still a tiny tiny fraction of overall energy. But their pace of improvement opens the possibility that — when we get serious — we'll be able to switch over to non-carbon energy more cheaply than people believe."
Image: Galyna Andrushko/Shutterstock.